Theoretical Study Of The Photocatalytic Hydrogen Production Properties For Doped Based G-C₃N₄ Nanocomposites

Graphitic carbon nitride（g-C₃N₄）has been widely investigated as a metal-free photocatalyst for water splitting.However,the rapid recombination of photoexcited carriers and narrow visible-light response region substantially limit its performance.Therefore,improving the structure of g-C₃N₄ to enhance its photocatalytic activity in the visible light range is a research hotspot of current researchers.In this work,we find suitable semiconductor materials to compound with g-C₃N₄,which can effectively reduce the rate of electron and hole recombination.Then,doping with impurity atoms in the composite material and it results in change of electronic structure and properties of the material,thereby enhancing the photocatalytic efficiency of g-C₃N₄.The geometrical,electronic and optical properties of Cu or/and N（co）doped TiO₂/g-C₃N₄ heterostructure systems have been investigated systematically on the basis of spin-polarized density functional theory calculations.Our calculated results indicate that the band gap of TiO₂/g-C₃N₄ heterostructure has an obvious narrowing compared with pure TiO₂（101）surface,and（Cu,N）codoping can induce some impurity states of N 2p and hybridized states of Cu 3d and N 2p appearing in the forbidden gap of TiO₂/g-C₃N₄heterostructure,which lead to a decrease of the photon excitation energy and an obvious redshift of the optical absorption edge.The charge density difference calculations of Cu or/and N（co）doped TiO₂/g-C₃N₄ heterostructure systems show that the excited electrons and holes will eventually accumulate in（co）doping TiO₂（101）surface and g-C₃N₄monolayer,respectively,which can effectively reduce the recombination of the photogenerated electron-hole pairs by the interfacial coupling of between TiO₂（101）surface and g-C₃N₄ monolayer.This result show that（Cu,N）codoped TiO₂/g-C₃N₄heterostructure is a preferable visible-light photocatalyst.Moreover,this work also systematically studied the geometrical,electronic,optical,charge transfer and photocatalytic mechanism of（F,Ti）codoped heptazine/triazine based g-C₃N₄heterostructure（ht-C₃N₄）using hybrid density functional approach.The interface interaction between heptazine and triazine g-C₃N₄ shows heptazine and triazine g-C₃N₄form a van der Waals heterostructure.The bandgap of（F,Ti）codoped ht-C₃N₄heterostructure is narrow（2.39 eV）,which enhances the absorption of visible light and leads to an obvious redshift of absorption edge.A type-II heterostructure is formed at the interface of（F,Ti）codoped ht-C₃N₄ heterostructure,and leads to high photocatalytic activity.Furthermore,Bader charge and charge density difference indicate that the internal electric field promotes the separation of electron-hole pairs in the ht-C₃N₄ interface and inhibits carrier recombination.Meanwhile,electrons in the conduction band of triazine g-C₃N₄ and holes in the valence band of（F,Ti）codoped heptazine g-C₃N₄ have enough redox ability.This work is helpful in understanding the mechanism of photocatalytic water splitting and relevant experimental observations.