Composite photocatalysts based on TiO2 – carbon for air pollutant removal: Aspects of adsorption

Abstract Immobilized composite powders of titania with various carbon content were tested with respect to their efficiency of degradation of impurities in air (toluene, acetaldehyde, NO) under UVA illumination in a single-pass flow-through reactor and ISO conditions. Addition of active carbon (AC) to titania resulted in increased conversion efficiencies of some pollutants. In the case of toluene as a test pollutant, an AC/TiO 2 ratio of 0.23 in the photocatalyst led to 47% conversion efficiency (against 36% without carbon). The presence of water in the gaseous reaction mixture was found to be essential for the degradation reactions to occur with an optimum at 50% RH. In gas phase degradation experiments with NO, a carbon to titania ratio of 0.7 led to the best results. For long time irradiation, accumulation of one of the reaction products, HNO 3 , in the catalyst layer was noticed resulting in a lower production of NO 2 . Photocatalytic removal of acetaldehyde was not improved by carbon loading; pure titania showed already a conversion efficiency of 75%. In general, although carbon loading helped in adsorption and preconcentration of pollutants, light absorption by carbon counteracted this effect.