Synthesis, Characterization And Photocatalytic Behaviors Of High Performance Nanoscale Photocatalysts

Environmental pollution has become a serious and global problem with the development of industry. Photocatalytic redox reactions used in degrading pollution organics have gained wide interest because of their simplicities,economic advantages and without the second pollution. The light source often used in AOP (AOP= Advanced Oridation Process) is UV light but researchers are interested in the solar or visible light in recent years owing to UV light is expensive and difficult to achieve. To improve the photoefficiency of the photocatalytic materials, many research groups have focused their attention on preparation of the nanometer photocatalysts and improve the activity of photcatalysts. The first nanocomposite catalyst that we prepared is the ZnS/TiO₂, where ZnS in the cubic phase was homogeneously distributed into the anatase TiO2 crystal lattice via microemulsion and temperature-programmed solvothermal treatment (200 oC, 2 oC/min). The resulting ZnS/TiO₂ nanocomposites, in a ZnS doping level at 2.1, 10.7, and 19.9 %, respectively, were cube-shaped with the particle sizes as large as 10 to 15 nm. The structures and physicochemical properties of the composites were characterized by powder X-ray diffraction (XRD), Raman scattering studies, UV diffuse reflectance spectroscopy (UV/DRS), photoluminescence (PL) spectroscopy, and transmission electron microscopy (TEM). Their visible-light photocatalytic activity was tested via photodegradation of an organophosphorus pesticide, parathion-methyl (MPT). It was found that introduction of ZnS into the anatase TiO2 crystal lattice was profitable to the enhancement of PL intensity or photocatalytic activity of the anatase TiO2 due to chemical interaction within the composites and/or the strong adsorption of the MPT molecule on the surface of the ZnS/TiO₂ composites. As-prepared second nanocomposite calalyst was nanosized ternary sulfide CdIn₂S₄, which is a novel and efficient photocatalyst, and it was simply prepared by a temperature- programmed hydrothermal method. Compared with the chemical transport method, a condition of our method for preparation of CdIn₂S₄ is mild. The structures and physicochemical properties of the composites were characterized by XRD, UV/DRS, and TEM. The product had a nanometer size (average particle size 13 nm) and strong absorption in the range of 200 to 580 nm, and the visible-light photoactivity of CdIn2S4 was tested via degradation of an aqueous methyl orange and compared with CdS. It can be seen that CdIn2S4 exhibited much higher visible-light photocatalytic activity. The photocatalytic activity of CdIn2S4 is mainly due to its intense absorption in visible-light and its photo-stability is higher than CdS.