Combination effect of activated carbon with TiO2 for the photodegradation of binary pollutants at typical indoor air level

Previously we identified that residence time and water vapor are the vital parameters that affect the photodegradation of indoor air pollutants at parts-per-billion (ppb) levels using TiO2. The presence of water vapor competes with pollutants for adsorption sites on TiO2 thus reducing the pollutant removal rate. By immobilizing TiO2 on activated carbon (AC), a satisfactory pollutant removal rate is achieved even at high water vapor levels. This study further examines the effect of TiO2 immobilized on AC by co-injecting binary pollutants simultaneously since the presence of other pollutants might have an inhibition effect on the photocatalytic activity under different humidity levels. 200 parts-per-billion NO, 20 ppb BTEX and 200 ppb SO2 were co-injected under different residence time and humidity levels to investigate their mutual effect on TiO2 and TiO2 immobilized on AC. Results showed that no significant pollutant removal difference was observed between TiO2 and TiO2 immobilized on AC at longer residence time. The presence of BTEX only reduced NO conversion by 5%. At evaluated humidity levels, however, a significant different pollutant removal rate was observed. The presence of BTEX reduced NO conversion by more than 10%. The use of TiO2 on AC, reduced both the competition effect of the pollutant and water vapor on TiO2. The inhibition effect of BTEX and SO2 on NO conversion was significantly reduced when TiO2 immobilized on AC compared to TiO2 only. The by-product, NO2, from the photodegradation of NO, was also reduced despite the presence Of SO2 and BTEX under high humidity level. (C) 2004 Elsevier B.V. All rights reserved.