Complementarity of Density Functional Theory and Nuclear Magnetic Resonance Tools To Probe the Nano-Layered Silicates Surface Chemistry and Morphology

Abstract

By combining experimental spectroscopic, structural and physical characterizations, and extensive Density Functional Theory (DFT) simulations, unprecedented insight is gained on the local surface properties of synthetic talc nanoparticles, their structure, morphology and particle size distribution. Basically, the Nuclear Magnetic Resonance (NMR) chemical shifts profiles of these nano-layered silicates were dissected thoroughly and revealed the existence of bulk and surface contributions in the 1 H and 29 Si spectra. Beyond the fact that a significant knowledge has been acquired on the overall structure of the synthetic talc nanoparticles (mixture of defective and non-defective layers, with defects rejected on the external interfaces), the highlighting of these signals enabled to access the average morphologies and particle sizes of the samples by decomposing the 29 Si NMR profiles into Lorentzian contributions. Finally, the particle size distributions in number were also described in terms of a Log-normal law.These distributions were compared to the particle sizes obtained from X-ray Diffraction (XRD), Brunauer−Emmett−Teller measurements (BET) and Dynamic Light Scattering (DLS) methods.The distributions of gyration radii determined by DLS are shown to match the distributions in size in consistence with the same morphology.

Spectroscopic Expression of the External Surface Sites of H-ZSM-5

“…1 H magic-angle spinning nuclear magnetic resonance spectroscopy ( 1 H MAS NMR), although less frequently applied, also provides valuable structural insights on the OH groups. − Three main regions are usually observed in 1 H NMR spectra of dehydrated H-ZSM-5 zeolite: − bridging OH groups resonances are expected at around 4 ppm, isolated or hydrogen-bond acceptor silanols between 1.3 and 2.2 ppm, whereas Al–OH groups associated with extra-framework aluminum (EFAl) are assumed to give rise to an intermediate signal close to 2.6 ppm. Broad signals at 5–6 ppm are usually assigned to adsorbed water molecules.…”

Nanosized Layered TOT Magnesium Silicates: Equilibrium Morphologies and Surface Speciation, a Computational and Experimental Study

“…The Q 4 contribution in the range [−108, −112] ppm is another indication of the presence of amorphous silica together with the CO stretching at 2185 cm –1 in the FTIR spectra of adsorbed CO as discussed in the previous section. The contributions in the other ranges will be discussed in depth in a companion paper on nanotalc …”

“…The contributions in the other ranges will be discussed in depth in a companion paper on nanotalc. 24 25 Mg shifts are compared in Figure 12 to the already published 25 Mg WURST-QCPMG NMR spectrum of MSH com, which shows only one peak. 6 The line-shape simulation with the Czjzek model gives an isotropic chemical shift, δ iso = 26 ppm, and a quadrupolar coupling constant, CQ = 3.5 MHz, in good agreement with Nied et al 1 The DFT prediction, average (24 ppm), and range of predicted values (17.3−31 ppm) merge all contributions at this scale but correspond well to the experimental peaks.…”

“…Our prediction of equilibrium morphology could not be directly verified from SEM and TEM images of MSH. It is however tested in more details together with the associated surface speciation through a multitechnique analysis of synthetic nanotalc samples covering a range of sizes and reported in a companion paper . On the basis of DFT models, the origin of some features in NMR spectra is interpreted in this paper in terms of structural defects in synthetic nanotalc.…”

In situ preparation of compounds using silanized mPEG inspired by talc-like structures

“…The low amount of Q 3 and the absence of the Q 4 type site suggested a highly defective structure. 25 Moreover, the presence of one resonance at −85 ppm could suggest that small particles with an important number of edge surface sites and/or incomplete condensation were formed. Furthermore, the signal at −78 ppm clearly suggested incomplete condensation of the structure.…”