Selenate adsorption on pre-coordinated Fe3+-silane complexes grafted on mesoporous silicas.

ABSTRACT

Fe3+ was coordinated N-[2-(aminoethyl)-3-aminopropyltriethoxysilane], AEAPTES, followed by being grafted on MCM-41, SBA-15 and Cab-O-sil M7D. The mixing ratio, n = [AEAPTES]/[Fe], in the above coordination reaction was varied from 1 to 3. These nine functionalized silicas, denoted as Fe(en)n-silica (n = 1, 2, 3 and silica = MCM-41, SBA-15 and M7D), were used for the adsorption of aqueous selenate. The saturation of adsorption isotherm occurred at Se/Fe = 2 on Fe(en)2- MCM-41 and Fe(en)2-SBA-15, while Fe(en)- and Fe(en)3-MCM-41 and Fe(en)- and Fe(en)3-SBA-15 adsorbed selenate until Se/Fe = 1. The saturation at Se/Fe = 1 was obtained for all absorbents prepared with M7D substrate, suggesting a transformation of the adsorption sites realized on Fe(en)2-MCM-41 and Fe(en)2-SBA-15. The concave curvature of the surface of mesoporous silicas is possibly critical to retain the coordination structure of adsorption sites. The largest capacity obtained among these adsorbents was 1.1 mmol/g, found on Fe(en)2-SBA-15. The structure of adsorption sites was analysed by X-ray absorption spectroscopies in order to obtain the evidences for the distortion of coordination structure induced by grafting and the bond formation between Se and Fe after adsorption.