Clarifying the role of silver deposits on titania for the photocatalytic mineralisation of organic compounds

The effect of silver deposits on titanium dioxide on the photocatalytic mineralisation of various organic compounds was investigated. A series of fourteen organic compounds comprising C, H and O atoms alone, were assessed to gain insights into the influence of photodeposited silver. Photodeposition of the silver provided a bimodal distribution of silver deposit sizes, comprising of deposits less than 5 nm and deposits approximately 100 nm in diameter. Silver deposits were found to promote, mildly deter or have a negligible effect on the mineralisation of the organics considered. Carboxylic acids generally experienced positive effects, deriving from their adsorption on TiO2 and susceptibility to photogenerated hole attack. Increasing chain length and the presence of additional methyl groups decreased the positive effects. Alcohols did not benefit by the presence of silver due to their limited adsorption on TiO2 at room temperature. Saccharides, while limited in their adsorption on TiO2, experienced increases in mineralisation rates up to eight times following silver deposition. Carboxylic acids are generated as intermediates during the oxidation of saccharides whose degradation may be enhanced by the silver deposits rather than the saccharides directly. Aromatics did not encounter any positive effects due to silver deposits. The negligible effects are thought to derive from intermediates generated during the early stages of degradation facilitating charge recombination or limiting the access of other intermediates more susceptible to hole attack to the TiO2 surface. (c) 2006 Elsevier B.V. All rights reserved.