Simultaneous capacitive removal of nitrate and phosphate pollutants via Zr-BTB@CNTs electrode for remediation of aquatic eutrophication

Abstract

The excessive influx of nitrogen and phosphorus, driven by accelerated urbanization, has become a predominant contributor to aquatic eutrophication and water quality deterioration. Herein, Zr-BTB@CNTs (ZB@C), a layered nanoscale metal-organic framework (MOF) material synthesized through a hydrothermal method coupled with carbon nanotubes, was comprehensively evaluated as capacitive deionization (CDI) anode for simultaneous capacitive removal of nitrate (NO₃⁻) and phosphate (PO₄³⁻) pollutants from water. The optimized ZB@20C exhibited electrosorption capacities of 222.1 mg g⁻¹ for NO₃⁻ and 159.9 mg g⁻¹ for PO₄³⁻ within 120 min, under an applied voltage of 1.2 V. Furthermore, ZB@20C retained high electrosorption capacities for both nitrate and phosphate across a wide pH range (3−11) and maintained over 80 % removal efficiency for both pollutants after 10 consecutive electrosorption-desorption cycles. Through DFT calculations, XPS, and FTIR analyses, the electrosorption mechanisms of ZB@20C were further elucidated: nitrate electrosorption primarily involves coordination interactions with Zr₆ clusters, while phosphate electrosorption mainly stems from lattice oxygen coordination and hydroxyl exchange. Finally, ZB@20C demonstrates strong resistance to ionic interference, effectively reducing nitrate and phosphate concentrations to below 10 mg L⁻¹ and 1.0 mg L⁻¹, respectively, in samples from Chaohu River, Nanfei River, and industrial wastewater, thereby meeting WHO standards.