Binder-free La(OH)3 supported activated carbon fiber electrode with N-doped C layer for efficient phosphate electrosorption

Abstract

Binder-free La(OH)3 supported activated carbon fiber (ACF) electrode with modification of N-doped C layer (named LNA) was developed for phosphate (P) electrosorption. The optimum electrosorption of P on LNA was achieved at pH = 4 and voltage = 4 V. The electrosorption capacity was 6.5 times that without voltage, and adsorption rate also increased by 9 times. The presence of 0.1 mol/L inorganic anions improved the electrosorption efficiency in the order of Cl->NO3–>SO42->HCO3–>CO32–. The regeneration study revealed that LNA still exhibited a high electrosorption capacity (29.91 mg/g) after 5 cycles. The mechanism of phosphate electrosorption of LNA was analyzed by kinetics, isotherms, FTIR and XPS, etc. The adsorption kinetics followed the pseudo-second-order model, and the adsorption equilibrium data were well described by the Langmuir isotherm. The Langmuir maximum electrosorption capacity of LNA was 70.66 mg/g. The electrosorption of phosphate was controlled by ion exchange, electrostatic attraction and the formation of surface complexes. N-doped C layer affected the local electronic structure of La and strengthened the interaction with lanthanum hydroxide, promoting the electrosorption of phosphate. The results demonstrated that LNA is a promising electrosorption material for efficient phosphate recovery.