Combination effect of activated carbon with TiO 2 for the photodegradation of binary pollutants at typical indoor air level

Abstract

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 TiO 2. The presence of water vapor competes with pollutants for adsorption sites on TiO 2 thus reducing the pollutant removal rate. By immobilizing TiO 2 on activated carbon (AC), a satisfactory pollutant removal rate is achieved even at high water vapor levels. This study further examines the effect of TiO 2 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 SO 2 were co-injected under different residence time and humidity levels to investigate their mutual effect on TiO 2 and TiO 2 immobilized on AC. Results showed that no significant pollutant removal difference was observed between TiO 2 and TiO 2 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 TiO 2 on AC, reduced both the competition effect of the pollutant and water vapor on TiO 2. The inhibition effect of BTEX and SO 2 on NO conversion was significantly reduced when TiO 2 immobilized on AC compared to TiO 2 only. The by-product, NO 2, from the photodegradation of NO, was also reduced despite the presence of SO 2 and BTEX under high humidity level.