Upconversion Photocatalytic Bactericidal Properties Of Rare-earth Doped TiO₂ Nanocrystallite

In this paper, new photocatalyst with upconversion emission properties, Er³⁺-Yb³⁺-Fe³⁺ tri-doped TiO₂ and Er³⁺-Yb³⁺/TiO₂ nano-powders at different calcined temperature (950℃-1050℃) were obtained by sol-gel method . We systemically studied photocatalytic bactericidal properties of samples and the upconversion bactericidal mechanism. The results are as follows:1. Er3+(10%)-Yb3+(10%)/TiO₂ samples at 950℃or 1000℃calcinations have apparently bactericidal action under the same experimental condition, and the bacterial survival rate reached 78% and 47% at 60min under 980nm laser irradiation. The result is consistent with their properties of UV-Vis adsorption and upconvertion emission spectra. The sample with stronger intensity of UV-Vis adsorption and upconvertion emission has better bactericidal action. The possible upconversion photocatalytic mechanism on Er3+-Yb3+co-doped TiO₂ is the result of the ultraviolet upconversion emission of doping rare-earth ions.2. Er3+(10%)-Yb3+(10%)-Fe3+(0.2%)tri-doped TiO₂ (1050℃) nano-powders, the minimal bacterial survival rate reached 35% at 60min under 980nm laser irradiation. According to the upconversion emission spectrum, UV-Vis adsorption and bactericidal rate of samples, the primal energy applied photocatalysis was brought by the upconversion emission of rare earth elements and the co-doping of rare earth and transition metal ions. It is found that the upconversion photocatalytic mechanism on Er³⁺-Yb³⁺-Fe³⁺ tri-doped TiO₂ is mainly due to the quenching of luminescence derived from the doping Fe3+ ions. The sample with stronger intensity of UV-Vis adsorption and quenching of upconvertion emission has better bactericidal effect. This result is different from above Er3+-Yb3+/TiO₂ nano-powders.3. In comparision with Er3+-Yb3+co-doped TiO₂ and Er³⁺-Yb³⁺-Fe³⁺ tri-doped TiO₂, it is thought that the realization of upconversion photocatalytic bactericidal action should be related to crystal structure of TiO₂ and its crystal structure distortion. It is very important to realize the photocalysis of TiO₂ under infrared light rather than ultraviolet radiation from which environment and human being was protected and abating the damage on human being. This work would be much more beneficial for the application of TiO₂ to the photodynamic therapy investigation and the inactivation of bacteria without the existence of ultraviolet radiation. It is also important to widen the application of upconversion materials on photocatalyze field and find new photocatalyst and photocatalytic mechanism.