Rapid synthesis of sodium silicate based hydrophobic silica aerogel granules with large surface area

• Aerogels with large surface area were get under ambient pressure using water glass.
• Optimum concentration of water glass was determined for silica aerogels with low density.
• Large amount of modification agent can be saved to completely modify the hydrogel.
• Proper amount of DMF makes a uniform pore size distribution of earned silica aerogels.

In this study, we tried to synthesize ultralow density and super hydrophobic silica aerogel with extra high specific surface area, by using absolutely cost effective processing from sodium silicate. Hydrosol was obtained through ion exchange. To reduce the processing time, the gels were mechanically agitated to granules before solvent exchange. N,N-Dimethylformamide (DMF), serving as drying control chemical additive (DCCA), was introduced to reduce shrinkage. When the molar ratio of Si in sodium silicate to DMF is 0.31, the pore size distribution is the narrowest. Before dried under ambient pressure, the gels were surface modified by Trimethylchlorosilane (TMCS) in order to make sure the aerogels are hydrophobic. And the proper molar ratio of TMCS to pore water is 0.0233 which is much lower than that in previous experiments. The resulting aerogels have well-developed mesoporous structure with extremely high specific surface area (817 m2/g) and super hydrophobicity (contact angle of 165°).

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