Molecular Tuning of Redox-Copolymers for Selective Electrochemical Remediation

Abstract

Molecular design of redox-materials provides a promising technique for tuning physicochemical properties which are critical for selective separations and environmental remediation. Here, the structural tuning of redox-copolymers, 4-methacryloyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl (TMA) and 4-methacryloyloxy-2,2,6,6-tetramethylpiperidine (TMPMA), denoted as P(TMA(x)-co-TMPMA(1-)(x)), is investigated for the selective separation of anion contaminants ranging from perfluorinated substances to halogenated aromatic compounds. The amine functional groups provide high affinity toward anionic functionalities, while the redox-active nitroxyl radical groups promote electrochemically-controlled capture and release. Controlling the ratio of amines to nitroxyl radicals provides a pathway for tuning the redox-activity, hydrophobicity, and binding affinity of the copolymer, to synergistically enhance adsorption and regeneration. P(TMA(x)-co-TMPMA(1-)(x)) removes a model perfluorinated compound (perfluorooctanoic acid (PFOA)) with a high uptake capacity (>1000 mg g(-1)) and separation factors (500 vs chloride), and demonstrates exceptional removal efficiencies in diverse per- and polyfluoroalkyl substances (PFAS) and halogenated aromatic compounds, in various water matrices. Integration with a boron-doped diamond electrode allows for tandem separation and destruction of pollutants within the same electrochemical cell, enabling the energy integration of the separation step with the catalytic degradation step. The study demonstrates for the first time the tuning of redox-copolymers for selective remediation of organic anions, and integration with an advanced electrochemical oxidation process for energy-efficient water purification.