La-doped activated carbon as high-efficiency phosphorus adsorbent: DFT exploration of the adsorption mechanism

Phosphorus removal and recovery are important because phosphorus is both a water contaminant and present in chemicals used in agriculture and various industries. As an extremely effective approach to achieve this objective, chemisorption has been identified as a suitable technology. Herein, the adsorption materials La-doped powdered activated carbon and granular activated carbon (La-PAC (D), La-GAC (D)) were prepared by a one-pot hydrothermal process. The strategy behind the adsorbents was based on the ability of La to compensate for the electronegativity and poor selectivity of the activated carbon matrix. Furthermore, the mass transfer rate was enhanced through the formation of vacancies in the structure of the doped material resulting in larger pore sizes, more adsorption sites, and contributions to the diffusion of phosphate molecules to the interior. The phosphate adsorption capacities of La-PAC (D) and La-GAC (D) were 202.43 mg g⁻¹ and 181.82 mg g⁻¹, respectively, which were superior to most adsorbents. The excellent properties could be maintained at low phosphorus concentrations in actual wastewater. The employed characterization methods combined with density functional theory calculations revealed that AC, La, and the doping structure improved the adsorption performance, and the main adsorption pathways of phosphate were electrostatic attraction and complexation. La-AC (D) could accelerate the development of adsorption materials for water pollution remediation.