Integrated design of a sustainable, magnetically recoverable, atom-economic lanthanum-adsorbent from cellulose nanofibers for advanced phosphate decontamination

The valorization of abundant and renewable cellulose nanofibers (CNF) offers a sustainable route for advanced adsorbent design. In this study, CNF serves as a functional and robust scaffold for the one-pot synthesis of an eco-friendly, magnetically recoverable composite (CNFeLa). Through grafting polyethyleneimine (PEI) onto CNF, well-dispersed nanoscale Fe₃O₄ and La(OH)₃ are homogeneously anchored, generating abundant active sites while enabling magnetic separation. The optimized CNFeLa₃ achieves a high P/La molar ratio of 1.73 and a normalized adsorption capacity of 384.6 mg P (g La) −1 , demonstrating excellent La atom economy that outperforms many reported La‑based adsorbents. CNFeLa₃ shows excellent phosphate adsorption capacity at low to medium concentrations (≤ 40 mg L⁻¹), with a removal efficiency exceeding 99%. It maintains high capacity over a broad pH range (3.0–11.0), showing only a 16.8% decrease at pH 11, and demonstrates strong selectivity against common competing anions (e.g., Cl⁻, NO₃⁻, SO₄²⁻). CNFeLa₃ demonstrates outstanding practical utility in fixed‑bed column tests, achieving a breakthrough of approximately 1166 bed volumes to reduce the phosphate concentration below 0.5 mg P L⁻¹, corresponding to a treatment capacity of approximately 8745 kg of wastewater per kg of adsorbent. Moreover, MTT assays and fluorescence staining confirm that CNFeLa₃ exhibits low cytotoxicity with approximately 96% cell viability after 24 h of co‑culture. By integrating the renewable CNF scaffold with high La efficiency, rapid magnetic recovery, and robust stability, CNFeLa₃ represents a sustainable and practical adsorbent for scalable phosphate remediation, aligning with the principles of green and efficient resource utilization from industrial crops.