Developing a visible light-driven heterogeneous chemo-enzymatic cascade for oxidation of aqueous organic compounds

This work focuses on the development of a modular chemo-enzymatic cascade promoted by a mesoporous silica modified with the photoredox catalyst eosin Y (EY). EY is covalently bonded to an SBA-15 matrix using APTES (3-aminopropyltriethoxysilane) as linker. The as-obtained support was characterized via X-ray diffraction (XRD) in order to elucidate its structure. Additionally, the FTIR spectrum for this material exhibited C-Br (669 cm^-1) bond signals corresponding to EY, as well as three peaks corresponding to amide I, II and III signals (1450-1750 cm^-1) indicating EY was successfully linked to the SBA-15 support. Furthermore, the DRS spectrum showed a 532.5 nm absorbance peak, which made the material very sensitive to the light source. Afterwards, the modified EY/SBA-15 material was suspended (1 g/L) in a phosphate buffer solution of phenol (20 ppm) and the enzymes (0.01 g/L each) superoxide dismutase (SOD, 3000 U/mg) and horseradish peroxidase (HRP, 150 U/mg). The suspension was exposed for 30 minutes to a green LED light (525 nm) in order to generate superoxide radicals (O₂^●-) which act as SOD substrate, in situ generating hydrogen peroxide (H₂O₂), substrate for HRP, which oxidizes and removes a model organic pollutant, phenol. During the catalytic evaluation, 1.13% of phenol was removed after irradiation of EY/SBA-15, whereas it increased to 17.70% after SOD and HRP addition. No activity was observed in absence of light. These results show that the chemoenzymatic cascade is functionally active, with HRP proving a more effective oxidizer than O₂^●- and other reactive oxygen species (ROS) obtained with the photoredox process involving EY/SBA-15. Furthermore, these preliminary results open a path for the study of different optimization parameters (enzyme immobilization, kinetic parameters, testing under different light sources). Finally, the nature of the cascade allows replacement of HRP with another enzyme in order to oxidize specific substrates for chemical synthesis.