Do Fe2O3/TiO2 heterojunctions improve the wastewater disinfection process?

Abstract

This work examines the photocatalytic capacity of Fe₂O₃-TiO₂ catalysts for inactivating Enterococcus faecalis in water and compares it to a peroxide-assisted process. The influence of H₂O₂, PMS, pH, and temperature is assessed. Material stability and free radical species involved in disinfection are also evaluated. The main findings indicate that Fe₂O₃-TiO₂ photocatalysts do not improve disinfection results compared to mesoporous TiO₂, achieving total disinfection after 90 min. Using PMS and H₂O₂ as oxidants in Catalytic Wet Peroxide Oxidation, system 0.15 mM PMS/0.5 g/L mTiO₂ under solar radiation reduced the required time to 10 min for total bacterial inactivation (extended to 30 min with diclofenac present due to competition for radicals), whereas H₂O₂ took approximately 70 min. The Fe₂O₃-TiO₂ heterojunction catalysts (Cat2 - Cat5) showed no improvement, likely due to bacteria-photocatalyst interactions preventing oxidants from reacting with Fe on the catalyst surface. EPR analyses revealed hydroxyl radicals as the predominant oxidizing species (over 90% abundance). Additionally, higher pH values (>6) decreased inactivation kinetics, while increasing the temperature to 40 °C improved it by up to 120%. The photocatalyst showed low stability from the fourth use, with a 40% decrease in bacterial inactivation kinetics.

Keywords: CWPO; Disinfection; Enterococcus faecalis; Heterojunction; Photocatalysis; Solar radiation.