Highly permeable MOF-808/PVDF mixed matrix membrane assisted by ionic liquid exhibits efficient photocatalytic self-cleaning ability in the treatment of dye wastewater

Abstract

Metal-organic frameworks (MOFs) possess various beneficial potentials, including the ability to enhance the porosity and water flux of membranes, and assist in the catalysis of the photodegradation of organic compounds such as dyes, through the interactions of the metal ions within MOFs. In this study, a MOF-808/polyvinylidene fluoride (PVDF) mixed matrix membrane (MMM) was constructed using the non-solvent induced phase separation (NIPS) method, in which, an ionic liquid, 1-butyl-3-methylimidazolium chloride was introduced as the co-solvent in the casting solution solvent, to increase the dispersibility and blending ratio of MOF-808 particles in the mixture. The optimal membrane with 1.5 wt% MOF-808 exhibited ultra-high water permeability (58.08 L·m⁻²·h⁻¹·bar⁻¹) and excellent rejection for various dyes (>90 %). The ESR spectroscopy test has proved the existence of •O₂^- and •OH in MOF-808/PVDF membrane under light irradiation, and the membrane exhibited outstanding photocatalytic self-cleaning ability, achieving a Congo Red (CR) degradation efficiency of 96.57 % under light exposure. Moreover, even after five photocatalytic self-cleaning cycles, the membrane flux almost recovered to its initial state, and the membrane maintained good CR rejection (>90 %). These observations provide ideas for developing high flux membrane technologies with photocatalytic capabilities, which will be applied for efficient treatment of practical dye wastewater.