156 “ . ”, 54, . II, , 2011 ANNUAL OF THE UNIVERSITY OF MINING AND GEOLOGY “ST. IVAN RILSKI”, Vol. 54, Part I, Mining and Mineral processing, 2011 ECO-FRIENDLY NANOPHOTOCATALYSTS FOR DISCOLORING OF AZO DYES IN INDUSTRIAL WASTEWATERS Alexandre Loukanov 1 *, Todor Rusnakov 1 , Nikolay Petrov 1 , Vladimir Blaskov 2 , Irina Stambolova 2 , Anatoli Angelov 1 , Seiichiro Nakabayashi 3 1 Dept. of Eng. Geoecology, University of Mining and Geology “St. Ivan Rilski”, 1700 Sofia, *E-mail: alex_loukanov@yahoo.com 2 Institute of General and Inorganic Chemistry, Bulgarian Academic of Sciences, 1113 Sofia, BULGARIA 3 Dept. of Chemistry, Faculty of Science, Saitama University, Saitama 338-8570, JAPAN ABSTRACT. The photocatalytic activity of nanostructured semiconductor TiO2 and ZnO thin films to destruct azo dye has been investigated and compared with that of Fe/FeO(OH) magnetic nanoparticles. Laboratory experiments have been carried out to evaluate the performance of applied nanomaterials by test with reactive black 5 (RB5) as a model pollutant. Special attention is focused on the possibilities for application of these materials in green Nanobiotechnology, e.g. their conjunction with microbiological processes for complete mineralization of the organic pollutants. In this report it is studied the correlation between absorbance changing and photocatalytic degradation of RB5 in wastewaters exposed to these environmentally friendly nanostructured oxides. Aliquots of model dye solution were illuminated with UV radiation in the presence of three types nanoparticles TiO2, ZnO and Fe/FeO(OH). Photodegradation rate constants and adsorption efficiency were determined using spectrophotometric methods. 1 *, 1 , 1 , 2 , 2 , 1 , 3 1 . , „ . ”, 1700 , 2 , , 1113 , 3 , , , 338-8570, * E-mail: alex_loukanov@yahoo.com . TiO2 ZnO. “ 5”. FeO(OH). . . , , . 1. Introduction The removal of organic pollutants as azo dies in wastewater of the textile industry is an important measure in environmental protection. Nanobiotechnology is a rapidly growing field with potential technological applications for remediation of such wastewaters. However, an important challenge for its green chemistry consists in developing of appropriate chemical processes for the treatment of pollutants, which might ensure the following step of mineralization by microorganisms. A perspective solution of this requirement could be the heterogeneous photocatalysis with semiconductor ZnO and TiO2 or reduction with zero valent iron nanoparticles (ZVIN). These three nanomaterials are eco-friendly with proven non- toxic and biocompatible properties (Matos et al. 2009). ZnO and TiO2 nanoparticles are the most used photocatalysts that show high efficiency for the oxidative photodegradation of hazardous aromatic macromolecules in polluted water and air (Choi 2006). Photocatalytic reactions occurring on semiconductor surface have many applications, in particular for discoloring of azo dyes in contaminated wastewaters (Karkmaz et al. 2004). Photocatalytic conversation or degradation with illuminated nanostructured oxides have been demonstrated for a huge number of substances, which are largely ascribed to the strong oxidation potential of their valence band holes and surface OH radicals (Kun et al. 2005, Ullah & Dutta 2008). ZnO powder has been demonstrated as an improved photocatalyst as compared to commercialized TiO2 one based on the larger initial rates of activities (Jung et al. 1997) its absorption efficacy of solar radiations (Sakthivel et al. 2003). However, their states of application and synthetic methods of preparation highly affect the reaction activity with pollutants. Laboratory research has established that FeO(OH) ZVIN are very effective in destroying a wide variety of common contaminants such as azo dyes, halogenated organic derivatives and other polychlorinated hydrocarbons and pesticides (Zhang 2003). ZVIN can reduce not only organic contaminants but also the inorganic anions nitrate, which is reduced to ammonia, perchlorate, selenate, arsenate, arsenite, chromate, but they are also efficient in removing dissolved metals from solution,