Chitosan Modified Diatomite Cross-Linked with Sodium Alginate and Polyethyleneimine Composite Gel Particles for Efficient Removal of Copper and Lead Ions

The utilization of advanced adsorbents for the removal of heavy metal ion pollution from organic dyes and industrial wastewater has garnered significant research interest. In this study, a novel composite gel consisting of chitosan modified diatomite (DE/CS), sodium alginate (SA), and polyethyleneimine (PEI) (DE/CS-PEI@SA) was synthesized using the ion crosslinking method. The composite gels were analyzed by scanning electron microscopy (SEM), X-ray diffraction (XRD), differential scanning calorimetry/thermal gravimetric analysis (DSC/TGA), and Brunauer–Emmett–Teller systems (BET). Their adsorption properties and mechanisms towards copper Cu(II) and lead Pb(II) ions were investigated using infrared, X-ray photoelectron spectroscopy (XPS), energy dispersive spectroscopy, (EDS) and Zeta potential analyses. The DE/CS-PEI@SA composite gels exhibited numerous uniform folds on its surface, boasting a specific surface area (18.96 m²/g) and a pore size ranging from 1.5 to 80.0 nm, demonstrating robust thermal stability pre- and post- adsorption. Notably, the composite gels demonstrated impressive adsorption capacities for Cu(II) (174.39 mg/g) and Pb(II) (295.04 mg/g), respectively. The incorporation of DE/CS and PEI into the composite gel contributed to a complex pore structure with numerous accessible sites. The adsorption behavior of the composite gel was effectively described by the pseudo-second-order kinetic model and the Langmuir isotherm model. The primary adsorption mechanism was characterized by single-molecule chemisorption, which encompassed coordination adsorption, ion exchange, and electrostatic attraction. Furthermore, the composite gel demonstrated significant efficiency in adsorption, cost-effectiveness, and ease of separation, making it a promising candidate for wastewater treatment applications.