Preparation, Property Of Novel Photocatalytic Materials And Photocatalytic Composite Materials

Semiconductor photocatalysis is one of the most promising methods for environment-organic-pollutant decontamination and energy production. The initial step of the photocatalytic process consists of the generation of electron-hole pair upon irradiation of a photon whose energy is equal to or higher than that of the band gap (E_g) of a photocatalyst. The photoinduced electron-hole pairs can either recombine in the bulk or travel up to the surface, and the separated electrons or holes at surfaces can participate in chemical reactions with species adsorbed on the semiconductors surface. Therefore, in order to search an effective photocatalyst a tremendous amount of research has been devoted to study and discover the influencing factors of the photocatalytic activity.In this dissertation, a model packing factor, based on the idea that dipole moment induced by distortion of local structures effectively separates electron and hole, was proposed. The pecking factor could reflect the capacity of the metal-oxygen polyhedral deformations, the spatial amplitude of atomic vibrations in the crystal lattice, and the consequent electron-hole separation and carrier transport. We took the isostructural MWO₄ (M = Ca, Sr, Ba) photocatalyst; MBiO₂Cl (M = Ca, Sr, Ba), and Sr₂Bi₂O₅, SrBi₂O₄, and BiVO₄ systems as examples to investigate the factors, which influence the photocatalytic properties of the semiconductors. The highlight of our work is to propose a universal model to rank photocatalytic materials with similar chemistry or crystal structure. The model suggests that lower crystal packing factor, higher ability of electron-hole separation and transfer, and commonly results in better photocatalytic activity. The model for structure-property relationship could be a new method to estimate the properties of photocatalysts. Besides these there systems, there are some 18 literature examples of such correlation-a lower PF being correlated to a higher photocatalytic activity-covering compounds of d⁰ cations (Ti⁴⁺, V⁵⁺, Nb⁵⁺, Ta⁵⁺, Cr⁶⁺, Mo⁶⁺ and W⁶⁺) and d¹⁰ cations (Ag⁺, Zn²⁺, Cd²⁺, Ga³⁺, In³⁺, Sn⁴⁺, Sb⁵⁺ and Bi³⁺). The further investigation indicates that the higher structural openness degree, corresponding to a lower packing factor, leads to the better photocatalytic activity.According to the model based on the concept of structural openness, layer-structure materials that possess open (local) structures were found to promote the generation and the separation of the charge carriers and can be used as efficient photocatalysts for water splitting and degradation of pollutants under light irradiation. Herein, we report some novel layered photocatalysts PbBiO₂Br (2.3 eV), PbBiO₂Cl (2.45 eV), MBiO₂Cl (M = Ca (3.39 eV), Sr (3.41 eV), Ba (3.07 eV)), CdBiO₂Cl (3.08 eV). This is another important photocatalyst system except the known systems of oxide, sulfide, oxysulfide, nitride, oxynitride, hydroxide, carbide and silicide. The internal electric fields are one of the important parameters to evaluate the ability of electron-hole separation and transport in the crystal lattice. Generally, the presence of internal electric fields between the layers are favorable for the efficient photoinduced electron-hole separation and transfer, which is also propitious to a high photocatalytic efficiency of oxyhalides.Besides, in order to enhance the photocatalytic activity, we also synthesize some compositions. The performance of the photocatalysis can be improved in several ways. One of the most effective approaches is to deposit metal particles on the surface of the semiconductors, which have been widely used as photocatalysts. The other is to synthesize semiconductor compositions. Herein, we developed a simple, convenient, readily available and very effective method to deposit the small and uniform-distributed Ag or Cu₂O nanoparticles over semiconductors by redox reaction of silver or copper ammonia.