The 10 most-cited articles in The Journal of Physical Chemistry, 2021

Inverse ZnO/Cu catalysts are key systems in the conversion of CO₂, a common atmospheric pollutant, into methanol, a high-value chemical and fuel. The chemistry of methanol and methoxy groups over inverse ZnO/Cu₂O/Cu(111) catalysts was investigated employing ambient pressure X-ray photoelectron spectroscopy (AP-XPS), scanning tunneling microscopy (STM), and calculations based on density functional theory (DFT). The results of AP-XPS show that the adsorption of methanol on the binary oxide substrate at 300 K leads to formation of *CH₃O and *HCOO species with a minor amount of *CHₓ. Most of the methoxy groups disappeared from the surface after heating to 450 K, the onset temperature for the formation of methanol during the hydrogenation of CO₂. The results of AP-XPS, STM, and DFT point to preferential adsorption of methoxy on the ZnO regions of the binary oxide. On the supported ZnO or on a ZnO–Cu₂O interface, the breaking of the O–H bond in methanol is an exothermic process with a negligible (1–2 kcal/mol) or non-existent energy barrier depending on the size and shape of the ZnO…

A new gold cluster compound [Au₂₃(NHCᵖᵗᵒˡ)₆(C≡CPh)₉]²⁺ (NHCᵖᵗᵒˡ = 1,3-di(para-methylbenzyl)benzimidazolin-2-ylidene) (Au₂₃NHCᵖᵗᵒˡ) was synthesized, and its geometric and electronic structures were compared to those of a known phosphine-protected analogue [Au₂₃(PPh₃)₆(C≡CPh)₉]²⁺ (Au₂₃PPh₃). Single-crystal X-ray diffraction analysis revealed that Au₂₃NHCᵖᵗᵒˡ has a common structural motif with Au₂₃PPh₃: a Au₁₇ core capped by six NHC ligands and surrounded by three Au₂(C≡CPh)₃ oligomers. However, a detailed inspection of the geometric structures elucidated two noticeable differences: (1) the Au₁₇ core of Au₂₃NHCᵖᵗᵒˡ is slightly elongated and sharpened along the C₃ axis compared with that of Au₂₃PPh₃ and (2) all of the phenyl rings of the alkynyl ligands in Au₂₃NHCᵖᵗᵒˡ face nearly parallel to the equatorial plane of the Au₁₇ core, whereas randomly aligned phenyl rings are found in Au₂₃PPh₃. Both clusters showed comparable stability at 60 °C in chloroform. UV–vis absorption spectroscopy and differential pulse voltammetry indicated that both clusters exhibit similar electronic structures,…

Persistent luminescence and photochromism are two fascinating optical properties that involve charge trapping via defects and their release due to an external stimulation. In both processes, it is possible to define “1” (or “on”) and “0” (or “off”) optical states. Consequently, materials with one of these phenomena find major interest in view of designing smart, anticounterfeiting, and optical information storage devices. Combining both processes within a single material can lead to a new generation of information storage phosphors, in which it may be possible to obtain three different optical states by playing on the external stimulations applied on the material. For that purpose, the elaboration of nickel-doped ZnGa₂O₄ spinel transparent nano-glass-ceramics is presented in this work. The short-wave infrared (SWIR) emission, a broad band located at ca. 1275 nm, arises from Ni²⁺ cations located in gallium octahedral sites. SWIR persistent luminescence, arising from the same doping ion transition, can also be monitored after UV charging. Interestingly, UV irradiation not only leads…

Achieving high-efficiency photocatalytic materials to convert CO₂ into high-value chemicals is still challenging. Herein, chlorine-doped g-C₃N₄ photocatalysts (Cl-CN) were successfully synthesized by a simple multiple calcination method. The as-prepared Cl-CN exhibited satisfactory photocatalytic activity in photoreduction of CO₂. The CO yield of Cl-CN was about 39.89 μmol/g. The DRS, UPS, and VB-XPS results indicated a narrower band gap, and the negatively shifted CB potential enhanced the CO₂ reduction ability. DFT calculations and the partial density of states revealed that the Cl 3p orbital greatly contributed to the CBM and VBM of Cl-CN, which caused the narrower band gap and an upshift of the conduction band by 0.14 eV over that of bulk-CN. The CO₂ conversion intermediate was investigated by in situ Fourier transform infrared spectroscopy, and the corresponding reaction mechanism was proposed according to the density functional theory calculations and experimental results, which showed that Cl doping and the C–Cl bond increased the photogenerated carrier lifetime and the CO₂…

Probing and understanding the local chemical environment of an active site is essential for designing high-performance single-atom catalysts (SACs). Density functional theory (DFT) calculations were performed to investigate the ligand configuration and site geometry of MgAl₂O₄-supported iridium single atoms (Ir₁) toward catalytic carbon monoxide (CO) oxidation. We employed MgAl₂O₄(111) and MgAl₂O₄(211) as the model substrates with adsorbed Ir single atoms of different site geometries. DFT calculations revealed that the Mg-site on MgAl₂O₄(111) and the step site on MgAl₂O₄(211) are the most stable adsorption sites for Ir single atoms. Irrespective of site choices, CO oxidation on supported Ir single atoms follows the Eley–Rideal (E–R) mechanism, in which the surface oxygen vacancies close to the Ir single atoms activate molecular O₂ with a negligible barrier and the rate-limiting step is the gas-phase CO directly attacking the O–Ir species that is modulated by a CO ligand. First-principles X-ray absorption near-edge spectra of reaction intermediates along with in situ/operando X-ray…

Cu-doped TiO₂ photocatalysts [Cu-(1 to 10) atom %] synthesized by the sol–gel method and thoroughly characterized using several techniques were evaluated for photocatalytic reduction of CO₂ under ambient conditions. These photocatalysts converted the reactant mixture of CO₂ and moisture selectively into methane and oxygen under visible irradiation without the use of any sacrificial agent. The Cu dopant considerably lowered the bandgap of TiO₂, thereby making it feasible for doped TiO₂ to absorb light in the visible region. Beyond 1% Cu doping the Cu-doped TiO₂ materials were far superior as compared to anatase TiO₂ for the reduction of CO₂ to CH₄, and the lowest doping (Cu-1%) concentration in TiO₂ lattice shows the maximum production of CH₄ (1081 μL/h/g), whereas the highest doping (Cu-10%) shows the least activity (200 μL/h/g). The photoreduction activity was found to decrease with increasing Cu concentration; under similar conditions without use of any cocatalysts. X-ray photoelectron spectroscopy (XPS) results along with cyclic voltammetry data (CV) indicate that the doped Cu…

The synthesis of high-quality WS₂ and more so of MoS₂ (multiwall) nanotubes in substantial amounts from oxide precursors is a very challenging and important undertaking. While progress has been offered by a recent report, the present work presents another step forward in the synthesis of MoS₂ nanotubes with a narrow size distribution and better crystallinity than before. Williamson–Hall analysis of the X-ray diffraction data is used to analyze the crystallinity and strain in the nanotubes. This analysis shows that the crystallinity and average diameter of the WS₂ and MoS₂ nanotubes reported here (type II) are better than those obtained according to the previous methods (type I). Size selection by centrifugation reported by others is used here to prepare several fractions of WS₂ and MoS₂ nanotubes according to their average diameter. The high refractive index of WS₂ and more so MoS₂ enables the nanotubes to trap light by total internal reflection, turning them into nanocylindrical resonators and thereby supporting cavity-mode resonances. The extinction, net absorption, and transient…

Perovskite nanocrystals (NCs) have gained great interest for next-generation light-emitting diodes (LEDs) prized for their spectrally tunable, narrow luminescence and their defect-tolerant electronic structure. Here, we provide a careful surface engineering to balance the passivation and charge injection by controlling the ligand density of didodecyl dimethyl ammonium bromide on NCs, which not only offers an improved photoluminescence quantum yield of >70% for NCs but also guarantees the effective charge injection and transportation of CsPbBr₃ NC films for fabricating LEDs. Additionally, the optimization of the hole transport layer was implemented to offer more balanced charge transportation, which further improved the performance of CsPbBr₃ NC-based LEDs with a peak external quantum efficiency of 13.4%.

The formation mechanism of the metastable M₂-phase VO₂, which is believed to be a true Mott insulator, has attracted great attention for understanding the intriguing physics of the metal–insulator transition of VO₂ and the promising application in ultrafast electronic switching devices. Herein, we conducted the hole-doping calculation regardless of the type of element and revealed theoretically that the hole carriers disentangle the complex Mott–Peierls relevance states of M₁-phase VO₂. The hole induces the zigzag dimerized V–V chains to separate into two different states: one remains paired but straight and the other remains zigzag but unpaired. The dedimerization weakens the intradimer hopping, which makes the superexchange interaction come into effect, consequently resulting in the formation of the spin antiferromagnetic ordering along the zigzag unpaired V–V chains, indicating that the Mott correlation plays a dominant role in the formation of M₂-VO₂. This work gives an insight into the mechanism of stabilizing the “true” Mott insulator M₂-VO₂, which would offer an opportunity…

Here, we report the effect of electron doping Zn for Cu on the physical properties of Cu₀.₅IrTe₂. Slight Zn doping concentration (x) becomes detrimental to the charge density wave (CDW) order, while the superconducting state can persist over a large change in chemical composition. The x dependence of the superconducting transition temperature (Tc) exhibits a weak dome-like shape with the highest Tc of 2.82 K at x = 0.5, whereas there is only a subtle change in Tc. The normalized electronic specific heat ΔCₑₗ./γTc value of 1.45 for the optimal doping composition Zn₀.₂₅Cu₀.₂₅IrTe₂ approaches the Bardeen–Cooper–Schrieffer (BCS) value (1.43), indicating the bulk nature of superconductivity. Magnetization and resistivity results further imply that our Zn-doped Cu₀.₅IrTe₂ are type II superconductors. We propose that these robust (ZnₓCu₁–ₓ)₀.₅IrTe₂ (0 ≤ x ≤ 0.9) superconductors may be suited to some research based on exfoliated crystal flakes and film devices.