Influence of phosphorous upon the formation of DMPO-[rad]OH and POBN-O2[rad]¯ spin-trapping adducts in carbon-supported P-promoted Fe-based photocatalysts

Abstract

Carbon-supported PO43−/Fe3+-based nanocomposites were prepared by a thermal hydrolysis method. The influence of the molar ratio PO43−/Fe3+ upon the kinetics of adsorption and photocatalytic degradation of methylene blue was evaluated. In terms of the surface reaction rate, up to 8 times higher photoactivity (99 % dye conversion) than the commercial F400 activated carbon (39 % dye conversion) was found for the sample containing a ratio PO43−/Fe3+ ca. 0.5. This composite was selected for a carefully study of spin-trapping of OH and O2‾ adduct formation. O2‾. A preferential formation of O2‾ and a strong inhibiting effect was observed in the formation of these reactive oxygen species attributed to the phosphate-based groups. In addition, a composite was prepared using the best carbon-supported P-Fe-based photocatalysts and a commercial TiO2. An inhibiting effect of the photocatalytic activity of TiO2 was observed in presence of P-containing catalysts in agreement with the decrease in the spin-trapping signals. A mechanism for the trimer aggregation of methylene blue adsorption on carbon-supported P-Fe-based nanocomposite following degradation under UV–vis irradiation is proposed.