Study On Ag@AgCl Modified Semiconductor Photocatalysts And Their Photocatalytic Performance

Photocatalytic degradation of organic pollutants has good prospects for application because of its advantages of complete decomposition,rapidity and low energy consumption.The traditional semiconductor photocatalysts were given more and more attention due to its non-toxic and good stability,however the wide band gap and photogenerated electron-hole pair recombination easily occuring,which affect the photocatalytic efficiency.In this paper,Ag/TiO₂,Ag@AgCl and Ag@AgCl/TiO₂ three kinds of modified semiconductor photocatalysts were prepared by making use of the surface plasmon resonance absorption of metallic Ag.The photocatalytic degradation of Rhodamine B simulated organic waste water was carried out with the modified semiconductor photocatalyst,and the corresponding photocatalytic degradation mechanism was explored.The photocatalytic degradation experiments show that the photodegradation rate of Ag/TiO₂ particles prepared by the photoreduction method with AgNO₃ and TiO₂ as raw materials is 2.72 times that of TiO₂;for Ag@AgCl cubic particles prepared by two different methods,the photodegradation rate of Ag@AgCl obtained by the glycol assisted reduction method is 1.57 times that of the products of the photoreduction method.The results show that the addition of Ag element into the traditional semiconductor photocatalyst can significantly improve the photocatalytic performance.Using AgNO₃ as silver source and HCl as chlorine source,AgCl/TiO₂ was prepared by depositing AgCl on the surface of TiO2 by precipitation method,and then Ag@AgCl/TiO2photocatalyst was synthesized by reducing part of AgCl to Ag0 by irradiation with Xenon lamp for 90 min.The optimum reaction conditions for the preparation of Ag@AgCl/TiO2 are as follows:the molar ratio of AgNO3 to TiO2=0.63,pH 7-9,90min,25?,and 0.5%accelerator EDTA dosage.The microstructure,surface analysis and optical properties of the Ag@AgCl/TiO2composite catalyst show that the structure of Ag@AgCl coating TiO2 was formed in the Ag@AgCl/TiO₂,and Ag particles were dispersed in the AgCl coating layer.There are four elements Ti,O,Ag,and Cl in the composite catalyst,and the Ag element exists in two valence states of Ag⁺and Ag⁰.The band gap width of Ag@AgCl/TiO₂ photocatalyst is reduced to 2.87ev,and Ag@AgCl/TiO₂ has the highest photogenerated electron and hole separation rate compared with TiO₂,Ag/TiO₂ and AgCl/TiO₂.Compared with the performance of Ag@AgCl/TiO₂,TiO₂,Ag/TiO₂ and AgCl/TiO₂photodegradation of Rhodamine B,it is found that the degradation rate of Ag@AgCl/TiO2composite catalyst is the highest,up to 99.5%after 30 minutes of visible light irradiation.The first-order kinetic simulation results of photodegradation reactions show that the degradation rate constant K value of Ag@AgCl/TiO₂ catalyst is 0.177min^-1,which is 32times of TiO2,12 times of Ag/TiO2 and 1.2 times of AgCl/TiO2.When the molar ratio of the raw material AgNO₃ to TiO₂ is 0.63,the photocatalytic performance of 0.63-Ag@AgCl/TiO₂is the best,and its degradation rate is 1.47 times of 0.47-Ag@AgCl/TiO2,and 1.45 times of0.94-Ag@AgCl/TiO₂.After 5 rounds recycling experiment,Ag@AgCl/TiO₂ photocatalyst still has good efficiency.