B ENVlROFlMENTAL Applied Catalysis B: Environmental 13 (1997) 289-297 ELSEVIER Photodegradation of phenol in water using silica-supported titania catalysts Luis J. AlemanyaY*, Miguel A. Bafiaresb, Encarnacibn Pardoa, Francisco Martin”, Mercedes Gal&-Fereresb, Jo& M. Blascoa ‘Departamento de Ingenierkz Q uimica, Facultad de Ciencias, Universidad de M cilaga, E-29071 M ilaga, Spain bInstituto de Catdlisis y Petroleoquimica, C.S.I.C. Campus, Universitario de Cantoblanco, E-28049 M adrid, Spain Received 9 August 1996; received in revised form 18 December 1996; accepted 27 December 1996 Abstract Titania-coated silica microspheres containing 0.5-3.0 theoretical layers of TiOZ have been prepared by homogeneous precipitation of Tit&. All these x Ti02-SiOz materials were characterized by X-ray diffraction and FT-Raman spectroscopy. TiOz species are distributed on the surface as small anatase crystals and possess a titania-like behavior with a performance equivalent to that of bulk TiOz for the photodegradation of phenol. The fraction of used titania is higher than that on bulk catalysts and the absorption of the irradiation by excess titania is prevented. The crystal size of titania particles is critical for optimum performance of the catalyst, since it determines the appropriate surface exposure of titanium sites. A minimum size appears to be required to efficiently mineralize phenol. 0 1997 Elsevier Science B.V. Keywords: Phenol; Photodegradation; Titania-silica catalyst 1. Introduction Heterogeneous photocatalysis by semiconductor powders has been applied to a wide range of processes [ 11. Phenol and phenolic compounds are common pollutants in industrial waste waters that may originate from coke ovens, petroleum manufacture, engineering workshops and paint stripping operations. The destruction of phenol by photocatalytic oxidation using suspensions of semiconductors has recently been addressed [1,2]. In slurry reactors, the catalyst particles must be separated from the liquid phase which involves a time and energy consuming process. To avoid the filtration/separation and catalyst recovery *Corresponding author. Fax: (+34 5) 2132000. 0926-860X/97/$17.00 fL2 1997 Elsevier Science B.V. All rights reserved PII SO926-3373(97)00006-4 steps, the active phase is fixed by different means [ 11. However, the system thus made do not perform well due to a bad catalyst-organic substrate interaction, and to the inefficient irradiation of the catalysts. For example, the reaction rate has been reported to be mass-transfer-limited on TiOz-coated sand [3]. The use of monolithic catalysts may provide an interesting option to circumvent these limitations. However, the use of 100% Ti02 monolithic structures will seriously limit the yield of the inner tubes by absorption of the irradiation. Interestingly, the use of silica as a support for the titania species has several advantages. Titania will be diluted in a UV-transparent material that must enable a better irradiation of the supported titania. In addition, anatase phase is stabilized by interaction with silica support [4,5] and it may provide additional