Preparation of CdS/TiO₂ Photocatalytic Material and Its Photocatalytic Reduction of U(Ⅵ)

Based on the photocatalytic reduction of U(Ⅵ), TiO₂ nanoparticles were prepared by chemical precipitation method. Then, CdS/TiO₂ composite nanoparticles were prepared by stepwise precipitation method with TiO₂ as matrix material, and the composite nanoparticles were characterized by scanning electron microscopy, X-ray diffraction and UV-visible diffuse reflectance spectroscopy which could be used to analyze the surface morphology, crystal shape and optical absorption characteristics of the materials. The performance of photocatalytic reduction of U(Ⅵ) in uranium containing wastewater was investigated under visible light irradiation. X-ray diffraction results show that TiO₂ nanoparticles exist in anatase type and rutile type, while CdS nanoparticles exist in cubic crystal type. Scanning electron microscopy results show that the particle sizes of CdS/TiO₂ composite nanoparticles range from 30 nm to 50 nm. UV-visible diffuse reflectance spectroscopy results show that compared with TiO₂ nanoparticles, CdS/TiO₂ composite nanoparticles have an absorption band from 395 nm to 550 nm, which show the characteristics of a double band gap. The above results indicate that the introduction of CdS in TiO₂ can expand the light response range of TiO₂ from ultraviolet region to visible light region, namely, the phenomenon of red shift occurs. Photocatalytic test results show that CdS/TiO₂ composite nanoparticles show good photocatalytic activity. The photocatalytic reduction efficiency of U(Ⅵ) reaches the highest value of 99.13% when the pH value of simulated wastewater is 6.0, the dosage of CdS/TiO₂ composite nanoparticles is 1.0 g/L and the photocatalytic reaction time is 2 h. The photocatalytic reduction reaction accords with the kinetic characteristics of quasi first order reaction. In order to verify the photocatalytic reduction effect of CdS/TiO₂ composite nanoparticles in real wastewater, the real wastewater of a tailing pond was taken as the research object. In the experiment, 1.0 g/L CdS/TiO₂ composite nanoparticles were added for photocatalytic reaction. The results show that the reduction rate of uranium in the real wastewater by CdS/TiO₂ composite nanoparticles is 90.4%, and the uranium concentration is 0.04 mg/L, which meets the national wastewater discharge standard. The prepared CdS/TiO₂ composite nanoparticles are visible light photocatalytic materials. The U(Ⅵ) in wastewater can be reduced to U(Ⅳ) by photocatalytic reduction technology. The overall process is simple, environment friendly and has a good prospect of popularization and application.