Silver metallisation of titania particles: effects on photoactivity for the oxidation of organics

The effects of silver metallisation of titania on the photoactivity were investigated for the oxidations of sucrose, salicylic acid and phenol. The activity of silver/titania particles was dependent on the nature of the organic photooxidised. This dependence was linked to the influence of the parent organic and the intermediate organics on the overall rate of reaction. Silver/titania enhanced the rates of sucrose oxidation by four times but possessed similar activities to bare fitania for salicylic acid and phenol oxidation. The enhanced activity of silver/titania for sucrose oxidation was postulated to be due to improved charge separation and to the operation of an alternative reaction mechanism involving both oxidative and reductive pathways. The lack of enhancement in salicylic acid oxidation was postulated to be due to the ability of salicylic acid and the intermediates to function as deep hole traps and mediate efficient charge separation on both bare and modified titania surfaces. Thus, surface metallisation was not required to further enhance charge separation. The absence of rate enhancement in phenol oxidation was explained by a reported oxidation-reduction recombination cycle between the intermediates, hydroquinone and benzoquinone. The recombination of holes and electrons in the cycle was promoted with silver/titania particles. It is postulated that this nullified the beneficial effects of enhanced charge separation. (C) 2003 Elsevier B.V. All rights reserved.