Oxygen-vacancy abundant δ-Bi2O3@PCNF anode for selective phosphate removal with exceptional capacity

Excessive phosphate concentration in waterbody will lead to eutrophication and deterioration of water quality. Capacitive deionization (CDI) is an environmental-friendly technique for ion removal, and the phosphate ions can be selectively removed and accumulated by designing the CDI electrode materials with specific phosphate bonding capability. Herein, a δ-Bi 2 O 3 -modified porous carbon nanofiber (δ-Bi 2 O 3 @PCNF) was constructed by solvothermal reaction in the presence of polyhydric alcohols. Due to abundant oxygen vacancies and high flexibility, the δ-Bi 2 O 3 @PCNF was used directly as a self-supporting CDI anode for selective phosphate adsorption. Under the optimized conditions, the adsorption capacity of phosphate arrived at 99.6 mg P/g in 50 mg P/L solution, and the adsorption maximum of 127.5 mg P/g was achieved according to Langmuir adsorption model. In the dual-anion solution containing PO 4 3 – and Cl – , the δ-Bi 2 O 3 @PCNF electrode still maintains the high selectivity, with a P separation factor of 22 (C PO 4 3 – /C Cl – = 1:5, molar ratio) in PO 4 3 – /Cl – mixture. By using the δ-Bi 2 O 3 @PCNF-based CDI device, the actual paddy drainage has realized the ultralow phosphate concentration down to 0.03 mg P/L. The related mechanisms involved in phosphate adsorption on δ-Bi 2 O 3 @PCNF were proposed. This work demonstrates the great potential of CDI technology for low-concentration phosphorus recovery, owing to the high selectivity of the δ-Bi 2 O 3 @PCNF electrode material.