Fabrication of phosphorus doping porous carbon derived from bagasse for highly-efficient removal of La3+ ions via capacitive deionization

Heteroatom doping is an effective method to improve the electrochemical properties of carbon materials. In this work, the bagasse-based phosphorus-doped porous carbon (PC-900) was prepared by phytic acid as activator and phosphorus dopant under hydrothermal conditions, which is evaluated for removal of La3+ in water via capacitive deionization (CDI) technology. The influence of working voltage and initial concentration of La3+ solution on the CDI process were analyzed. The results show that the activation of phytic acid promotes the formation of the well-developed microporous and mesoporous composite structure, and successfully achieved P-doping of porous carbon, which is essential for improving the electrosorption performance of La3+. The adsorption value is as high as 88.89 mg g−1 at the optimal working voltage of 1.8 V, which is 86% higher than that of un-doped carbon. Furthermore, PC-900 has also excellent selective behavior for La3+ in the La3+/Na+ and La3+/Ca2+ co-existence system, and the selection rate can reach 94.08% and 90.98%. The analysis of electrochemistry and capacitance contribution theory shows that PC-900 has pseudocapacitance and ideal electric double layers (EDLs) behavior. P-doping is conductive to enhance EDLs adsorption and introduce Faraday adsorption active sites such as C-P-O, C-P=O and P-O-P. Under the coordination and electrostatic attraction of these active sites, PC-900 exhibits excellent electrosorption capacity. Driven by the electric field, La3+ can not only enter the pore structure of PC-900 to form EDLs, but also form P2-O−(La3+) and La-O-P with surface groups through Faraday reaction. Phosphorus-doped porous carbon shows broad prospects for separation of rare earths in the application of CDI technology.