Electronic modulation of iron-bearing heterogeneous catalysts to accelerate Fe(III)/Fe(II) redox cycle for highly efficient Fenton-like catalysis

Heterogeneous Fenton-like reaction was a promising approach for generating •OH. However, the heterogeneous catalysts generally exhibited low activity because of slow reduction of Fe(III) in Fe(III)/Fe(II) redox cycle. Here, decreasing electron density was expected to quicken Fe(III) reduction and consequently enhance the catalytic activity of heterogeneous catalysts. This hypothesis was validated by the enhanced hydroxyl radicals generation and accelerated Fe(III) reduction on MIL-88B(Fe)-X (2-X-terephthalic acid, X = NH2, CH3, H, Br and NO2) by reducing electron density of Fe(III) with substituent of higher electrophilicity. MIL-88B(Fe)-NO2, with the substituent of highest electrophilicity among these catalysts, has the lowest electron density of Fe(III) and highest redox potential (EFe(III)/Fe(II) = 0.35 V). As a result, it exhibited the best catalytic performance, which was 1.7–20 times higher than that for other MIL-88B(Fe)-X and was comparable to that of homogeneous Fe2+. This study provides scientific basis for rational construction of highly effective heterogeneous Fenton-like catalyst.