Abstract
This paper reports the preparation of cast-in-situ, large-sized monolithic silica xerogels by a two-step acid–base catalyzed approach under ambient pressure drying. Low-cost industrial silica sol and deionized water were used as the silicon source and the solvent, respectively. Hexadecetyltrimethylammonium bromide (CTAB) was used as a modification agent. Different amounts of polyethylene glycol 400 (PEG400) was added as a pore-forming agent. The prepared silica xerogels under ambient pressure drying have a mesoporous structure with a low density of 221 mg·cm−3 and a thermal conductivity of 0.0428 W·m−1·K−1. The low-cost and facile preparation process, as well as the superior performance of the monolithic silica xerogels make it a promising candidate for industrial thermal insulation materials.
Highlights
SiO2 aerogel is a unique nanoporous material with an adjustable density between 3 and 500 mg·cm−3, a low thermal conductivity at room temperature, a high porosity (80%~99.8%), a high specific surface area (>1000 m2 ·g−1 ), a high visible-light transmittance, a low refractive index (~1.05), and a modifiable surface chemistry
The weak peaks at 2960, 2926, 2858, and 1468 cm for the as‐prepared PEG‐1 silica xerogel are attributed to the vibration modes of the C‐H bond [12,13,28], which indicates the existence of the residual carbonaceous organic components in the ambient pressure dried xerogels
The main reason for these results was that the decomposition decomposition of polyethylene glycol 400 (PEG400) increases the proportion of micro‐ and meso‐pores in the samples (as show of PEG400 increases the proportion of micro- and meso-pores in the samples, in Figure 5b), which is confirmed by the aforementioned SEM and the Fourier transform infrared (FTIR) analysis
Summary
SiO2 aerogel is a unique nanoporous material with an adjustable density between 3 and 500 mg·cm−3 , a low thermal conductivity at room temperature, a high porosity (80%~99.8%), a high specific surface area (>1000 m2 ·g−1 ), a high visible-light transmittance, a low refractive index (~1.05), and a modifiable surface chemistry. Based on Kanamori’s work, Shan et al [19] reported a base-catalyzed one-step synthesis of large-sized monolithic methyltrimethoxysilane-based PMSQ aerogels with deionized water as a solvent, followed by ambient pressure drying. These large-sized monolithic methyltrimethoxysilane-based PMSQ aerogels showed a low density of 75 mg·cm−3 and a low thermal conductivity of 0.036 W·m−1 ·K−1. We prepared large-sized monolithic xerogels by a two-step acid—base catalyzed approach under ambient pressure drying, using low-cost industrial silica sol as the silicon source and deionized water as the solvent to reduce the cost of this method. The solvent exchange process is no longer necessary, which simplifies the preparation process
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