Reducing active layer thickness of polyamide composite membranes using a covalent organic framework interlayer in interfacial polymerization

Polyamide (PA)-based thin-film composite membranes exhibit enormous potential in water purification, owing to their facile fabrication, decent performance and desirable stability. However, the thick PA active layer with high transport resistance from the conventional interfacial polymerization hampers their applications. The controllable fabrication of a thin PA active layer is essential for high separation efficiency but still challenging. Herein, a covalent organic framework TpPa-1 interlayer was firstly deposited on a polyethersulfone (PES) substrate to reduce the thickness of PA active layer in interfacial polymerization. The abundant pores of TpPa-1 increase the local concentration of amine monomers by adsorbing piperazine molecules, while hydrogen bonds between hydrophilic groups of TpPa-1 and piperazine molecules slow down their diffusion rate. Arising from those synergetic effects, the PA active layer is effectively reduced from 200 nm to 120 nm. By optimizing TpPa-1 interlayer and PA active layer, the water flux of resultant membranes can reach 171.35 L.m(-2).h(-1).MPa-1, which increased by 125.4% compared with PA/PES membranes, while the rejection rates of sodium sulfate and dyes solution remained more than 90% and 99%, respectively. Our strategy may stimulate rational design of ultrathin PA-based nanofiltration membranes with high performances. (C) 2019 The Chemical Industry and Engineering Society of China, and Chemical Industry Press Co., Ltd. All rights reserved.