Hydrophobicity Modulation in Chemically Robust Tröger’s Base Porous Organic Polymer (POP) for Sequestration of PFAS

Abstract

The effective sequestration of perfluoroalkyl substances (PFAS), particularly perfluorooctanoic acid (PFOA), from an aqueous environment is of paramount importance for environmental remediation. Commonly referred to as "forever chemicals", PFAS exhibit exceptional thermal and chemical stability, rendering them highly resistant to natural degradation. Despite the extensive exploration of various adsorbents for PFOA removal, the development of an efficient material that ensures high adsorption capacity, rapid kinetics, recyclability, and selective recovery remains a significant challenge. To address this, we rationally designed and synthesized a Tröger’s Base Porous Organic Polymer (TB-POP) as a tailored adsorbent for PFOA removal. The framework was further post-synthetically modified by incorporating bulky long-chain alkyl moieties to enhance its hydrophobic interactions. This study systematically investigates the synergistic role of hydrophobic interactions from the alkyl chains and electrostatic interactions from the cationic nitrogen sites in facilitating efficient PFOA adsorption. Experimental findings demonstrate that the introduction of long-chain alkyl groups significantly enhances the adsorption performance of TB-POP. The C12@TB-POP and C16@TB-POP variants exhibit remarkable PFOA uptake capacities of 1289 mg/g and 1314 mg/g, respectively. Kinetic studies further revealed an exceptionally high adsorption efficiency (>99%) at low PFOA concentrations, achieving equilibrium in under 15 minutes. Moreover, the excellent recyclability of these materials, maintaining consistent adsorption performance over five consecutive cycles, underscores their robustness and practical viability for real-world water treatment applications.