Redox Copolymers for the Electrochemically-Mediated Removal of per- and Polyfluoroalkyl Substances from Water

Abstract

The removal of toxic halogenated pollutants in water is a topic of increasing urgency nowadays. Anthropogenic organic pollutants, especially per- and polyfluoroalkyl substance (PFAS), have seen increased concentrations in groundwater1 and drinking water.2 Due to their chemical persistence, bioaccumulation, and potential adverse health effects,3 these molecules are at the center of attention for environmental management. New selective separation technologies for targeting these contaminants from very diluted streams must be developed since traditional treatment methods lack molecular selectivity, may require extensive chemicals for regeneration, and often involve energy-intensive processes. Therefore, we developed a system that utilizes a redox copolymer capable of selectively adsorbing long-chain4 and short-chain PFAS, and mediating adsorption and release solely by electrochemical control. These redox electrosorbent is composed of poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl) (PTMA) and poly(4-methacryloyloxy2,2,6,6-tetramethylpiperidine) (PTMPMA), shortly denoted as PTMA-co-TMPMA. We were able to adsorb and desorb perfluorooctanoic acid (PFOA) up to 1,000 mg PFOA/g adsorbent in a batch system. We also found electrocatalytic breakdown for the shorter chain PFAS molecule hexafluoropropylene oxide dimer acid (GenX) during electrochemical reduction. Tandem electrosorption and electrochemical oxidation effect using boron-doped diamond (BDD) was also studied, by combining our redox-polymer electrodes with advanced oxidation counter electrodes. Finally, we introduced our redox copolymer electrode into a flow cell system capable of successfully adsorbing and desorbing fluorinated substances. We envision these integrated electrochemical reactive separation technologies to play an important role going forward for emerging contaminant remediation. References: Bruton, T. A.; Sedlak, D. L., Treatment of Aqueous Film-Forming Foam by Heat-Activated Persulfate Under Conditions Representative of In Situ Chemical Oxidation. Environ Sci Technol 2017, 51 (23), 13878-13885.Gebbink, W. A.; van Asseldonk, L.; van Leeuwen, S. P. J., Presence of Emerging Per- and Polyfluoroalkyl Substances (PFASs) in River and Drinking Water near a Fluorochemical Production Plant in the Netherlands. Environ Sci Technol 2017, 51 (19), 11057-11065.Chou, W.-C.; Lin, Z., Probabilistic human health risk assessment of perfluorooctane sulfonate (PFOS) by integrating in vitro, in vivo toxicity, and human epidemiological studies using a Bayesian-based dose-response assessment coupled with physiologically based pharmacokinetic (PBPK) modeling approach. Environment International 2020, 137, 105581.Kim, K.; Baldaguez Medina, P.; Elbert, J.; Kayiwa, E.; Cusick, R. D.; Men, Y.; Su, X., Molecular Tuning of Redox-Copolymers for Selective Electrochemical Remediation. Advanced Functional Materials 2020, 30 (52), 2004635.

Unraveling the Role of Solvation and Ion Valency on Redox-Mediated Electrosorption through In Situ Neutron Reflectometry and Ab Initio Molecular Dynamics

“…PFPMAm was synthesized through free radical polymerization as previously described [gel permeation chromatography (GPC) in THF using polystyrene calibration yielding M n = 25.4 kg mol −1 , M w = 144.5 kg mol −1 , D̵ = 5.6]. 30 PVFc (16 mg, Polysciences, GPC-MALLS: absolute molecular weight M n = 1.5 kg mol −1 , M w = 3.2 kg mol −1 , D̵ = 2.2), 31 multiwalled carbon nanotubes (16 mg, as-produced cathode deposit, >7.5% MWCNT basis, O.D. × L 7−15 nm × 0.5−10 μm, Sigma-Aldrich), and chloroform (4 mL, >99.8%, Fisher Scientific) were sonicated in icy water (1 h) to form a PVFc-CNT ink.…”

Surface-Initiated Living Anionic Polymerization of Functional Methacrylates from the Surface of Organic Particles

“…The monomer synthesis of FMMA was accomplished starting from the reduction of ferrocenyl carbaldehyde 1 to hydroxymethyl ferrocene 2 (Scheme 1). 58 Ferrocenylmethyl methacrylate (FMMA) was prepared by using a novel synthesis way for this monomer (Scheme 1). For this purpose, we used a Steglich esterification protocol.…”

“…The purity of the monomer was also significantly increased compared to the literature, whereby one sublimation was sufficient for anionic polymerization compared to repeated sublimation and purification steps, as published before. 32,58 Polymerization of the three respective monomers was accomplished after the quick addition of the monomers to the particle dispersion, which was accompanied by loss of the red particle coloration. The decolorization was not immediately completed, and a vanishing red color could be observed for several minutes.…”

“…1-Methylnaphthalene was distilled twice under reduced pressure. Hydroxymethylferrocene, 58 poly(methyl methacrylate) (PMMA), 31 and poly(ferrocenylmethyl methacrylate) 32 (PFMMA) were synthesized as described previously.…”

Balance of Hydrophilicity and Hydrophobicity of Stimuli-Responsive Metallopolymer-Decorated Organic Particles

“…7 Recently, it was proven that ferrocene-containing polymers have high selectivity and sorption capacity for perfluorinated alkyl substances, making this class of materials a promising solution for global challenges. 8 However, a major disadvantage within these applications involves the leaching of the polymer from the electronic devices and the resulting limited long-term stability. To overcome this issue, the polymers can be covalently immobilized on surfaces.…”