Effective removal of Cu²⁺ and Pb²⁺ ions from aqueous solution using functionalized alginate aerogels adsorbent

A novel composite aerogel adsorbent, calcium alginate-tris(hydroxymethyl) aminomethane hydrochloride (CA-Tris), was synthesized through amidation reaction between sodium alginate (SA) and tris(hydroxymethyl) aminomethane hydrochloride (Tris) followed by Ca²⁺ cross-linking, and further applied for removing Cu²⁺ and Pb²⁺ ions from aqueous solutions. Results illustrated that, compared with calcium alginate (CA), the particle compression strength and the total pore surface area of CA-Tris aerogel were increased to 16.8 kg·cm^-2 and 10.51 m²·g^-1, respectively. In addition, CA-Tris demonstrated exceptional adsorption performance for heavy metal ions, with maximum adsorption capacities of 278.03 mg·g^-1 for Cu²⁺ and 354.69 mg·g^-1 for Pb²⁺ through a spontaneous monolayer chemisorption process that fitted Langmuir isotherm model and pseudo-second-order kinetic model. X-ray photoelectron spectrometer (XPS) and density functional theory (DFT) calculations revealed that ion exchange, electrostatic attraction and coordination complexation were the dominant mechanisms. Notably, CA-Tris maintained stable removal efficiencies of 77.14% for Cu²⁺ and 75.65% for Pb²⁺ after 10 successive adsorption-desorption cycles. The exceptional adsorption performance of this functionalized SA aerogel positioned it as a promising candidate for industrial wastewater remediation.