Synthesis, characterization, and adsorption properties of silica aerogels crosslinked with diisocyanate under ambient drying

Monolithic silica aerogels were prepared by sol–gel process via ambient drying process. TEOS and APTES were used as coprecursors and wet gels were crosslinked by three kinds of diisocyanate. The strengthened silica aerogels possess densities which range from 0.298 to 0.463 g/cm³, and the specific surface areas range from 81.17 to 135.48 m²/g. In this paper, silica aerogels crosslinked with different diisocyanate were used as adsorbents for the removal of heavy metals. At the same time, some factors such as the initial pH and concentration of heavy metals were investigated by a batch of experiments. The equilibrium sorption data have been fitted by different isotherm model, and the data fitting by Freundlich isotherm model indicates that the process of adsorption is favorable. Under the condition of the optimum adsorption pH, the maximum theoretical adsorption capacity computed from Langmuir model is 118.73 mg/g for Pb²⁺, 57.03 mg/g for Cr³⁺, and 60.86 mg/g for Cd²⁺, respectively with the silica aerogels crosslinked with 1,6-hexamethylene diisocyanate (HDI).