Controllable Preparation And Modifacation Of BiPO₄ Nano-photocatalyst

Given its larger dipole moments, monoclinic Bi PO₄（space group: P21/n） exhibited superior activity compared with commercial P25 for the degradation of dyes. Besides, the nature of Bi PO₄, such as low cost, high stability and corrosion-resistant, etc., become the potential advantages for its application in photocatalysis field. Furthermore, PO₄^3- has the induced effect that the dipole moment induces the formation of local fields preferring to attract holes and repel electrons, which helps the e-/h+ separation and benefits for the photocatalytic performance. Henceforth, Bi PO₄ has been intensively investigated for the degradation of abundant pollutants. However, the indirect band gap（about 3.8 4.1 e V） of Bi PO₄ lead the limitations of the absorption edge. Also, the significant combination of photo-generated charge carriers produces the low quantum efficiency of Bi PO₄ photocatalyst. Therefore, various studies have been conducted to boost the visible light absorption and improve the electron-hole separation efficiency of Bi PO₄.In this study, surface-modified Bi PO₄ aimed for quantum efficiency improvement and Bi/Bi PO₄ composites in order to broaden the light absorption were synthesized by a one-pot hydrothermal method and solvothermal method, respectively. Degradation of methyl orange（MO） and nitric oxide（NO） removal were used to evaluate the photocatalytic activity of as prepared samples. Then, the physicochemical property of resulting materials were characterized by X-ray diffraction（XRD）, scanning electron microscope（SEM）, transmission electron microscopy（TEM）, fourier transform infrared spectroscopy（FTIR）, ultraviolet-visible diffuse reflection spectroscopy（UV-vis DRS）, X-ray photoelectron spectroscopy（XPS）, photoluminescence spectra（PL）, thermogravimetric analysis（TGA）, etc. Except from these measurements, photoelectric property test of products and the identification of active free radicals through electron spin resonance spectral（ESR） have been conducted. Detail results we obtained from these work showed in the followings:1. PO₄^3--modified Bi PO₄ photocatalysts with different PO₄^3-/Bi molar ratios were controllably synthesized through a one-pot hydrothermal method, which became much more uniform and well crystallized compared with bare Bi PO₄. The modified Bi PO₄ can enhance the surface hydroxyl group concentration by water adsorption and improve its hydrophilic property which could facilitate the separation of photogenerated electrons and holes. Holes could trapped by hydroxy to form hydroxyl radical（?OH）, which eventually enhanced MO degradation efficiency.2. A series of Bi/Bi PO₄ composites were synthesized through a simple solvothermal method by adjusting the reaction times. The hot electrons generated from Bi through local surface plasma resonance（SPR） effect injected into the conduction band of Bi PO₄ to promote the formation of large amount of active species: superoxide radical（?O2-） and singlet oxygen（1O2）, which eventually realized the NO removal. Introduce of Bi in Bi/Bi PO₄ composites system can improve the NO removal efficiency of Bi PO₄ under visible light irradiation, which attributed to the SPR effect of Bi, lowered electrochemical impedance and enhanced separation efficiency of photogenerated electrons and holes.