Controlled mass transport as a means for obtaining selective photocatalysis

The photoinduced degradation of pollutants in water and air using titanium dioxide attracts an increasing attention. Unfortunately, titanium dioxide has very poor selectivity and cannot differentiate between highly hazardous contaminants that are often non-biodegradable and contaminants of low toxicity that are often very easy to handle biologically. A new approach for enhancing the photocatalytic degradation of specific contaminants in air or water is presented herein. The method is based upon selective physisorption of the contaminants on molecular recognition sites located in the vicinity of titanium dioxide micro-domains, followed by surface-diffusion of the contaminants to the photocatalytic sites. The feasibility of this approach is demonstrated using P-cyclodextrin as the host and 2-methyl- 1,4-naphthoquinone and the dye-stuff Chicago Blue as guests. A degradation rate increase of 200 and 70% relative to samples that did not contain the molecular recognition sites was found for the former contaminant and for the latter contaminant, respectively. This was achieved without any significant damage to the organic molecular recognition sites, thus encouraging attempts to materialize this approach on a practical level. (C) 2003 Published by Elsevier Science B.V.