Search for: All records

Redox-electrodes are designed to selectively bind platinum group metals by auto-oxidation, and release them electrochemically. The platform can efficiently recover PGMs from catalytic converter leachates, and contribute to energy-efficient technologies for materials recycling. 

Voids—the nothingness—broadly exist within nanomaterials and impact properties ranging from catalysis to mechanical response. However, understanding nanovoids is challenging due to lack of imaging methods with the needed penetration depth and spatial resolution. Here, we integrate electron tomography, morphometry, graph theory and coarse-grained molecular dynamics simulation to study the formation of interconnected nanovoids in polymer films and their impacts on permeance and nanomechanical behaviour. Using polyamide membranes for molecular separation as a representative system, three-dimensional electron tomography at nanometre resolution reveals nanovoid formation from coalescence of oligomers, supported by coarse-grained molecular dynamics simulations. Void analysis provides otherwise inaccessible inputs for accurate fittings of methanol permeance for polyamide membranes. Three-dimensional structural graphs accounting for the tortuous nanovoids within, measure higher apparent moduli with polyamide membranes of higher graph rigidity. Our study elucidates the significance of nanovoids beyond the nothingness, impacting the synthesis‒morphology‒function relationships of complex nanomaterials. 

Selective electrochemical separations can enable the recycling of valuable homogeneous catalysts for key industrial reactions. 

Per- and polyfluorinated alkyl substances (PFAS) are persistent contaminants that have been continuously detected in groundwater and drinking water around the globe. Hexafluoropropylene oxide dimer acid (tradename GenX) has been used to substitute traditional PFAS, such as PFOA, but its intense use has caused widespread occurrence in water streams and often in high levels. Here, we evaluate a redox-copolymer, poly(4-methacryloyloxy-2,2,6,6-tetramethylpiperidin-1-oxyl- co -4-methacryloyloxy-2,2,6,6-tetramethylpiperidine) (PTMA- co -PTMPMA), for the selective electrochemical removal of GenX. The amine functional groups promote affinity towards the anionic PFAS, and the redox-active nitroxide radicals provide electrochemical control for adsorption and desorption. Faster kinetics and higher uptake (>475 mg g −1 adsorbent) were obtained with the redox-copolymer when applying 0.8 V vs. Ag/AgCl potential compared to open circuit. The copolymer electrosorbents were evaluated over a wide pH range and diverse water matrices, with electrostatic-based mechanisms dependent on the state of protonation of the PFAS. Moreover, we translated the redox-electrodes from a batch to flow-by cell configuration, showing successful adsorption and release of GenX under flow and electrochemical control. Finally, prolonged exposure of GenX at reduction potentials generated smaller PFAS fragments at the redox-electrodes. To fully defluorinate GenX, the copolymer-functionalized electrodes were coupled with a boron-doped diamond (BDD) counter electrode for integrating separation and defluorination within the same device. The combined system demonstrated close to 100% defluorination efficiency. Thus, we highlight the potential of electroactive redox platforms for the reactive separation of fluorotelomers, and point to future directions for their practical implementation for water treatment. 

Abstract Advanced redox‐polymer materials offer a powerful platform for integrating electroseparations and electrocatalysis, especially for water purification and environmental remediation applications. The selective capture and remediation of trivalent arsenic (As(III)) is a central challenge for water purification due to its high toxicity and difficulty to remove at ultra‐dilute concentrations. Current methods present low ion selectivity, and require multistep processes to transform arsenic to the less harmful As(V) state. The tandem selective capture and conversion of As(III) to As(V) is achieved using an asymmetric design of two redox‐active polymers, poly(vinyl)ferrocene (PVF) and poly‐TEMPO‐methacrylate (PTMA). During capture, PVF selectively removes As(III) with exceptional uptake (>100 mg As/g adsorbent), and during release, synergistic electrocatalytic oxidation of As(III) to As(V) with >90% efficiency can be achieved by PTMA, a radical‐based redox polymer. The system demonstrates >90% removal efficiencies with real wastewater and concentrations of arsenic as low as 10 ppb. By integrating electron‐transfer through the judicious design of asymmetric redox‐materials, an order‐of‐magnitude energy efficiency increase can be achieved compared to non‐faradaic, carbon‐based materials. The study demonstrates for the first time the effectiveness of asymmetric redox‐active polymers for integrated reactive separations and electrochemically mediated process intensification for environmental remediation.