Environmental Purification with Use of Titanium Dioxide-Loaded Adsorbent Photocatalysts

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Photocatalytic degradation of numerous organic pollutants has been extensively studied using titanium dioxide as a photocatalyst to remediate the contaminated water and air. The photodegradation rates to be expected in practical applications are usually very low, because in most cases the concentration of target substances is low. If the adsorbent is used as the support for titanium dioxide, the pollutants must be concentrated around the photocatalyst. We have investigated the effect of the use of the adsorbents for titanium dioxide loading on the photodecomposition reaction of organic substrate and obtained the results described below.(1) The titanium dioxide-loaded adsorbent photocatalysts film had the different adsorbability of the gaseous propionaldehyde among the kind of adsorbent used. While the photodecomposition rate of propionaldehyde was enhanced by being adsorbed on the photocatalyst, the degree was greatly different among the kind of adsorbents used, and the conclusion was derived that both adsorbability and diffusibility of adsorbed substrates on photocatalysts playd crucial roles in determination of the photodecomposition rate. (2) The use of activated carbon as a support for titanium dioxide was found to enhance the rate of photodecomposition of propyzamide and to reduce the concentration of solution-phase intermediates. The use of activated carbon support has practical significance in the sense that adsorbed substrate is decomposed to carbon dioxide without releasing the intermediate to solution. (3) With studies on photodecomposition of 4-chlorotoluene dissolved in water on titanium dioxide-loaded activated carbon of various sizes (30-500 micrometer), the photodecomposition rate increased with decrease of the size of activated carbon, indicating that the diffusion of adsorbed substrate inside the activated carbon to the loaded titanium dioxide control the photodecomposition rate.