Silica-Based Composite Sorbents for Heavy Metal Ions Removal from Aqueous Solutions

Weak polyelectrolyte chains are versatile polymeric materials due to the large number of functional groups that can be used in different environmental applications. Herein, one weak polycation (polyethyleneimine, PEI) and two polyanions (poly(acrylic acid), PAA, and poly(sodium methacrylate), PMAA) were directly deposited through precipitation of an inter-polyelectrolyte coacervate onto the silica surface (IS), followed by glutaraldehyde (GA) crosslinking and extraction of polyanions chains. Four core-shell composites based on silica were synthesized and tested for adsorption of lead (Pb²⁺) and nickel (Ni²⁺) as model pollutants in batch sorption experiments on the laboratory scale. The sorbed/desorbed amounts depended on the crosslinking degree of the composite shell, as well as on the type of anionic polyelectrolyte. After multiple loading/release cycles of the heavy metal ions, the maximum sorption capacities were situated between 5-10 mg Pb²⁺/g composite and 1-6 mg Ni²⁺/g composite. The strong crosslinked composites (r = 1.0) exhibited higher amounts of heavy metal ions (Me²⁺) sorbed than the less crosslinked ones, with less PEI on the surface but with more flexible chains being more efficient than more PEI with less flexible chains. Core-shell composites based on silica and weak polyelectrolytes could act as sorbent materials, which may be used in water or wastewater treatment.