Preperation And Modification Of Silica Aerogels And Their Adsorption Performance

Nowadays the complex environmental pollution issues for our country consist of traditional pollution due to emission of a mass of CO₂ and new-type pollution caused by VOCs and their secondary products.At present,adsorption is the most useful and effective solution to solve these pollution.In order to prepare adsorbents with good adsorption performance to gaseous pollutants,the combination with physicochemical properties of adsorbent and the target adsorbate need to be understood comprehensively.Hence,it is required to systematically study the effect of pore structure and surface chemistry of adsorbent on the adsorption properties of adsorbates.Carbon material and mesoporous silica material are the typical gas adsorption materials.Carbon material-expanded graphite with macroporous structure was firstly modified by amine to prepare CO₂ capture material.But the results show that the open layer structure of expanded graphite is not favorable to the chemical adsorption of CO₂.In addition,mesoporous silica-silica aerogel was chosen to be the support.The CO₂ adsorption performance was tested by using this support after modification by amine,emphasis was placed on the effect of the pore structure of the support material on the carbon capture performance of solid amine materials.Subsequently,by using the superior pore structure of silica aerogel,the adsorption behavior of VOCs with different polarity on silica aerogel before and after hydrophobic modification under dry and high humidity conditions were tested to study influence of the surface chemistry and pore structure of adsorbent to adsorption behavior of adsorbate molecules on the adsorbent surface.In this experiment,the surface microstructures of adsorbents were characterized by physical adsorption instrument,mercury porosimeter,scanning electron microscope and transmission electron microscope,fourier transform infrared spectrometer and thermogravimetric analysis were used to analyze the functional groups on the surface of the adsorbent,the adsorption performance of the adsorbent was analyzed using a simultaneous thermal analyzer and gas chromatography.The research mainly includes:?1?A new solid amine adsorbent loaded with TEPA was prepared by wet impregnation,based on expanded graphite made from expansible graphite through thermal expansion.According to the characterization results,amine modification procedure have no significant effect on layered structure of expanded graphite.The CO2adsorption performance of adsorbent tested with 10%CO₂ in 75?shows that the maximum adsorption capacity of the amine-modified expanded graphite was 1.95 mmol/g for expanded graphite with pore volume of 3.14 m L/g,?2?In view of subpar capacity of amine modified expanded graphite,the other carrier-silica aerogel was utilized and did prepared CO₂adsorption material with excellent adsorption performance.Meanwhile,the effect of the pore structure of the carrier on the CO₂ adsorption behavior of amine-based solid adsorbent also be obtained in this experiment.A series of silica aerogel materials with mesoporous structure could be synthesized by changing aging temperature?the average pore diameter range from7.42 nm to 16.9 nm,the pore volume range from 1.35ml/g to 2.89ml/g,and the maximum pore size was obtained when the aging temperature was 90??.After impregnated with TEPA,the adsorption-desorption performance of this series of silica aerogel at different loadings were tested at 75?.This amine-modified sorbent reached the best CO₂ adsorption capacity of 4.34mmol/g when silica aerogel got the largest pore volume and loaded with 70%TEPA.The research shows that adsorption-desorption capacity of amine modified silica aerogel increased by the increasing of pore volume of carrier.But when the pore volume of silica aerogel is greater than 1.73ml/g,continuous increase of pore volume do not have significant influence to its amine efficiency and adsorption-desorption rate.?3?Silica aerogel which has mesoporous and microporous structure and a large specific surface area was hydrophobic modified by using precursor method.The obvious increase on average surface and micropore volume caused by modification leads to the increase of VOCs adsorption capacity.After the hydrophobic modification,the increase of methyl group on the surface of the adsorbent not only improved the adsorption capacity of the material under high humidity conditions,but also suggested that the adsorbent after the increase of the surface polarity showed better absorption efficiency for the ethyl acetate with a higher polarity.The research in this paper has guiding significance for choosing pore structure and chemical properties of support when preparing adsorbents for treating target gaseous pollutants.