In the present investigation, a comparative study of silver(I) catalysed photochemical oxidation of methylene blue (MB) and safranine-O (SO) by peroxydisulphate has been reported. The effect of different parameters, such as pH, concentration of peroxydisulphate, silver nitrate, and light intensity, on the reaction rate has been observed. The progress of the photochemical oxidation was monitored spectrophotometrically. The optimum conditions for photochemical oxidation were achieved. The dyes were completely oxidized and degraded into CO2 and H2O. A tentative mechanism for silver(I) catalyzed photochemical oxidation of these dyes by peroxydisulphate has also been proposed. 1. Introduction The nature has provided us a clean and green environment, but due to multifarious activities of human beings, it is being polluted with time. Water, which is an essential requirement for the life of man and many organisms, is being polluted as a result of numerous anthropological activities. Chemicals, food and beverage, textiles, pesticides and insecticides, dyeing and printing industries, and so forth are amongst main industries causing water pollution. Polluted water has detrimental effects on animals, plants life, and humans. Principal sources of water pollution are the dye based industries, where waste water is colored. This colored effluent of dyeing industries is toxic in nature. Therefore, removal of these toxic substances seems necessary. A number of attempts have been made for removal of toxic substances from polluted water by different methods like adsorption, thermal dehydration, chemical transformations, and so forth, but out of these, photocatalysis technology seems to be the most promising technique, as it is considered as a green technology. Heterogeneous photocatalytic treatment of simulated dye house effluents using novel TiO2 catalyst has been reported [1, 2]. Jonnalagadda et al. [3] observed the photodegradation of methyl orange in methanolic solution under both UV and visible radiations in the presence of Fe+2/H2O2. Oxidation of various substrates by peroxydisulphate ion is known to occur through several schemes: (i) a two-electron transfer by the direct reaction between the reductant and oxidant [4]; (ii) two successive reaction steps of one electron transfer from the reductant [5]; and (iii) a reaction initiated by the thermal decomposition of peroxydisulphate with no direct reaction between the reducing substrate and sulphate ion radical [6]. Here, the silver ion may react with persulfate ion to generate sulphate anion radical, which further
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