Preparation And Photocatalytic Property Of Tm³⁺-Yb³⁺/TiO₂/CdS Nano-composite Photocatalyst

Doping the rare-earth ion Tm3+, Yb3+ and compounding the narrow-band semiconductor CdS (Eg=2.5eV) with TiO2 seem to be an effective method. The upconversion luminescence effect of the rare earth ion can produce a higher excitation light. Compounding with the narrowband of CdS can expand the range of the absorption. Both modified methods not only inhibit the recombination of photo-generated electrons and holes, but also improve the photodegradation efficiency.1. A new Tm3+-Yb3+/TiO2/CdS nano-composite photocatalyst have been synthesized by a sol-gel method. UV-Vis diffuse reflectance spectra, X-ray diffraction (XRD), transmission electron microscopy (TEM) and X-ray photoelectron spectroscopy (XPS) were used to characterize the optical properties, structure and composition of samples.2. The photocatalytic degradation methyl violet and phenol were investigated in Tm3+-Yb3+/TiO2/CdS aqueous suspensions under the three-color light irradiation. The effects of the catalyst dosage, initial concentration of methyl violet or phenol, irradiation time and pH wree investigated. The results indicated that the nano-composite catalyst showed very high photocatalytic activity. When the amount of catalyst is controlled 1.5 g/L and the initial concentration of the dye is 20 mg/L in pH=3 system, the degradation efficiency of methyl violet was 98.13%. When the amount of catalyst is controlled 4.0g/L and the irradiation time is 12 h, the degradation efficiency of phenol was 73.52%. The phenol degradation rate reached 88.73% after 12 h with adding trace H2O2.3. The kinetic model of the photocatalystic degradation reaction of methyl violet and phenol had been researched and the possible energy transfer mechanism had been discussed also.