Photocatalyst Construction Based On Charge Separation And Catalytic Active Site Design For Efficient Catalytic Aerobic Oxidation

With the rapid development of coal chemical industry,petrochemical,and other industries,a large amount of waste water and toxic pollutants are produced,resulting in increasingly serious environmental pollution problems.Scientists have focused on phenolic compounds in wastewater and thiophene-type sulfides in fuel oil due to their stable aromatic conjugate structures as a typical class of difficult to completely remove organic pollutants.In the past decades,photocatalytic aerobic oxidation technology has broad application prospects in pollutant degradation and environmental remediation due to advantages such as mild reaction conditions,greenness,and efficiency.Nonetheless,there are still factors that limit the efficiency of photocatalytic aerobic oxidation,such as rapid recombination of photogenerated carrier,small specific surface areas for less active sites,and insufficient concentration of oxygen active species.Herein,bismuth oxyhalide and carbon nitride based photocatalysts were selected to improve the charge separation efficiency and design the catalytic active sites,respectively,so as to effectively improve the activity of photocatalytic oxidation reaction.Based on all above consideration,the specific research work carried out in this thesis is as follows:（1）The rapid recombination of photogenerated carriers limit the activity of photocatalytic aerobic oxidation for phenolic compounds in wastewater.In this experiment,Bi₂₄O₃₁Cl_xBr_10-xsolid solutions photocatalysts were constructed by changing the halogen type and ratio.Combining DFT calculations,Kelvin probe force microscopy,and zeta tests showed that with the increase of crystal structure asymmetry,a significant increase of IEF between[Bi₂₄O₃₁]and[X]layers was achieved,which greatly promoted the bulk-charge separation and migration efficiency,and then improved the activity of photocatalytic oxidation of phenolics.The experimental results show that the carrier density of Bi₂₄O₃₁Cl₄Br₆is 33.1 and 4.7 times higher than that of Bi₂₄O₃₁Cl₁₀and Bi₂₄O₃₁Br₁₀,respectively.Corresponding,the bisphenol A degradation activity of Bi₂₄O₃₁Cl₄Br₆is higher than others.This work reveals the intrinsic mechanism of the solid solution strategy to promote the bulk-charge separation and enhance the photocatalytic oxidation performance from the perspective of IEF,which provides a new way to design photocatalysts with excellent charge separation efficiency.（2）In response to the problem that the inorganic semiconductor photocatalytic oxidation of thiophene sulfides has insufficient reactive sites.Herein,a molecularly tunable carbon nitride organic photocatalyst was selected to obtain M₁U₃CN with a large specific surface area and abundant N_3Cvacancies by directly annealing the mixture of urea and melamine.Experiment results indicate that the photocatalytic oxidation of benzothiophene（BT）,dibenzothiophene（DBT）and 4,6-dimethyldibenzothiophene（4,6-DMDBT）in simulated gas/diesel with aromatic compounds was performed with high oxidation efficiency.Due to the construction of N₃C defect sites,the heptazine ring structure of M₁U₃CN photocatalyst can produce a localized non-uniform charge distribution,facilitating the separation of photogenerated carriers.Meanwhile,DFT and in-situ ESR tests show that M₁U₃CN has more N-C=N edge active sites,and its adsorption energy for O₂（-4.53 eV）is much higher than MCN（-0.095 eV）and UCN（-0.089 eV）,thus producing the high concentration of·O₂^-,¹O₂and h⁺active species;In addition,the defective heptazine ring and molecular microporous structure of M₁U₃CN also act as an efficient active site to capturing and activating DBT.Therefore,this work reveals the intrinsic mechanism for the enhanced activity of photocatalytic oxidation of thiophene sulfides from the perspective of precise construction of active sites,and provides a new effective strategy for improving the photocatalytic oxidation performance through rational design of photocatalysts.