Network-Polymer-Modified Superparamagnetic Magnetic Silica Nanoparticles for the Adsorption and Regeneration of Heavy...

Superparamagnetic magnetic nanoparticles (MNPs, Fe₃O₄) were first synthesized based on a chemical co-precipitation method, and the core-shell magnetic silica nanoparticles (MSNPs, Fe₃O₄@SiO₂) were obtained via hydrolysis and the condensation of tetraethyl orthosilicate onto Fe₃O₄ seed using a sol-gel process. Following that, MSNPs were immobilized using a three-step grafting strategy, where 8-hloroacetyl-aminoquinoline (CAAQ) was employed as a metal ion affinity ligand for trapping specific heavy metal ions, and a macromolecular polymer (polyethylenimine (PEI)) was selected as a bridge between the surface hydroxyl group and CAAQ to fabricate a network of organic networks onto the MSNPs' surface. The as-synthesized MSNPs-CAAQ nanocomposites possessed abundant active functional groups and thus contained excellent removal features for heavy metal ions. Specifically, the maximum adsorption capacities at room temperature and without adjusting pH were 324.7, 306.8, and 293.3 mg/g for Fe³⁺, Cu²⁺, and Cr³⁺ ions, respectively, according to Langmuir linear fitting. The adsorption-desorption experiment results indicated that Na₂EDTA proved to be more suitable as a desorbing agent for Cr³⁺ desorption on the MSNPs-CAAQ surface than HCl and HNO₃. MSNPs-CAAQ exhibited a satisfactory adsorption capacity toward Cr³⁺ ions even after six consecutive adsorption-desorption cycles; the adsorption efficiency for Cr³⁺ ions was still 88.8% with 0.1 mol/L Na₂EDTA as the desorbing agent. Furthermore, the MSNPs-CAAQ nanosorbent displayed a strong magnetic response with a saturated magnetization of 24.0 emu/g, and they could be easily separated from the aqueous medium under the attraction of a magnet, which could facilitate the sustainable removal of Cr³⁺ ions in practical applications.