Involved Member: Prof. Xiaoyan LI

Ammonium (NH₄+) 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 NH₄+ removal and recovery from wastewater. However, the coexisting sodium (Na+) in wastewater, with a similar hydrated radius to NH₄+, competes for the adsorption sites, resulting in low NH₄+ removal efficiency. Here, potassium dititanate (K₂Ti₂O₅ 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 NH₄+ removal over Na+. The mixed KTO-AC electrode exhibits a much higher specific gravimetric capacitance in NH4Cl solution than in NaCl solution. Compared with the pure AC electrode in the FCDI tests on NH₄+ removal from synthetic wastewater, 25 wt % KTO addition in the electrode mixture increases the adsorption selectivity from 2.3 to 31 toward NH₄+ over Na+, improves the NH4+ removal from 28.5% to 64.8% and increases the NH₄+ desorption efficiency from 35.6% to over 80%, achieving selective NH₄+ recovery and effective electrode regeneration. Based on DFT calculations, NH₄+ adsorption on the K₂Ti₂O₅ (0 0 1) surface is more thermodynamically favorable than that of Na+, which contributes to the high NH₄+ adsorption selectivity observed.
 

Reference:

Lin, L., Hu, J.H., Liu, J.H., He, X., Li, B. and Li, X.Y. (2020). Selective ammonium removal from 
synthetic wastewater by flow-electrode capacitive deionization using a novel K₂Ti₂O₅-activated carbon mixture electrode. Environmental Science & Technology, 54(19), 12723-12731.