Electrophoretic nuclei assembly of MOFs in polyamide membranes for enhanced nanofiltration

Thin film nanocomposite (TFN) polyamide (PA) membranes has drawn increasing attention due to the improved physicochemical properties of the top layer for versatile separation performance. However, the commonly used fabrication approach, lacking a controllable loading of nanofillers, leads to a random and insufficient distribution of nanofillers into the PA layer and generates interfacial defects that deteriorate the membrane performance. Herein, a rational strategy for incorporating metal-organic frameworks (i.e., ZIF-8) into the PA layer via electrophoretic deposition (EPD) was proposed. Driven by an external direct current field, the ZIF-8 nanoparticles were uniformly assembled onto a porous ultrafiltration (UF) substrate for fabrication of high-performance TFN nanofiltration membranes by vacuum-assisted interfacial polymerization (IP). The resultant TFN nanofiltration membrane yielded an enhanced water permeability of 22.4 ± 1.2 L·m −2 ·h −1 ·bar −1 , due to incorporation of ZIF-8 nanoparticles which created extra nano-channels for fast water permeation. Additionally, such an EPD process effectively tailored the membrane surface properties (e.g., zeta potential) and conferred a considerably high rejection for Na 2 SO 4 (96.9 ± 0.7%) but a low rejection for NaCl (18.9 ± 2.5%), demonstrating an excellent selectivity between SO 4 2− and Cl − ions. This study highlights the impressive efficacy of the EPD process in precisely anchoring nanomaterials to design high-performance TFN nanofiltration membranes for target separations. • Electrophoretic deposition (EPD) is used to assemble ZIF-8 into polyamide membrane. • Uniform and sufficient assembly of ZIF-8 is achieved by precisely controlling the ageing and EPD times. • Uniform ZIF-8 assembly into the polyamide layer creates extra nano-channels for enhanced flux. • ZIF-8 assembly by EPD tailors the surface charge of TFN membranes, yielding an enhanced selectivity between SO 4 2− and Cl − .