Functionalised micro-/mesoporous silica for the adsorption of carbon dioxide

Abstract

SBA-16 silica was synthesised using the tri-block copolymer F127 as a surfactant. The copolymer was eliminated by calcination to 823 K or extraction with ethanol. These materials were functionalised with the diamine (CH 3O) 3Si-(CH 2) 3-NH-(CH 2) 2-NH 2 by post-synthesis grafting. TGA and DRIFT infrared spectroscopy revealed that the copolymer was not removed completely by extraction. For both methods the cubic pore structure of the synthesised silica remained intact which was corroborated by nitrogen isotherms and TEM measurements. The adsorption of carbon dioxide was studied with microcalorimetry at 300 K and up to 35 bars. The grafted silica samples show high enthalpies [−(90–100) kJ mol −1] at low pressures for the carbon dioxide adsorption. This was attributed to the initial interactions of the gas with the amine modified silica surface. With increasing carbon dioxide pressures the enthalpies decreased to values close to those observed with the non-grafted silica. The amounts of CO 2 adsorbed at 30 bar were ∼6.5 mmol g −1 for the non-grafted silica samples and 5.4 (extracted sample) and 4.6 mmol g −1 adsorbent (calcined sample) for the grafted silica materials, respectively.