Influence of phosphorous upon the formation of DMPO-·OH and POBN-O2· ̄ T spin-trapping adducts in carbon-supported P-promoted Fe-based photocatalysts

MATOS, J.; ARCIBAR, J.; POON, P.; PECCHI, G.; RANGEL, J.:
Journal of Photochemistry and Photobiology A: Chemistry, Volume 391, 15 March 2020, 112362.

DOI: 10.1016/j.jphotochem.2020.112362

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.