Synthesis Of BiVO₄ And Its Composited Matrrials And Degradation Mechanism Of Toxic Organic Pollutants

There are two main issues impeding the development of photocatalysis.Firstly,the recombination of electron-hole pairs generated during the light irradiation which will result in the inefficient utilization of photons.Secondly,because of the similar reactive species there is non-specificity for the degraded substrate,which will lead to the waste of energy and low efficiency.By control preparing conditions,many photocatalyst materials with different architectures,structures and components were prepared to seeking ways to improve the utilization efficiency of protons.Also in recent years,the exploration of novel selective adsorbents has been stimulated.And,to date,a number of promising adsorbents with selective adsorption ability have been developed.But they can only condense and separate adsorbed substrates from their mother liquor.So,it is essential to develop new high efficient photocatalysts with selectivity to address these two problems properly.In this paper,BiVO₄and its composite photocatalytic materials were prepared by hydrothermal method.The effects of pH,reaction time and solvent on the crystal structure,composition and morphology of BiVO₄were investigated.At the same time,m-BiVO₄was prepared for the selective degradation of cationic dyes.The highly active and selective BiVO₄/BiOCl composite catalyst was prepared by soaking in hydrochloric acid.Using X-ray powder diffraction,scanning electron microscope and ultraviolet-visible diffuse reflection spectrum methods for the preparation of the physical characterization of the samples.The photocatalytic activity of three catalytic materials was compared,and the degradation mechanism of the photocatalytic degradation CYN was studied.The research contents and conclusions are as follows:1.Control the pH and reaction time of the precursor solution,and prepare BiVO₄and its complexes（BiVO₄/Bi₆O₆（OH）₃（NO₃）₃）by hydrothermal synthesis.Using X-ray powder diffraction,scanning electron microscope and ultraviolet-visible diffuse reflection spectrum methods for the preparation of the physical characterization of the samples,the results show that the precursor solution pH value between 1.14 to 9.01,the preparation of samples for the BiVO₄/Bi₆O₆（OH）₃（NO₃）₃compound,when the pH value increased by10.92 as the pure BiVO₄;The control medium pH was 7.17,and the reaction time was between 1 and 12 hours,and the BiVO₄/Bi₆O₆（OH）₃（NO₃）₃composite photocatalyst was obtained,which was pure BiVO₄when the reaction time was 18 h.With organic dye Rhodamine B（Rh B）as the substrate,examines the different conditions of preparation of BiVO₄or compound for the photocatalytic activity of photocatalyst,found that pH=7.17,water dicating 12 h of catalyst（BiVO₄/Bi₆O₆（OH）₃（NO₃）₃）activity of photocatalytic degradation of the above preparation of pure BiVO₄.The active species of BiVO₄/Bi₆O₆（OH）₃（NO₃）₃composite photocatalyst were analyzed for the degradation of Rh B photocatalysis,indicating that it mainly involved cavitation and superoxide oxidation in the process of degradation,and O₂·^-played a major role.2.Used the acetic acid and ammonia as solvent,pure monoclinic phase BiVO₄was synthesized under the condition of neutral.By testing the photocatalytic activity,found that the catalyst for the cationic dye degradation rate significantly higher than that of anionic dye,the determination of m-BiVO₄surface Zeta potential found under neutral condition m-BiVO₄surface of negative charge,may be due to electrostatic interactions make the m-BiVO₄selective adsorption of positively charged dyes.The effects of pH and the anionic surfactants on the degradation of dyes were further investigated,the results showed that pH and surfactants has been modified the surface charge on the m-BiVO₄,make the m-BiVO₄selective adsorption and degradation dyes which has opposite surface charges,thus prove the m-BiVO₄selective adsorption of cationic dye degradation to the surface charge.3.By soaking m-BiVO₄which has the peculiarity of selective degradation cationic dye with to enhance photocatalytic efficiency.Testing the catalyst activity after soaking,found that the concentration of hydrochloric acid was 0.05 mol/L has the best effect,the sample were characterized by X-ray powder diffraction,scanning electron microscope（SEM）and ultraviolet-visible diffuse reflection spectrum characterization methods,and the results indicated that BiOCl has been generated in the process of soaking formed the m-BiVO₄/BiOCl composite catalyst.The peculiarity of selective degradation cationic dye of still exists,but the photocatalytic activity is greatly increased.This is due to the BiOCl/BiVO₄p-n heterojunction composite has been prepared.The existence of this heterojunction electric field can effectively inhibit the recombination of the photogenerated electrons and holes,leading to the increase of the photocatalytic performance of the BiVO₄/BiOCl composite.And the degradation mechanism of CYN was studied by using the catalyst.4.The activity of the catalyst which prepared with different conditions were tested,and the composite catalyst BiVO₄/Bi₆O₆（OH）₃（NO₃）₃,m-BiVO₄/BiOCl photocatalytic activity was significantly higher than that of m-BiVO₄.The degradation mechanism of three kinds of catalysts for degradation of CYN was investigated.