Journal of Scientific & Industrial Research Vol. 75, October 2016, pp. 632-637 Photocatalytic Degradation of Nitrobenzene and Azo Dye Using Zinc Oxide Nanoparticles Prepared by Electrochemical Method V Anand and V C Srivastava* Department of Chemical Engineering, Indian Institute of Technology Roorkee, Roorkee, 247667, Uttarakhand, India. Received 1 June 2015; revised 02 November 2015; accepted 28 June 2016 Photocatalytic degradation of nitrobenzene (NB) and an azo dye (namely azophloxine) was carried out using zinc oxide (ZnO) nanoparticles which were prepared by electrochemical method using zinc electrodes in aqueous oxalic acid solution. Taguchi methodology was applied for studying the effects of four experimental parameters namely catalyst dosage (g/l), time of reaction (h), pH and H 2 O 2 dose. Degradation efficiency of NB was found to increase with an increase in H 2 O 2 concentration and decrease in catalyst dosage and pH. Maximum NB degradation efficiency of 98% was observed at catalyst dosage=1 g/l, pH=3, H 2 O 2 to C 6 H 5 NO 2 ratio of 7 mol/mol after 5 h of treatment. Similarly, maximum dye degradation efficiency of 58% and color removal efficiency of 78% was observed at catalyst dosage=1.25 g/l, pH=4, H 2 O 2 concentration of 8 mmol/l in 5 h. Overall, prepared ZnO nanoparticles performed better for NB degradation in comparison to azo dye degradation. Keywords: Photocatalytic Degradation, Zinc Oxide, Optimization, Taguchi Methodology. Introduction Nitrobenzene (NB) is yellowish organic compound widely used as a raw material in various industrial processes for making shoe and floor polishes, agricultural chemicals, pesticides, leather dressings, paint solvents, paper pulp production, dyes, rubber and explosives 1 . NB is a carcinogenic and mutagenic environmental pollutant which is eye and skin irritant and affects the central nervous system also 2-5 . Dye containing wastewaters generated in textile, paper, pigment industries, etc. and discharged to the aquatic bodies are highly harmful to the environment 6 . Various investigators have studied treatment of dye containing wastewaters by various methods 7,8 . Priyanka et al. 6 studied NB degradation using copper loaded activated carbon by catalytic oxidation and reported 89% total organic carbon removal. Photocatalytic degradation is one of efficient and non- polluting process for degradation of organic pollutants, dyes and nitrogenous organic compounds. During photocatalytic degradation, strong hydroxyl radicals are formed on the surface of photocatalyst which react with organic compounds and convert it into harmless compounds 9-11 . Optimization of processes can be done by two procedures namely sequential (with optimization of one parameter at a time) and simultaneous optimization. Sequential optimization requires large number of experiments, is time consuming and has slow convergence. However, simultaneous optimization gives better results in lesser time. In Taguchi’s orthogonal array (OA) design, a number of factors can be studied by a combination of experimental conditions with very less number of experiments 12,13 . In our previous study 14 , Taguchi methodology was used for optimizing the production of zinc oxide (ZnO) by electrochemical method. In present work, first ZnO nanoparticles were prepared by electrochemical method and further characterized by various instrumental techniques for determining its morphological and textural properties. ZnO nanoparticles were further used as photocatalysis for separately degrading NB and an azo dye (namely azophloxine). Taguchi methodology was used for studying the individual and interactive effect of four independent experimental parameters and maximising the degradation efficiencies. Materials and Methods Materials and experimental setup In the present study, only analytical reagent (AR) grade chemicals were used. All chemicals such as hydrogen peroxide (H 2 O 2 ), hydrogen chloride (HCl), azophloxine dye (chemical —————— *Author for correspondence E-mail: vimalcsr@yahoo.co.in