Preparation Of Silica Aerogel And Its Composites For Adsorption Application

With lots of excellent properties, low density, large specific surface area and low thermal conductivity for example, silica aerogel has attracted people’s attention for several years. While on the other hand, limited by frangibility of the pure silica aerogel, one of the key factors, silica aerogel is rarely applied in our daily life. Supercritical fluid drying is the well-developed drying method for silica aerogel. However, it requires a lot for the facilities and some danger may happen to the operators for the high pressure.In this paper, under ambient pressure, tetraethoxysilane (TEOS) and water glass were chosen to be the precursors to prepare nanoporous silica aerogels through sol-gel, aging, solvent exchange and surface modification. During the preparing process, the drying control chemical additive N, N-Dimethylformamide (DMF) was introduced to improve the aerogel’s pore size distribution. The effect of volume ratio of solvent (ethanol (for TEOS) or H2O (for water glass)) to precursor has been studied. Although silica aerogel with excellent properties can be obtained the above method, some flaws still exist:long preparing period for the method using water glass or high cost for the method using TEOS. For those reason, a new method, using cheap water glass as the precursor and organic solvent as the main solvent, is proposed which can shorten the preparation period or reduce the preparation cost. The effect of ethanol dosage on the property has been studied. As to the macroporous silica aerogel, we chose methyltrimethoxysilane (MTMS) as the precursor. In this section, the effect of solvent exchange process was studied. For the pore size is in order of micrometer, the traditional exchange process which uses n-hexane to exchange ethanol is not necessary under the premise that ethanol is the pore fluid, which was proved by the experiment and parameter comparison. Both the mseoporous and the macroporous silica aerogel are hydrophobic and oleophilic materials, which can absorb organic liquids from water effectively.To improve the poor mechanical property of the above silica aerogels, the polyurethane sponge was introduced in the preparation process as reinforcement measurement. Using TEOS and MTMS as the precursor respectively, the as-prepared sponge reinforced silica aerogels were prepared under ambient pressure with reinforced mechanical property as well as low density, large specific surface area, super hydrophobicity and oleophilicity. The absorption capacity to the organic liquids of the aerogel was also studied indicating that more than 0.7 ml organic liquids can be absorbed by 1 cm3 aerogel. And the adsorption-desorption recycle can be repeated for more than 10 times without any mechanical failure.In spite of the excellent absorption capacity, to overcome the low efficiency of traditional desorption methods (squeezing or distilling), the obtained sponge reinforced silica aerogel is inserted by a stainless steel pipe which is connected to a pump. The novel design can realize the aerogels’ continuous absorption ability. Indicated by the experiment results, the pumping rate is significantly affected by the aerogels’pore size and the organic liquids’ viscosity, which is consistent with the simple proposed model in this paper. Such an apparatus means that a small piece of this sponge-reinforced silica aerogel can continuously collect a large area of floating oil from a water surface with high speed and efficiency.