Quaternized cellulose nanofiber aerogel with shape-memory for selective and rapid phosphate removal from water

Adsorbent with highly selective, environmentally benign and easy-to-use virtues is ideal for scavenging phosphate from water. In this study, we have designed a novel shape-memory La(OH)₃-immobilized nanocellulose aerogel, quaternized cellulose nanofiber aerogel uniformly loaded with La(OH)₃ nanorods (La-Q). The combination of high-affinity La(OH)₃ and macroporous aerogel endowed the La-Q aerogel with ultrahigh adsorption rate constant of up to 0.0082 ± 0.0004 g mg^-1 min^-1, one to two orders of magnitude greater than that of the La(OH)₃ powders. The uniformly immobilized La(OH)₃ enabled a greatly enhanced La utilization efficiency, as evidenced by the higher amount of phosphorus adsorbed per gram of La (401.8 ± 5.3 mg P g(La)^-1) with regard to the La(OH)₃ powder (142.9 ± 1.8 mg P g(La)^-1). The La-Q aerogel exhibited a highly pH-dependent adsorption behavior, demonstrating stable adsorption capacity in neutral and weakly acidic phosphate solutions. The presence of typical anionic species including SO₄^2-, Cl^-, HCO₃^-, and NO₃^- did not significantly affect its adsorption capacity for phosphate, indicating interference-resistant adsorption ability due to the strong affinity. The formation of LaPO₄ complexes, as supported by XPS and XRD results, was responsible for the exceptional adsorption affinity. The good shape-recovery ability rendered easy reusability to the La-Q aerogel, which retained almost 80.2% of the original adsorption capacity after three cycles.