Ordered carbon molecular sieves exhibiting Bragg diffraction of X-ray lines have been synthesized for the
first time, using mesoporous silica molecular sieves as the template. Sucrose was converted to carbon inside
the mesopores of the silica molecular sieves through a mild carbonization process using a sulfuric acid catalyst.
The carbon molecular sieves were obtained after the removal of the silica framework using an aqueous solution
of sodium hydroxide. The X-ray diffraction, transmission electron microscopy, and pore size analysis showed
that the structure of the carbon molecular sieves consisted of a three-dimensional regular array of uniform
mesopores 3 nm in diameter. The structure was not simply a negative replica of the used silica template, but
the synthesis mechanism involved the unique transformation into a new ordered array that was triggered by
the removal of the silica frameworks. The highly ordered mesoporous texture suggested its scientific and
technological importance as a new shape-selective catalyst, adsorbent, sensor, and electrode material.
A disordered mesoporous silica material has been prepared using
polymerization of silicate anions surrounding
surfactant micelles in the presence of organic salts. The local
structure of the material has been investigated
using a transmission electron micrograph image of platinum wire grown
inside the mesopores. This micrograph
imaging technique, developed in the present work, clarifies that the
pore structure is a three-dimensional,
disordered network of short wormlike channels while the channel widths
are uniform. The fully disordered
channel branching similar to a three-dimensional fractal with
truly uniform channel widths distinguishes the
present material with respect to the recently found ordered mesoporous
molecular sieve MCM-41. The
branching channel structure has a remarkable advantage for adsorption
and catalytic applications, compared
with the MCM-41. The structure also exhibits outstanding
hydrothermal stability. The recognition of the
disordered, branching structure with uniform channel widths is expected
to open a new class of noncrystalline
molecular sieves, and the unique structures with good stability will
provide new opportunities for rational
design of heterogeneous catalysts, adsorbents, and other related
materials.
The synthesis and precise structural characterization of highly ordered three-dimensional close-packed cage-type mesoporous silica is reported. The siliceous mesoporous material is proven to be commensurate with
the face-centered-cubic Fm3m symmetry in high purity by a combination of experimental and simulated
powder X-ray diffraction (XRD) and transmission electron microscopy (TEM) analyses. The cage-type calcined
samples were additionally characterized by nitrogen physisorption. The aqueous synthesis method to prepare
large cage mesoporous silica with cubic Fm3m structure is based on the use of EO106PO70EO106 triblock
copolymer (F127) at low HCl concentrations, with no additional salts or organic additives. Here, emphasis is
put on the low HCl concentration regime, allowing the facile thermodynamic control of the silica−triblock
copolymer mesophase self-assembly. Further, simple application of hydrothermal treatments at various
temperatures ranging from 45 to 150 °C enables the tailoring of the mesopore diameters and apertures. The
combination of experimental and simulated XRD patterns and TEM images is confirmed to be a very powerful
means for the accurate elucidation of the structure of new mesoporous materials.
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