Water is extremely crucial in our environment for the regular weather and the co-evolution of life on Earth. Almost all of the water on the planet is saline, making it unfit for drinking and irrigation. Only 0.77% occurs as liquid fresh water and its distribution are very in homogeneous . Drinking water should be free of pathogenic germs and contamination by toxic compounds like pesticides and industrial chemicals. Clean and fresh drinking water is essential to human and other life . Water pollution is the contamination of water bodies, usually as a result of industrial wastes. For example, releasing inadequately treated wastewater into natural water bodies can lead to degradation of aquatic ecosystems. The waste bearing water, or effluent, and discharged into streams, lakes, or oceans, which in turn dispersed in the pollutants. Textile dyes and other industrial dyes are very easily mixed with fresh water from several industries . Besides, these dyes can be considered as major water pollutants owing to their contained highly toxic organic compounds. In the current year it is estimated that some 30,000 million liters of pollutants are entering our river systems every day, 10,000 million liters from industrial units alone . Synthetic azo dyes are among common environmental pollutants which are used in various 73 industries including textiles, papers, plastics, pharmaceuticals and cosmetic .
Advanced oxidation processes in a broad sense, are a set of chemical treatment procedures designed to remove organic and sometimes inorganic materials in water and waste water by oxidation through reactions with hydroxyl radicals (·OH) . In real-world applications of wastewater treatment, however, this term usually refers more specifically to a subset of such chemical processes that employ ozone (O3), hydrogen peroxide (H2O2) and/or UV light. Photocatalysis is the term can be generally used to describe a process in which light is used to activate a substance . Photocatalysis promises a solution to challenges associated with the intermittent nature of sunlight which is considered as renewable and ultimate energy source to power activities on Earth . Homogeneous photocatalysis refers to catalytic reactions in which both the reactants and the catalyst comprises only one phase and the photochemical process takes place in a homogeneous solution. There are 3 types of homogeneous photocatalysis are UV/H2O2, UV/O3 and UV/O3/H2O2 system. In Heterogeneous photocatalysis, UV/Semiconductor has most common are transition metal oxides and semiconductors, which have unique characteristics. Semiconductor photocatalysis has been gained great attention as a green approach for complete removal of organic pollutants using freely obtainable solar energy source without discharge any secondary pollution .
Titanium dioxide (TiO2) has been widely used as a photocatalyst in many environmental and energy applications due to its efficient photoactivity, high stability, low cost, and safety to the environment and humans . When used in water treatment applications, TiOS2 has a poor affinity toward organic pollutants, especially hydrophobic organic pollutants. Cadmium sulfide, a visible-light responsive photocatalyst with a band gap of 2.4 eV, is one of the most prominent semiconductor photocatalysts . In this study, the influences of Ag/CdS-WO2 Nano composite on the photodegradation of organic pollutant in aqueous solution were investigated. Hence, the objectives of this work are, (i) To synthesis Ag doped CdS-WO2 ternary nanocomposite via hydrothermal method. And prepare the photocatalyst with suitable semiconductor material. (ii) To characterized the synthesized material by using X-ray diffraction (XRD) and Fourier transform infrared (FT-IR), UV-vis diffuse reflectance spectra (DRS). (iii) To study the photocatalytic performance of the pure CdS, pure WO2, CdS-WO2 and Ag/CdS-WO2 photocatalyst by their ability in the photocatalytic degradation of Rhodamine-B (RhB) as a target textile pollutant under visible-light irradiation. (iv) To study the optimization of different process parameters and effects like pH, catalyst concentration, concentration of oxidants (persulphate), and irradiation time. (v) Finally, To propose a possible reaction mechanism related to the enhanced photocatalytic degradation of Ag/CdS-WO2 photocatalyst.