Preparation of Al₂O₃-SiO₂ composite aerogels and their Cu²⁺ absorption properties

Abstract

In order to remediate heavy metal ions from waste water, Al₂O₃-SiO₂ composite aerogels are prepared via a sol—gel and an organic solvent sublimation drying method. Various characterisation techniques have been employed including X-ray diffraction (XRD), Fourier transform infrared spectrometry (FTIR), scanning electron microscope (SEM), Energy-dispersion X-ray spectroscopy (EDX), Brunauer—Emmett—Teller (BET) N₂ adsoprtion isotherm, and atomic absorption spectrometer (AAS). XRD and FTIR suggest that the aerogels are composed of mainly Al₂O₃ and minor SiO₂. They have a high specific surface area (827.544 m²/g) and high porosity (86.0%) with a pore diameter of ∼20 nm. Their microstructures show that the distribution of Al, Si, and O is homogeneous. The aerogels can remove ∼99% Cu²⁺ within ∼40 min and then reach the equilibrium uptake (∼69 mg/g). Preliminary calculations show that the Cu²⁺ uptake by the aerogels follows pseudo second-order kinetics where chemical sorption may take effect owing largely to the high surface area, high porosity, and abundant functional groups, such as Al-OH and Si-OH, in the aerogel network. The prepared aerogels may serve as efficient absorbents for Cu²⁺ removal.

Keywords

heavy metal ion / aerogel / absorption / organic solvent sublimation drying / specific surface area / porosity

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