A Study On Photocatalysis Of Rare Earth Co-doped Nano-ZnO

In this article, ER-doped nano-ZnO powders were prepared by the method of polyacrylamide-gel, the influence of ER-doping on particle size,appearance and photocatalysis performance of nano-ZnO was researched, which have been separately characterized by XRD,TEM,UV spectrophotometer and UV-Vis.Nano-ZnO powders doped with different content of Tm3+, Yb3+ and Er3+ were prepared by the method of polyacrylamide-gel, when the dosage is 0.05mol%Tm3+, 0.1mol%Yb3+ and 0.03mol% Er3+,photocatalytic degradation rate achieves highest, and the degradation rate was 86.64%,87.96% and 78.39% respectively. The phase composition and microstructure were investigated by means of XRD and TEM. The results showed that the crystalline phases of the samples of ER-doped ZnO were hexagonal wurtzite, and the particle of ER-doped ZnO crystalline was spherical; But ER-doped ZnO caused different degree of crystal lattice expansion, the crystal irregularities facilitate ZnO particle surface chemical adsorption and increase catalytic activity. Yb3+-doped ZnO can inhibit the growth of grain, Er3+-doping can form atom clusters easily,along with the particle size increasing.In Yb3+-Er3+ and Yb3+-Tm3+ co-doped nano-ZnO systems, Yb3+ as diffuse and sensitization agent will transmit energy to activate ion Er3+ and Tm3+ and improve the photocatalytic activity, when the dosage is 0.05mol%Tm3+ and 0.05mol%Er3+, the best Yb3+-Er3+ co-doped sample YE10 is available, and the photocatalytic degradation rate was 90.94%. The best Yb3+-Tm3+ co-doped sample YT10,corresponding to 0.1mol%Yb3+ and 0.03mol% Tm3+, its degradation rate was 84.78%.The results indicated that under UV light, when the catalyst dose was 6.0g/L, the initial concertration of MB was 10mg/L, the pH value was 9, the efficiency of photocatalysis performance was the highest. And the influence degree of photocatalytic degradation rate is as follows:the pH value of MB>the initial concentration of MB>the catalyst dose of ZnO.When the catalyst dose was 4.0g/L, the initial concertration of MB was 15mg/L, the pH value was 6.5,photocatalytic degradation time was 4h, the efficiency of photocatalysis performance is as follows:Yb3+-Er3+>Yb3+-Tm3+>Yb3+>Tm3+> Er3+>pure ZnO,'and the degradation rate was90.94%,84.78%,78.86%,71.28%, 66.33% and 52.75% respectively. Photocatalytic reaction dynamics research shows that the photocatalytic degradation process of the samples conform to first-order kinetic rate constant k1.The k1 of sample G5,with the content are 0.05mol%Tm3+ and 0.05mol% Er3+, is 9×10-3,while the k1 of pure ZnO is 2.81×10-3.UV-Vis shows that ER-doped ZnO expand the visible absorption range 10-20nm. But the visible absorption threshold of ZnO catalyst is large, the ZnO catalyst photocatalytic degradation rate is not always high. Absorbing threshold for G4,with the content is 0.03mol% Er3+, is 402.5nm, while its degradation rate is only 66.33%. Absorbing threshold for G5 is 391.8nm, its degradation rate achieves 90.94%.Magnesium slag porous ceramic filter balls immobilized ZnO photocatalysts can significantly improve the efficiency of photocatalysis performance, when the dipping time was 5min, coating times was 2;the efficiency of photocatalysis performance was the highest, its degradation rate was 59.04% and it was higher 24.71% than that of un-supported ZnO.Too long dipping time and too many coating times will lead to the photocatalytic efficiency decreased.