Effective and Selective Removal of Phosphate from Wastewater Using Guanidinium-Functionalized Polyelectrolyte-Modified Electrodes in Capacitive Deionization

Abstract

The potential phosphorus shortage along with phosphorus pollution has drawn global attention, calling for effective technologies for phosphorus removal and recovery from wastewater. Capacitive deionization (CDI) is a promising technology for salt removal and nutrient recovery. However, their performances suffer from limited ion storage capacity and low selectivity, e.g., phosphate removal was lower than the other salts. Herein, guanidinium-functionalized polyelectrolyte-coated carbon nanotube (Gu-PAH/CNT) electrodes were prepared through the self-assembly technique. The Gu-PAH/CNT electrodes selectively adsorbed phosphate ions and prevented the repulsion of coions due to the combined effect of the ion-selective polyelectrolyte layer and the NH protons of Gu groups, resulting in strong electrostatic and hydrogen-bond interactions with phosphate ions. The Gu-PAH/CNT anode was coupled with a COOH-CNT cathode for selective capture of phosphate in a CDI device. The phosphate ion adsorption capacity of Gu-PAH/CNT electrodes is up to 23–30 mg PO43– g–1 in a phosphate solution with a wide pH range and mixtures (NaH2PO4/NaCl, NaH2PO4/Na2SO4, and NaH2PO4/NaNO3) at 1.2 V, presenting superior electroadsorption capacity, phosphate selectivity, and stable regeneration property. These encouraging results demonstrate that functionalized polyelectrolyte-modified electrode materials act as powerful platforms for effective and selective removal and recovery of specific contaminants from wastewater.