Application of airgel in the field of environmental cleanup

With the rapid economic development, global warming and air pollution, water pollution and other environmental problems have become more severe, ecosystems and human life and health constitute a serious threat. For greenhouse gases, volatile organic compounds (of VOCs), sulfur oxides (the SOx), and water emission control of atmospheric pollutants nitrogen oxides (NOx) such as purification and other environmental problems, has been developed stage adsorption, absorption, more purification techniques membrane separation method, biological method, a plasma method, a photo catalytic combustion method or the like. Wherein adsorption has a low cost, wide application range, easy to use, no secondary pollution and sorbent can be recycled, etc., it has been widely used in the field of environmental cleanup. As the core adsorption technology, the development of high-performance adsorbent has been a hot topic in the field.

aerogels or colloidal particles by aggregation of polymer molecules each other to form a nanoporous network structure, and the pores It is filled with a porous solid material in a gaseous dispersing medium. Airgel has a very high specific surface area, high porosity, open pore structure can be regulated, and easy to chemically modified surfaces diverse types and forms, in the gas adsorption clarifier, the water purification art show a broad environmental purification application prospects.

Second, the structural characteristics of aerogels

For the porous absorbing material, the specific surface area, pore structure and surface chemical properties is a critical factor affecting the adsorption properties. Nanoporous airgel has a continuous three-dimensional network structure, the porosity may be as high as 99.8%, wherein the specific surface area of ​​activated SiO2 aerogels and carbon aerogels are up to about 1000 m2 / g, 3300 m2 / g, high porosity providing a large specific surface area and surface active adsorption sites, it has a good adsorption performance, activated carbon adsorption capacity is 6 times of. In addition, the open pore structure of the airgel facilitate communication flow of the gas diffusion, gas molecules in contact with the adsorption sites easily. Therefore, whether or gas adsorption purification water purification, the airgel plays an important role. Notably, only rely on its own network structure of the airgel gas physical adsorption, the adsorption amount is limited, the adsorption selectivity is not high, the gas component coexisting in practical applications tend to competitive adsorptionTarget gas adsorption adversely affected. Thus, recent research focused on the most-modified airgel modified to enhance its adsorption of the target gas and / or selectivity.

in terms of CO2 adsorption, and SiC to SiO2 aerogels airgel, airgel new graphene aerogels, mainly through an amino functionality, the introduction of basic nitrogen-doped active site, etc., depend on the specific chemical adsorption aerogels while increasing the amount of CO2 adsorption and selectivity; for carbon aerogels may be by activation further enhance its surface area, and the simultaneous introduction of micropores and ultramicropores CO2 adsorption play a key role for efficient adsorption. In the adsorption purification of VOCs, the main problem is to rely on physical adsorption to overcome the competitive adsorption of water molecules, which mainly focused on by the introduction of a non-polar organic functional group hydrophobically modified airgel; and a metal oxide airgel and a new biomass-based airgel using its unique active site, often capable of chemisorption VOCs so as to achieve efficient purification of VOCs.

Third, the application of airgel PURIFICATION

Application of airgel in the field of environmental cleanup mainly adsorption purification and water purification both in the gas. Currently most research reports for environmental cleanup is mainly SiO2 aerogels and carbon aerogels. Further, in recent years, the application of metal oxide aerogels and new SiC airgel, airgel graphene and biomass in the environment based aerogels Purification is also reported.

1.SiO2 aerogels

of SiO2 aerogels having high adsorption efficiency as an adsorbent, to facilitate desorption, itself stable performance, etc., is the most studied, the most mature airgel material, first is applied to the field of gas adsorption purification. SiO2 airgel by an amino function or hydrophobically modified, can further enhance its adsorption performance of CO2 or VOCs. The modified SiO2 aerogels dried under humid conditions for 10% (volume fraction), respectively, CO2 adsorption amount up to 1.95 mmol / g and 6.97 mmol / g. Since water moleculesCompetitive adsorption, activated carbon, silica gel and other conventional physical adsorption type material of VOCs adsorption performance is significantly reduced in a damp environment. While the hydrophobic SiO2 airgel, can effectively inhibit the competitive adsorption of water molecules to improve the selectivity of the target material organic gas in a damp environment. Hydrophobic SiO2 aerogels for some volume of VOCs adsorbed benzene, toluene, carbon tetrachloride, etc. is much greater than the conventional activated carbon fibers and activated carbon adsorbent, and adsorption amount (0.12g / 100g) steam compared to hydrophilic SiO2 airgel (6g / 100g) was significantly decreased. The adsorption mechanism is as follows:

• (1) organic vapor adsorption and diffusion into the pores in the airgel pores;
• (2) adsorption process heat, low thermal conductivity so that the heat is retained airgel particles; the
• (3) airgel particles increase in temperature, reducing the amount of equilibrium adsorption of organic matter;
• (4) slow release of heat, the temperature of airgel particles decline in the equilibrium adsorption rate increases, the adsorption process continues.

of SiO2 aerogels can also be used for purification of water and oil absorption, fast, large nitrobenzene absorbed in water, oil, phenol and some of the volatile toxic pollutants, having a methylene blue dyes adsorbate up to 98 percent removal, purification in the ocean, water pollution and other petrochemical field has a relatively wide range of applications.

2. Carbon aerogels

As a new type of carbon airgel nanoporous carbon material, high porosity, large surface area, density of the wide range of features. Carbon airgel having a specific surface area and pore volume than SiO2 airgel, an airgel is another class of adsorbent material. In addition to using a similar method Modifications of SiO2 aerogels, the carbon airgel can be further increased by the activation of specific surface area and pore structure and surface chemistry to improve properties, in order to effectively improve the adsorption properties of CO2, VOCs\’s. Carbon aerogels used to remove toxic metals and organics in water, such as Hg2 +, Pb2 +, nitrobenzene, phenol and the like. OneIt means the carbon airgel is generally constant column structure, so that the water to be treated to flow therethrough, the metal impurities in the water will be adsorbed onto the airgel. In addition, carbon aerogels may also serve as electrical adsorption and electrocatalytic oxidation electrode wastewater treatment technology.

3. The metal oxide aerogels

rich metal oxide airgel surface active sites such as the central metal, and the like so as to have reactive hydroxyl unique adsorption properties, chemical adsorption can often occur, having a high adsorption capacity and selectivity. The MgO-Al2O3 airgel, basic adsorption sites present on the surface of three different intensities, typically VOCs to nine acetaldehyde, acetone and the like have good adsorption performance, activated carbon adsorption capacity is much larger than, and VOCs nanocrystalline surface occurred dissociative adsorption of many molecular layers.

4. Functional Cellulose aerogels

Functional Cellulose aerogels typically by freeze drying or supercritical drying out prepared, having a high specific surface area and porosity, not only in a traditional airgel , while incorporating its own good biocompatibility, biodegradable, and so environmentally friendly features, it has a natural advantage in adsorption of CO2, formaldehyde gas, and the removal of heavy metal ions in the wastewater, organic dyes, organic solvents and oils sewage .

5. SiC aerogels

aerogels typically restore the SiC -SiO2 composite of an organic airgel precursor carbonization and high temperature carbothermic preparation of the reaction. SiC robust airgel can be an effective vector for CO2 amino functionalized adsorbent prepared. Amino functionalized bulk SiC airgel, which is almost the same amount of CO2 adsorption on a 1% (volume fraction) at different temperatures (25 ~ 75 ℃), about 1.8 mmol / g under dry conditions. After the bulk SiC airgel simple separation after use, and again heat recoverable amino functionalized adsorption activity, and the CO2 adsorption performance of 12 repetitions by using at least still not significantly reduced, can be seen, SiC gas condensate gum has excellent reusability, can significantly reduce the cost.

6 graphene aerogels

graphene sheets are stacked with each other may be formed of porous graphite having a three-dimensional network structure alkenyl airgel, which combines both graphene electronic fast transmission rate, and the surface of the airgel containing groups rich in large surface area, high porosity features, further modifications and easy modification. Graphene airgel to CO2, SO2 higher adsorption capacity and faster adsorption rate, which is the maximum amount of adsorption of CO2 was 2.38 mmol / g (1000kPa), the maximum amount of adsorption of SO2 was 2.19mmol / g, within 5min to reach adsorption equilibrium.

IV Summary

aerogels having ultra high porosity, open communication mesoporous porosity and high thermal stability, which has a good adsorption capacity and reproducibility, and further enhance its adsorption performance in the environment by purification of the amino function, hydrophobically modified, and other means of activation, prospects. Current research on aerogels in environmental purification has made great progress in the study aerogels detection technology and processing methods should continue to strengthen in the future, based on the specific circumstances of pollutants present in the environment of reform and innovation of its, give full play to the airgel in the field of environmental cleanup role.