An effective structural doping approach has been described to modify the photoelectrochemical properties of g-C 3 N 4 by doping with nonmetal (sulfur or phosphorus) impurities. Here, the substitutional and interstitial doped models of g-C 3 N 4 systems were constructed with different doped sites, and then their dopant formation energies and electronic properties were performed to study the stability and visible-light photoactivity using firstprinciples density functional theory, respectively. Our results have identified that an S atom preferentially substitutes for the edge N atom of g-C 3 N 4 ; however, a P atom preferentially situates the interstitial sites of in-planar of g-C 3 N 4 . Furthermore, it is demonstrated that the doping with nonmetal impurities reduces the energy gap to enhance the visible-light absorption of g-C 3 N 4 . The increased dispersion of the contour distribution of the HOMO and LUMO brought by doping facilitates the enhancement of the carrier mobility, while the noncoplanar HOMO and LUMO favor the separation of photogenerated electron−hole pairs. Especially, P interstitial doping shows a prominent potential due to the appearance of a new channel for carrier migration. It should be pointed out that the proper doping form should be controlled, so that reasonable photoelectrochemical properties can be achieved.

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The electronic structures of ZnO were calculated using density functional theory, in which the electronic interactions are described within the GGA+U (GGA = generalized gradient approximation) formalism, where on-site Coulomb corrections are applied on the Zn 3d orbitals (U d ) and O 2p orbitals (U p ). The relaxed GGA+U calculation can correct completely the band gap, the position of Zn 3d states, the transition levels of O vacancy in band gap, and so on, which is different from other GGA+U (equivalent LDA+U) calculations partially correcting the energy band structure for fixed lattice constants. By comparing with experimental data, the pair of U d = 10 and U p = 7 eV was identified as an optimum choice for the energy band structure of W-ZnO. Then, the proper pair of U d and U p parameters was taken to predict the energy band structure of ZB-and RS-ZnO, of which the former is in good agreement with experimental values, and the latter is in dispute, relating to the decrease of the octahedral symmetry. Subsequently, we pay special attention to the possible causes of the decrease of lattice constants deriving from the +U correction. Further, the formation energies and transition levels of O vacancy in W-ZnO were calculated using three different schemes to address possible routes to presenting the defect states in band gap. Our results provide some guidance for improving electronic structure of ZnO using the GGA+U approach.

An effective codoping approach is described to modify the photoelectrochemical properties of anatase TiO2 by doping with nonmetal (N or C) and transition metal (Nb or Ta) impurities. Here, compensated and noncompensated codoped TiO2 systems are constructed with different proportions and dopant species, and then their dopant formation energies and electronic properties are calculated to study the stability and visible-light photoactivity by first-principles density functional theory incorporating the LDA+U formalism, respectively. The calculated results demonstrate that the codoping with transition metals facilitates the enhancement of the concentration of p-type dopants (N and C) in the host lattice. Especially, both 1:2 compensated Nb/C/Nb and Ta/C/Ta codopings not only reduce the energy gap to enhance the optical absorption and eliminate the local trapping to improve carrier mobility and conversion efficiency but also do not lower the reduction potential of the conduction band edge. Our designated strategies of codoped anatase TiO2 simultaneously meet the criteria for water splitting. It should be pointed out that, to be successful, the proper proportion of transition metal and nonmetal impurities in the host lattice should be controlled so that reasonable photoelectrochemical properties can be achieved.

Three kinds of crystal phase BiPO 4 (HBIP, nMBIP and mMBIP) were selectively synthesized by a hydrothermal method. The governed factors for the formation of three crystal phase of BiPO 4 were both on the acidity of the solution and reaction temperature. The BiPO 4 with nMBIP phase structure showed higher activity for degradation of MB solution under UV irradiation than HBIP and mMBIP. The catalytic activity per surface area activity of nMBIP (3.8Â10 5 h À1 m À2 ) was about ten times higher than that of P25(1.4Â10 4 h À1 m À2 ). The BiPO 4 with nMBIP structure exhibited the highest activity due to the most distorted PO 4 tetrahedron. The induce effect of the dipole moment derived from the distorted PO 4 tetrahedron promoting the separation of e À /h + pairs and further benefited for the photocatalytic reaction. This correlation may help to design and develop other oxoacid salt photocatalysts with high activity.

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Photocatalytic water splitting was observed on black phosphorus/BiVO4 heterostructure under visible light irradiation.