Journal of Molecular Catalysis A: Chemical 223 (2004) 161–165 Studies on the heterogeneous photocatalytic oxidation of 2,6-dinitrophenol in aqueous TiO 2 suspension B. Swarnalatha, Y. Anjaneyulu ∗ Center for Environment, Institute of Science and Technology (IST), Jawaharlal Nehru Technological University, Kukatpally Campus, Hyderabad, Andhra Pradesh 500 072, India Received 8 June 2003; received in revised form 22 March 2004; accepted 30 March 2004 Available online 21 September 2004 Abstract Studies on the heterogeneous photocatalytic oxidation of 2,6-dinitrophenol with different catalysts like TiO 2 , TiO 2 -P25, CdS, WO 3 and ZnO indicated aqueous TiO 2 -P25 suspensions exhibit maximum efficiency in photodegradation at the wavelength of 254 nm using an annular-flow type photo reactor with a 8 W low pressure mercury lamp as a UV light source. Operational parameters like variation of catalyst load, initial concentration of 2,6-DNP, irradiation time, pH, oxygen supply and nitrogen supply on the efficiency of degradation was also investigated and optimum conditions were established. All the experiments were carried out in a batch recirculation mode. The possible mechanisms for the photocatalytic degradation of 2,6-DNP are discussed. © 2004 Elsevier B.V. All rights reserved. Keywords: Annular-flow reactor; 2,6-DNP; Photocatalytic oxidation; Titanium dioxide 1. Introduction The elimination of toxic chemicals from waste water is presently of great concern, since their complete biodegrada- tion is usually very slow and requires several days or weeks. These pollutants may originate from industrial applications or from household and personal care areas. The search for effec- tive means of removing these compounds is of interest to reg- ulating authorities worldwide. Recently, it has been demon- strated that semi-conducting materials mediating photocat- alytic oxidation of organic compounds can be an alternative to conventional methods for the removal of organic pollutants in water and air [1–3]. Several studies of photocatalytic degrada- tion of dyes have been reported [4–9]. A variety of semicon- ductor materials (oxides, sulfides and others) acting as pho- tocatalysts have already been used. Titanium (IV) oxide sus- pended in water has proven to be one of the most active pho- tocatalyst. Extensive work has shown that a wide range of or- ∗ Corresponding author. Tel.: +91 40 23058 731; fax: +91 40 23058 731. E-mail address: yerramillia@hotmail.com (Y. Anjaneyulu). ganic pollutants in aqueous solutions containing UV light il- luminated TiO 2 particles are completely oxidized [2,10–13]. Nitro aromatic compounds are highly toxic to humans and animals with LD 50 in the range of 25–50 mg/kg [14]. Nitrogen-containing phenols are also of great concern not only because they cause severe health problems but also acts as poisons for catalysts [15]. San et al. [16], studied the photocatalytic degradation of 4-nitrophenol in aqueous TiO 2 suspensions. However, there is a very limited information on the photocatalytic degradation of nitrogen-containing phenols [17,18]. Nitro phenols are common components of industrial efflu- ents and have been detected in urban and agricultural wastes [19]. 2,6-dinitrophenol is one of the six possible dinitro phe- nol forms used in the synthesis of dyes, picric acid, picramic acid, wood preservatives, diaminophenoldyhydrochloride (a photographic developer), explosives and insecticides. The photocatalytic degradation of 2,6-dinitro phenol in aqueous titanium dioxide slurries was investigated using different catalysts, varying operational parameters like substrate concentration, catalyst load, irradiation period, 1381-1169/$ – see front matter © 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.molcata.2004.03.058