Tuning Lewis acidity of iron-based metal-organic frameworks for enhanced catalytic ozonation

Abstract

Lewis acid sites that originate from ligand missing defects inspire diverse important applications of metal-organic frameworks (MOFs), such as heterogeneous catalysis. However, the facile regulation of Lewis acidity that promises good properties remains a challenge. Herein, we report a simple strategy to tune the Lewis acidity of iron-based MOFs. By substituting Fe centers with Ce atoms in the node (a.k.a., Ce doping), the catalytic ozonation performance of developed iron-based MOFs was highly improved. We found that both the total Lewis acidity and the salicylic acid (SA) degradation rate of Ce-doping MIL-88A(Fe) linearly correlated to the suitable Ce substitution ratio. Notably, the degradation rate and TOC removal of MIL-88A(Fe0.80Ce0.20) was about 3 and 2 times higher than those of parent MIL-88A(Fe), respectively. Reactive oxygen species (ROS), including surface adsorbed hydroxyl radicals (OHads), superoxide radicals (O2−), and singlet oxygen (1O2) were responsible for SA destruction. MIL-88A(Fe0.80Ce0.20) with enlarged Lewis acidity substantially facilitated the generation of OHads and 1O2, leading to a more efficient SA degradation and mineralization. Moreover, Ce doping engineering also ameliorated the catalytic performances of MIL-53(Fe) and MIL-101(Fe), indicating that the tuning strategy we proposed is accessible and universal. This work may provide deep insights into highly efficient MOFs explorations for water purification.