Use of Zirconium…. By O.P.Panwar et al, Bulletin of the Catalysis Society of India, 7 (2008) 105-110 105 Use of Zirconium Phosphate as Photocatalyst in Photobleaching of Some Dyes O. P. Panwar, Anil Kumar, Mukesh Paliwal, Rameshwar Ameta # and Suresh C. Ameta Photochemistry and Solar Energy Laboratory, Department of Chemistry, M. L. Sukhadia University, Udaipur (Rajasthan)-313001, India # Govt. Meera Girls P. G. College, Udaipur – 313001, India E-mail: ameta_ra@yahoo.co.in E-mail: anilchohadia@yahoo.co.in Abstract - The photocatalytic bleaching of some dyes (eriochrome black-T, methylene blue and malachite green) was carried out in the presence of semiconducting zirconium phosphate and the progress of the reaction was observed spectrophotometrically. The effects of various operating variables like pH, concentration of dyes, amount of semiconductor and light intensity on the rate of bleaching was observed. A tentative mechanism has been proposed for the photocatalytic bleaching of dyes. Keywords: Photocatalytic bleaching, zirconium phosphate, photocatalyst, dyes 1. Introduction: Water is one of the fundamental requirements of life and any undesired addition of chemical substances leads to its contamination and it become unfit for human use particularly for drinking purposes. Generally, various dyes found in industrial effluents, ultimately, enter the aquatic ecosystem and can create various environmental and health hazards. These may have adverse, sometimes irreversible effects on animals and plants as well. The main purpose of wastewater treatment is the removal of foreign substances and colors present at toxic levels to make the water fit for industrial or domestic use. Adsorption, osmosis, flocculation and others have been used traditionally to remove dyes from water bodies, but all such methods suffer from various drawbacks. Photochemistry using semiconductor nanoclusters is involved in a group of waste treatment methods called Advanced Oxidation Processes (AOPs) such as photo-Fenton, photocatalysis and sonolysis. Extensive research in photocatalysis resulted in various applications based on the use of semiconductors. Photocatalytic bleaching was found to be the most promising process for wastewater treatment in which the semiconductor particles act as photocatalysts or short-circuited microelectrodes on excitation. This involves the generation of hydroxyl radicals used as the primary oxidant for degrading organic pollutants. Chen and Chou [1] reported photobleaching of methyl orange in aqueous solution with suspended titanium dioxide as photocatalyst. Photocatalytic degradation of cetylpyridinium chloride over TiO 2 has been reported by Singhal et al.[2] Similar photocatalytic reaction of xylidine ponceau and orange-G dyes by ZnO powder has been reported by Sharma et al . [3,4] Yoneyama et al.[5] studied the photocatalytic reduction of dichromate ions using WO 3 powder in acidic range. Costa et al.[6] proposed the mechanism of gas phase degradation of cyclohexanol and methylcyclohexanol catalysed by zirconium phosphate and phosphite. Shyama and Arakawa [7] have used zirconium dioxide as photocatalyst. Photocatalytic degradation of brilliant green over semiconductor ZnO powder suspended in aqueous solution has been reported by Ameta et al.[8] Ramazole red was degraded in presence of ZnO photocatalyst by Shivakumar et al.[9]. Neppolian et al.[10] reported photodegradation of some textile dyes over ZnO. A composite system of polycrystalline ZnO/ TiO 2 was reported and its photocatalytic activity was studied by Marei et al.[11]. Najuibet et al.[12] observed the triplet sensitized photobleaching of crystal violet. The oxidation of oxalate ions in aqueous dispersion of ZnO under UV- illumination was investigated by Domenech and Costa [13] they used oxalate ions as a scavenger for hole. TiO 2 sol-gel deposited over glass and its application as a photocatalyst for water decontamination has been reported by Gelover et al.[14] Kako et al.[15] have suggested some preventive methods against catalytic poisoning of TiO 2 photocatalyst by H 2 S. The effect of TiO 2 acidic pre-treatment on the photocatalytic phenol degradation was reported by Colon et al.[16] whereas photodegradation of lignin from black liquor using a UV/TiO 2 system was investigated by Ksibi et al.[17]. Enhanced efficiency of unsymmetrical versus symmetrical squaraine dyes sensitized nanocrystalline TiO 2 was reported by Alese et al.[18] Morwetz and Selli [19] investigated the effect of iron species in photocatalytic degradation of azo dye in TiO 2 suspension.