Effect of suspended TiO2 physicochemical characteristics on benzene derivatives photocatalytic degradation

Seven different TiO(2) samples suitable for water detoxification were systematically characterized according to their physicochemical properties. Except for one mixed catalyst anatase-rutile from Degussa P25, all photocatalysts had a pure anatase crystalline phase. The particle size of the TiO(2) samples varied from about 5 to 700 nm and was inversely correlated with the BET specific surface area (ABET). Surface properties of colloidal suspensions measured by electroacoustic methods were evaluated at different pH values. The aggregate size appeared to be dependent on the pH value of the solution. The isoelectric point (IEP) of the TiO(2) samples ranged from very acidic (IEP < 3) to neutral values. Four benzene derivatives were chosen as model pollutants to assess the TiO(2) samples efficiency on water detoxification. The organic degradation kinetics were influenced in a different way by the TiO(2) characteristics. The surface charge of TiO(2) samples was found to affect significantly the organic degradation kinetics. Indeed, the compounds degradation was greatly enhanced by acidic TiO(2). Moreover, the compounds primary degradation and the total mineralization were affected differently by the ABET. The primary degradation kinetics of strongly adsorbed pollutants, i.e. those containing a carboxyl group, benzoic acid (BA) and 4-hydroxybenzoic acid (HBA), is enhanced by large ABET, whereas phenol and 4-nitrophenol (NP) degradation was not. On the other hand, a small ABET was not advantageous, and there is an optimum value for an efficient total organic carbon (TOC) removal. In addition, the mixed crystalline structure, Degussa P25, showed a higher photoactivity than pure anatase TiO(2), as generally accepted and reported in previous studies. (C) 2007 Elsevier B.V. All rights reserved.