Construction and selective removal of Cd ion based on diatom-based Cd (II) ion-imprinted composite adsorbent

Abstract

The present work displays diatom as an ecofriendly material replace to the conventional costly synthetic matrixes for surface imprinting technology. In this study, novel green Cd (II) ion-imprinted composite adsorption material (SH/DE-IIP) was synthesized by surface ion-imprinting technique for selective removal of cadmium ions from aqueous solutions. Various characterization methods have confirmed the structural transformation on the diatom surface. The changes in surface morphology and structure were characterized by SEM. N2 adsorption-desorption analysis revealed the adsorption material possessed microporous structure. XRD and FTIR spectra have shown the functional monomers were successfully introduced into the surface of diatom by observing changes in characteristic functional groups. XPS spectra have shown the bonding relationship of the material with a coordination S-Cd bond, effectively utilizing the surface-active structure characteristic of diatom, and the three-dimensional cross-linked structures were presented after the cross-linking reaction. Due to the unique pore structure provided by diatoms, the mass transfer of the SH/DE-IIP was enhanced after functional modification, and SH/DE-IIP exhibited significantly improved adsorption efficiency for Cd(II) ions. Combined with XPS quantitative analysis, the calculation formula of grafting percentage for the diatoms and the functional monomers was derived, while a grafting model was constructed to evaluate the removal effect. The calculated grafting percentage indicated that the SH/DE-IIP provided a good compounding effect. The adsorption studies revealed the SH/DE-IIP possessed a good adsorption performance for Cd (II), and the adsorption equilibrium was reached in 30 min. The adsorption behaviors followed the pseudo-second-order kinetic model and the adsorption isotherms are described well by Langmuir isotherm adsorption model. The relative selectivity coefficients for Cd(II)/Ni(II), Cd(II)/Zn(II), and Cd(II)/Cu(II) were 1.56, 1.67, and 1.50, respectively. The more results showed that the SH/DE-IIP has the excellent selectivity and the good reusability. The obtained Cd ion-imprinted composite adsorption material exhibited a good directional removal performance for Cd (II) from aqueous solutions. This work not only provides a new material strategy for preparation of ion-imprinted materials, but also provides new insights into the structure of imprinted materials.