Effect of rutile phase on the photocatalytic properties of nanocrystalline titania during the degradation of p-coumaric acid

Nanocrystalline titania catalysts with high surface area (68-100 m(2)/g) with varying amounts of anatase and rutile phases were tested during the photocatalyzed degradation of p-coumaric acid. This is a pollutant found in agricultural waste waters originating from the wine and olive oil industry. The catalysts were prepared by the same route namely, the hydrolysis of alkoxides followed by densification under hydrothermal conditions (1500-4000 kPa). Hydrolysis of Ti-butoxide gives rise to predominantly anatase containing titania whereas the Ti-ethoxide hydrolysis leads to mixtures of anatase and rutile. Compared to pure anatase or rutile, titania containing both phases shows a significantly higher catalytic activity during the degradation of p-coumaric acid. After preliminary optimization experiments, the degradation of 0.1 mM p-coumaric acid was achieved in 45 min under light irradiation in the presence of H(2)O(2) The most efficient catalyst is TiO(2) containing 30% rutile and 70% anatase and is prepared by the hydrolysis of tetraisopropyl-orthotitanate. Pore size distribution measurements indicate the presence of mesopores of radii in the range 6-25 Angstrom which were responsible for the effective adsorption of the pollutant on the catalyst. Electrophoretic mobility measurements show the isoelectric point for the most efficient catalyst at pH 5.5. (C) 1998 Elsevier Science B.V.