Spatially Differentiated Solid – Liquid Interfaces in Covalent Organic Frameworks for Selective Adsorption

Abstract

Selective adsorption of small molecules from complex aqueous matrices is often limited by macromolecular fouling and inefficient mass transfer at hydrophobic particle surfaces. Here, we report a covalent organic framework (COF) adsorbent designed to create spatially differentiated solid–liquid interfaces through polyacrylamide (polyAM) grafting onto an alkyne-containing COF. Improved aqueous dispersibility, suppressed nonspecific protein adsorption, and retained pore accessibility are consistent with a hydrophilic exterior and accessible internal adsorption domains. Adsorption kinetic studies showed that COF-polyAM14k increased the apparent pseudo-second-order rate constant for rhodamine B adsorption from 0.027 to 0.626 g mg–1 min–1 and enabled efficient bisphenol A recovery from 10-fold-diluted milk. Subsequent amination of accessible residual alkyne sites via a thiol–yne click reaction with cysteamine hydrochloride shifted the zeta potential of COF-polyAM16k from approximately −32.0 to +8.4 mV and enhanced potassium indoxyl sulfate removal, consistent with a contribution from electrostatic interactions. These results support a spatially differentiated interfacial design strategy combining hydrophilic polymer modification with tunable adsorption functionality in COF adsorbents.