PNIPAM-functionalized LDH-La alginate hydrogel beads as a high-capacity and recyclable adsorbent for phosphate capture.

Phosphate-induced eutrophication has become a severe environmental issue, urging the development of high-performance adsorbents for complex water treatment. A hierarchical porous hydrogel bead LDH-La@PNIPAM/SA was constructed by compositing La3+-intercalated layered double hydroxide (LDH) into thermo-responsive poly(N-isopropylacrylamide)/sodium alginate network. The eggshell-like porous structure and PNIPAM effectively accelerate ion diffusion and overcome mass transfer resistance; La3+ confinement in LDH interlayers drastically reduces metal leaching and enables reversible desorption for recyclable use. The adsorbent delivers a maximum phosphate adsorption capacity of 91.35 mg P/g at pH 3, 15 °C with initial P concentration of 100 mg P/L, and shows strong anti-interference ability with 82.3% capacity retention after nine cycles. It keeps effluent phosphate below 0.5 mg P/L for 26.5 h in fixed-bed operation, and achieves >95% phosphate removal from real lake water spiked to 0.5 mg P/L. Inner-sphere La-O-P complexation is the dominant mechanism, combined with electrostatic attraction, ligand exchange and anion exchange. This work provides a stable, reusable and high-efficiency adsorbent for phosphorus wastewater treatment and eutrophication control.