Efficient multifunctional PPy-NTs/PEI@alginate@NiFe₂O₄ magnetic beads for heavy metals removal: Experimental design and optimization interpretations

A highly effective magnetic nanocomposite alginate beads (PPy-NTs/PEI@Alg@NiFe₂O₄) were synthesized using alginate as the encapsulation reagent and polypyrrole/polyethylene imine with nano NiFe₂O₄ as a functional filler to remove toxic Zn²⁺ and Pb²⁺ from polluted water. A response surface methodology (RSM) was used to statistically assess the influences of pH and the adsorbent dose on the adsorption performance. PPy-NTs/PEI@Alg@NiFe₂O₄ magnetic microbeads exhibited the optimal adsorption capacity q_e (18.6 mg/g) at pH 6 and a 2 mg/L dose for Zn²⁺ removal. In comparison, the optimal q_e (32.6 mg/g) was reached at pH 4.5 with a 1.5 mg/L dose for Pb²⁺ remediation. From batch experiments, maximal absorption capacities of 53.3 mg/g and 22 mg/g were achieved for Pb²⁺ and Zn²⁺, respectively, at 313 K. The pseudo-second-order kinetic model fitted the results well, suggesting that the chemisorption process regulates adsorption. Isotherm models indicate the presence of homogeneous adsorption sites from the well-fitting to Langmuir isotherm. An investigation of the effects of temperature and thermodynamic considerations revealed the endothermic nature of Zn²⁺ and Pb²⁺ absorption. The Fourier transform infrared spectra showed that -NH, -NH₂, and -COO^- are the main groups in PPy-NTs/PEI@Alg@NiFe₂O₄ composite beads that were responsible for Zn²⁺ and Pb²⁺ removal from polluted water.