Simultaneous Cr(VI) Reduction and Naphthalene Oxidation in Aqueous Solutions by UV/TiO2
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1045-V03-05
Simultaneous Cr(VI) Reduction and Naphthalene Oxidation in Aqueous Solutions by UV/TiO2 Ricardo Gutierrez, Sergio o Flores, Omar Rios, and Miguel Valenzuela Lab. Catalisis y Materiales, Instituto Politecnico Nacional, IPN-ESIQIE, Edificio 8, tercer piso, Zacatenco, Mexico City, 07738, Mexico ABSTRACT The photocatalytic reduction of Cr (VI) and oxidation of naphthalene using UV light and TiO2 were investigated with variations in the pH and Cr (VI)/naphthalene ratio. The photochemical reduction of Cr (VI) single system was not observed, whereas the photochemical oxidation of naphthalene was significantly high. However, the reduction reaction rates of Cr (VI) and oxidation of naphthalene were improved in the system UV/TiO2. The removal of Cr (VI) decreased dramatically with increasing pH, in contrast, the naphthalene removal was not influenced by the pH. The presence of naphthalene functioned as a hole scavenger enhancing the photocatalytic reduction of Cr (VI) by the photogenerated electrons, while the removal of naphthalene was decreasing at increasing Cr (VI) content. INTRODUCTION Hexavalent chromium is toxic and carcinogen, while Cr (III) is only slightly toxic and can be readily precipitated or sorbed on a variety or organic and inorganic substrates at neutral or alkaline pH [1]. The environmental importance of this process derives from the variety of sources which generate Cr (VI) in effluent streams: chrome plating, electronic, metallurgical, timber and leather tanning industries [2]. Conventional methods of treatment of contaminated Cr (VI) include chemical reduction, ion exchange, adsorption on activated carbon and bacterial reduction [3]. Advanced oxidation/reduction processes, including photocatalysis, represent a good alternative to remove simultaneously heavy metals and organics [4]. The photocatalytic reduction of Cr (VI) to Cr (III) has been widely studied in the presence of organic compounds [5]. Naphthalene degradation by photocatalysis has been also reported with a very low mineralization rate and forming several organic intermediates [6]. In general, the addition of organic compounds could accelerate the reduction of Cr (VI) [7-10]. Nevertheless, there is no report on the photocatalytic reduction of Cr (VI) in the presence of naphthalene. In this work, we studied the adsorption and the simultaneous photocatalytic reactions of naphthalene oxidation and Cr (VI) reduction under UV/TiO2. The effect of pH and Cr (VI)/naphthalene concentration ratio were mainly tested on the simultaneous removal of naphthalene and Cr (VI). EXPERIMENT Potassium chromate (K2CrO4) and naphthalene, both of analytical grade, were supplied by Reasol. Distilled water was used in all the experiments and its purity was tested by fluorescence spectroscopy. A 50 mg/l stock of naphthalene and K2CrO4 aqueous solutions were used to prepare all the samples required. A 1 mg/ml stock aqueous suspension of titanium dioxide (TiO2 anatase, Aldrich 99%+) was also prepared. The adsorption experiments were carried out at room temper
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