In this work, we employ hybrid density functional theory calculations to design a two-dimensional layered CdS/CN heterostructure for visible light photocatalytic water splitting to produce hydrogen. The calculation results show that the conduction band minimum (CBM) and the valence band maximum (VBM) of CN monolayers are lower than those of CdS nanosheets by about 0.76 eV and 0.44 eV, respectively. The type-II band alignment, density of states, Bader charge analysis, and charge density difference of the CdS/CN heterostructure indicate that the photogenerated electrons migrate from the CdS monolayer to the CN monolayer, favoring the separation and transfer of photogenerated charge carriers, which restrains the recombination of photogenerated carriers and enhances the photocatalytic efficiency. The calculated band gap and optical absorption spectra reveal that the two-dimensional layered CdS/CN heterostructure may be a potential photocatalyst for photo-electrochemical water splitting because of its appropriate band gap and excellent visible light absorption behavior. Moreover, the electronic and optical properties of the CdS/CN heterostructure can be effectively modulated by the strain. These findings suggest that the CN sheets are a promising candidate as metal-free co-catalysts for CdS photocatalysts, and also provide valuable information for experimentalists to design highly active and efficient visible light photocatalysts for water splitting.

BiOF/BiOI, BiOCl/BiOBr, BiOCl/BiOI, and BiOBr/BiOI superlattices are suitable for visible light photocatalytic degradation of organic pollutants.

The graphene-like ZnO (g-ZnO) nanosheets were synthesized and shown to exhibit highly photocatalytic activity for the degradation of RhB under ultraviolet irradiation. In this work, we utilize cationic–anionic passivated codoping to explore the potential of the g-ZnO nanosheet for the design of efficient water redox photocatalysts by employing density functional theory calculations with the hybrid HSE06 functional. Our calculations show that anion–cation passivated codoped systems not only are more favorable than the corresponding monodoping in the g-ZnO nanosheet due to the Coulomb interactions but also effectively reduce the band gap without introducing unoccupied states which accelerate the electron–hole recombination. The charge-compensated P–Sc and C–Zr codoped g-ZnO nanosheets are energetically favorable for hydrogen evolution but not insufficient to produce oxygen, indicating that they could serve as Z-scheme photocatalysts. The C–Ti, N–Y, and P–Y codoped systems may be potential potocatalysts for photoelectrochemical water splitting to generate hydrogen due to their appropriate band gaps and band edge positions. In particular, the charge-compensated P–Y codoped g-ZnO nanosheet has the most excellent stability and the largest absorption region of visible light among these codoped systems. Further, we show that P–Y passivated codoping can reduce the overpotentials for oxygen evolution reaction (OER) and hydrogen evolution reaction (HER) of the g-ZnO nanosheet, indicating that the OER or HER on the P–Y codoped g-ZnO nanosheet can be easier driven by the irradiation-generated holes or electrons.

By using the first-principles calculations in combination with the Boltzmann transport theory, we systematically study the thermoelectric properties of AlX (X = S, Se, Te) monolayers as indirect gap semiconductors. The unique electronic density of states, which consists of a rather sharp peak at the valence band maxima and an almost constant band at the conduction band minima, makes AlX (X = S, Se, Te) monolayers excellent thermoelectric materials. The optimized power factors at room temperature are 22.59, 62.59, and 6.79 mW m–1 K–2 under reasonable electronic concentration for AlS, AlSe, and AlTe monolayers, respectively. The figure of merit (zT) increases with temperature and the optimized zT values of 0.52, 0.59, and 0.26 at room temperature are achieved under moderate electronic concentration for AlS, AlSe, and AlTe monolayers, respectively, indicating that two-dimensional layered AlX (X = S, Se, Te) semiconductors, especially AlSe, can be potential candidate matrices for high-performance thermoelectric nanocomposites.

The photovoltaic performance of the organic–inorganic hybrid perovskite MAPbI3can be significantly improved by the substitution of Ge/Sn for Pb.

In this theoretical study, the double-hole-mediated codoping strategy has been adopted to improve the photocatalytic activity of cubic KNbO as compared with the corresponding individual doping. The strong double-hole-mediated dopant-dopant coupling significantly reduces the effective bandgaps for the anionic-anionic (N-N, P-P, N-P, C-S) codoped systems with removing the appearing acceptor states above the Fermi level. No dopant-O coupling occurs in the cationic-anionic (V-C, Ti-P, Ti-N, Zr-P, Zr-N, Sc-S, Y-S) codoped systems. The V-C and Ti-P codoping could lead to narrowed bandgaps without unfilled localized states appearing above the Fermi level. N, Ti, Zr, Sc, Y monodoping and Ti-N, Zr-P, Zr-N, Sc-S, Y-S codoping introduce unoccupied impurity states between the valence band maximum and conduction band minimum, which makes them unfavorable for photocatalysis as these impurity states may serve as electron-hole recombination centers. For P-P, N-P, and C-S codoped systems, the intermediate states are higher or close to the hydrogen evolution potential, which is thermodynamically unfavorable for production of both oxygen and hydrogen. Producing hydrogen only, the N-N and C-S codoped KNbO materials will be good choices for Z-scheme photocatalysis. V, S, and V-C codoped KNbO may be promising visible light photocatalysts for water splitting, as they have suitable effective bandgaps without the introduction of unoccupied impurity states above the Fermi level, and they also own proper band edge positions with respect to the water redox level. The calculated optical absorption curves also indicate that C, V, and S monodoping and N-N, V-C, and Ti-P codoping can effectively enhance the visible light absorption.

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