Visible-light-driven Photocatalytic Ozonation For Degradation Of Phenolic Pollutants

Phenolic pollutants are widely present in industrial wastewater such as petrochemicals,coking,pharmaceuticals,dyes,etc.,which are extremely harmful to human health.Among the treatment methods of many phenolic pollutants,photocatalysis technology and ozone catalytic oxidation technology have received more and more attention in the treatment of phenol-containing wastewater.Photocatalysis has the potential to non-selectively mineralize phenolic pollutants into inorganic ions,water and carbon dioxide,but the photogenerated electron-hole recombination rate is high and the degradation efficiency is low;ozone oxidation has a high degradation efficiency for phenolic pollutants,but it is difficult to mineralize the small molecule organics produced during the degradation process,and there is selectivity for the degradation of pollutants.Combining the photocatalysis technology and ozone catalytic oxidation technology can not only reduce the recombination rate of electrons and holes,increase the photocatalytic efficiency,enhance the catalytic oxidation ability of ozone;but also increase the utilization rate of ozone.It is a promising water treatment technology.In this thesis,starting from the preparation of a catalyst with visible light response,with different phenolic pollutants as the research object,a visible light catalysis-ozone catalytic oxidation system was constructed,and the degradation characteristics of phenolic pollutants under different oxidation methods were studied.,Gas flow rate,Au load,initial concentration of pollutants,pH value,catalyst stability and other factors were analyzed and discussed,and the following main conclusions were drawn:?1?Flower-shaped TiO₂ and Au nanoparticle-modified flower-shaped Au-TiO₂catalysts were prepared by hydrothermal method and deposition-precipitation method,respectively.During the deposition-precipitation process of Au nanoparticles and subsequent heat treatment,the crystal structure did not change significantly.Au nanoparticles were evenly deposited on the surface of TiO₂ with good dispersion and no obvious agglomeration.The particle size was 10?15 nm,there is obvious absorption in the visible region.?2?The prepared Au-TiO₂ catalyst achieves visible light response.The combination of Au nano-particle modified Au-TiO₂ photocatalysis and ozone catalytic oxidation has an obvious synergistic effect,which can further oxidize the generated small molecule intermediate product?oxalic acid?to CO₂ and H₂O.In the process of photocatalysis-ozone catalytic oxidation,the loading of Au in the Au-TiO₂ catalyst has a great influence on the degradation rate.When the Au content is 1.5%,the catalyst shows the best catalytic activity.The prepared flower-shaped Au-TiO₂ catalyst modified by Au nanoparticles has good stability and can be reused.?3?The degradation rates of phenolic pollutants in different reaction systems all follow:Au-TiO₂/O₃/Vis>Au-TiO₂/O₃>O₃>Au-TiO₂/Vis,and photocatalysis and ozone catalytic oxidation show Certain synergistic effect;the degradation rate of phenolic pollutants with different structures is different,and the order of magnitude is:salicylic acid>2-chlorophenol>phenol..?4?Increasing the initial concentration of pollutants will lead to a decrease in the degradation rate.This is because the catalytically active sites are occupied by intermediates produced by high initial concentrations of pollutants,resulting in a reduction in the reaction rate.The degradation rate of 2-chlorophenol was the fastest under neutral conditions,and the degradation rate reached 89%after 1 hour of reaction,while the degradation rates were only 82%and 65%under acidic and alkaline conditions.?5?The Au-TiO₂/O₃/Vis reaction system has a stronger oxidizing capacity than ozone alone,not only can degrade phenolic pollutants faster,but more importantly,the introduction of visible light catalysis can also degrade ozone alone.The oxalic acid,a small molecule intermediate product,is further degraded,and the synergistic effect of visible light catalysis and ozone catalytic oxidation is used to promote the further mineralization of phenolic pollutants.The flower-shaped Au-TiO2 catalyst prepared in this thesis has obvious absorption in the visible light region,and its catalytic performance is stable.The Au-TiO₂/O₃/Vis reaction system has a stronger oxidation capacity than ozone alone,which can be faster and more thorough It degrades phenolic pollutants,exerts the synergistic effect of the combination of visible light catalysis and ozone catalytic oxidation,and has broad application prospects in the field of industrial wastewater treatment.