Preparation of extractant-containing emulsion hydrogel microspheres from gelatin-sodium alginate composite materials for Zn2+ adsorption

In the field of aqueous metal ion removal, conventional metal ion extraction methods often face limitations such as low separation efficiency and leaching of extractants, leading to secondary environmental contamination. This study used the Pickering emulsion templating method, with gelatin-sodium alginate complexes as stabilizing particles, to fabricate a Pickering emulsion hydrogel (PEHGs) loaded with the zinc extractant dis(2-ethylhexyl) phosphoric acid (P204). The resulting hydrogel system not only improves emulsion stability but also effectively sequesters Zn²⁺ ions from aqueous solutions. Structural characterization was conducted using Fourier transform infrared spectroscopy (FTIR) and scanning electron microscopy (SEM). The influence of pH, adsorbent dosage, initial zinc concentration, and contact time on adsorption capacity was investigated by the study. Results showed that at pH 4, the PEHGs exhibited a maximum adsorption capacity of 13.47 mg g⁻¹ for Zn²⁺. The adsorption behavior follows pseudo-second-order kinetics and fits the Langmuir-Freundlich isotherm, suggesting a chemisorption-dominated mechanism. This corresponds to monolayer adsorption of a single solute from dilute solution onto heterogeneous surfaces. The adsorbent retains over 80% removal efficiency through five regeneration cycles, demonstrating excellent reusability. This study establishes a theoretical framework for preparing extractant-incorporated Pickering emulsion hydrogel microspheres using gelatin-sodium alginate composites. We developed an environmentally friendly and cost-effective adsorbent for heavy metal ions.