Enhanced electrosorption selectivity of phosphate using an anion-exchange resin-coated activated carbon electrode

Regenerable methods for phosphate (P) recycling have received intense attention due to their potential environmental and economic benefits. In this study, to improve the electrosorptive removal of P in mem-brane capacitive deionization, an activated carbon (AC) electrode was coated with a heterogeneous anion-exchange resin layer, and named the AE-AC composite electrode. It was shown that the AE-AC elec-trode exhibited a good capacitive behavior for electrical double-layer charging. The batch-mode experi-ments indicted that when the solution pH changed from 5 to 8, the predominant P species shifted from monovalent H2PO4- to divalent HPO42- that was preferentially electroadsorbed for competitive elec-trosorption with Cl-. Importantly, the AE-AC composite electrode significantly increased the selectivity coefficient of P over Cl- to 0.56 that was 2.24-fold greater than that of the uncoated AC electrode, at 1.2 V in single-pass mode operation. This improvement can be ascribed to the preferential transport of P through the thin coating layer containing quaternary amine functional groups. The permselectivity of the coating also significantly increased the electrosorption capacity of P from 0.031 to 0.101 mmol/g with a high charge efficiency (97%) by the reduction in the co-ion repulsion effect. When the reverse volt-age (-1.2 V) was applied, electroadsorbed P was reversibly desorbed from the AE-AC electrode in repeated operation. This work suggests that coating an anion-exchange resin layer on the surface of a car-bon electrode shows great potential to improve the selective removal of P through electrosorption. (C) 2021 Elsevier Inc. All rights reserved.

Automated summary

This study improved the electrosorptive removal of phosphate in membrane capacitive deionization by coating an activated carbon electrode with a heterogeneous anion-exchange resin layer. The AE-AC composite electrode significantly increased the selectivity coefficient of phosphate over chloride and improved the electrosorption capacity of phosphate.