TEM samples were prepared by dropping 10 lL of diluted solution in toluene onto 400-mesh carbon-coated copper grids by Finnpipette and slowly evaporating the solvent in air at room temperature. Many of these investigations have utilized ordered mesoporous silicas such as MCM-41 or SBA-15 as the inorganic component. These materials are in some regards ideally suited for this task, as they present the materials chemist with a highly ordered porous inorganic matrix, wherein well-developed silane chemistries can be exploited to build organic functionalities off the silica surface. In this vein there have been many investigations of the incorporation of organic functional groups into mesoporous silicas including the direct synthesis of hybrid materials, post-synthetic grafting, covalent versus non-covalent linkage, etc. [2,3,5] In general, a common theme of these investigations is that the organic moiety tethered to the surface is chemically ªsimpleº, often a single functional group. For hybrid materials to achieve their full potential the ability to synthesize complex/multifunctional organic moieties directly on the mesoporous substrate would be highly desirable.In the current report we describe the stepwise synthesis of a series of melamine-based dendrimers of various generations that are grown directly off the mesopore surface. While a few works have studied dendrimer±mesoporous silica hybrids formed via dendrimer physisorption, [6,7] and many works have studied the growth of dendrimers on nonporous silicas, [8±10] this is the first example we know of where complex organic macromolecules derived from multistep organic syntheses (e.g., six sequential reactions for the G3 (third-generation) dendrimer) have been grown using ordered mesoporous silica as a solid-phase support. As such we believe this work has important implications for organic±inorganic hybrid materials,
The synthesis of silica, silver bromide, and composite nanospheres made in the presence of block copolypeptide vesicles is reported. Hollow silica nanospheres of controllable size can be made with Lys:Phe 1:1 block copolypeptides, whereas at higher block ratios, uniform silica nanospheres are formed that are not hollow. Silver bromide nanospheres of controllable size in the range of 25−250 nm can also be formed, as well as silver bromide/silica core−shell particles. The silver bromide nanospheres can also be assembled into hollow rods in the presence of rhodamine 6G, and this process is reversible. The unique feature of this work is the ability to translate the information of an individual biomimetic supramolecular structure (e.g., vesicle) as a template into an inorganic material. The results show that block copolypeptides offer unique opportunities for assembling nanostructured materials.
A new porous material containing both micropores and mesopores has been synthesized by the self-assembly of silicalite-1 colloidal precursors at low temperatures and thoroughly investigated by diffraction, electron microscopy, porosimetry, and spectroscopy. Our "bottomup" approach yields mesoporous materials that contain a microporosity different from that of SBA-15. For the samples where the silicalite-1 mixture is aged at room temperature, we do not have conclusive evidence that silicalite-1 is responsible for the microporosity in our samples, as all analytical techniques are inconclusive. By contrast, samples where the silicalite-1 mixture is heated until Bragg reflections are observed appear by TEM to be heterogeneous materials containing both mesopores and domains of silicalite-1. Nitrogen and argon adsorption show that both the micropore size distribution and the total micropore volume of our samples are different from those of SBA-15. The conclusions from this study are fourfold: (1) we have created a material containing both micropores and mesopores that is very well ordered on the mesoscale, (2) our material has a larger micropore volume and different micropore size distribution than SBA-15 made under the same conditions, (3) we have achieved this high degree of structural ordering and uniformity without the need for high-temperature syntheses, and (4) it does not appear possible to use larger (∼50 nm) nanoparticles of silicalite-1 to fabricate homogeneous materials. The ability to synthesize these materials at low temperatures makes them (and the synthetic concept) ideal for extension into areas such as thin-film syntheses.
The low-temperature (368 K) synthesis of silicalite-1 nanocrystals in anionic microemulsions is reported. In the presence of AOT/isooctane mixtures silicalite-1 nanocrystals can be formed that are coffin-shaped and approximately 100 x 40 x 200 nm in size. This is in contrast to samples made without the microemulsion under the same conditions where irregular spherical particles approximately 100 nm in diameter are formed. The current work shows that, in contrast to previous work in this area, the anionic microemulsions cannot stabilize colloidal silica due to the strong repulsive electrostatic forces between the anionic silicate species and the surfactant headgroup. The crystal morphology of the silicalite-1 obtained is also shown to be sensitive to the surfactant identity as syntheses using SDS/heptane/butanol mixtures lead to different morphologies. It is also possible to uncouple zeolite nucleation from growth in these systems. This was demonstrated by adding a solution containing 25 nm silicalite-1 nanocrystals to the AOT/isooctane mixture, which leads to large micron-sized spheres of silicalite-1 containing large mesopores. This report demonstrates that anionic microemulsions lead to fundamentally different crystal habits than the nonionic or cationic microemulsions investigated previously. The future outlook for the use of microemulsion-mediated zeolite growth is also discussed.
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