Study On The Preparation Of Ag/Au Supported ZnO And Its Photocatalytic Degradation Lignin Model Compounds

The lignin emitted by industrial production is toxic,harmful and difficult to degrade,which seriously threatens the survival and development of human society.Industrial wastewater containing lignin model compounds(phenol,guaiacol,etc.)and phenolic compounds has become an environmental concern.Photocatalytic technology can degrade various refractory organic pollutants into small molecular inorganic substances at room temperature,thus achieving effective treatment of wastewater.Zinc oxide(ZnO)has high physical and chemical stability,and is inexpensive,non-toxic and harmless.Metal loading technology is one of the effective ways to improve the photocatalytic efficiency of ZnO.It has been reported that the model compounds of silver(Ag)and gold(Au)loaded nano-ZnO-degraded lignin are prepared by using tetramethylammonium hydroxide solution as raw material.This thesis mainly studies a series of ZnO,Ag-ZnO and Au-ZnO photocatalysts for the degradation of lignin model compounds such as phenol and guaiacol.The main contents are as follows:A series of ZnO,Ag-ZnO and Au-ZnO photocatalysts were prepared by sol-gel method.The photocatalysts were characterized by BET?XRD?SEM?UV-Vis and PL.The results showed that the prepared catalyst was hexagonal.Nano-ZnO of wurtzite structure and spherical particles of uniform particle size.The loading of Ag and Au does not change the morphological characteristics of ZnO,and the UV absorption spectrum has a red shift phenomenon,which is beneficial to the absorption of light and enables the photocatalyst to degrade organic pollutants under visible light.In the study of photocatalytic performance,the ratio of raw materials,calcination temperature,calcination time,amount of catalyst,initial concentration of solution,pH value of solution and reusability of phenol and guaiacol in ultraviolet light and visible light were discussed.The effect of degradation under the light source.The results showed that when the ratio of raw materials was 1:2,the loading of Ag was 3%,the loading of Au was 0.5%,the calcination temperature was 500?,the calcination time was 2 h,the amount of catalyst was 0.15 g,and the initial concentration was 2.1×10-4 M,when the solution is neutral or weakly acidic,the photocatalyst has better photocatalytic performance,and the degradation rate is basically unchanged after repeated use for 3 times.Under the optimal conditions,the degradation rates of phenol and guaiacol in the degradation of phenol and Ag-ZnO were 88.6%and 96.5%,respectively,which was nearly twice as high as that of pure ZnO(42.6%,49.2%).Ag degradation of phenol and guaiacol by ZnO under visible light is 73.6%and 78.9%,which is about six times higher than16.8%and 17.9%of pure ZnO.The degradation rate of Au-ZnO in phenol and guaiacol was 85.9%?84.3%,the degradation rate of phenol under visible light was 42.7%,and the degradation rate of guaiacol was 59.8%,which was larger than pure ZnO.The photocatalyst mechanism shows that the loading of Ag and Au can effectively reduce the electron-hole recombination,thereby improving the photocatalytic degradation efficiency.