Tuning the surface charge and pore size in IPN arrested ‘covalent organic nanostructures’ through in situ exchangeable bonds for removal of persistent contaminants

Abstract

Covalent organic framework (COF) although has proven to be a wonderful material for water remediation but their stability has been a long-standing challenge. Herein, to address this, a novel ‘giant’ COF containing thiol groups (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, also served as a versatile platform for membrane engineering, particularly for efficient interaction with heavy metals like mercury. Moreover, the in situ formation of dynamic bonds endowed the membrane with recyclability, a focal point of current membrane research that is not amenable using the conventional routes of introducing COF on thin film composite membranes. The structure of the synthesized SH-COF was assessed using DFT simulation 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%). The 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.