Fabrication And Properties Of Novel Titanium Dioxide-based Composite Photocatalysts

With the rapid development of industrialization,environmental pollution has become a major problem of social development.As a new wastewater treatment technology,photocatalytic technology has made great breakthroughs and become a hot research topic in recent years.The traditional photocatalytic material titanium dioxide,which can only be excited by ultraviolet light,has a wide band gap and low quantum yield.In view of the above key problems of titanium dioxide,this paper synthesized titanium dioxide matrix composites with high photocatalytic activity and larger visible light response range by using nano-silver and reduced graphene oxide as electron migration materials.The structure and morphology of the samples were studied by characterization method,including XRD,SEM,TEM,DRS and BET.The photocatalytic degradation activity of methylene blue and other dyes was evaluated by photocatalytic degradation.The main research contents and conclusions are as follows:Firstly,Ag@AgCl/TiO₂ composites were prepared by precipitation-photoreduction method.The results show that the presence of silver not only improves the photocatalytic activity of the composite catalysts,but also improves the stability of the materials.The effects of the ratio of titanium dioxide to silver chloride,photoreduction time,initial dye concentration and catalyst dosage on photocatalytic performance were systematically studied using methylene blue solution with a concentration of 10 mg/L as pollutant model.The results show that the material has the best performance when the mass ratio of titanium dioxide to silver chloride is 1:2 and the photoreduction time is 20 minutes.The degradation rate is 97.8%when the light is50 minutes.On the basis of material characterization and free radical capture experiments,we proposed the mechanism of degradation of organic pollutants by composite photocatalysts.In the process of photocatalysis,photogenerated carriers can be quickly separated due to the existence of the interface between TiO₂/Ag and Ag@AgCl.In addition,Cl^-can be oxidized to Cl⁰ by holes and directly participate in the degradation reaction.After the reaction is completed,Cl⁰ can be changed to Cl^-,thus forming Cl^-/Cl⁰ redox pairs and improving photocatalytic activity.Secondly,graphene oxide solution was prepared by improved Hummers method,and then RGO/TiO₂-Ag composite catalyst was prepared by one-step reduction with ascorbic acid as reductant in water bath at 95?C.The SEM,TEM,XRD and XPS characterization results showed that titanium dioxide and silver were successfully loaded on thin graphene.The effects of different graphene and silver loadings on the photocatalytic properties of the composite were investigated.The results showed that the composite catalyst had the best photocatalytic activity when the graphene loading was 4%and the silver loading was 5%.The degradation rate was 94.6%when the illumination lasted for 50 minutes.The results of transient photocurrent response test also show that RGO/TiO₂-Ag ternary composite has the highest photocurrent response value,reaching 8.9 uA/cm².In addition,we propose the mechanism of degradation of methylene blue by RGO/TiO₂-Ag composites:when visible light irradiates the surface of the material,photogenerated electrons and holes will be generated,and the photogenerated electrons will migrate rapidly to the surface of silver nanoparticles and graphene,thus accelerating the migration of photogenerated carriers and promoting photocatalytic reaction.