Molecular engineering of cellulose-rich Caragana fiber with phytic acid construct high-energy phosphate sites for efficient rare earth capture

Sustainable recovery of rare earth elements (REEs) by adsorption faces an inherent trade-off among capacity, kinetics, and stability. We report a molecular engineering strategy that converts Caragana fiber (CF), a cellulose-rich waste biomass, into a hierarchical adsorbent (PA-CF) using naturally derived phytic acid (PA). PA acts as a green catalyst that restructures the cellulose matrix and a grafting agent that introduces abundant high-energy phosphate binding sites. In this design, phosphate groups distribute throughout a covalently integrated network instead of on external or pore surfaces, mitigating interfacial limitations of conventional heterogeneous adsorbents. Under optimized conditions, PA-CF achieves adsorption capacities of 224.22 mg/g for La(III), 262.47 mg/g for Gd(III), and 327.87 mg/g for Lu(III). Site energy distribution analysis confirms that high-energy sites (~40 kJ/mol) dominate adsorption and provides a thermodynamic basis for understanding phosphate–REE binding. The adsorbent performs reliably in complex matrices (seawater, tap water) and tolerates competing ions (Na + , Mg 2+ , Zn 2+ , Al 3+ , Fe 3+ ). It retains >70% of initial capacity after five cycles. Mechanistic studies indicate adsorption proceeds mainly through chemical complexation and electrostatic interactions. These results show PA restructures cellulose into a covalently integrated network rather than surface-grafted ones, offering a transferable strategy for designing advanced carbohydrate-based materials for resource recovery.