The TiO2/SiO2 and ZnO/SiO2 composite films were prepared by sol-gel dip coating method. The surface morphology and crystal structure of thin films were characterized by means of scanning electron microscopy (SEM) with elementary dispersive X-ray analysis (EDX) and X-ray diffractometer (XRD). Optical properties of films have been investigated using ultraviolet and visible spectroscopy (UV-visible spectroscopy). The photocatalytic activity was established by testing the degradation and decolorization of methyl green (MG) from aqueous solution with artificial UV-light. 1. Introduction Nanomaterials may provide solutions to scientific and ecological challenges in the areas of catalysis, medicine, solar energy conversion, and water treatment [1, 2]. This increasing demand must be accompanied by “green” synthesis methods. In the global efforts to decrease generated hazardous waste, “green” chemistry and chemical processes are progressively integrating with contemporary developments in science and industry. Implementation of these sustainable processes should adopt the 12 fundamental principles of green chemistry [3]. These principles are gear to guide in minimizing the use of dangerous products and maximizing the efficiency of chemical processes. Hence, any synthetic route or chemical process should address these principles by using environmentally benign solvents and nontoxic chemicals [4]. From a biological and physiological point of view, the removal of poisonous chemicals from waste water is currently one of the most important subjects in pollution control. MG is a basic triphenylmethane-type dicationic dye, usually used for staining solutions in medicine and biology [5] and as a photochromophore to sensitize gelatinous films [6]. Triphenylmethane dyes are used widely in the textile industry for dyeing of nylon, wool, cotton, and silk as well as for coloring of waxes, varnish, oil, plastics, and fats. The application of illuminated semiconductors has been effectively working for the decomposition of variety of organic contaminants in water [7]. The major organic compounds that constitute the industrial wastewater include dyes, phenols, chlorophenols, aliphatic alcohols, aromatics, polymers, and carboxylic acids. Among these, toluene, salicylic acid, and 4-chlorophenol have been identified as a water pollutant arising from numerous sources including paper milling, textile, and cosmetic industries [8], causing bad odor to the water. Hence, the destruction of organic compounds is of considerable interest. Over the years, a large number of semiconductors have
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