The Prepration And Visible Light Photocatalytic Study Of Modified Nano-TiO₂

With excellent stability, nontoxicity, good activity and low-cost, Ti O2 has attracted much attention among numerous photocatalytic materials. However, the limited visible light absorption restricts its photocatalytic applications greatly. Modification of nano-Ti O2 is an effective way to break this limitation. In this paper, through a simple ultrasonic dispersion method, nano-Ti O2 was effectively composited with Cd S nanoparticles(NPs) with the help of L-Cysteine. The nanocomposite system and its visible light photocatalytic capacity were studied as follows.Firstly, we used L-Cysteine(L-Cys) as a dual-role reagent in the synthesis of Cd S NPs. The results showed that, as a stabilizer, the dosage of L-Cys could control the size of L-Cys-Cd S NPs when Cd S NPs was synthesized at room temperature. Furthermore, the size of Cd S NPs increased with the increase of hydrothermal temperature, accompanied by a phase change from unstable cubic phase to hexagonal phase. When using L-Cys as sulphur source and stabilizer, the morphology of Cd S varied with the different hydrothermal temperature, and tended to be nanorod at high temperature.P25,a widely used commercial nano-Ti O2, was chosen to be modified with L-Cys-Cd S which was synthesized at room temperature through a simple ultrasonic dispersion method. TEM showed that they were well composited and the light absorption of composite broadened to the visible region successfully. The visible light photocatalytic activity of modified nano-Ti O2 was characterized by both photodegradation of Rh B and photocatalytic splitting of water. The results showed that its degradation capacity was no better than P25, but hydrogen generation capacity was much better than P25. Based on such results and the previous study of L-Cys-Cd S, thermal treatment and dye sensitization were used to improve the degradation capacity and enhance hydrogen generation capacity. The results illustrated that proper hydrothermal treatment could significantly improve the degradation capacity. However, dye sensitization didn’t enhance hydrogen generation capacity much; the reason and mechanism needed further study.In addition, we studied in details that mechanism of our previous microwave method to produce Ti3+ self-doped nano-Ti O2 with high visible light photocatalytic activity. A new radical capture agent, methylene blue(MB), was used to verify the existence of hydroxyl radical and its effect. The influence of the drying process was also studied, and the results showed temperature was very important to the photocatalytic capacity but drying atmosphere had little influence. Three new kinds of commercial nano-Ti O2 was modified by the microwave method, and the results of visible light photodegradation of Rh B illustrated that this method was not fit for all kinds of Ti O2. The smaller the size of Ti O2, the better the Ti3+ self-doping effect worked. Based on the understanding of the mechanism of microwave method, a hydrothermal method was also developed with similar Ti3+ self-doping effect. Under proper conditions, hydrothermal process could also prepare the material with high visible light photocatalytic activity.