Accelerated photocatalytic degradation of organic pollutant over metal-organic framework MIL-53(Fe) under visible LED light mediated by persulfate

Photocatalysis based on metal-organic frameworks (MOFs) is being actively investigated as a potential technology in visible light harvesting and utilizing processes. Herein we report that MIL-53(Fe), an earth-abundant Fe-containing MOF material, shows photocatalytic activity for the degradation of Acid Orange 7 (AO7) from aqueous solution under visible LED light irradiation, yet the photocatalytic performance of bare MIL-53(Fe) was not satisfactory due to the fast recombination of photoinduced electron-hole pairs. This can be effectively overcome by adding the external electron acceptor (e.g., persulfate, PS) to the catalytic process. The accelerated photocatalytic degradation of AO7 is demonstrated by the result that the degradation efficiency of AO7 in the MIL-53(Fe)/PS/Vis process reached almost 100% within 90 min as compared to only 24% under the identical experimental conditions for the MIL-53(Fe)/Vis process. To investigate the mechanism of the MIL-53(Fe)/PS/Vis process, photoluminescence (PL) spectra, electrochemical measurements and electron paramagnetic resonance (EPR) analysis were performed. It was concluded that the efficient separation of photogenerated electrons and holes by the introduced PS and the subsequent formation of reactive radicals resulting from the activation of PS by photogenerated electrons accounted for the accelerated photocatalytic degradation of AO7 in the MIL-53(Fe)/PS/Vis process. Furthermore, the applicability of MIL-53(Fe) used in the persulfate-mediated photocatalytic process was systematically investigated in terms of the identification of reactive radicals, the reusability and stability of the photocatalyst, as well as the effect of operating parameters. The findings of this work highlighted the great potential of MOFs as photocatalysts and elucidated a new opportunity for persulfate remediation of contaminated water.