title: Pore size engineering in mesoporous silicas using supercritical CO2.
abstract: In this paper we investigate the use of supercritical carbon dioxide (sc-CO(2)) for synthesizing calcined mesoporous silicas with tunable pore sizes, wall thickness, and d spacings. Small angle neutron scattering was used to probe the controlled swelling of the triblock copolymer surfactant templating agents, P123 (PEO(20)PPO(69)PEO(20)), P85 (PEO(26)PPO(39)PEO(26)), and F127 (PEO(106)PPO(70)PEO(106)), as a function of CO(2) pressure. The transition from the liquid crystal phase to the calcined mesoporous silicas, formed upon condensation and drying, was also studied in detail. Powder X-ray diffraction, transmission electron microscopy, and nitrogen adsorption techniques were used to establish pore diameters, silica wall widths, and the hexagonal packing of the pores within the calcined silicas. Using a direct templating method, the diameters of mesopores and the spacing between the pores could be tuned with a high level of precision. The swelling process was observed to have no detrimental effects on the quality of silica formed, a distinct advantage over conventional swelling techniques, and all of the silicas synthesized in this study were highly ordered over distances of at least 2000 A.
authors.affiliation: Department of Chemistry, Material Section and Supercritical Fluid Centre, University College Cork, Cork, Ireland.
authors.forename: John P
authors.initials: JP
authors.lastname: Hanrahan
authors.forename: Mark P
authors.initials: MP
authors.lastname: Copley
authors.forename: Kirk J
authors.initials: KJ
authors.lastname: Ziegler
authors.forename: Trevor R
authors.initials: TR
authors.lastname: Spalding
authors.forename: Michael A
authors.initials: MA
authors.lastname: Morris
authors.forename: David C
authors.initials: DC
authors.lastname: Steytler
authors.forename: Richard K
authors.initials: RK
authors.lastname: Heenan
authors.forename: Ralf
authors.initials: R
authors.lastname: Schweins
authors.forename: Justin D
authors.initials: JD
authors.lastname: Holmes
mesh_terms: D000327:Adsorption; D000536:Aluminum Hydroxide / Q000737:chemistry; D002245:Carbon Dioxide / Q000737:chemistry*; D008276:Magnesium Hydroxide / Q000737:chemistry; D046529:Microscopy, Electron, Transmission; D009584:Nitrogen / Q000737:chemistry; D044367:Phase Transition; D016062:Porosity; D012822:Silicon Dioxide / Q000737:chemistry*; D013499:Surface Properties; D013501:Surface-Active Agents / Q000737:chemistry*; D014961:X-Ray Diffraction
chemical_list: D013501:Surface-Active Agents; D002245:Carbon Dioxide; C010467:hydrotalcite; D000536:Aluminum Hydroxide; D012822:Silicon Dioxide; D009584:Nitrogen; D008276:Magnesium Hydroxide