Enhanced photocatalytic activity and stability of alumina supported hematite for azo-dye degradation in aerated aqueous suspension

Abstract

Silica supported hematite (Fe2O3/silica) that is more active but less stable than the supported hematite for organic photodegradation in aqueous solution has been reported. In this work, we report on alumina supported hematite (Fe2O3/alumina) with significantly improved activity and stability. The catalysts were prepared by mixing alumina with a pre-made colloidal iron oxide at various loading (0–100wt %), followed by sintering at different temperatures (200–900°C). Solid characterization with X-ray diffraction and N2 adsorption showed that hematite particles were small in size, and large in surface area, as compared with the unsupported hematite prepared in parallel. The catalyst activity was evaluated with anionic Orange II as a model substrate, and the reaction was carried out in aerated aqueous suspension under light irradiation at wavelengths longer than 320nm. As the Fe2O3 loading on alumina or the catalyst sintering temperature increased, the apparent rate constant of dye degradation increased, and then decreased. The maximum rate of dye degradation was obtained with 25wt % Fe2O3/alumina, sintered at 400°C. Moreover, five consecutive experiments for dye photodegradation showed that Fe2O3/alumina was much more stable than Fe2O3/silica, due to alumina that has a positively charged surface and thus facilitates the dissolved iron species back onto iron oxide. The higher activity of Fe2O3/alumina than Fe2O3/silica and bare hematite is ascribed to the combined effect between the reduced particle size of hematite and the enhanced surface adsorption of dye on the catalyst.