The effect of activated carbon adsorption on the photocatalytic removal of formaldehyde

Photocatalysis is an emerging and promising technology for indoor air purification. This photocatalytic method is effective in the case of a higher pollutant concentration, but its wide application in indoor air purification is limited due to the low level of indoor air contaminants. In order to improve the removal of pollutants in indoor air, we evaluated the photocatalytic performance over the nanosized TiO₂ particles immobilized on the surface of activated carbon (AC) filter for the removal of formaldehyde (HCHO). It is shown that the photocatalytic reaction rate increased because the AC could adsorb the pollutants from the diluted air stream to generate a high concentration of the pollutants on the catalyst surfaces. The photocatalytic reaction took place from the diffusion control process to the photocatalytic reaction control process with the rise in flow velocity. In the former process, the photocatalytic reaction rate increased, whereas in the later process photocatalytic reaction rate changed little with increasing flow velocity. The flow velocity was lower over the TiO₂/AC catalyst than over the TiO₂/glass catalyst when the photocatalytic reaction was switched from the diffusion control process to the photocatalytic reaction control process. It is also observed that the indoor low-concentration HCHO could be photocatalytically degraded over TiO₂/AC, with the HCHO concentration in the product mixture falling into the standard range that is specified by the indoor air quality standard of China.