Construction and selective study of diatom-based Cd(Ⅱ) ion-imprinted adsorbents

Abstract

Diatom is a natural active amorphous material. A diatom-based ion-imprinted composite adsorption material was prepared by the surface ion imprinting technology with diatom as matrix, mercaptopropyltrimethoxysilane(MPS)as the functional monomer, Cd(Ⅱ)as the template ion, and epichlorohydrin(ECH)as the cross-linking agent. The changes in surface morphology were characterized by SEM.The process of diatom surface fabric transformation was studied by XPS and FT-IR. The results show that the hydrolyzed MPS and the diatom surface active silane hydroxyl group are combined by dehydration condensation, and this process introduces the functional group (—SH) into the diatom surface. The ECH and —SH form network imprinted-sites under the effect of cross-linking. Combined with XPS semi-quantitative analysis, the formula for the degree of grafting of MPS on the surface of diatom is derived, and the grafting mode of the diatom-based Cd(Ⅱ) ion-imprinted composite adsorbent is determined. The grafting method of MPS on the surface of diatoms is mainly single-grafting, and accompanied by double-grafting;and the mechanism of adsorption between SH/DE-ⅡP and Cd(Ⅱ) ions is through the coordination of the lone pair of S atoms of MPS with Cd. The adsorption mechanism between SH/DE-ⅡP and Cd(Ⅱ) ions is the coordination of Cd with the lone pair of electrons.These lone pairs of electrons come from the S atom on —SH.The selective adsorption results show that the diatom-based Cd(Ⅱ) ion-imprinted composite adsorbent can selectively adsorb Cd(Ⅱ) ions. The removal rate of Cd(Ⅱ) ions in aqueous solution has increased from 24.4% to 97%, and it has the ability to directionally remove Cd ions.

Keywords

• diatom
• ion-imprinting
• structure
• grafting
• selectivity