Selective Ammonium Removal from Synthetic Wastewater by Flow-Electrode Capacitive Deionization Using a Novel K<sub>2</sub>Ti<sub>2</sub>O<sub>5</sub>-Activated Carbon Mixture Electrode
Lin Lin, Jiahui Hu, Jiahua Liu, Xin He, Bing Li, Xiao-yan Li
Abstract
Ammonium (NH 4 + ) in wastewater is both a major pollutant and a valuable resource. Flow-electrode capacitive deionization (FCDI) is a promising technology for chemical-free and environmentally friendly NH 4 + removal and recovery from wastewater. However, the coexisting sodium (Na + ) in wastewater, with a similar hydrated radius to NH 4 +, competes for the adsorption sites, resulting in low NH 4 + removal efficiency. Here, potassium dititanate (K 2 Ti 2 O 5 or KTO) particles prepared by the electrospray method followed by calcination were mixed with activated carbon (AC) powder to form a novel KTO-AC flow-electrode for selective NH 4 + removal over Na + . The mixed KTO-AC electrode exhibits a much higher specific gravimetric capacitance in NH 4 Cl solution than in NaCl solution. Compared with the pure AC electrode in the FCDI tests on NH 4 + removal from synthetic wastewater, 25 wt % KTO addition in the electrode mixture increases the adsorption selectivity from 2.3 to 31 toward NH 4 + over Na +, improves the NH 4 + removal from 28.5% to 64.8% and increases the NH 4 + desorption efficiency from 35.6% to over 80%, achieving selective NH 4 + recovery and effective electrode regeneration. Based on DFT calculations, NH 4 + adsorption on the K 2 Ti 2 O 5 (0 0 1) surface is more thermodynamically favorable than that of Na +, which contributes to the high NH 4 + adsorption selectivity observed.