Development of TiO2/activated carbon composite photocatalyst for the removal of methanol and hydrogen sulfide from paper mills

The objective of this study was to investigate the technical efficacy of in-situ treatment of pulp and paper emissions via adsorption and photocatalytic regeneration.; Firstly, activated carbon was coated with a commercially available photocatalyst by a spray desiccation method. The spent TiO2/AC was regenerated by UV light irradiation. The photocatalytic regeneration is ascribed to both desorption from AC and photocatalytic degradation on TiO2.; In order to improve the photocatalytic degradation rate, the synthesis of TiO2/AC composites by dry impregnation method was developed. The composites prepared using various hydrolysis and calcination conditions were evaluated. High hydrolysis temperature resulted in rough particulate coating layers with higher surface area. The TiO2 loading was positively correlated with the precursor concentration although the TiO2 loading in the study range (2--8 wt%) was not critical to the photocatalytic performance. The moisture in carbon was beneficial for the hydrolysis of precursor (titanium tetra-isopropoxide, TTIP) and improved the composite performance. Under proper preparation conditions, the TiO2/AC composite outperformed the composite prepared by spray desiccation at removing methanol.; The BioNuclear AC support itself was a good H2S remover. After coating TiO2 by dry impregnation, H2S removal efficiency of TiO2/AC decreased compared with the virgin AC due to the change of surface pH. Under UV light irradiation, H2S removal efficiency of TiO2/AC composite doubled, and its sulfate conversion efficiency was higher than that of AC. The formation of sulfate is preferred for water regeneration.; TiO2/AC composite photocatalyst was also prepared by a novel microwave-assisted impregnation method and was employed for the removal of methanol from humid air streams. A commercial microwave oven (800 W) was used as the microwave source. Under 2450 MHz microwave irradiation, TTIP was quickly hydrolyzed and anatase TiO2 was formed in a short time (<20 minutes). Due to the volumetric heating and selective heating of microwave, the solvent and by-products were quickly removed which reduced energy consumption and processing time. The formed submicron TiO2 particles were mainly deposited on the external surface of carbon and had photocatalytic activity.