The synthetic conditions of highly ordered and thermally stable mesoporous molecular sieves from a layered silicate kanemite are established. We divided the formation process of the mesoporous materials from kanemite into two elemental processes: i) exchange of Na+ in the interlayer of kanemite for alkyltrimethylammonium cations and ii) condensation of silicates and formation of a three dimensional silicate framework. Higher pH (over 11.5) at the cation-exchange process and the subsequent pH adjustment at 8.5 at the condensation process were best suited for the formation of mesoporous products with high regularity and thermal stability. Removal of partially dissolved kanemite during the cation-exchange process avoided the formation of amorphous materials as a by-product. Structures of some intermediate silicate/surfactant complexes supported the proposed folded sheets mechanism for the formation of the mesoporous molecular sieves. Syntheses by using alkyltrimethylammonium with different alkyl-chain lengths are also reported.
A formation mechanism for monodispersed mesoporous silica spheres was investigated from the viewpoint of both particle growth and the progress of the condensation of the silica precursor. The particle growth of monodispersed mesoporous silica spheres was studied by TEM observation. The development of the mesopores was examined by in situ X-ray diffraction measurements. The condensation reaction of the silica precursor was analyzed by silicic acid titration and pH-conductivity measurements during the synthesis. It was found that small particles emerged suddenly after the commencement of the synthesis, and then the residual silica precursors reacted preferentially with the surface silanols on these existing particles. This led to the formation of monodispersed mesoporous silica spheres. Conversely, new small particles emerge throughout the synthesis in the case of a heterogeneous system. To confirm the preferential reaction of the silica precursors with the surface silanols, expansion of the existing particles was carried out by adding more silica precursor after the completion of the synthesis. It was found that the sizes of the particles were enlarged by the successive addition of more of the silica precursor. Surprisingly, the radial alignment of the hexagonal mesopores was still retained in the expanded particles. In addition, by the addition of a different silica precursor to the initial one, highly monodispersed core/shell mesoporous silica spheres possessing a hydrophilic core and a hydrophobic shell were successfully obtained for the first time.
Highly crystalline Ni-doped β-FeOOH(Cl) nanorod catalysts for efficient electrochemical water oxidation were successfully synthesized by a one-pot ambient temperature synthesis.
Mesoporous manganese oxide was prepared by using a straightforward, template-assisted method. The resulting material was crystalline and of uniform pore diameter. The material was characterized by HR-TEM, HR-SEM, XRD, XPS, and EXAF-XANES, and pore size distributions were calculated from nitrogen sorption studies. These materials with very high surface area of 316 m 2 /g have a novel hierarchical structure with spherical particles (<1 µm size), which are composed of γ-manganese oxide nanofibrous aggregates with intraparticle mesoporosity. The materials show an exceptionally high ability to eliminate volatile organic compounds (VOCs) at room temperature and the ability increases with increasing temperature. The results indicate that these materials are very promising for applications to emission control and to indoor air purification, as sorbents and catalysts. The materials show very high performance in room temperature removal of NO x and SO 2 even at low concentrations. The VOCs removal ability was further enhanced after Au deposition by a vacuum-assisted laser ablation (VALA) method. Detailed characterization reveals the role of lattice defects, strong metal-support and adsorbate-adsorbent interactions, along with readily available lattice oxygen for the elimination of VOCs.
Mono-dispersed mesoporous silica spheres with ordered hexagonal regularity were synthesized from tetramethoxysilane and dodecyltrimethylammonium bromide as a surfactant under very specific conditions. By adjusting the optimum concentrations of the reactants, silica particles with diverse morphology were obtained at higher initial concentrations. Dilution of the reactants led to the formation of silica spheres with various sizes and relatively less mesoporous regularity. Mono-dispersed silica spheres could not be obtained when hexadecyltrimethylammonium bromide and tetradecyltrimethylammonium bromide were used as surfactants.
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