Synthesis Of Amino-functionalized Porous Silicas And Their CO₂-adsorption Properties

It is well known that carbon dioxide (CO2) has become an important global issue due to the significant and continuous rise in anthropic CO2 emissions to the atmosphere and their connection with global climate change. Two kinds of amino-functionalized porous silicas (AFPS), i.e. amino-functionalized SBA-15 and porous silicas templated by anionic surfactants, have been studied in this dissertation. To improve adsorption capacity of CO2 on the AFPS at ambient temperature and atmospheric pressure, this study has been focused on investigating the effects of experimental conditions such as pH value, aging temperature, types of anionic surfactant etc., on AFPS adsorption properties for CO2. Inherently, the synthesized porous silicas have been characterized by the FT-IR, in-situ FT-IR, N2 adsorption-desorption, elemental analysis, SEM, TG-DTA, TPD, XRD, and TEM techniques. The obtained results are summarized as follows:(1) One-pot synthesis of amino-functionalized SBA-15 and their CO2-adsorption properties.Amino-functionalized SBA-15 mesoporous materials were synthesized by a one-pot strategy. The characterized results show that all the obtained materials have a typical meso-SBA-15 structure when the molar ratios of APTES to (APTES+TEOS) in the synthetic solutions are below 0.20 or the molar ratios of APTMS to (APTMS+TEOS) in the synthetic solutions are below 0.10, while the meso-structure could be collapsed when these ratios are more than the corresponding values (0.20 or 0.10) because of the adverse effect of amino groups on the formation of SBA-15. However, with the aid of fluoride ions, even at a molar ratio of APTES to (APTES+TEOS) of 0.25 or a molar ratio of APTMS to (APTMS+TEOS) of 0.30, the amino-functionalized SBA-15 mesoporous material with a larger pore size and a higher BET surface area could be synthesized. The results from CO2 adsorption on the synthesized amino-functionalized SBA-15 mesoporous materials show that under the same conditions the adsorbed amount of CO2 increases with increasing the APTES (APTMS) amount in the synthetic solution and the amino-functionalized SBA-15 mesoporous material synthesized with the aid of fluoride ions has a higher amount adsorbed for CO2 adsorption at 101 kPa and 25℃, compared to those prepared without introduction of fluoride ions.(2) Synthesis, amino-functionalization of SBA-15 with a high Si-OH density and their C02-adsorption properties.SBA-15 materials with a high Si-OH density have been successfully prepared by adding HAc solution into HCl solution, because Ac- can slow down the hydrolysis-condensation reaction of silica alkoxides. The amino-functionalized SBA-15 (AF-SBA-15) materials have been obtained via tetraethylenepentamine (TEPA) loaded onto the SBA-15 with a high Si-OH density. The experimental results show that when the mass ratios of TEPA to SBA-15 are below 0.6, the structure of AF-SBA-15 are identical to that of pure SBA-15. When the mass ratio of TEPA to SBA-15 is 0.1, the adsorption capacity of CO2 on the prepared AF-SBA-15 decreases with increasing temperature, while when the mass ratio of TEPA to SBA-15 is 0.6, the adsorption capacity of CO2 on the synthesized AF-SBA-15 increases with increasing temperature.(3) Effects of extractive method, aging temperature, pH value and and reactant composition on the adsorption properties of CO2 over the amino-functionalized porous silicas templeted by anion surfactants.Using N-lauroylsarcosine sodium (Sar-Na),3-aminopropyltrimethoxysilane (APTMS) and TEOS as structure-directing agent (SDA), co-structure-directing agent (CSDA) and silicon source, respectively, the pre-products of amino-functionalized mesoporous silicas have been prepared by a sol-gel method. The template in the pre-products can be efficiently removed by extraction either using a basic solution of monoethanol amine (MEA) in ethanol or an acetonitrile solution acidified with HCl. The experimental results indicate that, when compared to the adsorbent treated with acidic acetonitrile, the adsorbent treated with the MEA-ethanol solution has a much higher adsorption capacity towards CO2, exhibits a higher degree of reversibility in the adsorption process, and has a much higher CO2/N2 selectivity.The results from both elemental analysis and TEM characterizations show that the amount of amino groups inside the mesoporous materials is greatly controlled by the aging temperature and pH value of the synthetic solution. The adsorption of CO2 on the synthesized materials implies that the low aging temperature and relatively low pH value of the synthetic solution would be benefit to enhance the adsorbed amount of CO2 on the resulted materials.The results from CO2 adsorption on the amino-functionalized mesoporous silicas templeted by anion surfactants also show that the ratio of APTMS to TEOS is a key parameter that affects the CO2 adsorption capacity. When a miture of 0.6 ml APTMS and 3.0 ml TEOS is added into a solution containing 39 ml HCl(0.1 mol/l),70 ml H2O and 1.76 g Sar-Na, the synthesized adsorbent exhibites a much higher CO2 adsorption capacity, compared to those synthesized under other conditions, for example, a mixture of 0.3 ml APTMS and 3.0 ml TEOS added into a solution containing 13 ml HCl (0.1 mol/1),70 ml H2O and 0.59 g Sar-Na.(4) Preparation of amino-functionalized porous silicas templeted by dodecanoic acid and their CO2-adsorption properties.Using dodecanoic acid (DAA), APTMS and TEOS as SDA, CSDA, and silicon source, respectively, the pre-products of amino-functionalized mesoporous silicas have been prepared by a sol-gel method. The template in the pre-products can be efficiently removed by extraction using a basic solution of MEA in ethanol. The results from CO2 adsorption show that, when the content of APTMS in the synthetic system is increased, the adsorption capacity of CO2 adsorption on the synthesized adsorbent is increased as well. However, when the volume ratio of APTMS to DAA is above 2.2:3.0, the adsorption capacity of CO2 decreases with increasing the content of APTMS. Additionally, a systematic investigation on the effects of the use of alcohols, such as methanol, ethanol, propanol, and butanol, on the adsorption properties of CO2 on the resulted adsorbents indicates that the adsorbent synthesized by the use of ethanol has the highest adsorption capacity towards CO2.