Journal of Colloid and Interface Science 300 (2006) 244–252 www.elsevier.com/locate/jcis Photocatalytic degradation of aniline at the interface of TiO 2 suspensions containing carbonate ions Anil Kumar ∗ , Nupur Mathur Department of Chemistry, Indian Institute of Technology Roorkee, Roorkee 247667, India Received 19 January 2006; accepted 17 March 2006 Available online 27 March 2006 Abstract The degradation of aniline has been investigated using aqueous TiO 2 suspensions containing carbonate ions as photocatalyst. The addition of carbonate to Degussa P-25 increased the number of active adsorption sites at its surface. For the TiO 2 suspensions containing carbonate ions the intensity of adsorption of aniline increased to 6.9 × 10 2 from 5.5 × 10 2 mol −1 dm 3 in case of bare TiO 2 suspensions. This in turn results in the increased interfacial interaction of the photogenerated charge carriers with the adsorbed aniline and thus enhancing the rate of its photodecomposition to 6.5 × 10 −6 mol dm −3 s −1 compared to 2.7 × 10 −6 mol dm −3 s −1 in the absence of Na 2 CO 3 . The maximum efficiency of this photocatalyst has been obtained upon addition of 0.11 mol dm −3 of Na 2 CO 3 at pH 10.8. The photocatalytic action is understood by the simultaneous interaction of intermediates, • OH and CO •− 3 , and their reactivity with aniline. Azobenzene, p-benzoquinone, nitrobenzene, and NH 3 have been identified as the major products of the photooxidation of aniline. Both the reactant and products have been followed kinetically. The photodegradation follows Langmuir–Hinshelwood Model. The mechanism of the occurring reactions has been analyzed and discussed. In the presence of Na 2 CO 3 ,3 × 10 −3 mol dm −3 of aniline could be photodegraded completely in about 6 h while all organic intermediates decomposed completely within about 10 h.  2006 Elsevier Inc. All rights reserved. Keywords: Photocatalysis; Photodegradation; Aniline; TiO 2 suspensions; Suspensions carbonate; Bicarbonate; Adsorption; Interfacial interaction; Azobenzene; Ammonia; Alkalinity 1. Introduction Photocatalysis initiated by semiconductors has drawn con- siderable attention over the last three decades in view of their potential applications in synthetic work and environmental re- lated problems [1–5]. In these studies both pure TiO 2 and TiO 2 based catalysts have been extensively employed as photocata- lysts. Fascination about the use of these materials has mainly aroused because of TiO 2 being cost effective, photostable, and having high redox activity and selectivity [1]. In a large number of investigations TiO 2 P-25 (Degussa) has been employed as a photocatalyst, which contains TiO 2 in both rutile (30%) and anatase (70%) phases. It is the anatase phase, which demon- strates high photoactivity [4]. * Corresponding author. Fax: +91 1332 273560. E-mail address: anilkfcy@iitr.ernet.in (A. Kumar). In the recent past a number of strategies have been em- ployed to improve the separation of charge in these systems by intercepting e − and h + prior to their recombination. These objectives have been achieved by modifying surface properties through: surface complexation [6,7], by addition of electrolytes [8,9] and lanthanide oxide [10], by doping of alkali [11], al- kaline earth [12], and transition [12–16] metal ions. Lately, a number of investigations have focused on the use of anions to influence the catalytic action [8,9,17–21]. Their addition causes both the inhibition [18–20] and enhancement [8,9,17] in cat- alytic action of TiO 2 . In TiO 2 -mediated photooxidation of ani- line, the influence of various anions, viz. ClO − 4 , NO − 3 , SO 2− 4 , PO 3− 4 , Cl − , etc., has been investigated [21] in which ClO − 4 and NO − 3 had insignificant effect whereas SO 2− 4 , PO 3− 4 , Cl − retarded the rate. In the present work we have examined the effect of addition of carbonate ions on the photocatalytic activity of TiO 2 for the degradation of aniline. Aniline is known to be one of the more 0021-9797/$ – see front matter  2006 Elsevier Inc. All rights reserved. doi:10.1016/j.jcis.2006.03.046