Photocatalytic reduction of nitrite and nitrate ions over TiO2 semiconductors

Abstract

Photocatalysis has recently gained attention in the field of pollutant degradation [1-4]. Among the various semiconductors employed, anatase phase of TiO2 appears to be a promising photocatalyst [5, 6]. TiO; has become a benchmark semiconductor, showing the best compromise between catalytic performance and stability at any pH value of aqueous dispersion. It has been reported that for the same photoreaction, the preparation of TiO2 and its thermal treatment significantly affect the activity of the semiconductors. Indeed, preparation parameters influence the photoactivity since the physico-chemical features are determined by the catalyst's origin and preparation. The sol-gel method provides a convenient method for the preparation of several inorganic oxides with tailored physical and chemical properties. We report here the synthesis and photocatalytic performance of TiO2 prepared by a sol-gel method and compare its activity with a commercial sample of T iQ (J. T. Baker, USA). TiO2 gels were prepared by the acid catalysed solgel method. The sol was prepared by mixing Ti(IV) isopropoxide with anhydrous 2-propanol, H20 and HNO3 at ambient temperature with stirring. A series of gels with varying ratio of alcohol, water content and different molar ratio between titanium (IV) isopropoxide and acid was prepared, The gels were dried at 383 K for 12h. Crystallization to anatase was achieved in air by heating at 823 K for 24 h. Titanium hydroxide was precipitated by reacting an aqueous solution of TiC14 with an aqueous ammonia solution (25 wt%). This was done by adding the latter drop-wise to the metal solution at room temperature, with vigorous stirring owing to the exothermicity of the reaction. After standing for 24 h at room temperature, the solid was filtered and repeatedly washed with double distilled water until free of chloride ions. The resulting solid was dried at 393 K for 24h and then fired in air at 823 K for 24 h. X-ray diffractograms were obtained for the powdered samples using a Philips diffractometer (Philips Generator, Holland; Model PW 1130) provided with an online recorder and dot-matrix printer (Tele type, USA). The diffraction patterns were recorded at room temperature using Ni-filtered CuKa radiation (/1, = 0.154 18 nm) for all samples. A