Photocatalytic decolourisation and degradation of ReactiveOrange 4by TiO 2-UV processM.Muruganandham,M.Swaminathan *Department of Chemistry,Annamalai University,Annamalai Nagar 608002,India Received 2June 2004;received in revised form 12August 2004;accepted 3January 2005Available online 24March 2005AbstractThe photocatalytic decolourisation and degradation of an azo dye Reactive Orange 4(RO4)in aqueous solution with TiO 2-P25(Degussa)as photocatalyst in slurry form has been carried out using UV-A light (365nm).There is a significant difference in adsorption of dye on TiO 2surface with the change in the solution pH.The effect of various parameters such as catalyst loading,pH and initial concentration of the dye on decolourisation and degradation have been determined.The dye is decolourised in 80min and completely degraded in 180min under optimum conditions.The degradation was strongly enhanced in the presence of electron acceptors such as H 2O 2,(NH 4)2S 2O 8and KBrO 3.The photodecolourisation and degradation kinetics are discussed in terms of Langmuir e Hinshelwood kinetic model.The degradation intermediates were analysed by GC e MS technique.Ó2005Elsevier Ltd.All rights reserved.Keywords:Photocatalysis;Photocatalytic degradation;Azodyes;Reactive Orange 4;Adsorption;TiO 2C UV-light1.IntroductionDye wastewater pollutants are the major sources of environmental pollution [1].Textile wastewater intro-duced intensive colour and toxicity to aquatic system.Reactive dyes are widely used in the textile industries because of its simple dyeing procedure and stability during washing process [2].But,the main drawback of reactive dyes is low-fixation rate on the fabrics [3].In order to overcome these difficulties electrolyte must be added to the dye bath.The added electrolyte is also discharged along with dye thus additionally polluting the water.Dyes possess complex aromatic structure.Hence,conventional biological treatment methods are ineffective for decolourisation and degradation [4].Some physical and chemical techniques are currentlyavailable for the treatment of dye effluent [5].But these processes have only limited success.In recent years,attention have been focused on heterogeneous photocatalysis for the treatment of recalcitrant chemicals present in the waste water [6].Due to the high photocatalytic activity and stability of Titanium dioxide,it is generally used as a photocatalyst for the removal of organic pollutants [7,8]and dye pollutants [9e 12].For practical application of dye wastewater treatment by TiO 2-UV process,there is a need to determine the optimal conditions of experimental parameters for economic removal of the dye.In the present investiga-tion,we have undertaken a reactive class monoazo dye Reactive Orange 4and examined the various parameters to find out the optimum conditions for removal of colour and aromatic part of the dye.Reactive Orange 4dye (C.I.No.18260,M.F.Z C 23H 13N 6O 10S 3Cl 2Na 3.Molecular weight Z 769.21)is extensively used in dyeing the textile fabrics.The chemical structure and its absorption maxima are given in Table 1.*Corresponding author.Tel./fax:C 914144220572.E-mail address:chemsam@yahoo.com (M.Swaminathan).0143-7208/$-see front matter Ó2005Elsevier Ltd.All rights reserved.doi:10.1016/j.dyepig.2005.01.004Dyes and Pigments 68(2006)133e142www.elsevier.com/locate/dyepig
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