The Preparation Of Co,Y And Co-Y Doped TiO₂ Photocatalysts By Microwave Hydrothermal Method And Their Photocatalytic Activity

In this paper,cobalt-doped TiO₂,yttrium-doped TiO₂,and yttrium-cobalt co-doped TiO₂,were prepared by microwave hydrothermal method,and methyl orange was used as a simulated pollutant under ultraviolet light irradiation.Degradation experiments were carried out to investigate the photocatalytic degradation activity of the catalyst under four degradation conditions:ultraviolet,ultrasound,ultrasound-ultraviolet and visible light,so as to explore the influence of catalyst preparation conditions on the photocatalytic activity.The effects of six factors,including element doping amount,microwave hydrothermal synthesis power,microwave hydrothermal synthesis time,microwave hydrothermal synthesis temperature,drying temperature and drying time,on the photocatalytic activity of the catalyst were discussed separately,and the photocatalytic activity was desorbed by XRD and N₂ adsorption.Analytical and test methods such as SEM,XPS,etc.were used to test and characterize the catalyst,explore the influence of preparation conditions on the structural characteristics of the photocatalyst,and the influence of different structural characteristics on the photocatalytic activity,and analyze the reasons;at the same time,the concentration of hydroxyl radicals,The effects of superoxide radicals and photogenerated electrons on photocatalytic performance,the main results obtained are as follows:1.Preparation of cobalt-doped TiO₂ photocatalyst TiO₂-Co by microwave hydrothermal method and its photocatalytic activityTiO₂-Co is prepared by microwave hydrothermal synthesis method,the best preparation conditions are:n(Co²⁺):n(Ti⁴⁺)=1.0%,microwave hydrothermal synthesis power 600W,microwave hydrothermal synthesis temperature 150℃,microwave hydrothermal synthesis time 2.5h,drying temperature 80℃and drying time 2h.After30 minutes of degradation of methyl orange solution under self-made UV lamp irradiation,the degradation rate of methyl orange reached 98.02%;in microwave（MW）,ultraviolet（UV）,microwave-ultraviolet（MW-UV）and microwave-ultrasound-ultraviolet（MW-UT-UV）The methyl orange solution is degraded under four conditions.The best conditions for the degradation of the methyl orange solution are microwave-ultrasound-ultraviolet;when the methyl orange solution is degraded by visible light,the methyl orange is almost completely degraded in 5 hours.Through XRD,SEM and N₂adsorption and desorption analysis,it is found that TiO₂-Co mainly exists in a mixed structure of amorphous TiO₂ and anatase TiO₂,with low crystallinity.Due to insufficient physical grinding,the size of an object is not seen after magnification,but there are spherical particles scattered on the surface,and there is a small amount of accumulation.The pore diameter is mainly concentrated in 5-10nm,which is a mesoporous material;through EDS and XPS analysis,it is found that TiO₂-Co is doped with cobalt,but because the radius of cobalt ions is small,it will enter the TiO₂ lattice,so the detection peak is weak.2.Preparation of yttrium-doped TiO₂ photocatalyst TiO₂-Y by microwave hydrothermal method and its photocatalytic activityTiO₂-Y is prepared by microwave hydrothermal synthesis method,the best preparation conditions are:n(Y³⁺):n(Ti⁴⁺)=0.6%,microwave hydrothermal synthesis power 600W,microwave hydrothermal synthesis temperature 135℃,microwave hydrothermal synthesis time 2h,drying temperature 80℃and drying time 3h.After 30minutes of degradation of methyl orange solution under self-made ultraviolet lamp irradiation,the degradation rate of methyl orange reached 99.18%;in microwave（MW）,ultraviolet（UV）,microwave-ultraviolet（MW-UV）and microwave-ultrasound-ultraviolet（MW-UT-UV）Degradation of methyl orange solution under four conditions,the best conditions are microwave-ultrasound-ultraviolet;when using visible light to degrade methyl orange solution,methyl orange is almost completely degraded in 2.5h.Through XRD,SEM and N₂ adsorption and desorption analysis,it is found that TiO₂-Y mainly exists in a mixed structure of amorphous TiO₂ and anatase TiO₂,with low crystallinity,and due to insufficient physical grinding,the size is not one piece after magnification.But there are a large number of uniform and small spherical particles distributed on the surface,the pore diameter is mainly about 5nm,which is a mesoporous material;through EDS and XPS analysis,it is found that TiO₂-Y is indeed doped with yttrium,and the surface is loaded with a small amount of yttrium oxide;Through PL and free radical tests,it is found that the fluorescence intensity of TiO₂-Y is low,and the hydroxyl radical and superoxide anion act together to photocatalyze the reaction.3.Preparation of yttrium and cobalt co-doped TiO₂ photocatalyst and its photocatalytic activity by microwave hydrothermal methodThe yttrium and cobalt co-doped TiO₂-Co-Y were prepared by microwave hydrothermal synthesis.The best preparation conditions were:n(Y³⁺):n(Ti⁴⁺)=0.8%,n(Co²⁺):n(Ti⁴⁺)=1.0%,Microwave hydrothermal synthesis power 600W,microwave hydrothermal synthesis temperature 150℃,microwave hydrothermal synthesis time2.5h,drying temperature 80℃and drying time 2h.After 30 minutes of degradation of methyl orange solution under self-made UV lamp conditions,the degradation rate of methyl orange reached 87.09%;in microwave（MW）,ultraviolet（UV）,microwave-ultraviolet（MW-UV）and microwave-ultrasound-ultraviolet（MW-UT）-UV)The methyl orange solution is degraded under four conditions.The best conditions are microwave-ultrasound-ultraviolet;when the methyl orange solution is degraded by visible light,the methyl orange is almost completely degraded in 5 hours.Through XRD,SEM and N₂ adsorption and desorption analysis,it is found that TiO₂-Co-Y mainly exists in a mixed structure of amorphous TiO₂ and anatase TiO₂,with low crystallinity,and due to insufficient physical grinding,the size is different after magnification,spherical particles are distributed on the surface,but the particles are stacked and unevenly dispersed,and the pore size distribution is uneven,mainly concentrated at about 0-15nm,which is a mesoporous material;through EDS and XPS analysis,it is found that TiO₂-Co-Y is doped with yttrium and cobalt elements,and a small amount of yttrium oxide is supported on the surface;through PL test,it is found that the fluorescence intensity of TiO₂-Co-Y is higher,indicating that TiO₂-Co-Y photogenerated electron-hole recombination rate is high,which is not conducive to photocatalytic reaction.The results of this paper show that the preparation of TiO₂ by microwave hydrothermal synthesis has the characteristics of faster heating and uniform heating than ordinary hydrothermal synthesis.The photocatalytic activity of TiO₂-Y prepared by microwave hydrothermal synthesis is better than that of TiO₂-Co and TiO₂-Co-Y,under different degradation conditions,microwave ultrasonic ultraviolet degradation efficiency is better.Under visible light conditions,TiO₂-Y can completely degrade methyl orange solution in 2.5h.The analysis found that the three materials of TiO₂-Y,TiO₂-Co,and TiO₂-Co-Y are all amorphous TiO₂ mixed with anatase phase TiO₂.The lower crystallinity promotes the photocatalytic activity of TiO₂.