The structural, electronic, and optical properties of a g-C3N4(001)/BiVO4(010) nanocomposite have been investigated using first-principles calculations. The results indicate that g-C3N4(001) can stably adsorb onto the BiVO4(010) surface, and it tends to form a regular wavy shape. The calculated band gap of the g-C3N4(001)/BiVO4(010) nanocomposite is narrower compared with that of BiVO4 or BiVO4(010), primarily due to the introduction of N 2p states near the Fermi level. The g-C3N4(001)/BiVO4(010) nanocomposite has a favorable type-II band alignment; thus, photoexcited electrons can be injected into the conduction band of g-C3N4(001) from the conduction band of BiVO4(010). The proper interface charge distribution facilitates carrier separation in the g-C3N4(001)/BiVO4(010) interface region. The electron injection and carrier separation can prevent the recombination of electron-hole pairs. The calculated absorption coefficients indicate an obvious redshift of the absorption edge, which is in good agreement with the experimental results. Our calculation results suggest that the g-C3N4(001)/BiVO4(010) nanocomposite has significant advantages for visible-light photocatalysis.

Stable ferroelectricity with an in-plane spontaneous polarization of 2.00 × 10−10 C/m is found in two-dimensional (2D) β-GeS monolayers from theoretical calculations, which can be effectively tuned by the applied tensile strains. The Curie temperature of the monolayer is evaluated to be 358 K by ab initio molecular dynamics simulations. Remarkably, the 2D ferroelectricity is found to exist in 2D few-layer β-GeS nanosheets which could be synthesized in experiments. The strong spontaneous polarization and giant pyroelectric coefficient accompanied by the appearance of phase transition near room temperature facilitate the development of β-GeS monolayers or nanosheets for applications in ferroelectric, pyroelectric, and piezoelectric devices with superior performance.

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The geometry structure, electronic structure, and band edge positions of Zn-doped Bi 2 WO 6 have been studied using first-principles method. Bi 1.75 Zn 0.25 WO 6 has a high quantum efficiency (QE) caused by the large mobility along different orientations and the efficient photogenerated-electron trap. It exhibits the enhanced visible-light absorption capability (α) owing to the large increase of the density of electrons in the valence band maximum (VBM) and decrease in the band gap. The interactions are both strengthened between layers and among atoms within (Bi 2 O 2 ) n layers. These strengthened interactions induce enhanced stereochemically active Bi lone pair effect, which is identified as the cause of its unique electronic structure. Furthermore, the valence band (VB) and conduction band (CB) edges of Zn-doped Bi 2 WO 6 are slightly shifted upwards. This indicates that the dominant active species during photocatalytic reaction for Bi 1.75 Zn 0.25 WO 6 are not only hole and electron but also ·O 2 − ion and ·OH radical. PACS: 71.15.Mb

Mo or W atom doping on V site can form continuum states above conduction band edge of BiVO4. Mo/W/Mo and W/Mo/W co-doped BiVO4 have relatively small formation energies and band gaps, which is particularly suitable for visible-light photocatalysis.

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An experimentally synthesized graphene/Bi2WO6 composite showed an enhancement of the visible-light photocatalytic activity, while the underlying mechanism is not known. Here, first-principles calculations based on density functional theory were performed to explore the various properties of the graphene/Bi2WO6(010) composite aiming at gaining insights into the mechanism of its photocatalytic activity. The stability, electronic properties, charge transfer, and visible-light response were investigated in detail on the Bi2WO6(010) surface coupled with graphene. An analysis of charge distribution and Bader charge shows that there is a strong covalent bonding between graphene and the Bi2WO6(010) surface. The covalent interaction induces a small bandgap in graphene. The interband transition of graphene and the surface states of the Bi2WO6(010) surface would cause the absorption spectrum of graphene/Bi2WO6(010) to cover the entire visible-light region and even the infrared-light region. The photogenerated electrons flow to graphene from the conduction band of Bi2WO6 under the built-in electric field and band edge potential well. Thus, graphene serves as a photogenerated electron collector and transporter which significantly reduces the probability of electron-hole recombination and increases catalytic reaction sites not only on the surface of graphene but on also the surface of Bi2WO6. The decrease of charge recombination is possibly responsible for the enhancement of the visible-light photocatalytic activity of the graphene/Bi2WO6(010) nanocomposite.