BiOCl-based Photocatalytic Material Performance Optimization And The First Principles Study

Among new photocatalytic materials, the bismuth oxychloride (BiOCl) photocatalyst has greatly attracted the attention of researchers as an effective catalytic material due to its particular layer structure, electronic properties, superior UV light photocatalytic activities and stabilities. However, its potential for photocatalytic application is seriously confined due to its large band gap (3.40eV), which absorbs less than-4%of the whole solar photon spectrum and poor charge carriers transfer. In the manuscript, we manily use two solutions to solve these two problems:formation heterojunction and doping.First, BiOCl/Bi2WO6heterojunction with chemically bonded interface was synthesized via a facile one-step solvothermal method. The heterojunction yielded twice higher photodegradation rate of Rhodamine B under visible light irradiation compared to their individual components. Theoretical studies based on density functional theory calculations indicated that the enhanced photosensitized degradation activity could be attributed to the favorable band offsets across the BiⅠ-O-BiⅡ bonded interface, leading to efficient interfacial charge carrier transfer. Then, first principles calculations based on density functional theory were carried out to explore the interfacial properties of WO3/BiOCl heterojunction aiming at gaining insights into the roles the interface played in the overall photocatalytic performance. The density of states analysis showed that the interfacial structures resulted in a suitable band alignment to separate the excited carriers into two sides of the interface and thus the electrons-holes recombination could be effectively suppressed.Secondly, first-principle calculations have been carried out to investigate structural stabilities, electronic and optical properties of3d transition metal (V, Cr, Mn, Fe, Co, Ni, Cu, W) doped BiOCl. Substitutional3d transition metal (V, Cr, Fe, Co, Cu) doping leads to discrete midgap states within the forbidden band gap, which has adverse effect on the photocatalytic properties. On the other hand, the3d transition metal (Mn, Ni) doped bismuth oxychloride BiOCl structure induces a continuum of hybridized states in the forbidden gap, which favors electrons and holes transport and could result in enhancement of visible light activity. Tungsten chloride (WCl6) is widely used as reactant in the synthesized process of BiOCl. Thus tungsten may naturally exist in the product of BiOCl, which shows wider optical absorption and enhanced photocatalytic performance compared with pure BiOCl without WCl6as a reactant. Thus, tungsten atom may exist in BiOCl samples. The structures of tungsten substitutional, interstitial and in the form of WO6-ligand-doped BiOCl are examined. The result show that the WO6-ligand-doped BiOCl structure induces a continuum of hybridized states in the forbidden gap, which favors electrons and holes transport and could result in enhancement of visible light activity. In addition, the band gap of WO6-BiOCl decreases by0.25eV with valence band maximum (VBM) shifting upwards compared to that of pure BiOCl. By calculating optical absorption spectra of pure BiOCl and WO6-ligand-doped BiOCl structure, it is found that absorption peak of WO6-ligand-doped BiOCl structure has a red shift towards visible light compared with that of pure BiOCl, which agrees well with experimental observations.This paper provides a new method, thought and theoretical foundation for modifying BiOCl towards visible light responsive photocatalyst.