The Influence Of Band Structure And Cocatalyst On Visible-light Photocatalytic Ozonation Process

Solar light is the energy source of the whole creatures on the earth.Utilizing the solar energy to solve the challenging water pollution problem has been regarded as one of the most promising water treatment technologies.But due to the quite low efficiency of the existing photocatalysts,single photocatalytic process still cannot meet the application requirements.However,introducing ozone into the photocatalytic system,so called photocatalytic ozonation has been reported to be an intriguing process which can trigger a synergy effect between the ozone and photocatalysis.The synergy effect produced much more reactive oxygen species thus strongly enhanced the pollutants removal rate.In the present work,novel tungsten oxide and bismuth vanadate were synthesized and used as model catalysts to elaborate the influence of band structure and cocatalyst on photocatalytic ozonation process.Some key results are concluded as follows:（1）Three kinds of WO₃ with different crystalline phase and mainly expose facets were synthesized by hydrothermal or calcination method.They all triggered a synergy effect between ozone and photocatalysis thus strengthening the degradation results of oxalic acid and cephalexin.The band structures of the prepared WO₃ were gained through XPS and UV-Vis DRS data.Combining the band structures and degradation results,we found that more negative conduction band position favors the photocatalytic ozonation process due to the dominated role of the ozone one-electron reduction reaction.（2）In situ EPR and online DMOP trapping technologies confirms that hydroxyl radical（·OH）can be generated through two pathways:（i）ozone one-electron reduction;（ii）photogenerated holes oxidizing OH^-.Together with our previous work on g-C₃N₄photocatalytic ozonation,WO₃ photocatalytic ozonation complements the photocatalytic ozonation theory.（3）The two main roles of ozone in photocatalytic ozonation were summarized:（i）direct oxidation of the pollutants till formation of refractory intermediates,（ii）efficient trapping of photoelectron that cannot be done by O₂.The latter is crucial because it not only separates the hole-electron pairs which improved the photocatalytic efficiency but also induces the·O₃^--mediated pathway for·OH formation.Moreover,the intrinsic charge separation ability of WO₃ in photocatalytic ozonation,is not that important when comparing with it in photocatalysis（only in the presence of O₂）.Based on the radical mechanism,the pH effect was comprehensively studied.（4）The influence of metal oxide cocatalyst on photocatalytic ozonation were preliminarily studied.A kind of dendritic BiVO₄ was synthesized and modified by manganese oxide（MnO_x）.Degradation results,radicals inhibiting results and in situ EPR results jointly proved that MnO_x played a triple role here:（i）strengthening the light absorption;（ii）promoting the h⁺transfer process and simultaneously enhancing the separation of electron-hole pairs;（iii）functioning as efficient catalyst of catalytic ozonation.