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

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.