Efficient recovery of rare metal lanthanum from water by MOF-modified biochar: DFT calculation and dynamic adsorption

Abstract In this research, a novel metal-organic framework-modified biochar composite (MIL-88b@BC) was created for the first time by modifying rice husk biochar using the excellent adsorption properties of metal-organic framework (MOF), as well as reducing the solubility of MOF using biochar as a substrate, aiming to improve the understanding of the adsorption characteristics of rare-earth metal recycling and to predict its adsorption mechanism. Density functional theory (DFT) computations allowed for rationally constructing the adsorption model. According to DFT calculations, the primary processes involved in the adsorption of La 3+ were π–π interaction and ligand exchange, wherein the surface hydroxyl group played a crucial role. MIL-88b@BC interacted better with La 3+ than biochar or MOF did. Accompanying batch tests with the theoretical conjecture's verification demonstrated that the pseudo-second-order model and the Langmuir model, respectively, provided a good fit for the adsorption kinetics and isotherms. The maximum La 3+ adsorption capacity of MOF@BC (288.89 mg g −1 ) was achieved at pH 6.0, which was significantly higher than the adsorbents' previously documented adsorption capacities. Confirming the DFT estimations, the adsorption capacity of BC@MIL-88b for La 3+ was higher than that of MOF and BC. Additionally, MOF@BC can be recycled at least four times. To mitigate the growing scarcity of rare earth elements (REEs) and lessen their negative environmental effects, this work laid the path for effectively treating substantial volumes of wastewater produced while mining REEs. Highlights The novel composite adsorbent was prepared by MOF and biochar in situ growth method. The adsorption mechanism was innovatively investigated based on DFT calculations. Ligand exchange and La–O–Fe formation dominated in lanthanide ion removal. Graphical Abstract