Thermodynamics of CO2 adsorption on functionalized SBA-15 silica. NLDFT analysis of surface energetic heterogeneity

Abstract

Siliceous SBA-15 mesoporous molecular sieves were functionalized with different amounts of 3-aminopropyl-trimethoxysilane. To obtain a more detailed insight into the material properties of the prepared samples, their textural parameters were combined with results of thermal analysis. Adsorption isotherms of carbon dioxide on parent and functionalized SBA-15 were measured in the temperature range from 273 to 333 K. From the temperature dependence of CO(2) isotherms the isosteric adsorption heats of CO(2) were determined and discussed. Information about the surface energetic heterogeneity caused by tethered 3-aminopropyl groups were obtained from CO(2) adsorption energy distributions calculated using the theoretical CO(2) adsorption isotherms derived from the non-local density functional theory. The values of isosteric heats and the energy distributions of CO(2) adsorption detect highly energetic sites and enabled quantification of their concentrations.

MgO-modified mesoporous silicas impregnated by potassium carbonate for carbon dioxide adsorption

“…The isotherms on parent silicas SBA-15, SBA-16 and MCM-48-ls are almost linear and they reveal that pure silica does not interact very strongly with CO 2 because the surface hydroxyl groups are not able to induce sufficiently strong interactions and other adsorption sites are missing. The weak interaction of CO 2 with surface of Al-SBA-15 silica was also reported [22]. In addition, the size of the pores is too large to influence the adsorption by the effect ''from the top'' as recently described by Nachtigall et al [39,40] and which is so important in the case of CO 2 adsorption in microporous zeolites.…”

“…To prepare magnesium oxide of small particles exposing more adsorption centers into the gas phase, we have focused on introduction of MgO into mesoporous molecular sieves benefiting from thermal stability and large surface area of mesoporous silicas. In our previous study we have shown that potassium cations in Al-SBA-15 dramatically enhance adsorption of CO 2 in the region of low equilibrium pressures [22].…”

“…In the case of physical adsorption of CO 2 , nanoporous materials are primarily investigated, including alkali-metal exchanged zeolites [5][6][7][8][9][10][11][12][13], amino-modified [14][15][16][17][18][19][20][21][22] and alkali-modified [23] mesoporous silicas, and recently also metal-organic frameworks [24][25][26] or organo-modified mesoporous silicas [27]. These adsorbents differ from each other based on their chemical composition, structure and type of adsorption sites and also adsorption enthalpy.…”

Carbon dioxide adsorption using amine-functionalized mesocellular siliceous foams

“…Grafting method, based on the chemical reaction between surface silanol groups and organosiloxane molecules, has been employed to incorporate aminated organosilanes into a wide range of silica porous supports. Organosilanes, such as 3-aminopropyltrimethoxysilane (APTMS) [33][34][35][36][37][38], N-(2-aminoethyl)-3-aminopropyltrimethoxysilane [39][40][41][42], and diethylenetriamino-trimethoxysilane [39,40,43,44], have been grafted on different mesoporous silicas and evaluated their adsorption capacities toward CO 2 . The influence of amine structure [39,40,44], pore structure [45,46], amine surface density [47], stability and adsorption mechanism [34,[48][49][50] were studied.…”

CO2 adsorption on amine-modified mesoporous silicas

“…There are two main classes of such adsorbent materials: amines covalently bound to the silica support via silane chemistry and amines such as polyethylenimine (PEI) physically impregnated into the silica support. Organosilanes, such as 3-aminopropyltrimethoxysilane (APS) [6][7][8], N-(2-aminoethyl)-3-aminopropyltrimethoxysilane (AEAPS) [9][10][11][12] and diethylenetriamino-trimethoxysilane (TA) [10][11][12][13], have been grafted on a series of mesoporous silicas via chemical reaction between surface silanol groups and organosiloxane molecules, and evaluated their adsorption capacities toward CO 2 . When the grafting method is used, CO 2 adsorption capacity depends on the amine density and the total nitrogen content.…”