Selective adsorption of phosphate by carboxyl-modified activated carbon electrodes for capacitive deionization

Abstract

Capacitive deionization (CDI) has been considered as a promising technology for removing phosphate from water but suffer inferior selectivity and electrosorption performances for phosphate of current carbon electrodes in CDI. Herein, we achieved highly selective phosphate removal from a ternary effluent of Cl−, , and by using nitric acid-treated activated carbon (AC) with various modification times and pure AC as the anode and cathode, a novel phosphate selective asymmetric CDI reactor. The results showed that carboxyl groups greatly grafted on the materials after modification (varying from 0.00084 to 0.0012 mol g−1). The phosphate selectivity of the present research was higher than that of unmodified CDI, and it increased with the increase of carboxyl groups content. The highest phosphate selectivity (2.01) in modified materials is almost six times higher than that of pure AC. Moreover, the modified electrodes exhibited good regenerative ability with a phosphate desorption efficiency of around 72.12% during the adsorption/desorption process and great stability during the cycling experiment. These results demonstrated that the innovative application of nitric acid-modified AC can effectively selectively remove phosphate from mixed anion solution, opening a hopeful window to selective adsorption in water treatment by CDI.

Sustained Phosphorus Removal and Enrichment through Off-Flow Desorption in a Reservoir of Membrane Capacitive Deionization

“…15−18 A recent study of recovering P using CDI reported a PAC of 1.21 mg P/g electrode (activated carbon). 19 Besides the low adsorption capacity of activated carbon, the co-ion expulsion effect further reduced its PAC. 20 To address these limitations, guanidiniumfunctionalized polyelectrolyte-coated carbon nanotube (Gu-PAH/CNT) electrodes were fabricated to selectively extract phosphate ions due to stronger electrostatic and hydrogenbond forces between the ions and electrode interface.…”

“…Traditional CDI consists of two activated carbon electrodes and a feed chamber formed between the electrodes. , During CDI operation, charged species are captured and adsorbed through the electrical double layer (EDL) established on the electrode surface under an applied electrical potential . Many research studies have explored CDI as a device for P removal, and a common understanding reached is that the P adsorption capacity (PAC) of activated carbon electrodes in CDI is limited and requires improvement. − A recent study of recovering P using CDI reported a PAC of 1.21 mg P/g electrode (activated carbon) . Besides the low adsorption capacity of activated carbon, the co-ion expulsion effect further reduced its PAC .…”

A Review on Lanthanum-Based Materials for Phosphate Removal

“…Lanthanum-based adsorbents have been successfully employed in diverse water sources, including freshwater bodies, industrial effluents, and wastewater. Their versatility makes them suitable for a range of applications where phosphate removal is a priority [23]. In the 3-6 pH range, the La-phosphate complex was found to be stable, with no phosphate release or solubility products detectable.…”