Comparative Study of Microwave-Assisted and Supercritical Drying for the Synthesis of Highly Porous Silica Aerogel: A Promising Adsorbent for Phenol Removal from Wastewater

The removal of phenol from wastewater is crucial because of its harmful influences on human health, soil quality, and aquatic ecosystems. Among the different methods used for phenol removal, adsorption has gained popularity as an affordable and effective approach. Silica aerogel, with its highly porous structure and substantial surface area is recognized as an exceptional absorbent for phenol removal. However, achieving the desired porous structure and surface area in silica aerogel necessitates the challenging technique of supercritical drying. Highly porous silica aerogel was synthesized using sol-gel and microwave irradiation as drying method in this research. The physicochemical and textural properties of the prepared silica aerogel samples were characterized using XRD, BET/BJH, SEM-EDX, and FT-IR analyses. XRD analysis demonstrated that both samples of silica aerogel exhibited a broad peak, indicating the presence of pure silica without any impurity peaks. The surface area of the silica aerogel prepared using microwave irradiation drying was found to be 762.94 m²/g, while that prepared using supercritical drying was 590.47 m²/g, as determined by BET/BJH analysis. The adsorption test showed that acidic pH conditions are optimal for phenol adsorption on silica aerogel due to its pHpzc (point of zero charge) and the protonation of phenolate ions. The results demonstrated that the silica aerogel prepared using microwave drying achieved a remarkable phenol removal efficiency of 91.03% from a baseline concentration of 100 mg/L at pH 4, over a duration of 135 min. The results demonstrated that surface adsorption process aligns with the Freundlich isotherm model and follows pseudo-first-order kinetics.