Amino organosilane grafted ordered mesoporous alumina with enhanced adsorption performance towards Cr(vi)

Abstract

Ordered mesoporous alumina (MA) was successfully modified with three amino organosilanes including 3-aminopropyltriethoxysilane (1N), N-(β-aminoethyl)-γ-aminopropylmethylbimethoxysilane (2N) and N-3-trimethoxysilylpropyldiethylenetriamine (3N) via a facile grafting method, and the as-prepared amino organosilane grafted MA–1N, MA–2N and MA–3N show enhanced adsorption performance towards Cr(VI) removal from wastewater. Their physicochemical properties and the MA before modification were comparatively characterized by FT-IR, TEM, XRD, N₂ adsorption–desorption, CHNS elemental analysis, zeta potential measurements and XPS. Their adsorption performance was also comparatively studied along with the effect of contact time, adsorption isotherms, multi-metal ion adsorption, interference of co-existing anions and regeneration ability in batch experiments. It was found that their adsorption kinetics data were better fitted by the pseudo-second order model; adsorption isotherms were better described by the Langmuir isotherm for MA–1N, the Freundlich isotherm for MA–2N and the Temkin isotherm for MA–3N. Among them, MA–2N shows the maximum adsorption capacity of 137.9 mg g⁻¹ which is more than twice the 59.4 mg g⁻¹ of MA. The residual concentration of Cr(VI) with a concentration of 50 mg L⁻¹ when treated with MA–2N meets the emission standard of the World Health Organization (WHO). Moreover, MA–2N shows better selectivity toward Cr(VI), and can reduce relatively more Cr(VI) to low toxicity Cr(III). More results were found that Cr(VI) is adsorbed on the surface through a monodentate ligand or bidentate ligand, and then Cr(VI) is reduced to Cr(III) by an adjacent electron donor, after which Cr(III) is co-precipitated with the adsorbents. All the amine-grafted samples show good reusability for 5 cycles. These results indicated that the amino organosilane grafted ordered MA with high adsorption capacity, good selectivity and favourable reusability is a promising candidate for Cr(VI) removal, in combination with its low cost and energy saving preparation process.