Facile Synthesis of Zinc-oxide/Silica Aerogel and Their Application in Water Remediation

Abstract

Highly porous zinc-oxide/silica aerogels and xerogels were prepared via a one-pot sol-gel process at room temperature using propylene oxide as the gelation initiator. For aerogel preparation, the solvent was extracted with supercritical carbon dioxide, while for xerogel preparation, ambient evaporation was performed. The structure and surface properties of the obtained materials have been investigated via a broad range of structural, textural, and morphological characterization before and after calcination. The aerogels and xerogels have a high surface area of 192 and 105 m²/g, respectively, and an open pore structure of 0.7 and 0.2 cm³/g, which enable an effective adsorption-desorption process. The zinc-to-silica molar ratios are stoichiometric, closely matching those of the initial solution. Zinc oxide-based materials are well known to have a wide range of applications in adsorption processes. To evaluate the capacity of the aerogels and xerogels to absorb dyes, methylene blue (MB) and Congo red (CR) were selected as model compounds, as they exhibit different electronegativities, and a series of batch adsorption experiments were performed at ambient temperature. Both aerogels and xerogels exhibited a high adsorption capacity for both MB and CR dyes, with maximum adsorption capacities of up to 72 mg/g and 58 mg/g, respectively, in 30 minutes. Among the evaluated isotherms, equilibrium data was found to best fit the Langmuir model based on a higher value of the coefficient R² = 0.999. The adsorption process follows pseudo-second-order kinetics.