A comprehensive study was conducted on mesoporous MCM-41.
Spectroscopic examinations demonstrated
that three types of silanol groups, i.e., single,
(SiO)3Si−OH, hydrogen-bonded,
(SiO)3Si−OH-OH−Si(SiO)3,
and geminal, (SiO)2Si(OH)2, can be
observed. The number of silanol groups/nm2,
αOH, as determined by
NMR, varies between 2.5 and 3.0 depending on the template-removal
methods. All these silanol groups
were found to be the active sites for adsorption of pyridine with
desorption energies of 91.4 and 52.2 kJ
mol-1, respectively. However, only free
silanol groups (involving single and geminal silanols) are
highly
accessible to the silylating agent, chlorotrimethylsilane.
Silylation can modify both the physical and chemical
properties of MCM-41.
The discovery of mesoporous molecular sieves, MCM-41, which possesses a regular hexagonal array of uniform pore openings, aroused a worldwide resurgence in this field. This is not only because it has brought about a series of novel mesoporous materials with various compositions which may find applications in catalysis, adsorption, and guest-host chemistry, but also it has opened a new avenue for creating zeotype materials. This paper presents a comprehensive overview of recent advances in the field of MCM-41. Beginning with the chemistry of surfactant/ silicate solutions, progresses made in design and synthesis, characterization, and physicochemical property evaluation of MCM-41 are enumerated. Proposed formation mechanisms are presented, discussed, and identified. Potential applications are reviewed and projected. More than 100 references are cited. 2079
We demonstrated a facile route for one-pot synthesis of visible light responsive nitrogen doped anatase TiO(2) sheets with dominant {001} facets from TiN. The synthesized anatase TiO(2) sheets show a strong and stable capability of generating photocatalysis active species of *OH radicals and hydrogen evolution from splitting water under visible light irradiation.
The authors of this Communication wish to cite additional papers relevant to their work. Reports by Fornasiero et al. [23a] and Sun et al., [23c] both dealing with B,N-codoped TiO 2 , were inadvertently omitted from the references cited in this Communication. In those reports, nitrogen doping was realized not by thermal treatment route in the presence of an ammonia atmosphere, but by a wet-chemistry route, and no B À N bond was formed. The complete reference [23] is given below. [23] a)
Constructing photocatalytically favorable surface structure in synthesizing photocatalysts plays an important role in enhancing the photocatalytic activity of semiconductor photocatalysts. In this report, oxygen-deficient anatase TiO2 sheets with dominant {001} facets were synthesized via a facile one-pot hydrothermal route with solid metallic titanium diboride as precursor. In contrast to anatase TiO2 sheets with dominant {001} facets free of oxygen deficiency and surface fluorine, anatase TiO2 sheets with oxygen deficiency and surface fluorine are subject to obvious surface reconstruction as evidenced by two new Raman-active modes at 155 and 171 cm−1 and the weakened B1g mode at 397 cm−1. Further analysis based on X-ray photoelectron spectroscopy (XPS) spectra of Pt 4f and F 1s provided a clear evidence for the greatly strengthened interaction between Pt-loaded and TiO2 matrix as a result of a special electron-transfer process on the reconstructed surface structure of TiO2 with both oxygen deficiency and fluorine. Importantly, the reconstructed surface structure as well as the strengthened interaction between Pt-loaded and TiO2 matrix can substantially enhance the hydrogen evolution rate from photocatalytic water splitting reactions.
A yolk-shell structure with a distinctive core@void@shell configuration is synthesized using a facile vesicle template strategy. S. Z. Qiao, G. Q. Lu, and co-workers describe in their Communication on page 4981 ff. how the size of both core and shell are tunable. In addition, loading these mesoporous materials with gold nanocatalysts and their drug-release capability were investigated.
Seriously aggregated LDH agglomerates can be dispersed by a hydrothermal treatment into homogeneous stable suspensions that contain LDH particles in the range of 50-300 nm.
A nitrogen-doped porous carbon monolith was synthesized as a pseudo-capacitive electrode for use in alkaline supercapacitors. Ammonia-assisted carbonization was used to dope the surface with nitrogen heteroatoms in a way that replaced carbon atoms but kept the oxygen content constant. Ammonia treatment expanded the micropore size-distributions and increased the specific surface area from 383 m(2) g(-1) to 679 m(2) g(-1). The nitrogen-containing porous carbon material showed a higher capacitance (246 F g(-1)) in comparison with the nitrogen-free one (186 F g(-1)). Ex situ electrochemical spectroscopy was used to investigate the evolution of the nitrogen-containing functional groups on the surface of the N-doped carbon electrodes in a three-electrode cell. In addition, first-principles calculations were explored regarding the electronic structures of different nitrogen groups to determine their relative redox potentials. We proposed possible redox reaction pathways based on the calculated redox affinity of different groups and surface analysis, which involved the reversible attachment/detachment of hydroxy groups between pyridone and pyridine. The oxidation of nitrogen atoms in pyridine was also suggested as a possible reaction pathway.
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