The 100 most-cited articles in The Journal of Physical Chemistry C, 2019

The term "nanoparticle stability" is widely used to describe the preservation of a particular nanostructure property ranging from aggregation, composition, crystallinity, shape, size, and surface chemistry. As a result, this catch-all term has various meanings, which depend on the specific nanoparticle property of interest and/or application. In this feature article, we provide an answer to the question, "What does nanoparticle stability mean?". Broadly speaking, the definition of nanoparticle stability depends on the targeted size dependent property that is exploited and can only exist for a finite period of time given all nanostructures are inherently thermodynamically and energetically unfavorable relative to bulk states. To answer this question specifically, however, the relationship between nanoparticle stability and the physical/chemical properties of metal/metal oxide nanoparticles are discussed. Specific definitions are explored in terms of aggregation state, core composition, shape, size, and surface chemistry. Next, mechanisms of promoting nanoparticle stability are…

Doping and functionalization of graphene significantly modulate its properties and extend its application potential. Detailed and accurate chemical characterization of the final material is critical for understanding its properties and reliable design of new graphene derivatives. Spectroscopic methods commonly used for this purpose include Raman, Fourier transform infrared (IR), and X-ray photoelectron spectroscopy (XPS). However, the correct interpretation of observed bands is sometimes hampered by ambiguities when assigning measured binding energies or IR/Raman peaks to specific atomic structures. N-doped graphene has many potential applications but can contain several different chemical forms of nitrogen whose relative abundance strongly affects the doped material’s properties. We present clear spectroscopic fingerprints of the various chemical forms of nitrogen that can occur in N-doped/functionalized graphene to facilitate the identification and quantification of the different forms of N present in experimentally prepared samples. The calculated XPS binding energies of the N 1s…

Abstract Impedance spectroscopy has been widely applied over the last decades to study electrochemical systems and solid-state devices. However, performing impedance spectroscopy on emerging photovoltaics presents new challenges related to the unusual material properties and complex device architectures. This review provides an introduction to impedance spectroscopy for researchers in photovoltaics and closely related fields. The review begins with a list of practical guidelines for performing measurements and analyzing data. After this, the mathematical basics are reviewed, and an introduction to circuit elements is given. This is followed by tips for collecting reliable data and reducing artifacts in the frequency spectra. The review then surveys common approaches in the field for analyzing data, including performing equivalent circuit modeling, analysis of capacitance-frequency spectra, and carrier mobility measurements. The underlying assumptions of each analysis approach, as well as the advantages, limitations, and potential pitfalls are discussed.

Surface areas of metal–organic frameworks (MOFs) have been commonly characterized using the Brunauer–Emmett–Teller (BET) method based on adsorption isotherms of nonreactive nitrogen or argon. Recently, some discrepancies between surface areas computed from the BET method and those from geometric methods were reported in the literature. In this study, we systematically evaluated the BET and geometric surface areas of over 200 geometrically diverse real MOFs as well as CNTs with varying pore sizes as model systems to achieve a comprehensive understanding of the limitations of the BET and geometric methods. We compared the BET and geometric surface areas to the true monolayer area, which is determined by directly counting the number of molecules included in the monolayer of the surface from molecular simulation snapshots. Furthermore, we found that the excess sorption work (ESW) method or a combination of ESW and BET methods can potentially help facilitate a more accurate estimation of the surface area, particularly in cases where the structures show relatively less complex isotherms…

Not all nanopores are created equal. By definition, nanopores have characteristic diameters or conduit widths between ∼1 and 100 nm. However, the narrowest of such pores, perhaps best called Single Digit Nanopores (SDNs) and defined as those with regular diameters less than 10 nm, have only recently been accessible experimentally for precision transport measurements. This Review summarizes recent experiments on pores in this size range that yield surprising results, pointing toward extraordinary transport efficiencies and selectivities for SDN systems. These studies have identified critical gaps in our understanding of nanoscale hydrodynamics, molecular sieving, fluidic structure, and thermodynamics. These knowledge gaps are, in turn, an opportunity to discover and understand fundamentally new mechanisms of molecular and ionic transport at the nanometer scale that may inspire a host of new technologies, from novel membranes for separations and water purification to new gas-permeable materials and energy storage devices. Here we highlight seven critical knowledge gaps in the study of…

Plasmonic photothermal therapy (PPTT), a type of treatment involving the intravenous or intratumoral injection to introduce gold nanoparticles to cancerous cells and the subsequent exposure to heat-generating near-infrared (NIR) light, is a potentially favorable alternative to traditional treatments of localized tumors such as chemotherapy, radiotherapy, and surgery. The current main concern of PPTT, however, is the feasibility of the treatment in clinical settings. Since PPTT’s initial use 15 years ago, thousands of studies have been published. In this feature article, we summarize the most recent scientific progress, including the efficacy, molecular mechanism, toxicity, and pharmacokinetics of PPTT in vitro with cancer cells and in vivo through mouse/rat model testing, animal clinical cases (such as dogs and cats), and human clinical trials. Given the benefits of PPTT, we believe that it will ultimately become a human clinical treatment that can aid in our ultimate goal of beating cancer.

The composition, structure, and the formation mechanism of the solid–electrolyte interphase (SEI) in lithium-based (e.g., Li-ion and Li metal) batteries have been widely explored in the literature. However, very little is known about the ion transport through the SEI. Understanding the underlying ion diffusion processes across the SEI could lead to a significant progress, enabling the performance increase and improving safety aspects of batteries. Herein, we report the results of first-principles density functional theory calculations on the dominant diffusion pathways, energetics, and the corresponding diffusion coefficients associated with Li diffusion through the polycrystalline SEI. This paper is particularly concerned with the Li diffusion through the grain boundary (GB) formed between the three major inorganic components of the SEI, such as Li 2 O, LiF, and Li 2 CO 3 . It is found that Li diffusion occurs through the numerous open channels formed by the GB. The energetics and potential barriers vary significantly depending upon the structure of these channels, with the general…

Low-cost and efficient electrocatalysts are urgently required for the N 2 reduction reaction (NRR) to produce NH 3 under ambient conditions. By using first-principles calculation, we systematically investigated the NRR catalytic activity of the transition metal (TM, including Mn, Fe, Co, and Ni) monomer-, dimer-, and trimer-anchored graphdiyne (GDY) monolayers. It is shown that most of the TM monomer- and dimer-anchored GDY monolayers have enhanced NRR catalytic activity compared with the Ru(0001) stepped surface. Especially, the Co dimer-anchored GDY monolayer (Co 2 @GDY) exhibits the best NRR catalytic activity with the onset potential of −0.43 V and a high ability to suppress the competing hydrogen evolution reaction. The high NRR catalytic activity of Co 2 @GDY could be attributed to the localized electronic states near the Fermi level and the strong electron-donating ability of the GDY monolayer. Furthermore, an approximate linear trend between the predicted onset potential and the N adsorption energy is revealed, which may act as a simple descriptor for the intrinsic NRR…

Density functional theory calculations are potentially useful for both understanding the activity of experimentally tested catalysts and screening for new catalyst materials. For electrochemical oxygen evolution reaction (OER) catalysts, these analyses are usually performed considering only the thermodynamics of the reaction path, which typically consists of adsorbed OH*, O*, and OOH*. Scaling relationships between the stability of these intermediates lead to a limiting potential volcano whose optimum is constrained by the roughly constant offset between the binding energies of OH* and OOH*. In this work, we evaluate OER kinetics at rutile IrO 2, RuO 2, RhO 2, and PtO 2 surfaces by computing reaction barriers with an explicit model of the electrochemical interface. We conclude that the kinetics of proton transfer between oxygen atoms at the surface and in the electrolyte is facile and that O–O bond formation is most likely rate-determining in all cases. Combining these results with a microkinetic model and a scaling relationship for the OOH* formation barrier, we construct a new…

The chemical bonds between a transition metal (M) and oxygen (O) are of major importance in catalysis, mineralogy, biology, and astrophysics, and an adequate theoretical description of these bonds is thus highly needed. This paper establishes that despite recent debate on its accuracy for transition-metal systems, CCSD(T) is an excellent benchmark standard for transition-metal oxide interactions, with errors approaching those of experiment. We conclude this from a study of all 60 M–O and M + –O bond dissociation enthalpies (BDEs) of the 3d, 4d, and 5d metals, constituting a balanced data set in terms of d q configurations that also enable an assessment of the trend chemistry in oxygen’s ability to bind to transition metals. The BDEs decrease toward the right of the transition-metal series, with humps at groups 4, 5 and 8, 9. The linear trend follows the increasing electronegativity when going from the left to the right, whereas the humps are caused by differential occupation of bonding δ-orbitals and antibonding π-orbitals. We show that the BDEs correlate strongly with oxophilicity…

Abstract Understanding the electron transport through transition-metal dichalcogenide (TMDC)-based semiconductor/metal junctions is vital for the realization of future TMDC-based (opto-)electronic devices. Despite the bonding in TMDCs being largely constrained within the layers, strong Fermi-level pinning (FLP) was observed in TMDC-based devices, reducing the tunability of the Schottky barrier height. We present evidence that metal-induced gap states (MIGS) are the origin for the large FLP similar to conventional semiconductors. A variety of TMDCs (MoSe2, WSe2, WS2, and MoTe2) were investigated using high-spatial-resolution surface characterization techniques, permitting us to distinguish between defected and pristine regions. The Schottky barrier heights on the pristine regions can be explained by MIGS, inducing partial FLP. The FLP strength is further enhanced by disorder-induced gap states induced by transition-metal vacancies or substitutionals at the defected regions. Our findings emphasize the importance of defects on the electron transport properties in TMDC-based devices and…

Abstract Following our recent study demonstrating predominant Li-ion hopping conduction in sulfolane (SL)-based highly concentrated electrolytes with LiBF4, LiClO4, and lithium bis(fluorosulfonyl)amide, herein a systematic study on transport properties and Li-ion coordination of SL-based electrolytes with lithium bis(trifluoromethanesulfonyl)amide was performed. In the highly concentrated region, Li ions clearly diffuse faster than SL and TFSA anions. The two oxygen atoms of the SL sulfonyl group tend to coordinate to two different neighboring Li ions and TFSA anions form ionic clusters with Li ions, verifying the previous observation of the unusual Li-ion conduction and its relevance to the SL- and anion-bridged, chainlike Li-ion coordination structure for the SL-based concentrated systems with other Li salts. Moreover, addition of hydrofluoroether (HFE) to the SL-based concentrated electrolytes greatly enhances diffusion coefficients but fragments the chainlike Li-ion coordination to smaller clusters, leading to a reduced contribution of Li-ion hopping to the overall Li-ion…

Photocatalytic water splitting has received much attention for the production of renewable hydrogen from water, and two-dimensional (2D) materials show great potential for use as efficient photocatalysts. In this paper, the stabilities and electronic and optical properties of Janus group-III monochalcogenide M 2 XY (M = Ga and In and X/Y = S, Se, and Te) monolayers were investigated using first-principles calculations. The band gaps of the Janus M 2 XY monolayers are in the range of 1.54–2.98 eV, which satisfies the minimum band gap requirement of photocatalysts for overall water splitting. Indirect-to-direct band gap transitions occur in the M 2 XTe (M = Ga and In and X = S and Se) monolayers. These transitions were induced by the valence band maximum at the Γ point, being composed of the p x and p y orbitals of the M and Y atoms in M 2 XTe instead of the p z orbitals of the M and X atoms in the MX and other M 2 XY monolayers. The Janus M 2 XY monolayers have a considerable optical absorption coefficient (∼3 × 10 4 /cm) in the visible light region and an even larger absorption…

Recently, lead halide perovskite (LHP) materials have shown potential for many optoelectronic applications. However, the structural instability and toxicity concerns necessitated robust and heavy-metal-free alternatives. We report a synthetic route to Cs 2 AgInCl 6 double-perovskite nanocrystals (DP NCs) that have the crystal structure replacing two lead ions in LHP by a pair of silver and indium ions. Cubic-shaped Cs 2 AgInCl 6 DP NCs were obtained with a narrow size distribution, which showed superior stability against moisture that rivaled core–shell-structured CdS/ZnS NCs. Cs 2 AgInCl 6 DP NCs showed discrete optical properties: (i) multiple absorbing states that resolved the parity-forbidden band-edge transition at 3.33 eV and next—following higher order parity—allowed transition at 4.88 eV and (ii) multiple emission states that consisted of the band edge emission at 350 nm and emissions from defective states that peaked at 395 nm. The synthetic route was further exploited for isovalent doping with lanthanide ions, which yielded Yb-doped, Er-doped, and Yb/Er-codoped Cs 2 AgInCl…

The flexible metacomposites with tunable negative permittivity have great potential in wearable cloaks, stretchable sensors, and thin-film capacitors, etc. In this paper, the flexible graphene/polydimethylsiloxane (GR/PDMS) metacomposites with tunable negative permittivity were prepared by an in situ polymerization method. The ac conductivity behavior, dielectric property, and impedance performance of the resulting composites with different graphene mass ratios (0–4 wt %) were studied. With the increase of graphene, the conductive mechanism of the resulting composites changed from hopping conduction to electron conduction, along with the change of microstructure. When graphene content in the composites came up to 3 wt %, the negative permittivity conforming to Drude model was observed. Further investigation revealed that there is a corresponding relationship between the permittivity and the reactance. It is demonstrated that the inductive character is responsible for the negative permittivity, while the capacitive character results in the positive permittivity.

RuO 2 is one of the most active electrocatalysts toward oxygen evolution reaction (OER), but it suffers from rapid dissolution in electrochemical environments. It is also established experimentally that corrosion of metal oxides can, in fact, promote catalytic activity for OER owing to the formation of a surface hydrous amorphous layer. However, the mechanistic interplay between corrosion and OER across metal-oxide catalysts and to what degree these two processes are correlated are still debated. Herein, we employ ab initio molecular dynamics-based blue moon ensemble approach in combination with OER thermodynamic analysis to reveal a clear mechanistic coupling between Ru dissolution and OER at the RuO 2 (110)/water interface. Specifically, we demonstrate that (i) dynamic transitions between metastable dissolution intermediates greatly affect catalytic activity toward OER, (ii) dissolution and OER processes share common intermediates with OER promoting Ru detachment from the surface, (iii) the lattice oxygen can be involved in the OER, and (iv) the coupling between different OER…

Ferromagnetic ordering of monolayer vanadium dichalcogenides (VSe 2 and VS 2 ) has been predicted by density functional theory (DFT), and suggestive experimental evidence for magnetic ordering in VSe 2 monolayers has been reported. However, such ferromagnetic ordering would be in stark contradiction to the known paramagnetic nature of the bulk VSe 2 . Herein, we investigate the electronic structure of VSe 2 monolayers by angle-resolved photoemission spectroscopy (ARPES) and first-principles DFT. The ARPES measurements demonstrate the absence of spin-polarized bands for monolayers in close correspondence to nonmagnetic nature of the bulk VSe 2 . We demonstrate that the stabilization of the nonmagnetic state occurs due to the appearance of a charge density wave (CDW) state in VSe 2 monolayers. In contrast to well-established 4 × 4 × 3 periodicity of the CDW in bulk VSe 2, we identify a √3 × √7 unit cell for VSe 2 monolayers from both scanning tunneling microscopy imaging and first-principles calculations. Moreover, DFT predicts that the √3 × √7 charge order state is energetically…

Two-dimensional (2D) transition-metal carbides (MXenes) as electrode materials have attracted much attention because of their excellent energy storage properties and electrical conductivity. In this work, we study the properties of the V 3 C 2 MXene anode for metal-ion (Li, Na, K, and Ca) batteries by means of density functional theory computations. Based on our calculated results, V 3 C 2 exhibits excellent properties such as structural stability, good electrical conductivity, fast charge–discharge rates, and high theoretical storage capacity. In particular, owing to its low diffusion barrier (0.04 eV for Li, 0.02 eV for Na, 0.01 eV for K, and 0.04 eV for Ca) and high storage capacity (606.42 mA h g –1 for both Li and Na, 269.86 mA h g –1 for K, and 539.71 mA h g –1 for Ca), V 3 C 2 monolayers are predicted to be promising anode materials especially for lithium-ion batteries and sodium-ion batteries. Our work provides a new avenue for the design of novel 2D materials for energy applications.

Cs 2 AgInCl 6 double perovskite (DP) is a direct band gap, stable, and environmentally benign material with a three-dimensional perovskite structure. However, the band gap (∼3.3 eV) is too wide for optoelectronic applications in the near-infrared (NIR) region. To achieve optical functionality in the NIR window, we have doped Yb 3+ in both microcrystals and colloidal nanocrystals of Cs 2 AgInCl 6 DPs. Our Yb-doped Cs 2 AgInCl 6 DP microcrystals and nanocrystals show NIR emission at ∼994 nm (1.24 eV), whereas the band gap of the hosts is in the UV region. Therefore, the Yb-emission does not suffer from self-absorption. The microcrystals exhibit a single-exponential decay with 2.7 ms long lifetime corresponding to 2 F 5/2 → 2 F 7/2 transition of Yb 3+ f electrons. The nanocrystals show biexponential decay (3 ms and 749 μs), probably because of the proximity of Yb to the surface of nanocrystals. Interestingly, NIR emission and perovskite structure of samples are stable for >3 months in ambient conditions for future optoelectronic applications.

Abstract The magnetization dynamics involved in applying an alternating field are composed of a superposition of Néel and Brownian relaxations. To evaluate the mechanisms of magnetic relaxations, it is necessary to individually evaluate the Néel and Brownian regimes. In this study, by applying a fast responding pulse field, the two-step magnetization response of magnetic nanoparticles dispersed in a fluid in the Brownian regime occurred after the Néel regime. We isolated Néel and Brownian relaxations from an experimentally observed superposition relaxation system by fitting the theoretical calculation to the measured time evolution response of the magnetization, which was in agreement with the susceptibility that was measured through applying an alternating magnetic field. The dependence of Néel and Brownian relaxation’s dominance in the superposition system on relaxation times was clearly observed. In particular, the effect of dipole interactions on Néel and Brownian relaxation times were confirmed by changing the particle concentration in a magnetic fluid. Elucidation of the…

This work demonstrates the chiral-induced spin selectivity effect for inorganic copper oxide films and exploits it to enhance the chemical selectivity in electrocatalytic water splitting. Chiral CuO films are electrodeposited on a polycrystalline Au substrate, and their spin filtering effect on electrons is demonstrated using Mott polarimetry analysis of photoelectrons. CuO is known to act as an electrocatalyst for the oxygen evolution reaction; however, it also generates side products such as H 2 O 2 . We show that chiral CuO is selective for O 2; H 2 O 2 generation is strongly suppressed on chiral CuO but is present with achiral CuO. The selectivity is rationalized in terms of the electron spin-filtering properties of the chiral CuO and the spin constraints for the generation of triplet oxygen. These findings represent an important step toward the development of all-inorganic chiral materials for electron spin filtering and the creation of efficient, spin-selective (photo)electrocatalysts for water splitting.

Aggregation-caused quenching (ACQ) has long been a problem that inhibits the application of organic light-emitting materials in organic light-emitting diodes, especially near-infrared (NIR) materials. Figuring out the reasons that induce ACQ is important for the quantum efficiency enhancement of NIR materials. In this paper, an NIR molecule (TPA-QCN) with thermally activated delayed fluorescence (TADF) is studied based on first-principles calculations and excited-state dynamics investigation in both toluene and in the aggregation state. Our calculation indicates that aggregation can induce a smaller energy gap between the first singlet excited state and the first triplet excited state, which is favorable for TADF. Both the decreased fluorescent rate and the increased nonradiative rate will induce emission quenching in the aggregation state. Based on detailed analyses of the reorganization energy and intermolecular interaction, we find that the hydrogen bond will induce enhanced contribution to the reorganization energy from C–H stretching vibration modes and thus a larger…

Recent investigations have revealed that some transition-metal dichalcogenides (TMDs), such as MoS 2 and WS 2, are excellent candidates for high-efficiency photocatalysts for water splitting. However, the high recombination rate of photogenerated carriers greatly hinders their practical application. A promising solution involves developing novel TMDs-based van der Waals (vdW) heterostructures with type-II band alignment. In this study, we used first-principles calculations to design two new heterostructures—MoS 2 /BSe and WS 2 /BSe—as potential photocatalysts and investigated their structures, stabilities, and electronic and optical properties. We found that both MoS 2 /BSe and WS 2 /BSe vdW heterostructures are stable and possess inherent type-II band alignment, which significantly suppresses the recombination of photogenerated carriers. Furthermore, their band edges straddle the redox potential of water, making them suitable for use as photocatalysts in water splitting. They also possess significant built-in electric fields, relatively high carrier mobilities, and excellent…

A novel flexible zinc oxide/poly(vinylidene fluoride) (ZnO/PVDF) nanocomposite was prepared by electrospinning for fabricating a piezoelectric nanogenerator (PNG). The ZnO nanoparticles (NPs) and nanorods (NRs) were used as nanofillers of piezoelectric PVDF to prepare fibrous nanocomposite membranes. It has been found that the addition of piezoelectric ZnO NPs and NRs can improve the overall performance of the PNGs fabricated with the electrospun membranes. A large electrical throughput (open circuit voltage ∼85 V and short circuit current ∼2.2 μA) from the ZnO NR/PVDF fiber membrane-based PNG (ZR-PNG) indicates that ZnO NRs are effective functional fillers for PVDF. The high aspect ratio and flexibility characteristics of ZnO NRs were found to be highly beneficial for improving the piezoelectric properties of the nanocomposites. ZnO NRs act as nucleating agents of β-phase PVDF, and ZnO NRs can also produce piezoelectric charges when they deform with the composite fibrous membrane. It has been concluded that the obvious synergistic effects between the piezoelectric nanofillers and…

This work is devoted to the development of quantitative structure–property relationship (QSPR) models using machine learning to predict CO 2 working capacity and CO 2 /H 2 selectivity for precombustion carbon capture using a topologically diverse database of hypothetical metal–organic framework (MOF) structures (358 400 MOFs, 1166 network topologies). Such a diversity of the networks topology is much higher than previously used (<20 network topologies) for rapid and accurate recognition of high-performing MOFs for other gas-separation applications. The gradient boosted trees regression method allowed us to use 80% of the database as a training set, while the rest was used for the validation and test set. The QSPR models are first built using purely geometric descriptors of MOFs such as gravimetric surface area and void fraction. Additional models which account for chemical features of MOFs are constructed using atomic property weighted radial distribution functions (AP-RDFs) with a novel normalization to accommodate the size diversity of the MOF database. It is shown that the best…

The spin–orbit charge-transfer-induced intersystem crossing (SOCT-ISC) in Bodipy-phenoxazine (BDP-PXZ) compact electron-donor/-acceptor dyads was studied. PXZ is the electron donor, and BDP is the electron acceptor. The molecular geometry is varied by applying different steric hindrance on the rotation about the linker between the two subunits. Charge-transfer (CT) absorption bands were observed for the dyads with more coplanar geometry (electronic coupling matrix elements is up to 2580 cm –1 ). Ultrafast charge separation (0.4 ps) and slow charge recombination (3.8 ns, i.e., SOCT-ISC process) were observed. Efficient ISC (Φ T = 54%) and long triplet-state lifetime (τ T = 539 μs) were observed for the dyads. Notably, the triplet-state lifetime is 2-fold of that accessed with heavy-atom effect, indicating the advantage of using a heavy-atom-free photosensitizer. The low-lying CT state in the dyads in polar solvents was confirmed with intermolecular triplet photosensitizing method. Time-resolved electron paramagnetic resonance spectroscopy show that the electron spin polarization of…

The wet chemical processes of LiFePO 4, hydrothermal synthesis and hydrometallurgical recovery, are of great importance during the life cycle of LiFePO 4 . To analyze these two processes, E-pH diagrams for the Li-Fe-P-H 2 O system are plotted from 298 to 473 K in this study. The E-pH diagrams can well explain the practical operating conditions of hydrothermal synthesis and hydrometallurgical recovery and provide thermodynamic basis for them. Besides, suitable conditions for the hydrothermal synthesis of LiFePO 4 are obtained from the E-pH diagrams, including high temperature, low redox potential, optimum pH 7.8–8.4, and excess stoichiometric lithium. As found in the E-pH diagrams, LiFePO 4 will change to ferric phosphate by promoting the redox potential, while lithium will be extracted to the aqueous solution. Based on the above results, a method is proposed for the selective leaching of lithium from spent LiFePO 4, which is successfully verified by leaching experiments. At room temperature (298 K), neutral pH (7.0), and low liquid–solid ratio (5:1), 95.4% of lithium can be…

In this article, experimental and classical mechanics-based approaches have been used to study the reinforcing capabilities of hexagonal boron nitride (h-BN) nanosheets for polyethylene (PE)-based nanocomposites. Experiments were performed with h-BN nanoflakes and high-density polyethylene-based nanocomposites. Experimental results reported 27.0 and 64.1% improvement in tensile strength and Young’s modulus for 5 wt % h-BN loading in PE, respectively. Experimental analysis helps in developing a micro- and macrolevel understanding of the mechanical behavior of BN/PE nanocomposites, whereas the strength of these nanocomposites is governed by interfacial properties. Interfacial properties can be easily captured using atomistic simulations such as molecular dynamics. Molecular dynamics-based atomistic models were developed to study the effect of aspect ratio, weight fraction, morphology, distribution of h-BN nanosheets, and strain rate loading on mechanical properties of the nanocomposite. A reactive force field was employed to simulate the mechanical behavior of polyethylene and h-BN…

The ever-increasing power of modern supercomputers, along with the availability of highly scalable atomistic simulation codes, has begun to revolutionize predictive modeling of materials. In particular, molecular dynamics (MD) has led to breakthrough advances in diverse fields, including tribology, catalysis, sensing, and nanoparticle self-assembly. Furthermore, recent integration of MD simulations with X-ray characterization has demonstrated promise in real-time 3-D characterization of materials on the atomic scale. The popularity of MD is driven by its applicability at disparate length/time scales, ranging from ab initio MD (hundreds of atoms and tens of picoseconds) to all-atom classical MD (millions of atoms over microseconds), and coarse-grained (CG) models (micrometers and tens of microseconds). Nevertheless, a substantial gap persists between AIMD, which is highly accurate but restricted to extremely small sizes, and those based on classical force fields (atomistic and CG) with limited accuracy but access to larger length/time scales. The accuracy and predictive power of…

The unexpected visible-light absorption, low recombination of electron–hole pairs, and high carrier mobility are found in a novel two-dimensional (2D) InSe/Zr 2 CO 2 van der Waals heterostructure for overall water splitting photocatalysis. The photocatalytic mechanism has been systematically investigated using first-principles calculations for the first time. We prove that the 2D InSe/Zr 2 CO 2 heterostructure is a robust and promising visible-light photocatalyst with several distinct advantages, as follows. It has a direct band gap of 1.81 eV, which is a more favorable band gap for visible-light photocatalysis. Its type-II band alignment directly leads to a significant electron–hole separation with electrons (holes) localized in the InSe (Zr 2 CO 2 ) monolayer. The indirect band gap of the InSe (Zr 2 CO 2 ) monolayer further suppresses the electron–hole recombination in it. Naturally, the recombination of the photogenerated electrons and holes is greatly suppressed in the InSe/Zr 2 CO 2 heterostructure, which improves the solar energy utilization effectively. Moreover, a large…

The exciton band dispersion in π-stacks of conjugated organic chromophores is a critical factor in determining the photophysical response and transport properties. In such stacks, the exciton band width and, in particular, the curvature at the band center, is determined by an interference between short-range coupling due to wave function overlap and long-range Coulomb coupling arising from transition dipole–dipole interactions. The interference can be completely destructive, yielding a dispersionless “flat” band resulting in an unusual situation where the aggregate displays monomer-like properties, despite having closely spaced chromophores. Coupled chromophores such as these are called “null aggregates” and the perfect balance of interactions that leads to them are referred to as “null points”. Here, we study two perylene diimide (PDI) derivatives where positive long-range coupling induces H-aggregate behavior, whereas counteracting short-range coupling induces J-aggregate behavior. As such, both derivatives display so-called HJ-aggregate properties but are shown here to straddle a…

In this work, we have assessed coumarin as a quantitative probe for hydroxyl radical formation in heterogeneous photocatalysis. Upon reaction with the hydroxyl radical, coumarin produces several hydroxylated products, of which one, 7-OH-coumarin, is strongly fluorescent. The fluorescence emission is strongly affected by inner filtering due to the presence of coumarin. Therefore, we performed a series of calibration experiments to correct for the coumarin concentration. From the calibration experiments, we could verify that the inner-filtering effect can be attributed to the competing absorption of the fluorescence excitation light between coumarin and 7-OH-coumarin. Through judicious calibration for the inner-filtering effects, the corrected results for the photocatalytic system show that the rate of hydroxyl scavenging is constant with time for initial coumarin concentrations of ≥50 μM under the conditions of our experiments. The rate increases linearly with coumarin concentration, as expected from the Langmuir–Hinshelwood model. Within the coumarin concentration range used here,…

A comprehensive mechanistic framework is key to the effective utilization of model catalytic reactions. Although the reduction of 4-nitrophenol by borohydride has emerged as one of the most widely used model reactions for accessing the catalytic activity of nanostructures, there still exist knowledge gaps. The cause of the induction time, which is a period at the beginning of the reaction where no reaction seemingly occurs, has long been the subject of debate. Recent work provides compelling experimental evidence that links the induction time to the consumption of dissolved oxygen within the aqueous reactants and provides a mechanistic understanding based on a previously unknown side reaction. A concern has, however, been raised that the proposed mechanism is unable to account for prior work showing the induction time to be independent of the borohydride concentration. Here, a systematic study is presented that re-examines this dependency where reactions are simultaneously monitored using spectroscopy and an in situ dissolved oxygen probe. The dependency is shown to be far more…

Herein, a one-step solvothermal method was applied to produce CuBi 2 O 4 /CuO heterojunctions containing nanocolumns with small platelike nanoparticles homogeneously distributed over its surface. The photocatalytic activity of the heterojunctions was evaluated through the photodegradation of Methylene Blue (MB) dye and Metronidazole (MTZ) under simulated solar light and visible light irradiation, respectively. The heterojunction CuBi 2 O 4 /CuO-b showed an enhanced photocatalytic performance with 98% removal of MB (@2 sun simulated solar irradiation) and 36% removal of MTZ (@1 sun visible light) within 60 min of irradiation, compared to the results obtained with the pristine materials (CuO and CuBi 2 O 4 ) or the other composite synthesized CuBi 2 O 4 /CuO-a. The apparent quantum efficiency for MB photocatalytic degradation using the optimized photocatalyst and 180 min of light irradiation is ∼2.1%, under the excitation wavelength of 540 nm. This enhanced photocatalytic performance is a result of an effective charge separation through a type-II heterojunction, indicating that…

This work presents a more realistic study on the potential of titanium carbide MXene (Ti 3 C 2 T x ) for gas sensing, by employing first principle calculations. The effects of different ratios of different functional groups on the adsorption of NH 3, NO, NO 2, N 2 O, CO, CO 2, CH 4, and H 2 S gas molecules on Ti 3 C 2 T x were analyzed. The results indicated that Ti 3 C 2 T x is considerably more sensitive to NH 3, among the studied gas molecules, with a charge transfer of −0.098 e and an adsorption energy of −0.36 eV. By analyzing the electrostatic surface potential (ESP) and the projected density of states (PDOS), important physical and mechanical properties that determine the strength and nature of gas-substrate interactions were investigated, and also, the significant role of electrostatic effects on the charge transfer mechanism was revealed. Further, the Bader charge analysis for the closest oxygen and fluorine atoms to NH 3 molecule showed that oxygen atoms have 60% to 180% larger charge transfer than fluorine atoms, supporting that Ti 3 C 2 T x substrate with a relatively…

Dexterity in the application of defect engineering implicates modification in the physical properties of two-dimensional (2D) transition metal dichalcogenides (TMDs) to enhance their effectiveness toward nanoelectronics applications. Subsequently, the existence of various types of defects in monolayer MoS 2 has been employed to inculcate and implement their significance in enhancing the Li/Na-ion storage capability of MoS 2 monolayers as anodes of lithium ion batteries (LIBs) and sodium ion batteries (SIBs). DFT calculations have guided us to traverse the effect of various point and antisite defects on Li/Na adsorption energy and the diffusion barrier of monolayer MoS 2 . Before looking into Li/Na adsorption properties of defective MoS 2, the structural stability of various defects is explored with relevance to their formation energy. This also germinates the quest for the most stable defective structures that could be a reliable anode material for LIBs and SIBs. Enhanced adsorption is found for both Li/Na ions in the case of defective MoS 2 over that corresponding to pristine MoS 2…

The functionality of many biological systems depends on reliable electron transfer with minimal heating. Interestingly, nature realizes electron transport via insulating molecules, in contrast to man-made electronic devices which are based on metals and semiconductors. The high efficiency of electron transfer through these organic molecules is unexpected for tunneling-based transport, and it is one of the most compelling questions in the field. Furthermore, it has been shown that the electron tunneling probability is strongly spin-dependent. Here, we demonstrate that the chiral structure of these molecules gives rise to robust coherent electron transfer. We introduce spin into the analysis of tunneling through organic helical molecules and show that they support strong spin filtering accompanied by enhanced transmission. Thus, our study resolves two key questions posed by transport measurements through organic molecules.

The electrochemical activity of the basal plane and edge plane of graphite has long been a subject of an extensive debate. While significant advances have been made, several gaps still exist in our understanding of this issue, namely, the relative differences in the electrochemical activity of the perfect basal plane and perfect edge plane and the dependence of measurable electrochemical quantities on the edge/defect density of the basal plane. In this work, we employ a microdroplet electrochemical cell technique and atomic force microscopy to measure localized electrochemical properties of the graphitic surface with known edge coverage. The electron transfer rate, capacitance, and density of electronic states of the perfect basal plane and perfect edge plane are estimated, and a qualitative model is proposed for the dependence of the electrochemical quantities on the defect density of the basal plane.

A series of Er-doped TiO 2 photocatalysts, using Er(NO 3 ) 3 ·6H 2 O precursor ranging from 0.5 to 2 mol %, were synthesized via sol–gel method with titanium(IV) isopropoxide solution as reactant. The structure and properties of as-prepared samples were characterized by scanning electron microscopy, transmission electron microscopy, X-ray diffraction, UV–vis spectroscopy, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy, thermogravimetric analysis, photoluminescence, electrochemical impedance spectroscopy, and photocurrent. The as-synthesized Er-doped TiO 2 nanoparticles demonstrated improved photocatalytic activities for the photodegradation of selected volatile organic compounds, including acetaldehyde, o -xylene, and ethylene. Additionally, high photodegradation of acetaldehyde was recorded in the visible region (λ > 420 nm). XPS analysis revealed that a handful of Er in anatase TiO 2 was presented in the form of Er 2 O 3, which benefited by increasing the specific surface area ranging from 59.28 to 110.34 m 2 /g and consequently enhanced the…

Thorough analyses of structural factors in catalysis are interesting because they allow the massive prescreening of potential optimum compositions. Overall, this article shows how the orbital physics of magnetic compositions relates with spin–lattice interactions and then band gaps and bond lengths together become relevant descriptors in catalytic oxygen technologies. Active electrocatalysts for the oxygen evolution reaction (OER) include magnetic oxides with metals at relatively high oxidation states, so chemisorbed molecular O 2 is not very stable. On the other hand, ideal compositions for the oxygen reduction reaction (ORR) have metals in a comparatively lower oxidation state, which can supply electrons to activate O 2 molecules toward electron-richer oxygen atoms. Spin–lattice interactions in these strongly correlated oxides relate the orbital configurations and oxidation state with distinctive metal–oxygen bond distances, indicating localized or itinerant electronic behavior and selectivity in oxygen electrochemistry. OER at low overpotentials coincides with anti-Jahn–Teller…

How magnetism emerges in low-dimensional materials such as transition metal dichalcogenides at the monolayer limit is still an open question. Herein, we present a comprehensive study of the magnetic properties of single-crystal and monolayer VSe 2, both experimentally and ab initio . Magnetometry, X-ray magnetic circular dichrosim (XMCD), and ab initio calculations demonstrate that the charge density wave in bulk stoichiometric VSe 2.0 causes a structural distortion with a strong reduction in the density of states at the Fermi level, prompting the system toward a nonmagnetic state but on the verge of a ferromagnetic instability. In the monolayer limit, the structural rearrangement induces a Peierls distortion with the opening of an energy gap at the Fermi level and the absence of magnetic order. Control experiments on defect-induced VSe 2−δ single crystals show a breakdown of magnetism, discarding vacancies as a possible origin of magnetic order in VSe 2 .

Anion-exchange membrane fuel cells and electrolyzers offer a unique opportunity of using non-noble metal electrocatalysts for catalyzing the sluggish oxygen reduction and oxygen evolution reactions (ORR and OER). In recent years, various Mn-based oxides were identified as promising catalysts for both reactions. While electrocatalytic activity of such oxides is well addressed, their stability is still to be proven. Herein, we investigate the stability of four main manganese oxide allotropes by following their Mn dissolution rate in operando ORR and OER conditions. Using an electrochemical on-line inductively coupled plasma mass spectrometer, we uncover unexpected instability of this class of catalysts, with different degradation mechanisms identified under OER and ORR conditions. The reason for their degradation is shown to be related to the production of hydrogen peroxide species on manganese oxides during ORR. Furthermore, we discuss how limits in thermodynamically stable windows of each Mn oxidation state lead to increased dissolution during applications with high potential…

The study of interactions between Au nanostructures and living cells is a fundamental aspect that can be applied for promising applications in nanomedicine. In the present work, we performed coarse-grained molecular dynamics (MD) simulations to observe the internalization pathways of Au nanostructures (nanospheres, nanocages, nanorods, nanoplates, and nanohexapods) into an idealized mammalian plasma membrane at an unprecedented level of complexity. Compared with a simple lipid bilayer model consisting of two lipid species, the different cellular uptake pathways of the gold nanoparticle (AuNP) were found. We highlight that the complexity of the lipid bilayer models plays an important role in the uptake pathway of nanoparticles (NPs). The permeability of aggregated AuNPs was much less than the NP counterpart. Spherical AuNPs showed pronounced size and surface charge dependence in their translocation through the plasma membrane. The translocation rates of different Au nanostructures were also evaluated, and we found that the Au nanohexapod exhibited highest cellular uptake.…

Comprehensive experimental and density functional theory simulations have been performed for the enhanced photoelectrochemical performance of γ irradiated g-C 3 N 4 and its heterojunction with BiVO 4 . The structure and morphology of g-C 3 N 4 @BiVO 4 as a heterojunction were analyzed and verified from the correlation of experimental and theoretical data. It is found that γ radiations have changed the bonding structure of g-C 3 N 4, which ultimately reduces the optical band gap energy. Moreover, the performance of γ irradiated g-C 3 N 4 is two-fold, compared to that of the nonirradiated one, and increases from 3.59 to 5.86 μA cm –2 at 1.23 V versus Ag/AgCl in 0.5 M Na 2 SO 4 electrolyte solution (pH 7). Finally, it is observed that the performance of γ irradiated g-C 3 N 4 in the g-C 3 N 4 @BiVO 4 heterojunction increased from 0.53 to 1.38 mA cm –2, compared to that of the nonirradiated one. In summary, it has been concluded that γ irradiated g-C 3 N 4 and its heterojunction can potentially be applied in PEC solar water splitting.

The possibility to control and transform the magnetic domain structure during the growth process of NiFe nano-objects with the ability to realize single-, two-, and multidomain states within a single particle is shown. It was found that a single-domain state is possible when the crystallite size corresponds to the particle size. The configuration of polycrystalline NiFe nanoparticles determined the transition between two-domain and multidomain states. This was made possible by the controlled growth of NiFe nano-objects in the initial stages of electrolyte deposition. Among other things, it was shown that an increase in the nanoparticles density in arrays of zero-dimensional objects near the percolation threshold reduces the domain magnetic moment due to the enhancement of the magnetic exchange interaction and partial reorientation of the magnetization vectors. At the same time, the size of the domain wall remains insensitive to particle size, filling density, and value of the domain magnetic moment.

We provide a visualization method to observe the photoinduced charge transfer and electron–hole coherence in the two-photon absorption (TPA), especially including the optical properties in the “hidden” intermediate states in TPA. A new method for analyzing the characteristics of two-photon excitation is proposed using a two-step process, which is closest to the physical reality process. These visualization methods include transition density matrix, charge density difference, and transition dipole moment in TPA involving both ground and excited state wavefunctions and the transition dipole moments among electric transitions from ground to intermediate and to final excited states. Our visualization method of photoinduced CT and electron–hole coherence in TPA can promote deeper understanding and design molecules with large cross sections in TPA.

Van der Waals heterostructures (vdWHs) are attracting a lot of interest for fundamental studies and fabricating novel devices. Currently, most vdWHs exhibit type-I or type-II band alignment, and few systems have been shown to be in the type-III class. Herein, we show first-principles evidence that WTe 2 /HfS 2 vdWH possesses the long-sought type-III band alignment with a broken gap, providing a promising platform for developing tunnel field-effect transistors. Moreover, the electronic features of WTe 2 /HfS 2 vdWH can be effectively modulated via external strain and electric field. Particularly, an interesting transition from type-III to type-II band alignment can be observed in WTe 2 /HfS 2 vdWH upon the application of strain or electric field, which holds great potential for designing multifunctional devices. Our study not only predicts an extraordinary vdWH with type-III band alignment but also provides an outstanding candidate for realizing multiple band alignment transformation.

Low-dimensional all-inorganic metal halide perovskites have been demonstrated as excellent building blocks for high-performance optoelectronic devices. Although many progresses have been achieved in low-dimensional all-inorganic perovskites, the substitution of toxic Pb is urgent for further optoelectronic applications. Here, we present the growth of lead-free all-inorganic CsSnX 3 (X = Cl, Br, and I) perovskite nanowire (NW) arrays on a mica substrate by a solid-source chemical vapor deposition method. All of the lead-free all-inorganic CsSnX 3 perovskite NW arrays epitaxially grow on the mica substrate to form equilateral triangles. The band gaps of the as-prepared CsSnX 3 perovskite NW arrays decrease from 1.84 to 1.34 eV with X changes from Br to I. The high crystallinity is confirmed by the strong photoluminescence (PL) emission peaks and uniform two-dimensional PL mapping images. In the end, the as-prepared high-quality CsSnI 3 perovskite NW array is then configured into a near-infrared photodetector for the first time, exhibiting fast rise and decay time constants of 83.8 and…

Toward the development of classical force fields for the accurate modeling of clay mineral-water systems, we have extended the use of metal–O–H (M–O–H) angle bending terms to describe surface Si–O–H bending for hydrated kaolinite edge structures. Kaolinite, comprising linked octahedral Al and tetrahedral Si sheets, provides a rigorous test by combining aluminol and silanol groups with water molecules in hydrated edge structures. Periodic density functional theory and classical force fields were used with molecular dynamics to evaluate the structure, dynamics, hydrogen bonding, and power spectra for deriving optimum bending force constants and optimal equilibrium angles. Cleavage energies derived from density functional theory molecular dynamics calculations indicate the relative stabilities of both AC 1 and AC 2 edge terminations of kaolinite where Si–OH and Al–(OH 2 ) or Si–OH, Al–OH, and Al–(OH 2 ) groups exist, respectively. Although not examined in this study, the new Si–O–H angle bending parameter should allow for improved modeling of hydroxylated surfaces of silica minerals…

Type II van der Waals (vdW) heterobilayers of six group III chalcogenide monolayers (MX; M = Ga, In; X = S, Se, Te) have been systematically investigated and compared with the pristine monolayers via hybrid HSE06 functional based DFT calculations in order to evaluate their utility in photocatalysis and 2D excitonic solar cells. The interfacial binding energies of the type II vdW heterobilayers reported herewith, using DFT-D3, is found to vary from −15 to −25 meV/Å 2, which is higher than that in graphite (−12.0 meV/Å 2 ). Out of the three stacking orders in the heterobilayers studied in this work, the most energetically favorable one has been considered for photocatalytic and solar cell applications. The various aspects of stabilities of these heterobilayers, such as, energetic, lattice dynamical, and mechanical, have been confirmed. Our investigation shows that InS/InSe and GaTe/InS heterobilayers are semiconductors having a direct band gap of 2.31 and 1.28 eV respectively, although the individual monolayers show indirect band gaps. The power conversion efficiency is found to reach…

Controlled synthesis of atomically precise metal nanoclusters (MNCs) and fundamental understanding of their physical properties have emerged as an active area of research because of their potential applications in healthcare and energy-related materials. In the present study, atomically precise copper nanoclusters (Cu NCs) have been synthesized from nonluminescent plasmonic copper nanoparticles (Cu NPs) by core etching with excess reduced glutathione (GSH). Electrospray ionization (ESI) mass spectrometry confirms the formation of kinetically controlled, polydisperse Cu 34–32 (SG) 16–13 NCs at room temperature and monodisperse Cu 25 (SG) 20 NCs at elevated temperature (70 °C). Cu 34–32 (SG) 16–13 NCs exhibit weak red emission (625 nm), while Cu 25 (SG) 20 NCs emit intense blue luminescence at 442 nm with 9.7% quantum yield. Rational tuning of reaction temperature, pH, GSH concentration, and reaction time are crucial for the composition and emission band tuning of atomically precise Cu NCs. Interestingly, Cu 34–32 (SG) 16–13 NCs exhibit an aggregation induced emission (AIE) with…

The introduction of metal–organic framework materials into photocatalysts is considered to be an effective strategy for improving the transfer and separation efficiency of photogenerated electron–hole pairs. In the present study, we demonstrate the delicate construction of NH 2 -UiO-66/ZnIn 2 S 4 (NU66/ZIS) composites as bifunctional photocatalysts with the degradation efficiency of malachite green (98%) and the hydrogen evolution rate of a 10% NU66/ZIS composite reaching up to 2199 μmol h –1 g –1 . The characterization of unique ZIS/NU66 shows that it can efficiently facilitate the separation and transfer of light-induced charges and exposed rich active sites for photocatalyst redox reaction. Moreover, the results of vitro cytotoxicity assay suggest that NU66/ZIS composites are potential safety photocatalysts to the environment and human beings. Furthermore, the DFT calculation indicates that the Zr site of NU66 and In site of ZnIn 2 S 4 interface should be the main active center in NU66/ZIS heterojunctions.

Abstract The TM-doped Si-based semiconductor clusters have aroused increased attention in a lot of fields. Here, we have performed a structural search of the global minimum for neutral and anionic Sin and La2Sin (n = 1–12) clusters by utilizing the efficient CALYPSO structural searching method with subsequent DFT optimization at the B3LYP level. A large population of low energetic and stable clusters is obtained, and then, the most stable isomers for different cluster sizes are confirmed in light of their total energy and PES spectra. The effect of dopants on the geometries and electronic properties of silicon clusters and their anions are investigated. It is found that the La atoms as well as charges generate distinct influences on them. In all most stable structures of La2Sin0/–, the impurity La atoms prefer the convex-capped positions of the skeleton and act as the electron donators. The analysis of stability reveals that La2Si3 with a bitriangular pyramid framework is very stable across the cluster size range of n = 1–12. The reason might be that there is pd hybridization…

Metal–organic frameworks (MOFs) are extensively employed for environmental remediation due to their outstanding physical and chemical properties. Herein, we have demonstrated the complete and simplistic synthesis of CdS/MIL-53(Fe) using the solvothermal method. The prepared MOF was characterized thoroughly in terms of structural, crystalline, optical, compositional, and textural properties with the help of FESEM, TEM, PXRD, FTIR, PL, EDS elemental mapping, and N 2 adsorption–desorption analysis. The as-synthesized CdS/MIL-53(Fe) was employed for the decomposition of ketorolac tromethamine (KTC) in the aqueous phase under 330 min of visible light illumination. CdS/MIL-53(Fe) showed improved degradation efficiency (80%) for the removal of KTC as compared to pristine MIL-53(Fe). The primary reason attributed for the improvement in photocatalytic efficiency is the formation of the CdS-MIL-53(Fe) heterostructure, which assists in transfer and separation of generated photoinduced carriers. Moreover, the mechanism for the photodegradation of KTC with CdS/MIL-53 was proposed based on the…

Abstract We expose significant changes in the emission color of carbazole-based thermally activated delayed fluorescence (TADF) emitters that arise from the presence of persistent dimer states in thin films and organic light-emitting diodes (OLEDs). Direct photoexcitation of this dimer state in 1,2,3,5-tetrakis(carbazol-9-yl)-4,6-dicyanobenzene (4CzIPN) reveals the significant influence of dimer species on the color purity of its photoluminescence and electroluminescence. The dimer species is sensitive to the sample preparation method, and its enduring presence contributes to the widely reported concentration-mediated red shift in the photoluminescence and electroluminescence of evaporated thin films. This discovery has implications on the usability of these, and similar, molecules for OLEDs and explains disparate electroluminescence spectra presented in the literature for these compounds. The dimerization-controlled changes observed in the TADF process and photoluminescence efficiency mean that careful consideration of dimer states is imperative in the design of future TADF…

Electrochemical CO 2 reduction reaction (CO 2 RR) to fuels represents one of the most attractive approaches to mitigate our pressing energy and environmental threats. Cu is the best known metal catalyst that can produce an appreciable amount of hydrocarbons from CO 2, but it suffers from a high overpotential and poor selectivity. In this work, by means of first-principles calculations, we predict that Cu-based single-atom alloys (SAAs) could be exceptional electrocatalysts for CO 2 RR. In particular, we predict that Co@Cu SAA could be a promising catalyst on which methanol can be produced at a low overpotential and high selectivity. The isolated Co atoms lead to a narrowed d-band and an upshifted d-band center which can stabilize chemisorbed CO 2 on a surface, significantly lowering the reaction barrier. The narrowed Co d-band increases the bonding to a key intermediate, which in turn eliminates the need for its migration and enables a selective and efficient production of CH 3 OH through the pathway of CO 2 → COOH* → CO* → COH* → CHOH* → CH 2 OH* → CH 3 OH.

Theoretical estimation of the activation energy of electrochemical reactions is of critical importance but remains challenging. In this work, we address the usage of an implicit solvation model for describing hydrogen evolution reaction steps on Pt(111) and Pt(110) and compare with the “extrapolation” approach as well as single-crystal measurements. We find that both methods yield qualitatively similar results, which are in fair agreement with the experimental data. Care should be taken, however, in addressing spurious electrostatic interactions between periodically repeated slabs in the VASPsol implementation. Considering the lower computational cost and higher flexibility of the implicit solvation approach, we expect this method to become a valuable tool in electrocatalysis.

On the basis of the first-principles calculation, single transition-metal (TM) atoms of first and second transition series are anchored on the β 12 phase of the boron monolayer (BM) electrocatalyst for the sustainable production of ammonia (NH 3 ) by reducing nitrogen (N 2 ). We have found a new type of electrocatalyst, i.e., V atom support on the β 12 -BM (V/β 12 -BM), which has a low onset potential (0.28 V), low cost, high stability, high selectivity, and high efficiency under mild conditions. The difference charge density and local density of state further demonstrated that there is an “acceptance–donation” interaction between TM atom and N 2, and the ionization of 1π orbital of N 2 can greatly elongate the N–N bond length, leading to the activity enhancement of N 2 . We also point out that the bonding orbital (1π) and antibonding orbital (1π*) of N 2 play a crucial role in increasing the activity of N 2 . Further, the climbing nudged elastic band method and molecular dynamics simulation indicate that V/β 12 -BM has high dynamic and thermodynamic stabilities. Moreover, V/β 12…

Instability of perovskite photovoltaics is still a topic that is currently under intense debate, especially the role of the water environment. Unraveling the mechanism of this instability is urgent to enable practical application of perovskite solar cells. Here, ab initio metadynamics is employed to investigate the initial phase of a dissolution process of CH 3 NH 3 PbI 3 (MAPbI 3 ) in explicit water. It is found that the initial dissolution of MAPbI 3 is a complex multistep process triggered by the departure of I – ion from the CH 3 NH 3 I-terminated surface. Reconstruction of the free-energy landscape indicates a low energy barrier for water dissolution of MAPbI 3 . In addition, we propose a two-step thermodynamic cycle for MAPbI 3 dissolution in water at a finite concentration that renders spontaneity to the dissolution process. The low energy barrier for the initial dissolution step and the spontaneous nature of MAPbI 3 dissolution in water explain why water immediately destroys pristine MAPbI 3 . The dissolution thermodynamics of all-inorganic CsPbI 3 perovskite is also…

Doping with heteroatoms is being used as an effective way to change electronic structure of electrode materials for advanced storage systems. Herein, β-MnO 2 and rare earth (cerium) doped MnO 2 cathode materials have been successfully prepared for aqueous zinc ion batteries. Cerium doping induced structural transformation of MnO 2 from β- to α-phase, along with the evident improvement of conductivity, stability, and reversibility. Compared to the undoped β-MnO 2, the doping cathode possessed excellent cycling stability at a high rate of 5 C and higher rate capability. Cyclic voltammetry curves, electrochemical impedance spectroscopy, galvanostatic intermittent titration technique, scanning electron microscopy, and transmission electron microscopy measurements demonstrated that cerium doping caused fast Zn 2+ diffusion and excellent electrochemical stability.

The Z-scheme zinc molybdate/bismuth iron tungstate/reduced graphene oxide (ZnMoO 4 /BiFeWO 6 /rGO, ZM/BFW/rGO) ternary composite photocatalyst was prepared with rGO acting as an electron transmission mediator. The physicochemical properties of the materials were characterized by using a range of techniques such as SEM, TEM, EDS, FTIR, Raman, BET, TGA, and UV–vis DRS. The optical properties of the materials showed that ZM/BFW/rGO absorbed more visible light than the pristine ZnMoO 4 (ZM) and BiFeWO 6 (BFW). Thermal analysis showed enhanced stability of the ternary composite due to incorporation of thermally stable ZM. The composite material was used for photocatalytic degradation of 30 mg L –1 anthraquinonic acid blue 25 (AB 25) as the model pollutant under visible light irradiation. A degradation efficiency of 98% was achieved after 180 min degradation using ZM/BFW/rGO, while ZM and BFW showed only 24% and 36% dye removal efficiencies. About 70% total organic carbo (TOC) was attained with a ternary composite photocatalyst. The enhanced degradation was attributed to the formation of…

Highly exposed active facets and surface oxygen vacancies (OVs) are beneficial for the photocatalytic removal of various harmful organic compounds. In this study, uniform Zn 2+ -doped BiOI microspheres, assembled by ultrathin nanosheets with highly exposed {001} facets, with OVs were successfully synthesized for NO removal under visible light irradiation. The phase structure and chemical states are analyzed by means of X-ray diffraction and X-ray photoelectron spectroscopy, respectively. The transmission electron microscopy observations reveal that replacing Bi 3+ with Zn 2+ can lead to the increased exposure of the {001} facets. X-ray photoelectron and electron paramagnetic resonance spectroscopy results confirm that low-state Zn 2+ increases the number of OVs, indicating that an increased number of OVs and a reduced thickness of the nanosheets can enhance the photocatalytic activity for the removal of NO. The photo-oxidative removal efficiency of NO over 3%Zn-BiOI reaches 53.6% and remains highly stable (52.9%) for up to 210 min under visible light irradiation. The calculation of…

This work reports on the development of ionic liquid (IL)/poly(vinylidene fluoride) (PVDF) actuator composites. ILs sharing the same anion (bis(trifluoromethylsulfonyl)imide, [TFSI] − ), and different cations belonging to the families of pyridinium, imidazolium, and ammonium ions, comprising an alkyl side chains with variable length, were used. The physical–chemical properties, thermal behavior, mechanical, electrical, and bending responses of the PVDF/IL composites were evaluated. The incorporation of ILs into the PVDF matrix leads to an increase of the electroactive β phase content. Moreover, the β phase content increases with the increase of the IL alkyl chain length. The degree of crystallinity depends on the IL chain length as well as on the mechanical properties, revealing the plasticizing behavior exerted by the IL. The electrical conductivity decreased with the increase of the cation alkyl chain size. The highest bending response was observed for the [Pmim][TFSI]/PVDF and [Pmpip][TFSI] composites (where Pmim and Pmpip represent propylimidazolium and…

Oxidation of finely divided molybdenum sulfide in ambient air has been studied for air exposure times from 10 min to 1 year to clarify the nature of the reaction products and the mechanistic steps. At the initial steps, for air exposure times from several minutes to several hours, rapid oxidation of MoS 2 edges occurs with simultaneous formation of hydroxyl species and surface disulfide S 2 2– moieties as attested by 1 H NMR, X-ray photoelectron spectra, and temperature-programmed reduction. Prolonged air exposure of MoS 2 nanodispersions leads to deep oxidation. According to the results of X-ray absorption spectroscopy, UV–visible, and electron paramagnetic resonance spectroscopies, the main oxidation products are soluble paramagnetic molybdenum blue species and sulfuric acid. As shown by EXAS fitting, the major product is oxo-bridged dimolybdenyl Mo(V, VI) species. Ambient moisture plays an important role in the oxidation process as it contributes to the formation of sulfuric acid which leads to liquescence of the material and to deep oxidation without formation of a protective…

Development of new approaches to the noncontact optical thermometry is of great importance for modern science and technology. In the current work, single-phase YVO 4:Eu 3+ nanoparticles prepared via the modified Pechini technique were studied as luminescence thermometers. Thermal sensing was performed using two different ratiometric approaches: utilizing the luminescence intensity ratio between transitions emitted from two thermally coupled excited levels (emission spectrum) and between transitions originating from different thermally coupled low-lying levels (excitation spectrum). The first technique allows determining temperature within the 298–873 K range, whereas the second one allows determining temperature within 298–473 K. The spectral position of the 5 D 0 (1)– 7 F 1 (2) band was also suggested as a temperature-dependent parameter. Thermometric performance of YVO 4:Eu 3+ nanophosphors including absolute and relative sensitivities, minimum temperature uncertainty, and repeatability was obtained and discussed.

Utilization of non-lithium-ion batteries in next-generation renewable energy storage is hindered by the lack of appropriate electrode materials with desired electrochemical performance. Motivated by low peeling-off energy (Jing et al. Nano Lett. 2017, 17 (3), 1833−1838), an experimentally available two-dimensional material, nominated as GeP 3, is investigated as the anode for non-lithium-ion batteries (Na +, K +, Ca 2+, Mg 2+, Al 3+ ) based on density functional theory calculations. The electrochemical properties, i.e., ion intercalation mechanism, diffusion behavior, and theoretical capacities of different metal ions in GeP 3, are systematically investigated. A semiconductor-to-metal transition and improved conductivity are observed due to ions intercalation in the GeP 3 electrode. Even though the charge storage mechanism of Na and Ca ions is quite different, the GeP 3 monolayer has exhibited a high theoretical capacity of 1295.42 mAh g –1 for both Na + and Ca 2+ ions. Furthermore, collective Na ions transport at the phase boundary indicates that the sodiated GeP 3 electrode favors…

Nitric oxide electroreduction reaction (NOER) is one of the most attractive routes for ammonia synthesis and pollutant treatment. However, the current research efforts toward the NOER mainly focus on metal surface catalysts, while low-cost and high-efficiency single-atom catalysts (SACs) are rarely explored. Herein, using first-principles computations, we systematically investigate the NOER performance of a series of transition-metal-atom-decorated graphitic carbon nitride monolayer (g-C 3 N 4 ) and identify single Cu-atom-decorated g-C 3 N 4 (Cu@g-C 3 N 4 ) as the most promising SAC candidate for the NOER. Our results indicate that Cu@g-C 3 N 4 harbors excellent catalytic activity for the NOER with a quite low limiting potential of 0.371 V and, interestingly, is promising to be synthesized due to extremely high stability. Most importantly, Cu@g-C 3 N 4 can efficiently suppress the competing hydrogen evolution reaction, in favor of achieving high Faradaic efficiency. Our work provides a promising SAC candidate for the NOER to resolve environmental pollution and sustainable ammonia…

g-C 3 N 4 @ZIF-67 composite photocatalyst-supported NiSx are successfully prepared by a hydrothermal method using g-C 3 N 4 and ZIF-67 as carriers. The synthesized composite catalyst has an efficient photocatalytic H 2 production effect. Under visible light irradiation, the maximum H 2 production within 5 h over the [g-C 3 N 4 @ZIF-67/(10%wt)NiSx] photocatalyst is 208 μmol, which is 8.32 times higher than that of pure g-C 3 N 4 . Based on the analysis of scanning electron microscopy and transmission electron microscopy, it is not only known that g-C 3 N 4 and ZIF-67 provide space for the loading of NiSx nanoparticles but also that ZIF-67 as a carrier framework can effectively reduce the particle size of NiSx nanoparticles and increase the dispersion of NiSx. Further studies of photoluminescence (PL), time-resolved PL, i – t, linear scanning voltammetry, electrochemical impedance spectroscopy, and Mott–Schottky curves, we can not only know that the modification of NiSx nanoparticles do enhance the electron transfer ability but also that the matched conduction band position between…

Poly(ethylene oxide) (PEO) is the most widely used compound as a solid-state (solvent-free) polymer electrolyte for Li batteries, mainly due to its low glass transition temperature ( T g ) and ability to dissolve Li salts. It is also frequently suggested that its cathodic stability renders it possible to operate with Li metal anodes in the design of high energy density storage devices. However, little is still known about the true interfacial chemistry between Li metal and PEO and how these two materials interact with each other. We are here exploring this relationship by the means of density functional theory (DFT)-based modeling. Using bulk structures and isolated PEO chains, we have found that there is a strong thermodynamic driving force to oxidize Li metal into lithium oxide (Li 2 O) when PEO is decomposed into C 2 H 4 and H 2, irrespectively of the PEO oligomer length. Explicit modeling of PEO on a Li(100) surface reveals that all steps in the decomposition are exothermic and that the PEO/Li metal system should have a layer of Li 2 O between the polymer electrolyte and the…

Halide perovskites such as methylammonium lead iodide (MAPbI 3 ) currently attract considerable attention because of their excellent optoelectronic properties and performance in solar cell devices. Despite tremendous research efforts to elucidate their fundamental properties, ion migration with the presence of ionic defects is still not fully understood. Here, various types of ionic defects for specific (100) and (112) lattice facets in single-crystal MAPbI 3 have been investigated systematically. Our measurements reveal significant anisotropic properties. Photoluminescence (PL) and electrical transport measurements show that the (100) facet has higher PL intensity and over 1 order lower trap density compared to that of the (112) facet. We find that the facet-dependent variations of contact potential difference measured with Kelvin probe force microscopy under different bias voltages and light illuminations provide insights into different types of ionic defects on the surface of MAPbI 3 single crystals. We also observe a completely different ion migration behavior on specific…

In this article, we derive and discuss a physics-based model for impedance spectroscopy of lithium batteries. Our model for electrochemical cells with planar electrodes takes into account the solid–electrolyte interphase (SEI) as a porous surface film. We present two improvements over standard impedance models. First, our model is based on a consistent description of lithium transport through electrolyte and the SEI. We use well-defined transport parameters, e.g., transference numbers, and consider convection of the center-of-mass. Second, we solve our model equations analytically and state the full transport parameter dependence of the impedance signals. Our consistent model results in an analytic expression for the cell impedance including bulk and surface processes. The impedance signals due to concentration polarizations highlight the importance of electrolyte convection in concentrated electrolytes. We simplify our expression for the complex impedance and compare it to common equivalent circuit models. Such simplified models are good approximations in concise parameter ranges.…

We develop parameters for the interlayer Kolmogorov–Crespi (KC) potential to study structural features of four transition-metal dichalcogenides (TMDs): MoS 2, WS 2, MoSe 2, and WSe 2 . We also propose a mixing rule to extend the parameters to their heterostructures. Moiré superlattices of twisted bilayer TMDs have been recently shown to host shear solitons, topological point defects, and ultraflat bands close to the valence band edge. Performing structural relaxations at the density functional theory (DFT) level is a major bottleneck in the study of these systems. We show that the parametrized KC potential can be used to obtain atomic relaxations in good agreement with DFT relaxations. Furthermore, the moiré superlattices relaxed using DFT and the proposed force field yield very similar electronic band structures.

The thermal stability of anatase titanium dioxide (TiO 2 ) is a prerequisite to fabricate photocatalyst-coated indoor building materials for use in antimicrobial and self-cleaning applications under normal room light illumination. Metal doping of TiO 2 is an appropriate way to control the anatase to rutile phase transition (ART) at high processing temperatures. In this work, ART of indium (In)-doped TiO 2 (In–TiO 2 ) was investigated in detail in the range of 500–900 °C. In–TiO 2 (In mol % = 0–16) was synthesized via a modified sol–gel approach. These nanoparticles were further characterized by means of powder X-ray diffraction (XRD), Raman, photoluminescence (PL), transient photocurrent response, and X-ray photoelectron spectroscopy (XPS) techniques. XRD results showed that the anatase phase was maintained up to 64% by 16 mol % of In doping at 800 °C of calcination temperature. XPS results revealed that the binding energies of Ti 4+ (Ti 2p 1/2 and Ti 2p 3/2 ) were red-shifted by In doping. The influence of In doping on the electronic structure and oxygen vacancy formation of…

Glass–ceramic solid electrolytes have been reported to exhibit high ionic conductivities. Their synthesis can be performed by crystallization of mechanically milled Li 2 S–P 2 S 5 glasses. Herein, the amorphization process of Li 2 S–P 2 S 5 (75:25) induced by ball milling was analyzed via X-ray diffraction (XRD), Raman spectroscopy, and 31 P magic-angle spinning nuclear magnetic resonance (NMR) spectroscopy. Several structural building blocks such as [P 4 S 10 ], [P 2 S 6 ] 4–, [P 2 S 7 ] 4–, and [PS 4 ] 3– occur during this amorphization process. In addition, high-temperature XRD was used to study the crystallization process of the mechanically milled Li 2 S–P 2 S 5 glass. Crystallization of phase-pure β-Li 3 PS 4 was observed at temperatures up to 548 K. The kinetics of crystallization was analyzed by integration of the intensity of the Bragg reflections. 7 Li NMR relaxometry and pulsed field-gradient (PFG) NMR were used to investigate the short-range and long-range Li + dynamics in these amorphous and crystalline materials. From the diffusion coefficients obtained by PFG NMR,…

Layered lead halide perovskites such as butylammonium lead bromide (BA 2 PbBr 4 ) possess a multiple-quantum-well structure, which is expected to enhance the interaction between the excitons and Mn dopants. Therefore, doping Mn in large single crystals of layered perovskites may induce interesting magneto-optic and magneto-electric properties, with minimal contributions from the detrimental grain boundary effects. Furthermore, these single crystals show stark differences in excitonic absorption and emission (dual emission) compared with the measurements done on the ensemble of corresponding microcrystals. Therefore, exploring the exciton–Mn interactions by performing measurements on one large crystal is important. We report the one-pot synthesis of centimeter-sized Mn-doped BA 2 PbBr 4 single crystals to study the exciton–Mn interaction measured on a single crystal. Mn-doped BA 2 PbBr 4 single crystal shows dual excitonic emission, and both of the excitonic features transfer their energies nonradiatively to Mn dopants, yielding Mn d–d emission with quantum yield ∼26%. The Mn…

The results of our combined experimental (FTIR, XPS, HAADF-STEM, EXAFS) and density functional theory study reveal that Pd ions in zeolites, previously identified as Pd +3 and Pd +4 , are in fact present as super electrophilic Pd +2 species (ion pairs with the negatively charged framework oxygens). In this contribution we re-assign the spectroscopic signatures of these species, discuss the unusual coordination environment of “naked” (ligand-free) Pd +2 in SSZ-13, and their complexes with CO and NO. With CO, non-classical, highly positive [Pd(CO) 2 ] 2+ ions are formed with the zeolite framework acting as a weakly coordinating anion (ion pairs). Non-classical carbonyl complexes also form with Pt +2 and Ag + in SSZ-13. The Pd +2 (CO) 2 complex is remarkably stable in zeolite cages even in the presence of water. Dicarbonyl and nitrosyl Pd +2 complexes, in turn, serve as precursors to the synthesis of previously inaccessible Pd +2 -carbonyl-olefin [Pd(CO)(C 2 H 4 )] and -nitrosyl-olefin [Pd(NO)(C 2 H 4 )] complexes. Overall, we provide novel insight into the interactions of divalent…

Ultrathin two-dimensional Janus-type platinum dichalcogenide crystals formed by two different atoms at opposite surfaces are investigated by performing state-of-the-art density functional theory calculations. First, it is shown that single-layer PtX 2 structures (where X = S, Se, or Te) crystallize into the dynamically stable 1T phase and are indirect band gap semiconductors. It is also found that the substitutional chalcogen doping in all PtX 2 structures is favorable via replacement of surface atoms with a smaller chalcogen atom, and such a process leads to the formation of Janus-type platinum dichalcogenides (XPtY, where X and Y stand for S, Se, or Te) which are novel single-layer crystals. While all Janus structures are indirect band gap semiconductors as their binary analogues, their Raman spectra show distinctive features that stem from the broken out-of-plane symmetry. In addition, it is revealed that the construction of Janus crystals enhances the piezoelectric constants of PtX 2 crystals significantly both in the in-plane and in the out-of-plane directions. Moreover, it is…

Searching for efficient electrode materials with high power density, fast charge/discharge rate, and high conductivity is one of the key challenges in the development of metal ion batteries. Herein, by means of first-principles computations, we demonstrated that the two-dimensional Nb 2 S 2 C monolayer is a promising anode material for metal ion batteries. The Nb 2 S 2 C monolayer has rather good kinetic and thermodynamic stability, and it is metallic with considerable electronic states at the Fermi level. The production of the Nb 2 S 2 C monolayer from its experimentally known bulk phase via exfoliation strategies should be rather feasible because of the small cleavage energy of 0.38 J/m 2 . All the studied metal atoms, including Li, Na, K, and Mg, can be effectively adsorbed on the surface of the Nb 2 S 2 C monolayer with pronounced charge transfer. Especially, the diffusion of Li, Na, and K atoms on the Nb 2 S 2 C monolayer is rather feasible with a diffusion barrier of 0.23, 0.11, and 0.07 eV, respectively, whereas Mg has a relatively high diffusion barrier of 0.47 eV.…

In this paper, we present results from the detailed investigations on the synthesis, optical, emission, electrochemical, and ultrafast nonlinear optical (NLO) properties along with the excited state dynamics of zinc(II) 2,10,16,24-tetrakis(9-phenyl-9 H -carbazol-2-yl)phthalocyanine ( CBZPC1 ) and zinc(II) 2,10,16,24-tetrakis(4-(9 H -carbazol-9-yl)phenyl)phthalocyanine ( CBZPC2 ). Due to the presence of carbazole moieties, the Soret band was found to be broadened. The emission studies performed using different solvents revealed the fluorescence yields in the range of 0.10–0.27 and the time-resolved fluorescence data revealed radiative lifetimes of, typically, a few nanoseconds. Femtosecond transient absorption measurements indicated the formation of triplet states within the first nanosecond of photoexcitation. From the cyclic voltametric studies, the oxidation and reduction processes were found to be ring centered. Spectral changes in the UV–visible absorption were recorded by means of spectro-electrochemical analysis at an applied potential. The DFT and TD-DFT analysis was employed…

Abstract Divalent-cation-based batteries are being considered as potential high energy density storage devices. The optimization of electrolytes for these technologies is, however, still largely lacking. Recent demonstration of the feasibility of Ca and Mg plating and stripping in the presence of a passivation layer or an artificial interphase has paved the way for more diverse electrolyte formulations. Here, we exhaustively evaluate several Ca-based electrolytes with different salts, solvents, and concentrations, via measuring physicochemical properties and using vibrational spectroscopy. Some comparisons with Mg- and Li-based electrolytes are made to highlight the unique properties of the Ca2+ cation. The Ca-salt solubility is found to be a major issue, calling for development of new highly dissociative salts. Nonetheless, reasonable salt solubility and dissociation are achieved using bis(trifluoromethanesulfonyl)imide (TFSI), BF4, and triflate anion based electrolytes and high-permittivity solvents, such as ethylene carbonate (EC), propylene carbonate (PC), γ-butyrolactone (gBL),…

Polynitrogen compounds especially pentazolate anion complexes recently have attracted substantial attention due to their promising potential as high-energy-density materials. Here, using a machine-learning-accelerated crystal structure search method and first-principles calculations, we predict a new hybrid compound by inserting a large fraction of nitrogen into alkaline-earth metals. It is a new stoichiometric type MN 10 (M = Be, Mg), which possesses a metal-centering octahedral pentazolate framework with the space group Fdd 2. This type of ionic-like molecular crystal is found to be energetically more favorable than the mixtures of M 3 N 2 or MN 4 compounds and pure nitrogen and is possibly synthesized at relatively low pressures (around 12 GPa for MgN 10 ). The ab initio molecular dynamics simulations show that they are metastable and can be quenched to ambient conditions once synthesized at high pressure. Moreover, decomposition of this polymeric MN 10 structure can release a large amount of energy and shows high performance in detonation. The detonation velocity and pressure of…

Robust quantum energy storage devices are essential to realize powerful next-generation batteries. Herein, we provide a proof of concept for a loss-free excitonic quantum battery (EQB) by using an open quantum network model that exhibits exchange symmetries linked to its structural topology. By storing electronic excitation energy in a symmetry-protected dark state living in a decoherence-free subspace, one can protect the charged EQB from environment-induced energy losses, thereby making it a promising platform for long-term energy storage. To illustrate the key physical principles and potential functionality of this concept, we consider an open quantum network model of a para -benzene-like structure. We demonstrate through numerical simulations the immunity of the charged EQB to environmentally induced losses and further show how to harness the stored energy by adding a symmetry-breaking perturbation (SBP) to the network. We also investigate the impact of static disorder and temperature fluctuations of the SBP on the performance of the EQB during its storage and discharge phases.…

For the first time, the presence of the critical point (CP) of fluids confined in nanopores is unambiguously demonstrated and measured using a differential scanning calorimeter with an isochoric cooling procedure. The behavior of the CP of CO 2 and C 2 H 6 in SBA-15 is found to deviate from theoretical predictions. The heat involved in capillary condensation is also discussed. The new and simple method of measurement introduced in this study opens the way to further investigate the criticality of fluids confined in nanopores.

Structural and optical properties of antimony-containing sodium borate glasses were studied and their ultrafast third-order nonlinear optical (NLO) properties have been evaluated using Z -scan measurements with femtosecond (fs) pulses (∼150 fs, 80 MHz) at 750, 800, and 880 nm wavelengths. Glasses in the (mol %) 20Na 2 O–(80 – x )B 2 O 3 – x Sb 2 O 3 (where x = 0, 10, 20, and 30) system have been fabricated via melt quench technique. The structural modifications were analyzed using the Raman and magic angle spinning (MAS)-nuclear magnetic resonance (NMR) ( 11 B MAS-NMR and 23 Na MAS-NMR) techniques. The optical absorption spectra revealed that the absorption edge was red-shifted, suggesting the decrease in band gap energy with increase of antimony content in the glasses. Raman scattering results revealed that the boroxol rings are depressed with the incorporation of Sb 2 O 3 for replacing B 2 O 3 . 11 B MAS-NMR results showed a progressive increase of B 4 units at the expense of B 3 units. The Raman and 11 B MAS-NMR results support the formation of Sb 5+ ions due to oxidation of Sb…

Applications of photon upconverting nanoparticles (UCNPs) in biological imaging and solar energy conversion demand that their anti-Stokes luminescence be both tunable and efficient. Rational design of more efficient UCNPs requires an understanding of energy transfer (ET) between their lanthanide dopants, dynamics that are typically characterized by measuring luminescence lifetimes. Existing knowledge, however, cannot explain basic observations in lifetime experiments, such as their dependence on excitation power, significantly limiting the generality and reliability of lifetime measurements. Here, we elucidate the origins of the ET dynamics and luminescence lifetimes of Yb 3+ -, Er 3+ -co-doped NaYF 4 UCNPs using time-resolved luminescence and novel applications of rate equations and stochastic simulations. Experiments and calculations consistently show that at high concentrations of Er 3+, the luminescence lifetimes of UCNPs decrease as much as six-fold when excitation power densities are increased over 6 orders of magnitude. Since power-dependent lifetimes cannot be explained by…

The integration of ferromagnetic and semiconducting properties in a single two-dimensional (2D) material has been recognized as a fertile ground for fundamental science as well as for practical applications in information processing and storage. CrI 3 monolayer has recently drawn much attention due to its 2D long-range ferromagnetic (FM) order. However, its Curie temperature ( T C ) is too low (∼45 K) for practical spintronic applications. Here, we show that the in-plane FM coupling of CrI 3 can be remarkably enhanced by constructing a 2D heterostructure where CrI 3 monolayer is supported on a nonmagnetic normal semiconductor/insulator substrate. Choosing MoTe 2 monolayer as a substrate, we find that the CrI 3 /MoTe 2 2D heterostructure is an intrinsic semiconducting ferromagnet with T C of ∼60 K. The T C can be further increased to ∼85 K by applying an out-of-plane pressure of ∼4.2 GPa. The doubling of the T C in this 2D heterostructure comes from the introduction of extra spin superexchange (Cr–Te–Cr) paths. Our findings provide a promising pathway to improve ferromagnetism in 2D…

Two-dimensional polyaniline with structural unit C 3 N is an indirect semiconductor with 0.4 eV band gap, which has attracted a lot of interest because of its unusual electronic, optoelectronic, thermal, and mechanical properties useful for various applications. Adsorption of adatoms is an effective method to improve and tune the properties of C 3 N. Using first-principles calculations, we investigated the adsorption of adatoms, including H, O, S, F, Cl, B, C, Si, N, P, Al, Li, Na, K, Be, Mg, Ca, Sc, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, and Zn, on C 3 N. Depending on the adatom size and the number of valence electrons, they may induce metallic, half-metallic, semiconducting, and ferromagnetic–metallic behavior. In addition, we investigate the effects of an electrical field, charging, and strain on C 3 N and found how the electronic and magnetic properties are modified. Semi- and full hydrogenation are studied. From the mechanical and thermal stability of C 3 N monolayer, we found it to be a hard material that can withstand large strain. From our calculations, we gained novel insights into…

Thermal Al 2 O 3 atomic layer etching (ALE) can be accomplished using sequential fluorination and ligand-exchange reactions. HF can be employed as the fluorination reactant, and Al(CH 3 ) 3 can be utilized as the metal precursor for ligand exchange. This study explored the effect of HF pressure on the Al 2 O 3 etch rates and Al 2 O 3 fluorination. Different HF pressures ranging from 0.07 to 9.0 Torr were employed for Al 2 O 3 fluorination. Using ex situ spectroscopic ellipsometry (SE) measurements, the Al 2 O 3 etch rates increased with HF pressures and then leveled out at the highest HF pressures. Al 2 O 3 etch rates of 0.6, 1.6, 2.0, 2.4, and 2.5 Å/cycle were obtained at 300 °C for HF pressures of 0.17, 0.5, 1.0, 5.0, and 8.0 Torr, respectively. The thicknesses of the corresponding fluoride layers were also measured using X-ray photoelectron spectroscopy (XPS). Assuming an Al 2 OF 4 layer on the Al 2 O 3 surface, the fluoride thicknesses increased with HF pressures and reached saturation values at the highest HF pressures. Fluoride thicknesses of 2.0, 3.5, 5.2, and 5.5 Å were…

Wettability of alkylated quartz surfaces is of primary importance in several technological applications, including the development of oil and gas reservoirs and carbon geo-sequestration. It is intuitively understood and experimentally confirmed that hydroxylated quartz surfaces are hydrophilic. By gradually saturating a hydroxylated (001) α-quartz surface with pentyl groups, we show using molecular dynamics simulations that the surface can also exhibit extreme hydrophobicity. Within a range of surface pentyl group density from 0.29 to 3.18/nm 2, the contact angle of a water droplet under 10 MPa pressure of carbon dioxide at 300 K changes from 10–20 to 180°. This study has shown that a complete description of wettability of alkylated quartz surfaces requires three contact angles—one at the tip level of pentyl groups and two at the level of the quartz surface. The latter two are the contact angle of the spherical droplet and the hidden contact angle of a water “skirt” formed between the tip level of pentyl groups and the quartz surface. Analysis of the hidden contact angle unveils a…

Quantum chemistry-based codes and methods provide valuable computational tools to estimate reaction energetics and elucidate reaction mechanisms. Electronic structure methods allow directly studying the chemical transformations in molecular systems involving breaking and making of chemical bonds and the associated changes in the electronic structure. The link between the electronic structure and chemical bonding can be provided through the crystal orbital Hamilton population (COHP) analysis that allows quantifying the bond strength by computing Hamilton-weighted populations of localized atomic orbitals. Another important parameter reflecting the nature and strength of a chemical bond is the bond order that can be assessed by the density derived electrostatic and chemical (DDEC6) method which relies on an electron and spin density-partitioning scheme. Herein, we describe a linear correlation that can be established between the DDEC6-derived bond orders and the bond strengths computed with the COHP formalism. We demonstrate that within defined boundaries, the COHP-derived bond…

Abstract A general transmission line model that is able to describe accurately the measured impedance spectra of uncycled and cycled lithium electrodes is introduced. The model has all the essential features that are contained in analytical solutions for determining the impedance response of porous electrodes. In addition to that, it allows easy coupling between the various phenomena met in lithium anodes in contact with a separator: transport through a solid electrolyte interphase film, transport across “live lithium dendrites”, reaction inside “live lithium dendrites”, transport across “dead dendrites”, diffusion in a porous separator, and so forth. The model is used for quantitative analysis of measured impedance spectra collected at different C-rates and after different numbers of charge–discharge cycles. Further, combining impedance spectroscopy with scanning electron microscopy, several unique correlations between the morphological development of lithium anodes and development of impedance spectra are identified and discussed. Finally, several simplified schemes that allow…

Luminescence thermometry in the second and third optical windows of biological tissues has gained importance in recent years due to the reduction of both absorption and scattering effects in human tissues, which substantially increase its applicative potential. In this work, we present a luminescent thermometer based on SrTiO 3:Ni 2+,Er 3+ nanocrystals, which is the first reported study of nanothermometry based on Ni 2+ ion luminescence. The SrTiO 3:Ni 2+,Er 3+ nanocrystals were successfully synthesized using the Pechini method. The spectroscopic properties of obtained nanocrystals were investigated in a wide temperature range, namely, between −150 and 210 °C. It was found that Ni 2+ ions in the SrTiO 3 matrix are characterized by broadband emission localized in the II optical window at about 1200 nm, which additionally changes its spectral position toward longer wavelengths with the rise of temperature. Three temperature-dependent parameters were studied for luminescence thermometry: changes in the emission intensity of the Ni 2+ band, the spectral shift of its maximum, and the…

Transient photovoltage (TPV) is a technique frequently used to determine charge carrier lifetimes in thin-film solar cells such as organic, dye-sensitized, and perovskite solar cells. As this lifetime is often incident light intensity-dependent, its relevance to understanding the intrinsic properties of a photoactive material system as a material or device figure of merit has been questioned. To extract complete information on recombination dynamics, TPV measurements are often performed in conjunction with charge extraction (CE) measurements, to determine the photogenerated charge carrier density and thereby the recombination rate constant and its order. In this communication, the underlying theory of TPV and CE is reviewed and expanded. Our theoretical findings are further solidified by numerical simulations and experiments on organic solar cells. We identify regimes of the open-circuit voltage within which accurate lifetimes and carrier densities can be determined with TPV and CE experiments. A wide range of steady-state light intensities is required in performing these…

Abstract We report that UV–ozone treatment of TiO2 anatase thin films is an efficient method to increase the conductance through the film by more than 2 orders of magnitude. The increase in conductance is quantified via conductive scanning force microscopy on freshly annealed and UV–ozone-treated TiO2 anatase thin films on fluorine-doped tin oxide substrates. The increased conductance of TiO2 anatase thin films results in a 2% increase of the average power conversion efficiency (PCE) of methylammonium lead iodide-based perovskite solar cells. PCE values up to 19.5% for mesoporous solar cells are realized. The additional UV–ozone treatment results in a reduced number of oxygen vacancies at the surface, inferred from X-ray photoelectron spectroscopy. These oxygen vacancies at the surface act as charge carrier traps and hinder charge extraction from the adjacent material. Terahertz measurements indicate only minor changes of the bulk conductance, which underlines the importance of UV–ozone treatment to control surface-based defects.

Zinc substitution is often proposed as an efficient strategy to improve the performances of spinel ferrite nanoparticles, particularly related to their application as theranostic agents. In this work, a series of 8 nm spinel ferrite nanoparticles of formula Co x Zn y Fe 3–( x + y ) O 4 is synthesized by thermal decomposition with the purpose of investigating the role of Zn 2+ ions in modifying the structural and magnetic properties. Contrary to most of the literature on this subject, where the sum of Co and Zn is kept constant ( x + y = 1), here, the amount of Co is maintained at ca. x = 0.6, corresponding to the maximum of magnetic anisotropy of the Zn-undoped system, whereas the amount of Zn is progressively varied along the series from y = 0.05 to 0.4. This approach allows enlightening the effect of the Zn introduction on the magnetic and crystal structures and, particularly, on magnetic anisotropy, which is deeply investigated by several complementary techniques. A significant increase of the saturation magnetization, M S, upon the Zn content up to y = 0.4 is confirmed only at…

Controlling the electronic coupling between electron donor and acceptor subunits in a dyad is pivotal for the development of novel organic materials, for instance, thermally activated delayed fluorescence (TADF) materials and triplet photosensitizers. Herein, we prepared two compact electron donor/acceptor dyads based on phenothiazine (PTZ) and naphthalimide (NI) with different conformation restrictions induced by the C–N ( NI-N-PTZ ) or C–C ( NI-C-PTZ ) linkers. The effect of electronic coupling (matrix elements, V DA ) on the photophysical properties, especially the intersystem crossing (ISC) and the TADF, were investigated. NI-C-PTZ shows stronger ground-state electronic coupling ( V DA = 2548 cm –1 ) compared to NI-N-PTZ ( V DA = 870 cm –1 ). TADF was observed only for NI-N-PTZ due to its smaller electronic coupling. Time-resolved electron paramagnetic resonance (TREPR) spectroscopy indicated the presence two triplet excited states and three ISC mechanisms in NI-N-PTZ with different electron spin polarizations (ESP): radical pair ISC (RP-ISC) and spin–orbital charge transfer ISC…

Organic light-emitting materials with thermally activated delayed fluorescence (TADF) are promising for promoting the efficiency of organic light-emitting diodes (OLEDs) without any precious metals. However, the device performance of the deep-red/near-infrared (DR/NIR) TADF-OLEDs remains backward compared with that of blue, green, and orange-red TADF-OLEDs. In this contribution, a donor–acceptor type TADF emitter, 2-( tert -butyl)-6-(4-(diphenylamino)phenyl)phenanthro[4,5- abc ]phenazine-11,12-dicarbonitrile, namely, TPA-PPDCN, containing a large rigid phenanthro[4,5- abc ]phenazine-11,12-dicarbonitrile as an acceptor unit and a triphenylamine (TPA) as a donor moiety, is designed and synthesized. The compound exhibits excellent thermal stability, small singlet–triplet energy split and a strong DR/NIR emission with the photoluminescence quantum yields of 73–87% in doped thin films. More importantly, highly efficient DR and NIR OLEDs with emission peaks at 664 and 692 nm and the maximum external quantum efficiencies of 20.2 and 16.4%, respectively, have been achieved, which represent…

In this work, the structure of water and its interactions with various carbon dioxide reduction intermediates adsorbed on a Cu(211) surface is investigated using density functional theory. We find that the presence of adsorbates has a significant and adsorbate-specific effect on the local water structure and that solvation can stabilize adsorbate conformations different from those found in vacuum. We describe relationships between the hydrogen bonding capability of an adsorbate, the dipole moment of the adsorbate, the energetic strength of water–adsorbate interactions, and the change induced in the local water orientation by the adsorbate. Mechanistic implications are discussed. We investigate and quantify the error associated with using arbitrary locally optimized solvent structures in calculations of relevant physical quantities, such as solvated binding energies and work functions. Possible effects of thermal motion on calculations of the work function are investigated using ab initio molecular dynamics.

Cost effective inhibition of mild steel corrosion employing eco-friendly materials is a high priority subject for industries these days. Therefore, in this work, a series of N -(benzo[ d ]thiazole-2-yl)-1-phenylethan-1-imines [ N -(benzo[ d ]thiazole-2-yl)-1-phenylethan-1-imine (BTPEI), N -(benzo[ d ]thiazole-2-yl)-1-(3-chlorophenyl) ethan-1-imine (BTCPEI), N -(benzo[ d ]thiazole-2-yl)-1-( m -tolyl) ethan-1-imine (BTTEI), and N -(benzo[ d ]thiazole-2-ylimino) ethyl) aniline (BTPIA)] for mild steel protection in 1 M HCl were explored by adopting methods like gravimetric analysis, adsorption isotherms, and electrochemical methods, for example, electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. Different spectral characterization methods such as FTIR and 1 H NMR were used to confirm the synthesized derivatives. The experimental results affirmed that all of the inhibitors are proven to be very efficient for combating corrosion for mild steel in acidic media. The determined thermodynamic and activation parameters were used to provide a further understanding of…

High-entropy oxides (HEOx) are multicomponent (≥5) complex oxides that possess material properties and functions unexpected from their constituent simple oxides. Previous studies demonstrated that a cation-doped HEOx, MgCoNiCuZnO 5, shows good catalytic activity, excellent ionic conductivity, and high energy storage. The structural and mechanical stabilities of materials are pivotal to their applications. However, how temperature and pressure influence the structural stability of cation-doped HEOx and how doping affects the mechanical properties are yet to be understood. In this work, we investigated the structural stabilities of undoped and Li/Mn-doped MgCoNiCuZnO 5 in heating or under compression using in situ synchrotron X-ray diffraction (XRD), and determined their elastic moduli using high-pressure XRD. Our results show that the HEOx compounds are structurally stable at temperatures up to ∼450 °C or at pressures up to ∼50 GPa, and that Li/Mn doping makes the HEOx more compressible. Our molecular static (MS) calculations predicted that the formation reaction of a HEOx is…