Preparation And Photocatalytic Properties Of Rare Earth Doped TiO₂ And ZnWO₄ With Different Morphologies

In recent years, semiconductor photocatalysts have attracted much attention due to their potential applications in the complete mineralization of organic pollutants in air and waste water. TiO₂ has been considered as a promising photocatalyst. However, because of its wide band gap (Eg, anatase = 3.2 ev) and the rapid recombination of photogenerated electron and hole pairs, it is still a problem which make its applications. In this paper, main points are as follows:1. A series of pure and rare earth ion doped TiO₂ nanoparticles with high photocatalytic activities were prepared by a sol-gel method. The as-prepared catalysts were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM) and diffuse reflectance spectroscopy (DRS). The results indicate that rare earth ion doping can effectively reduce the crystalline size, inhibit the anatase-to-rutile phase transformation and surpress the recombination of the photogenerated electron-hole pairs. The photocatalytic activities of samples were evaluated by the photodegradation of methyl orange (MO) aqueous solution under 300 W high pressure mercury lamp irradiation. Photodegradation results reveal that doping can greatly improve the photocatalytic activity of TiO₂ and the optimal dosage exists.2. ZnWO₄ hollow microspheres were prepared via a novel bio-template route by using yeast cells as templates. The as-prepared new photocatalyst was characterized by XRD, SEM , TEM, PL and FT-IR. The mechanism of the formation of ZnWO₄ hollow spheres is proposed via a two-step encapsulation and one-step caclition process, the encapsulated spheres were calcined at 750°C to remove the yeast templates, and then resulting in ZnWO₄ hollow spheres. The photocatalytic property of ZnWO₄ hollow spheres was examined by the degradation of Rhodamine B. The result showed that its high photocatalytic activity.3. ZnWO₄ nanorod samples was successfully synthesized by hydrothermal process with Zn(CH3COO)2·2H₂O and Na₂WO₄·2H₂O starting materials in the presence of PVP. ZnWO₄ soya bean-like and rod-like nanocrystals were synthesized by a template-free hydrothermal method with ZnCl2,citric acid,H₂WO₄ or Na₂WO₄·2H₂O as starting materials starting materials. ZnWO₄ powders with different morphologies were characterized by XRD, TEM and PL. The higher photocatalytic activity was found to be in samples consisting of nanorod and soya bean-like crystallites among all the samples.