High-performance electrosorption of lanthanum ion by Mn3O4-loaded phosphorus-doped porous carbon electrodes via capacitive deionization

Transition-metal-oxide@heteroatom doped porous carbon composites have attracted considerable research interest because of their large theoretical adsorption capacity, excellent electrical conductivity and well-developed pore structure. Herein, Mn3O4-loaded phosphorus-doped porous carbon composites (Mn3O4@PC-900) were designed and fabricated for the electrosorption of La3+ in aqueous solutions. Due to the synergistic effect between Mn3O4 and PC-900, and the active sites provided by Mn–O–Mn, C/PO, C–P–O and Mn–OH, Mn3O4@PC-900 exhibits high electrosorption performance. The electrosorption value of Mn3O4@PC-900 was 45.34% higher than that of PC-900, reaching 93.02 mg g−1. Moreover, the adsorption selectivity reached 87.93% and 89.27% in La3+/Ca2+ and La3+/Na+ coexistence system, respectively. After 15 adsorption-desorption cycles, its adsorption capacity and retention rate were 50.34 mg g−1 and 54.12%, respectively. The electrosorption process is that La3+ first accesses the pores of Mn3O4@PC-900 to generate an electric double layer (EDL), and then undergoes further Faradaic reaction with Mn3O4 and phosphorus-containing functional groups through intercalation, surface adsorption and complexation. This work is hoped to offer a new idea for exploring transition-metal-oxide @ heteroatom doped porous carbon composites for separation and recovery of rare earth elements (REEs) by capacitive deionization. [Display omitted] •Mn3O4@PC-900 was used in the field of CDI for the separation of REEs.•The La3+ adsorption capacity of Mn3O4@PC-900 was 45.34% higher than that of PC-900.•The synergistic effect between Mn3O4 and PC-900 contributes to the electrosorption.•The electrosorption mechanism is intercalation, surface adsorption and complexation.•Mn–O–Mn, C/PO, C–P–O and Mn–OH are the active sites for Faraday adsorption.