Directional and rapid electron transfer in perylene diimide modified iron-manganese bimetallic metal-organic frameworks for enhanced photo-Fenton process

Abstract

Bimetallic metal-organic frameworks (MOFs) with iron and another transition metal in the inorganic nodes, as newly developed photo-Fenton catalysts, have gained an ample attention because of the synergistic effect and enhanced properties compared to the monometallic counterparts. However, the photo-Fenton application of bimetallic MOFs still faces the obstacle of unsatisfactory photogenerated electrons transfer due to the fast recombination of photogenerated electron-hole pairs. In this work, perylene diimide (PDI) was modified upon bimetallic NH2-MIL-88B(Fe, Mn) (FM88B) via the ammonolysis process to construct PDI/FM88B heterojunction structure. The constructed heterostructure mediated the directional transfer of photogenerated electrons from PDI (electron donor) to FM88 (electron acceptor). The built-in electric field (BIEF) between PDI and FM88B promoted the separation and directional transfer of photogenerated electron-hole pairs. The interfacial amide bond as the high-speed electronic transmission channel reduced the transfer distance and energy barrier of photogenerated electrons from PDI to FM88B, accelerating the photogenerated electrons delivery. As a result, both Fe(III)/Fe(II) and Mn(III)/Mn(II) redox couples were continuously and rapidly cycled, ultimately boosting the performance of FM88B for H2O2 activation. Compared with FM88B, the optimal 6%PDI/FM88B exhibited excellent degradation performance against tetracycline (TC) (degradation efficiency and apparent rate constant, as 89% and 0.067 min−1) and notable synergy between photocatalysis and Fenton-like process (synergistic factor of 77.61%). DFT calculation and HPLC-MS analysis were used to verify the possible degradation pathways of TC. Meanwhile, the corresponding toxicity changes during TC degradation were studied in detail. This work paves the way for improving the heterogeneous photo-Fenton performance of the bimetallic MOFs in environmental remediation.