The 10 most-cited articles in The Journal of Physical Chemistry, 2019

The NH₃ synthesis from N₂ electrochemical reduction under mild conditions is a great challenge. In this study, we investigated a series of transition-metal-embedded MoSSe nanosheets with S or Se vacancy based on the density functional theory calculations. Our results revealed that Mo-embedded MoSSe with S vacancy exhibits the best catalytic performance following the alternating mechanism. The potential-limiting step is the first hydrogenation of the adsorbed N₂ with a barrier of 0.49 eV. The relatively low ΔG of 0.58 eV for NH₃ desorption allows the rapid removal of the products from the catalyst. The high stability of the adsorbed N₂H species implies the great catalytic activity of the Mo-embedded MoSSe. By comparing the adsorption strength between single H atom and N₂ molecule on the active site, the Mo-doped MoSSe possesses a much higher selectivity on nitrogen reduction reaction. Our research may provide insightful ideas for the efficient electrochemical reduction of N₂ to NH₃ in ambient conditions.

Molecular grafted carbon nitride (CN) nanosheets coupled with V₂O₅ to form a novel Z-scheme heterojunction photocatalyst V₂O₅/CNX (X is 2-aminobenzonitrile) by a facile in situ growth method was acquired. Its photocatalytic properties were investigated by hydrogen evolution and degradation of rhodamine B under simulated sunlight irradiation. It was found that the assembled heterojunction could remarkably enhance photocatalytic activity in contrast to pure CN, V₂O₅, and previous reported heterojunctions. The great improvement of photocatalytic activity can be attributed to molecular grafting and the formation of the Z-scheme heterojunction, resulting in a remarkable red shift of the optical absorption, a rapid separation of charge carriers, an increase of specific surface area, and introduction of defects. Moreover, exfoliation of bulk CNX into ultrathin nanosheets increases mobility of charges and specific surface area. Different wt % ratios of V₂O₅-loaded heterojunctions were prepared, and 2% of V₂O₅-loaded heterojunctions were found to display optimal catalytic efficiency. The…

Nanoparticle stability against coarsening is one of the keys to allow better exploitation of the properties of nanoscale materials. The intrinsically high interfacial energies of nanoparticles constitute the driving force for coarsening, and therefore can serve as targets to design materials with improved thermal stability. In this study, we discuss the surface engineering of TiO₂ nanocatalysts for artificial photosynthesis by exploiting the spontaneous segregation of Ba²⁺ ions to the interfaces of TiO₂ nanocrystals. Ba²⁺ is a strong candidate for photoelectrocatalytic reduction of CO₂ and its effects on interfacial energies lead to a remarkable increase in thermal stability. By using a systematic lixiviation method, we quantified the Ba²⁺ content located at both the surface and at grain boundary interfaces and combined with direct calorimetric measurements of surface energies and microstructural studies to demonstrate that Ba²⁺ excess quantities directly impact coarsening of TiO₂ nanocatalysts by creating meta-equilibrium configurations defined by the Ba²⁺ content and segregation…

In recent years, TiO₂(B) has been widely used in photocatalysis, electrocatalysis, and lithium-ion batteries due to its unique crystal structure. However, as a metastable phase semiconductor, TiO₂(B) is prone to transform into the stable anatase or rutile phase at high temperature. Therefore, the low crystallinity of TiO₂(B) was usually formed at low temperature. Both of the above two concerns restrict its application in photocatalysis. In this research, we found that an appropriate amount of HF could inhibit the phase transformation process from TiO₂(B) to anatase. XRD patterns and Raman spectra showed that when 0.3 wt % HF was added prior to the calcination, a large amount of TiO₂(B) could be maintained even at 750 °C. Thus, the sample with TiO₂(B)/anatase heterophase junction structure was obtained at high temperature, which exhibited the enhanced photocatalytic activity both for pollution degradation and hydrogen production. The phase transformation mechanism was finally revealed by DFT calculations. It was demonstrated that the F anions adsorbed on the surface of TiO₂(B) could…

The catalytic reduction of 4-nitrophenol to 4-aminophenol by using aqueous sodium borohydride (NaBH₄) solution is the most widely used model reaction to evaluate the catalytic activity of nanoparticles (NPs). It is generally believed that NaBH₄ is the hydrogen source for the −NO₂ to −NH₂ conversion. Water can also contribute hydrogen for the molecular conversion, but this potential hydrogen source has been overlooked since solvents are typically not involved in the chemical reactions. Surprisingly, through simple experiments using isotopic solvent (D₂O) or reducer (NaBD₄), we find that the reduction reaction cannot proceed without the presence of water or other protic solvents. The vibrational spectroscopic analysis of the final reduction products also confirms that the hydrogen atoms in this conversion originate from the protic solvent. Therefore, it is water (or any protic solvents) rather than the hydride reducer that provides the hydrogen for the formation of the 4-aminophenol product. A reaction mechanism for the hydride reduction of 4-nitrophenol is proposed according to this…

Valleytronics is proposed as a novel approach to information storage by utilizing the valley degree of freedom where the valley polarization in monolayer transition metal dichalcogenides (TMDs) can be tailored by magnetic proximity effects (MPE), etc. The 2H-VS₂ monolayer on valleytronics is limited due to the valence band maximum (VBM) located at Γ. The MPE of the two-dimensional (2D) ferromagnetic monolayer on spontaneously valley-polarized TMDs is rarely reported. Here, the electronic structure and magnetic properties of 2D 2H-VS₂/Cr₂C heterostructures with different stacking patterns have been investigated systematically. When V atoms locate right above Cr atoms, the heterostructure shows semiconducting characteristics where the VBM of 2H-VS₂ turns from Γ to K′. The valley polarization of VS₂ is preserved in all heterostructures with spin–orbital coupling, which can be modulated by the magnetization direction, biaxial strain, and interfacial distance. Tensile strain increases valley polarization. Different stacking patterns affect the magnetic anisotropy energy of monolayer VS₂.…

The heteroatom doping of graphene is a useful method to amplify the outstanding properties of graphene. However, it is difficult to control the disposition of the dopants. By means of first-principles calculations, we show that the substrate-induced doping of epitaxial graphene leads to the formation of silicon doped graphene with a precise location of the dopants in the valley regions between crests. According to our results, in the valleys silicon dopants greatly prefer to replace the carbon atoms of the buffer layer which are bonded to the substrate by a large amount of energy. This selective doping suggests that a siligraphene layer in the g-SiC₃ form would be an excellent model for a buffer layer grown on nanometer-sized areas of SiC, thus paving the way to the synthesis of a new two-dimensional material. We predict a stable antiferromagnetical (AF) ordering that behaves electronically as a semiconductor, degenerated with the highest ferromagnetic configuration of the system. A net magnetic moment of 0.65 μB per Si dangling bond was found for both the AF and the most stable…

In the present study, a ternary combination of graphitic carbon nitride (g-C₃N₄), carbon nanodots (CDs), and ferrous ion (Fe(II)) was proposed. The g-C₃N₄/CDs/Fe(II) composite was prepared through thermal polymerization of urea and citric acid, followed by impregnation with Fe(II). The fabricated composite was characterized using transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and N₂ adsorption/desorption isotherms. The results demonstrated that CDs were embedded in the interlayer of g-C₃N₄ while Fe(II) was grafted onto the surface. The degradation activity of the composite for methylene blue (MB) was systematically investigated. The optimal content of CDs was confirmed to be 3% and a higher Fe(II) content was observed to lead to a greater degradation rate. However, in order to avoid high iron leaching, which may lead to the precipitation of iron, exorbitant Fe(II) content must be deprecated. Besides, the loading of Fe(II) on the g-C₃N₄/CDs composite disrupts the acidic…

We report gas-phase photocatalytic CO₂ reduction with Cu₂O/TiO₂ photocatalysts of varying surface passivation. With taurine adsorbed on the photocatalyst surface, the CH₄ production rate increases and CO production rate decreases compared to photocatalysts with no ligand treatment. When ethylenediamine is present on Cu₂O/TiO₂ photocatalysts, CO selectivity enhances significantly. In situ Fourier transform infrared spectroscopy and density functional theory calculation reveal that the surface ligands on the photocatalyst surface alter the binding strength of reaction intermediates (e.g., CO) on surface atoms of the photocatalysts. Our findings cast light on a new design principle for the catalyst surface in selective CO₂ conversion.

Recently, there has been an increase in research relating to the search for new optoelectronic materials for photovoltaic devices and light-emitting diodes. This research focuses on developing materials that not only possess the required optoelectronic properties (high absorption, efficient photon emission, and high charge-carrier mobilities) but are also solution-processable, which can reduce fabrication costs. Ternary ionic crystal structures, such as lead-halide perovskites, have emerged as a class of such suitable materials. However, the most promising structures, which exhibit the highest device efficiencies, rely on toxic lead as a cationic species, thereby hindering commercial application. Here, we synthesize and characterize CsCuCl₃ and Cs₂CuCl₄ nanocrystals. These nanocrystals exhibit bright broad band green emission from copper defects when excited below 300 nm. We show that by employing a variety of ratios of coordinating solvents during synthesis, we can tailor the morphology of the nanoparticles produced, allowing us to produce structures such as dots, platelets, and…