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

Yu-Yi Shen; Chung-Chun Hsu; Shao-Wei Tsai; Chia-Hung Hou

doi:10.1016/j.jcis.2021.04.129

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

J Colloid Interface Sci. 2021 Oct 15:600:199-208. doi: 10.1016/j.jcis.2021.04.129. Epub 2021 Apr 30.

Authors

Yu-Yi Shen¹, Chung-Chun Hsu¹, Shao-Wei Tsai¹, Chia-Hung Hou²

Affiliations

¹ Graduate Institute of Environmental Engineering, National Taiwan University, No.1, Sec. 4. Roosevelt Rd., Taipei 10617, Taiwan.
² Graduate Institute of Environmental Engineering, National Taiwan University, No.1, Sec. 4. Roosevelt Rd., Taipei 10617, Taiwan; Water Innovation, Low Carbon and Environmental Sustainability Research Center, National Taiwan University, Taipei 10617, Taiwan. Electronic address: chiahunghou@ntu.edu.tw.

PMID: 34015512
DOI: 10.1016/j.jcis.2021.04.129

Abstract

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 membrane 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 electrode exhibited a good capacitive behavior for electrical double-layer charging. The batch-mode experiments indicted that when the solution pH changed from 5 to 8, the predominant P species shifted from monovalent H₂PO₄^- to divalent HPO₄^2- that was preferentially electroadsorbed for competitive electrosorption 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 voltage (-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 carbon electrode shows great potential to improve the selective removal of P through electrosorption.

Keywords: Anion-exchange resin; Capacitive deionization; Phosphate; Selectivity.