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In this work, we have investigated how the typical honeycomb arrangement of SBA-15 and the mechanisms of CO 2 uptake are affected by the addition of chemicals upon synthesis (to modify pore width and length) and post-synthesis amine functionalization. SBA-15 was synthesized hydrothermally by a conventional route (S00) and such synthesis was then subject to modifications: by adding heptane as a swelling agent (S10) and increasing amounts of ammonium fluoride (S11, S12, S13 and S14) to shorten channels length. All of the synthesized silicas were then subject to APTES grafting and PEI impregnation. CO 2 isotherms were obtained for the pure and amine-loaded samples. They were fitted to the Dual-Site Langmuir model for all functionalized adsorbents, so that it was possible to discriminate the relative importance of chemisorption and physisorption sites. The increasingly disordered frameworks brought about by fluoride addition led to the formation of mesocellular silica foams (MCFs), which were not advantageous to increase CO 2 uptakes in the case of amine-grafting because they have a lower silanol density and hence bind less nitrogen as compared to the conventional SBA-15. In the case of PEI-impregnation, it was found that an addition of a low amount of fluoride is important in the regulation of the chemisorption/physisorption ratio. Promising CO 2 uptakes (2.3 mmol CO 2 /g or 4.6 mmol/g PEI at 25 °C and 1 bar) were found for a load of 50% (wt) PEI in MCF synthesized with the highest NH 4 F/SiO 2 molar ratio (equal to 0.065), which was attributed to a better accessibility of amino groups to CO 2 , as compared to the conventional SBA-15 support subject to the same PEI load.

The CO 2 adsorption capacity of different APTES-grafted mesoporous silicas of SBA-15 type has been investigated and the influence of support textural properties and the role of the presence of silanol groups on the adsorption capacity are analyzed. Four adsorbents based on SBA-15 were prepared using tetraethyl orthosilicate (TEOS) as silicon source, with and without the addition of trimethyl-benzene (TMB) and n -heptane as swelling agents, and adding in some cases ammonium fluoride as a solubility enhancer. 3-(triethoxysilyl)propylamine (APTES) was then used as grafting agent by reaction with free silanol groups on the silica surface so as to provide pending amino groups for CO 2 capture. The adsorption behavior for all supports was adequately described by a Freundlich model, whereas for the APTES-grafted silica, a dual-site Langmuir model was applied, which allowed us to quantify and qualify two different adsorption sites. The addition of n -heptane as swelling agent led to pore sizes beyond 10 nm and improved significantly the grafting efficiency, leading to higher CO 2 uptakes as compared to the starting supports. At 1 bar and 25 °C and anhydrous conditions, CO 2 uptakes of 2.4 mmol g −1 or 0.64 mol CO 2 per mol N were achieved (which reveals a significant contribution of physisorption). This sample could be successfully regenerated at 100 °C, maintaining a constant capacity for 3 adsorption–desorption cycles. At 0.15 bar and 60 °C, anhydrous conditions, CO 2 uptake reaches 1.5 mmol g −1 . This value may be theoretically doubled in the presence of humidity, and there is room for further improvement if supports with the same pore size (13 nm) and higher surface areas (e.g. 1000 m 2 /g) are successfully synthesized.

This work studies the structural and chemical modifications of functionalised porous phosphate heterostructures (PPH) of zirconium phosphate. The modification consists in incorporation of propionitrile at two different percentages, but pressure was also applied in order to obtain pressurized discs. The application of pressure (4 T cm 2 ) provokes a migration of nitrile groups to the surface as observed by XPS analysis and it seems to be responsible for the drastic porosity decrease obtained by N 2 adsorption. Electrochemical characterization of the pressured-discs in contact with NaCl solutions at different concentrations was also carried out. These results show the cation exchange capacity of PPH, which is slightly reduced in the case of the functionalised materials with nitrile groups (10% lower cation transport number), while diffusional permeability and electrical resistance values also confirm structural changes for the modified materials.