Mechanism and stability of an Fe-based 2D MOF during the photoelectro-Fenton treatment of organic micropollutants under UVA and visible light irradiation.

This work reports the novel application of an Fe-based 2D metal-organic framework (MOF), prepared with 2,2'-bipyridine-5,5'-dicarboxylate (bpydc) as organic linker, as highly active catalyst for heterogeneous photoelectro-Fenton (PEF) treatment of the lipid regulator bezafibrate in a model matrix and urban wastewater. Well-dispersed 2D structures were successfully synthesized and their morphological, physicochemical and photocatalytic properties were assessed. UV/Vis PEF using an IrO2/air-diffusion cell with an extremely low catalyst concentration (0.05 g L-1, tenfold lower than reported 3D MOFs) outperformed electro-oxidation with electrogenerated H2O2, electro-Fenton and visible-light PEF. Its excellent performance was explained by: (i) the enhanced mass transport of H2O2 (and organic molecules) at the 2D structure, providing active sites for heterogeneous Fenton's reaction and in-situ Fe(II) regeneration; (ii) the ability of photoinduced electrons to reduce H2O2 to •OH, and Fe(III) to Fe(II); and (iii) the enhanced charge transfer and excitation of Fe-O clusters, which increased the number of electron-hole pairs. LC-QToF-MS and GC-MS allowed the identification of 16 aromatic products of bezafibrate. The complete removal of four micropollutants mixed in urban wastewater at pH 7.4 revealed the great potential of (Fe-bpydc)-catalyzed PEF process.