Mesoporous maltose/calcium oxalate hybrid material with abundant reaction sites and its efficient Pb(ii) removal from diverse water bodies

Abstract

Pb(II) shows severe toxicity even at trace levels due to non-biodegradability and biomagnification. At present, high capacity and selectivity, as well as stability of adsorbents, are still the main indices for evaluating practical applications. Here, calcium oxalate was modified using maltose (Ma-COM) and used to adsorb Pb(II) from wastewaters. The morphology, crystal structure, stability and other properties of Ma-COM were investigated by SEM, XRD, TGA, FTIR, TEM, zeta potential and N₂ isotherm measurements. The effects of temperature, Pb(II) concentration, contact time, pH value and coexisting ions on Pb(II) adsorption by Ma-COM were systematically studied. The results showed that the adsorption capacity of Pb(II) by Ma-COM was 1941.6 mg g⁻¹ at pH 4.0. The Pb(II) removal efficiency with the concentration of 250 mg L⁻¹ could reach 92% within 60 min. Especially, Ma-COM could perfectly overcome the defects of the traditional CaCO₃, which could not be directly used in acidic heavy metal wastewater due to acid instability, and thus complemented the adsorption of Pb(II) with conventional CaCO₃ under neutral conditions. The adsorption mechanism involved the synergistic effect of ion exchange, complexation and electrostatic interaction. Furthermore, the material showed high selective adsorption of Pb(II), and the divalent cations coexisted had a negligible effect on Pb(II) adsorption. Importantly, Ma-COM exhibited excellent adsorption for Pb(II) in diverse actual water samples, such as dye wastewater, domestic sewage, sewage effluents and river water, and the treated water could be safely discharged. As an environmentally green, economical and efficient adsorbent, Ma-COM showed great potential in the treatment of acid lead-containing wastewater.