Investigation on photocatalytic degradation of ethyl violet dyestuff using visible light in the presence of ordinary rutile TiO2 catalyst doped with upconversion luminescence agent

To use solar irradiation or interior lighting efficiently, a new photocatalyst with high catalytic activity in visible light was sought. In this work, an upconversion luminescence agent, 40 CdF2·60 BaF2·1.0 Er2O3, was synthesized and its fluorescent spectrum was determined. It is found that this upconversion luminescence agent can emit five upconversion fluorescent peaks below 387 nm under the excitation of 488 nm visible light. The upconversion luminescence agent has revealed an improvement over ordinary titanium dioxide (TiO2) in photocatalytic activity under visible light irradiation for the photocatalytic degradation of ethyl violet in aqueous solution as a model compound. The TiO2 photocatalyst doped with upconversion luminescence agent was characterized by X-ray diffraction (XRD) and transmission electron microscope (TEM). The photocatalytic degradation of ethyl violet was tracked by UV–vis and 1H-NMR spectra, and the influences of irradiation time, initial concentration of ethyl violet, addition amount of TiO2 catalyst and initial pH value were also investigated. To affirm the complete mineralization, the total organic carbon (TOC) was also tested. The degradation rate of ethyl violet in the presence of doped rutile TiO2 photocatalyst reached 87.08% at 4.0 h visible light irradiation, which was obviously higher than the corresponding degradation rate (35.42%) in the presence of undoped rutile TiO2 powder. The research results show that the upconversion luminescence agent is necessary to transform visible lights into ultraviolet lights and thus make the best use of visible lights. By calculation, the upconversion efficiency of the emission peak at 380 nm was estimated to be about 0.78%. The TiO2 powder doped upconversion luminescence agent under visible light irradiation is able to decompose the ethyl violet in aqueous solution efficiently, therefore, this method may be envisaged as a technology for treating dyes wastewaters using solar energy, especially at textile industries in developing countries.