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Query: UMLS:C0042571 (
vertigo
)
7,148
document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)
29Si solid-state NMR allows us to distinguish silicon atoms involved in siloxane bridges (Q4), single silanol (Q3) and geminal silanol groups (Q2) on the surface of silica. The relative proportions of each species can be obtained by Magic Angle
Spinning
(MAS) associated with 1H-->29Si crosspolarization (CP/MAS). This preliminary study deals with the silicon functionality of
MCM
-41, a purely siliceous, amorphous and mesoporous silica. From the 29Si spectra the relative proportions are estimated to be 3.7% Q2 27.3% Q3 and 69.0% Q4, while the ratio Q2/Q2 + Q3) is 0.12. These results are found to be in perfect agreement with a binomial probability distribution of sites.
...
PMID:High-resolution 29Si solid-state NMR study of silicon functionality distribution on the surface of silicas. 897 Jan 8
In this paper, the
MCM
-41 has been modified by impregnation with zeolite A to prepare a kind of new adsorbent. The adsorption of TC from aqueous solutions onto modified
MCM
-41 has been studied. It was discovered that the adsorption capability of zeolite A modified
MCM
-41 (A-MCM-41) increased dramatically after modification. The modified
MCM
-41 was characterized by X-ray diffraction (XRD), nitrogen adsorption-desorption, Fourier Transform Infrared (FTIR) analysis, Transmission electron microscopy (TEM) images, and
29
Si and
27
Al Magic Angle
Spinning
Nuclear Magnetic Resonance (MAS NMR) spectra. The modified
MCM
-41 structure was still retained after impregnated with zeolite A but the surface area and pore diameter decreased due to pore blockage. The adsorption of TC on modified
MCM
-41 was discussed regarding various parameters such as pH, initial TC concentration, and the reaction time. The pH effects on TC adsorption indicated that the adsorbents had better adsorption performances in acidic and neutral conditions. The adsorption isotherms were fitted well by the Langmuir model. The adsorption kinetics was well described by both pseudo-second order equation and the intra-particle diffusion model. The adsorption behavior in a fixed-bed column system followed Thomas model. The adsorption behavior of TC was the chemical adsorption with an ion exchange process and electrostatic adsorption.
...
PMID:MCM-41 impregnated with A zeolite precursor: Synthesis, characterization and tetracycline antibiotics removal from aqueous solution. 2497 87
Mesoporous silica encapsulated Pt (Pt@mSiO
2
) and PtSn (PtSn@mSiO
2
) nanoparticles (NPs) are representatives of a novel class of heterogeneous catalysts with uniform particle size, enhanced catalytic properties, and superior thermal stability. In the ship-in-a-bottle synthesis, PtSn@mSiO
2
intermetallic NPs are derived from Pt@mSiO
2
seeds where the mSiO
2
shell is formed by polymerization of tetraethyl orthosilicate around a tetradecyltrimethylammonium bromide template, a surfactant used to template
MCM
-41. Incorporation of Sn into the Pt@mSiO
2
seeds is accommodated by chemical etching of the mSiO
2
shell. The effect of this etching on the atomic-scale structure of the mSiO
2
has not been previously examined, nor has the extent of the structural similarity to
MCM
-41. Here, the quaternary Q
2
, Q
3
and Q
4
sites corresponding to formulas Si(O
1/2
)
2
(OH)
2
, Si(O
1/2
)
3
(OH)
1
and Si(O
1/2
)
4
, in
MCM
-41 and the mesoporous silica of Pt@mSiO
2
and PtSn@mSiO
2
NPs were identified and quantified by conventional and dynamic nuclear polarization enhanced Si-29 Magic Angle
Spinning
Nuclear Magnetic Resonance (DNP MAS NMR). The connectivity of the -Si-O-Si
-
network was revealed by DNP enhanced two-dimensional
29
Si-
29
Si correlation spectroscopy.
...
PMID:Atomic-Scale Structure of Mesoporous Silica-Encapsulated Pt and PtSn Nanoparticles Revealed by Dynamic Nuclear Polarization- Enhanced 29Si MAS NMR Spectroscopy. 3118 24
