Facile Preparation of Millimeter‐Sized Sodium Alginate‐Silica Composite Spheres for Highly Selective Adsorption of Heavy Metal Ions

Abstract

Millimeter‐sized (∼3.5 mm) sodium alginate‐silica composite spheres with macroporous structure and functional groups of amino‐ (NH2‐SiO2/SA) and sulfhydryl (SH‐SiO2/SA), respectively, were successfully prepared by a simple hydrothermal copolycondensation. The obtained materials were characterized by FT‐IR, SEM, XPS, N2 adsorption‐desorption techniques, and their heavy metal ion adsorption performance was evaluated in detail under different conditions. Characterization results revealed that the functional group plays a key role in the selectivity of metal ions, that is, NH2‐SiO2/SA preferentially adsorbs the relatively hard Pb(II) ions while SH‐SiO2/SA favors the softer Ag(I) ion, which is attributed to the fact that S atoms are softer donor than N atoms. The adsorption kinetics and the adsorption equilibrium fitted well with the pseudo‐second‐order model and Langmuir adsorption isotherms, respectively. The adsorption experiments showed the maximum adsorption capacities of Pb(II) for NH2‐SiO2/SA and Ag(I) for SH‐SiO2/SA are 460 mg/g and 417 mg/g, respectively, giving good stability without a significant decrease in 5 recycles. Therefore, the synthesized materials display promising adsorbents for recycling heavy metal pollutants from wastewater due to their good selectivity, high adsorption capacity, stability and easy recovery due to their large size.