Constructing zirconium based metal–organic frameworks based electrically-driven self-cleaning membrane for removal of tetracycline: Effect of ligand substitution

Abstract

Herein, UiO-66-X (X = H, NH2, Br, NO2) were employed to construct the electrocatalytic membranes by blending with conductive graphite and Polyvinylidene fluoride (PVDF) for removal of tetracycline under low current density of 0.01 mA/cm2. The physicochemical and electrochemical properties of the fabricated membrane were investigated systematically. Results showed that ligand substitution reduced the molecular weight cutoff (MWCO) and pure water flux of UiO-66-X based membranes in the order of –Br > –NO2 > –NH2 due to the size exclusion effect. In addition, compared with UiO-66, UiO-66 functionalized with electron-donating group (–NH2) endowed the electrocatalytic membrane with superior anti-fouling ability using bovine serum albumin (BSA) as model foulant, and inferior tetracycline removal and self-cleaning property, while the opposite phenomenon occurred for the functionalization of electronic-accepting groups (–Br and –NO2) owing to the promoted electrocatalytic activity and inhibited oxygen evolution side reaction. Notably, UiO-66-NO2/Graphite/PVDF membrane removed 99.5 % of tetracycline and flux of fouled membrane was almost fully recovered by electric field for six cycles under low current density of 0.01 mA/cm2. •OH and •O2– radicals played dominant roles in tetracycline removal by electrocatalytic membranes and three degradation pathways of tetracycline were proposed according to the liquid chromatography-mass spectrometry. Electrically-driven self-cleaning mechanism was related to the reduced fouling potential of BSA after oxidation degradation. This work gets new insights into the effect of ligand substitution on the performance of Zr-MOFs based electrocatalytic membrane for antibiotics removal.