First-principles calculations were performed to investigate the stabilities, and electronic and piezoelectric properties of Janus SnXY monolayers (X = O, S, Se, Te; Y = O, S, Se, Te; X ≠ Y).

Sn vacancies can work as an effective source for p-type conduction under both Sn- and Se-rich conditions while n-type conduction is unlikely to be realized due to the absence of the effective intrinsic source.

g-C 3 N 4 photocatalysis is a safe and green approach for H 2 O 2 production, but the activity of pristine g-C 3 N 4 photocatalysts is unsatisfactory. At present, most of the modifications on g-C 3 N 4 photocatalysts for H 2 O 2 production have focused on thermodynamic processes, few have considered the kinetic aspects. Herein, the surface N-hydroxymethylation of g-C 3 N 4 photocatalysts for the efficient kinetic production of H 2 O 2 is reported. Through the reaction of formaldehyde with the amino moieties (-NH 2 ) on the g-C 3 N 4 surface, N-hydroxymethyls groups (-NH-CH 2 -OH) are introduced on typical g-C 3 N 4 photocatalysts. Relative to the pristine g-C 3 N 4 photocatalysts, the modified g-C 3 N 4 photocatalysts have over 1280% higher activity for H 2 O 2 production in pure water system, and impressive solar-to-chemical conversion efficiency. The experimental investigations and theoretical calculations reveal that the introduction of -NH-CH 2 -OH on the g-C 3 N 4 photocatalysts does not change their morphology, light absorption intensity and edges, band positions, charge separation and transfer properties, but markedly improved the H 2 O dehydrogenation and O 2 adsorption properties of g-C 3 N 4 . As a result, the reduction kinetics of O 2 to H 2 O 2 on the g-C 3 N 4 photocatalysts with -NH-CH 2 -OH is more energetically favorable. This work provides a useful reference and inspiration to achieve the effective modification of g-C 3 N 4 or other metal-free photocatalysts from the kinetic perspective.

To reveal the role of oxygen vacancies in the solar water oxidation of α-Fe 2 O 3 photoanodes, the kinetic and thermodynamic properties that are closely related to the water oxidation reaction of the α-Fe 2 O 3 photoanode containing oxygen vacancies were investigated. Compared with the pristine α-Fe 2 O 3 photoanode, the presence of surface oxygen vacancies can improve the water oxidation activity and stability of the α-Fe 2 O 3 photoanode simultaneously, but the bulk oxygen vacancies have a negative effect on the water oxidation performance of the α-Fe 2 O 3 photoanode. In thermodynamics, our investigations revealed that the presence of surface oxygen vacancies narrows the space charge region width of the α-Fe 2 O 3 photoanode, which could boost the charge separation and transfer efficiency of the α-Fe 2 O 3 photoanode during water oxidation. Because the surface property and hydrophilicity of α-Fe 2 O 3 are modified owing to the presence of surface oxygen vacancies, the water oxidation kinetics of the α-Fe 2 O 3 photoanode with surface oxygen vacancies is obviously boosted. Our findings in the present work provide comprehensive understanding of the thermodynamic and kinetic differences for α-Fe 2 O 3 photoanodes with and without oxygen vacancies for solar water oxidation.

We present density-functional theory calculations of the dehydrogenation of CH x (x = 1-4) on surfaces, where the Au atoms are substituted on the Ni surface with the ratio of Au atoms to the total stepped Ni atoms being 1 : 4, 1 : 2 and 3 : 4, respectively. To evaluate the role of Au at the step-edge on the process of methane dehydrogenation, CH x adsorption and dissociation on a pure Ni(211) surface is also conducted. Our results show that Au addition weakens the adsorbatesubstrate interaction. With the increase of the Au concentration, the binding energies of CH x gradually decrease and correlate well with the number of Au atoms on each model. On the Ni(211) surface, methane experiences a successive dehydrogenation process at the step-edge site in which carbon is eventually formed. As Au is introduced, the relative formation rate of carbon is greatly hampered even with a small amount of Au addition, while an appropriate amount of Au modification on the Ni catalyst has little effect on the activity of the CH x dissociation. Finally, we also demonstrate that the active center for CH x dissociation is dynamic with the variation of the Au concentration.

A facile Fe-doped carbon quantum dot based fluorescent sensor for dopamine sensing and bioimaging was constructed.

First-principles investigations are performed on the stabilities and electronic and optical properties of SnSe 2(1−x) S 2x (x = 0.0625, 0.25, 0.5, 0.625, 0.8125, and 1.0) monolayer alloys by using density functional theory calculations. It is found that, above a critical temperature of 702 K, the mixing of SnSe 2 and SnS 2 is likely to form random alloys. The calculated negative substitution energy of S at the Se site of SnSe 2 suggests an alternative strategy for the synthesis of the alloys, i.e., by the substitution of S for Se in SnSe 2 monolayers. It is also shown that, due to the lattice mismatch and the pronounced charge transfer between SnSe 2 and SnS 2 , the band-gap values of the alloys deviate strongly from the concentration-averaged values of the constituents. Moreover, the dielectric functions of the alloys are determined to be anisotropic, with optical properties along the xy plane being more susceptible to the S content than those along the z direction, and the alloying enhances the absorption strength in the visible spectral region. We hope that these insights will be useful for future applications of SnSe 2(1−x) S 2x alloys.

The manipulation of photoelectrodes' electron− hole pairs toward low recombination is the fundamental strategy to achieve high solar-to-hydrogen conversion efficiency in photoelectrochemical (PEC) water splitting cells. Herein, we demonstrate that a magnet placed parallel to a photoelectrode can improve the water splitting activity of typical BiVO 4 and α-Fe 2 O 3 photoanodes as well as Cu 2 O/CuO and p-Si(111) photocathodes by restraining the nonradiative recombination of their carrier. Our investigations indicate that magnetic field-assisted PEC water splitting is a more effective approach than the conventional PEC water splitting. Magnetic field assistance provides a new, effective, and general strategy to improve the activity of photoelectrodes for solar water splitting and the other PEC reactions.