Tuning the surface charge and pore size of IPNs arrests covalent organic nanostructures through in situ exchangeable bonds for the removal of persistent contaminants

Abstract

Covalent organic frameworks (COFs) have proven to be a wonderful material for water remediation, but their stability has been a long-standing challenge. Herein, to address this problem, a novel ‘giant’ COF containing thiol group (SH-COF) was synthesized and infused into a sequential interpenetrating polymeric matrix through the formation of exchangeable imine bonds in situ. This COF-tagged IPN membrane, besides enhancing its stability, served as a versatile platform for membrane engineering, particularly for efficient interaction with heavy metals such as mercury. Moreover, the in situ formation of dynamic bonds endowed the membrane with recyclability, a focal point of current membrane research, which is not amenable using the conventional routes of introducing COFs on thin-film composite membranes. The structure of the synthesized SH-COF was characterized using DFT simulations to gain insights from a fundamental perspective. The SH-COF inclusion within the membrane structure not only reduced the pore size but also facilitated the incorporation of significant numbers of charge-carrying centers. These engineered membranes exhibited high and sustained water flux for 3 weeks, along with enhanced separation capabilities for dyes (>99%), antibiotics (>97%), and monovalent salts (>98%). Thiol groups facilitated effective mercury removal (up to 97%), while the hydrophilic surface maintained antifouling properties and tolerance to chlorine. Importantly, these membranes are non-cytotoxic and re-processable, making them promising candidates for advancing sustainable water treatment technologies. This research has the potential to address the adverse effects of microplastic pollution resulting from inadequate membrane disposal practices. Furthermore, it presents a timely solution for the development of environmentally friendly and sustainable membranes.