Photodegradation of volatile organic compounds (VOCs) and NO for indoor air purification using TiO2: promotion versus inhibition effect of NO

The feasibility of applying photocatalytic technology for removal of nitrogen oxide (NO) and volatile organic compounds (VOCs) at typical indoor air level using TiO2 (Degussa P-25) were investigated. Benzene, toluene, ethylbenzene and o-xylene (BTEX) were chosen because they are the most abundant in the indoor environments. The concentrations conducted for this study is 200 parts per billion (ppb) NO and less than 100 ppb for BTEX respectively. Sensitive analyses were conducted for NO, BTEX and a mixture of NO and BTEX under different residence time, levels of humidity and initial concentrations. Under the experimental conditions, it was found that the presence of NO promoted the photodegradation of BTEX under low and high humidity levels. However, at moderate humidity levels, the presence of NO reduced the photodegradation of BTEX. The promotion effect decreased with decreasing residence time. The overall photodegradation of NO and BTEX decreased acutely in relation to increasing humidity. In addition, NO2 was found to react with BTEX as well.