Highly efficient and selective adsorption of phosphorus and mechanism study by La-Zr co-modified hydrogel beads with 3D network structure

A novel La-Zr@SA/NIPAM adsorbent was synthesized through bimetallic modification of sodium alginate (SA) and acrylamide (NIPAM)-based hydrogel for efficient phosphate removal. Compared to conventional adsorbents, La-Zr@SA/NIPAM exhibits abundant active sites and remarkable selectivity for phosphorus, with a maximum adsorption capacity of 105.3 mg/g for phosphate. The material properties were thoroughly characterized using scanning electron microscopy-energy dispersive X-ray analysis (SEM-EDS), N 2 adsorption/desorption isotherms, Fourier transform infrared (FTIR), and X-ray photoelectron spectroscopy (XPS) techniques. N 2 adsorption/desorption isotherms analysis showed that the specific surface area was 125 m 2 /g and consisted mainly of mesopores, and the network structure was clearly observed in the SEM images to provide a good support structure for the adsorbent. Meanwhile, the study investigated the impacts of pH, temperature, concentration, coexisting competitive ions, recycling regeneration, and actual wastewater on phosphate adsorption. The adsorption process is exothermic and spontaneous, favored by higher temperatures. Kinetic and thermodynamic studies support pseudo-secondary kinetics and Langmuir modeling indicating monolayer chemisorption. Cycle regeneration and real wastewater experiments demonstrated that La-Zr@SA/NIPAM maintained 80 % phosphate removal even after six regenerations. The phosphate removal mechanism involves electrostatic attraction, ligand exchange, and complexation. Moreover, the treatment of real wastewater is similar to the experimental results and also has a significant effect on the removal of other ions, which highlights the great potential of this method in mitigating phosphorus pollution.