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The thermoresponsive polymer poly-N-isopropylacrylamide (PNIPAAM) was grafted in mesoporous SBA-15 silica. The grafting process consists of three steps: (i) increasing the amount of surface silanol groups of SBA-15 by hydroxylation, (ii) attachment of an anchor (1-(trichlorosilyl)-2-(m/p-(chloromethylphenyl)ethane) and finally (iii) the polymerization of the monomers (NIPAAM) onto the anchor. After each step, the materials were characterized regarding the porosity, using inert gas (argon, nitrogen) physisorption measurements. Also, the structure was investigated by small-angle X-ray diffraction analysis and thermogravimetric analysis was used for determination of the amount of grafted material. A total of 17% by weight of organic material was introduced in the porous host and the structure was preserved during the grafting process. Physisorption measurements revealed that the anchor is mainly located in the intrawall pores present in SBA-15. Consequently, the polymer is preferentially located in the intrawall pores or in the vicinity thereof. The final mesopore volume is 0.47 cm(3) g(-1) as compared to 0.96 cm(3) g(-1) for the pure SBA-15. The surprisingly large loss of mesopore volume and an almost constant mesopore diameter is consistent with a partial sealing of the mesopore volume in the composite materials. The potential thermocontrol combined with the large mesoporosity and the possible "storage space" provided by the sealed mesopore volume leads to a material with possibilities for various applications., (This journal is © the Owner Societies 2012)

Plugged mesoporous SBA-15 having a 2-D hexagonal pore structure could be directly synthesized under acidic conditions using P123 as a supramolecular template, sodium metasilicate and alcoholamines. The use of alcoholamines seemed to play roles as capturing agents for silica sources that could form internal porous plugs., (© The Royal Society of Chemistry 2011)

The combination of physisorption experiments with simultaneous in situ small-angle X-ray and neutron scattering (SAXS/SANS) was used to elucidate the porosity in mesoporous silica with a trimodal pore structure. The material ("KLE-IL") contains spherical mesopores of 14 nm in diameter, worm-like mesopores (2-3 nm), and micropores, templated by a block copolymer and an ionic liquid surfactant, while the micropores originate from the hydrophilic block of the block copolymer. The main objective of the study was the quantification of the microporosity and the small mesopores and to find out if they are indeed located between the larger, spherical mesopores. Our in situ SAXS/SANS experiments took advantage of contrast matching of nitrogen (SANS, T = 77 K) and dibromomethane (SAXS, T = 290 K). By using the latter gas with a slightly larger kinetic diameter, it was possible to judge the accessibility of the pores under ambient conditions. The in situ experiments were supported by high-precision ex situ physisorption. Using suitable approaches for the SAXS/SANS analysis, it was possible to separate the content of the micropores and small mesopores.

In order to elucidate the role of the flow-through characteristics with regard to the column performance in high-performance liquid chromatography (HPLC) native and n-octadecyl bonded monolithic silica rods and columns, respectively of 100 mm length and 4.6 mm ID with mesopores in the range between 10 and 25 nm and macropores in the range between 0.7 and 6.0 microm were examined by mercury intrusion/extrusion, scanning electron microscopy, image analysis and permeability. The obtained data of the flow-through pore sizes and porosity values as well as surface-to-volume ratio of the stationary phase skeleton enabled to predict their influence to the chromatographic separation efficiency. Our data demonstrate that mercury porosimetry is a reliable technique to obtain all the characteristic parameters of the flow-through pores of silica monoliths. An important result of our examination was that the surface-to-volume ratio of monolithic silica skeletons had more significant impact to the separation process, rather than the average flow-through pore sizes. We could also show the essential differences between the particulate and monolithic stationary phases based on theoretical computation. The results, obtained from other characterization methods also indicated the structural complexity of monolithic silica samples. Permeability of columns is a generally applicable parameter to characterize all chromatographic phases no matter the chemistry or format. The correlation coefficient obtained for mercury intrusion and permeability of water was 0.998, though our investigation revealed that the surface modification is more likely influencing the obtained results. Further, the assumption of the cylindrical morphology of flow-through pores is not relevant to the investigated monolithic silica columns. These results on the morphology of the flow-through pores and of the skeletons were confirmed by the image analysis as well. Our main finding is that the flow-through pore sizes are not relevant for the estimation of the chromatographic separation efficiency of monolithic silica columns.

Our focus in the present study is to apply high specific surface area silica nanostructured porous materials (about 2200 m2/g, as synthesized, and 600-700 m2/g, after stabilization) to adsorb ammonia (NH3) for hydrogen storage and other chemical and pollution abatement applications. We describe here the synthesis, and characterization of these silica materials, and the adsorption study of N2 and NH3. These materials were obtained with the help of a modification of the Stöber-Fink-Bohn (SFB) method. The main change, made here to the SFB method, was the use of amines, i.e., triethylamine as catalysts instead of ammonium hydroxide. The silica materials have been characterized with the help of SEM and FTIR Spectrometry. The N2 adsorption study was carried out with the help of the Quantachrome-Autosorb-1 and the NH3 adsorption with the Quantachrome-Autosorb-l-C. The amount of hydrogen adsorbed in the form of NH3 in the studied silica samples at: P=760 [Torr] (1.01325 x 10(5) [Pa]), was 2 [wt.%] and the amount of hydrogen stored in the form of NH3 at about: P=7500 [Torr] (10.0 x 10(5) [Pa]), in the studied stabilized silica samples was 11 wt.%, a magnitude higher than the goal figure of 6.5 [wt.%] established by the United States of America, Department of Energy.

Native and n-alkyl-bonded (n-octadecyl) monolithic silica rods with mesopores in the range between 10 and 25 nm and macropores in the range between 1.8 and 6.0 microm were examined by mercury intrusion/extrusion, inverse size exclusion chromatography (ISEC) and nitrogen sorption. Our results reveal very good agreement for the mesopore size distribution obtained from nitrogen adsorption (in combination with an advanced NLDFT analysis) and ISEC. Our studies highlight the importance of mercury porosimetry for the assessment of the macropore size distribution and show that mercury porosimetry is the only method which allows obtaining a combined and comprehensive structural characterization of macroporous/mesoporous silica monoliths. Our data clearly confirm that mercury porosimetry hysteresis and entrapment have different origin, and indicate the intrinsic nature of mercury porosimetry hysteresis in these silica monoliths. Within this context some silica monoliths show the remarkable result of no entrapment of mercury after extrusion from the mesopore system (i.e. for the first intrusion/extrusion cycle). The results of a systematic study of the mercury intrusion/extrusion behavior into native silica monoliths and monoliths with bonded n-alkyl groups reveals that the macro (through) pore structure, which controls the mass transfer to and from the mesopores, here mainly controls the entrapment behavior. Our data suggest that mercury intrusion/extrusion porosimetry does not only allow to obtain a comprehensive pore structure analysis, but can also serve as a tool to estimate the mass transport properties of silica monoliths to be employed in liquid-phase separation processes.

The pore hierarchy of a hierarchical porous SiO2 with 14 nm spherical mesopores and 3 nm worm-like pores (KLE1C16) is studied by small-angle neutron scattering (SANS) in combination with in-situ nitrogen sorption at 77 K. A novel setup is used developed at Hahn-Meitner Institute, Berlin. It is demonstrated that in these materials indeed all of the large mesopores are connected through the smaller ones, thus providing invaluable insights into the general phenomenon of pore connectivity in mesoporous materials.