Nanoporous anodic aluminum oxide-confined ZIF-67 for efficiently activating peroxymonosulfate to degrade organic pollutants

Abstract

The limited mass transfer of short-lived radical species is an inherent drawback of heterogeneous oxidation processes. Herein, we fabricated zeolitic imidazolate framework (ZIF)-67 loaded nanoreactors with precise pore sizes based on anodic alumina oxide (AAO) templates to achieve nanoscale spatial confinement for enhanced radicals-mediated oxidation reactions. The prepared ZIF-67@AAO membrane/peroxymonosulfate (PMS) system exhibits perfect catalytic performance with a rhodamine B (RhB) removal of 100 % within 60 s under an AAO pore size of < 20 nm. The reaction rate constant of RhB degradation by the ZIF-67@AAO<20 nm/PMS system was 2.52 and 893 times that by the ZIF-67@AAO200–300 nm/PMS and ZIF-67/PMS system (no confinement), respectively. The ordered mesoporous structure of the ZIF-67@AAO nanoreactors provided many channels for PMS and RhB molecules to enter the confined inner space of the catalyst, leading to a significant improvement in catalytic performance under nanoconfinement. Radical quenching and electron paramagnetic resonance (EPR) results indicated that SO4−, ·OH, 1O2, and O2− were generated in the ZIF-67@AAO/PMS system, and their amounts were affected by spatial confinement and achieved the maximum at a pore size of < 20 nm. Furthermore, the ZIF-67@AAO catalytic membrane exhibited attractive long-term operation stability with perfect activity and neglectable Co leaching. The results of this study provide an important reference for designing novel catalytic membranes for water decontamination.