Defect engineering of NH2-MIL-88B(Fe) using different monodentate ligands for enhancement of photo-Fenton catalytic performance of acetamiprid degradation

Engineering of monodentate ligands induced defects was proposed to modify NH2-MIL-88B(Fe) in order to promote its synergetic photo-Fenton catalytic degradation performance for acetamiprid (ACTM) as model neonicotinoid insecticides. Three monodentate ligands with different coordination groups (benzoic acid, pyrrole and pyrrole-2-carboxylic acid) were applied to in-situ induce ligand vacancies on NH2-MIL-88B(Fe). Effect of defect coordination mode on its photo-Fenton catalytic performance was investigated through the ACTM degradation reaction. Ligand defects on NH2-MIL-88B(Fe) would generate three merits: (1) it can modulate surface properties to enhance adsorption affinity towards ACTM; (2) it can introduce large amount of monodentate ligands and ligand vacancies in MOFs to promote light absorption and electron-hole separation capacity for photo-catalysis; (3) it can increase the amount of Fe Lewis acid sites to improve redox capacity of Fe2+/Fe3+ for Fenton-catalysis. In this work, Pyrrole-2-carboxylic acid (Pac) was proved to introduce more monodentate ligands in MOFs and generate more ligand vacancies as well. As a result, ACTM can be easily captured by defective NH2-MIL-88B(Fe) and degraded by in-situ triggered oxidative reaction through the synergistic photo-Fenton catalysis. Performance measurements showed that Pac-MIL88(Fe) achieved 7.3 times higher adsorption rate and 5.5 times higher catalytic rate for ACTM than that of pristine MIL88(Fe). Moreover, total organic carbon (TOC) conversion reached 97.0% within only 90 min using Pac-MIL88(Fe) as photo-Fenton catalyst, showing 1.7 times higher than pristine MIL88(Fe). Thus, the in-situ fabrication of ligand defect-containing MIL88(Fe) can be foreseen of potential for designing new MOFs for wider practical applications.