An immobilized iron-oxides catalytic platform for photocatalysis and photosynthesis: Visible light induced hydroxylation reactions

In this paper, we investigate the use of an iron-oxides photoactive coating to perform visible-light induced hydroxylation reactions, both for the photocatalytic degradation of azo-dyes pollutants and for the photosynthesis of guaiacol, a pharmaceutical and industrial intermediate for the synthesis of vanillin. A hierarchical micro/nano structured iron-oxides thin film was fabricated by pulsed laser deposition as the heterogeneous catalyst platform. A fluorescence assay based on coumarin/hydroxycoumarin conversion revealed the ability of the film to generate hydroxyl radicals in photo-Fenton-like mode. The process was then employed for the photocatalytic degradation of methyl-orange (MO) and acid orange 7 (AO7), with yields of 80% and 90% in 4 h irradiation respectively; in both cases hydroxylated intermediates were revealed by ESI-MS. When the substrate was switched to anisole, the hydroxylation process resulted in the accumulation of guaiacol, providing a proof-of-concept for heterogeneous photosynthesis. Investigation on H2O2 concentration, solvent and oxygen presence effects provided insights into optimization routes. These results, obtained with visible light and non-hazardous, scalable materials and reaction conditions, pave the way for the industrial application of photosynthetic methods.