Controllable Synthesis Of V₂O₅ And BiF₃/BiOCl Used For Removal Dyes In Wastewater

This thesis mainly contains two important parts. One is controlable synthesis of L-shaped V2O5 and application in methylene blue (MB) adsorbtion; the second part is to fabricate heterojunction and investigate its photocatalytic activities for degrading methyl orange (MO).(1) In the first part, V2O5 with an interesting "L"-shape was successfully prepared by a simple hydrothermal method without using any surfactant or template.The formation mechanism of "L"-shaped V2O5 has been proposed. We have also investigated the effect of fluoride on the morphology, crystal structure and adsorption ability of the samples. The samples were characterized by scanning electron microscopy (SEM), high-resolution transmission electron microscopy(HRTEM) with select area electron diffraction (SAED), X-ray diffraction (XRD),Fourier transform infrared spectrum (FT-IR), UV-vis diffuse reflectance spectra(UV-DRS), Photoluminescence (PL) spectra and N2 sorption isotherms. It is found that the addition of fluoride can refrain the formation of "L"-shaped V2O5, resulting in the high-energy {010} facets exposed and the increased oxygen vacancy. The density functional theory (DFT) calculations and PL spectra further confirm the results above. As a result, F-doped V2O5 shown a significantly improved adsorption capacity for methylene blue (MB) than undoped one. The adsorption kinetics well follows a pseudo-second-order model, with the higher correlation coefficients (R)than 0.99.(2) To date, it is still a big challenge to investigate the charge transfer behavior from bulk to surface for the solar energy conversion and utilization. Herein, the BiF3/BiOCl heterojunction has been prepared through a mild post-synthesis method.Surface photovoltage spectra (SPV) results show that only negative SPV signal can be observed for BiOCl, suggesting that the photogenerated electrons mainly move to the surfaces and accumulate on the surface; both negative and positive signals can be observed for 38% BiF3/BiOCl, indicating that photogenerated electrons and holes can both move to the surfaces and accumulate on the surface; but nearly no SPV signal can be observed for BiF3, demonstrating that nearly no electrons or holes can accumulate on the surface. Furthermore, under ultraviolet light irradiation (X < 420 nm), the degradation rate was 5.3 and 5.8 times higher than that of BiOCl and BiF3 for the degradation of 2-nitrophenol, respectively. We hold that the charges transfer and separation efficiency of BiF3/BiOCl have been significantly improved by the synergetic effect of the surface electric field, bulk internal electric field and interface electric field. This work could help us to intensively understand the charge transfer behavior of a heterojunction photocatalyst.