Nuclear Magnetic Resonance Spectroscopy

Sanz, J.; Massiot, Dominique

doi:10.1016/b978-0-08-098259-5.00010-x

Cited by 9 publications

(4 citation statements)

References 98 publications

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“…Clays have been studied using a large variety of techniques, with differential scanning calorimetry (DSC), infrared spectroscopy (IR), X-ray scattering techniques (WAXS, SAXS), neutron scattering (QUENS), and NMR among the most important. Within the NMR technique, several choices are possible: high field spectroscopy such as MAS NMR spectroscopy 2 to study the chemical environment of protons and other nuclei as well as the dynamics of water at short time scales, 3,4 low field relaxometry to obtain the dynamic of water at long time scales 5 (microseconds and more), and 1 H and 2 H low field relaxation 6 to study accessibility and mobility.…”

Section: ■ Introductionmentioning

confidence: 99%

Water Orientation in Smectites Using NMR Nutation Experiments

Fleury¹,

Canet²

2014

J. Phys. Chem. C

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We observed the arrangement of water molecules when confined in the interlayer space of smectites using low field nutation experiments. Despite the presence of paramagnetic impurities that prevent such observation at high field, we can determine the amount of water in strong interaction with the clay surface, i.e., water molecules which are partially oriented within each platelet. The experiments do not require the orientation of the clay platelets relative to the magnetic field. We present the NMR theory, the signal processing, and the results on a series of 4 homoionic smectites (Na, Ca, Mg, and K) at different relative humidities in order to vary the water content and the basal spacing. In these systems, we found that between 0.5 and 2.5 water molecules per ion are oriented.

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Section: ■ Introductionmentioning

confidence: 99%

Water Orientation in Smectites Using NMR Nutation Experiments

Fleury¹,

Canet²

2014

J. Phys. Chem. C

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“…For instance, montmorillonite structure alteration was found to take place at a 6 M HCl concentration, as illustrated by progressive IR intensity decay for the OH bending (930-800 cm −1 ) and Al-O-Si (524 cm −1 ) vibrations [13]. 29 Si NMR analysis revealed that sepiolite and kaolinite acid attacks promote octahedral cation extraction resulting in layered porous silica [178]. In addition, pH decreases down to 2-3, i.e., close to the pH of zero-charge (pH ZC ) of the silicic fraction of bentonites is supposed to cause progressive to total suppression of the surface charge and reduce the retention capacity restricting adsorption to hydrophobic interaction [159].…”

Section: Constraints In Clay Materials Stability For Dairy Technologymentioning

confidence: 99%

Role of Clay Substrate Molecular Interactions in Some Dairy Technology Applications

Azzouz,

Arus,

Platon

2024

IJMS

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The use of clay materials in dairy technology requires a multidisciplinary approach that allows correlating clay efficiency in the targeted application to its interactions with milk components. For profitability reasons, natural clays and clay minerals can be used as low-cost and harmless food-compatible materials for improving key processes such as fermentation and coagulation. Under chemical stability conditions, clay materials can act as adsorbents, since anionic clay minerals such as hydrotalcite already showed effectiveness in the continuous removal of lactic acid via in situ anion exchange during fermentation and ex situ regeneration by ozone. Raw and modified bentonites and smectites have also been used as adsorbents in aflatoxin retention and as acidic species in milk acidification and coagulation. Aflatoxins and organophilic milk components, particularly non-charged caseins around their isoelectric points, are expected to display high affinity towards high silica regions on the clay surface. Here, clay interactions with milk components are key factors that govern adsorption and surface physicochemical processes. Knowledge about these interactions and changes in clay behavior according to the pH and chemical composition of the liquid media and, more importantly, clay chemical stability is an essential requirement for understanding process improvements in dairy technology, both upstream and downstream of milk production. The present paper provides a comprehensive review with deep analysis and synthesis of the main findings of studies in this area. This may be greatly useful for mastering milk processing efficiency and envisaging new prospects in dairy technology.

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“…Thus, Q 0 corresponds to monosilicates, Q 1 to disilicates and chain end groups, Q 2 to internal groups in chains, Q 3 to chain branching sites and Q 4 to the three-dimensional cross-linked framework. In the case of untreated sepiolite, whose structure is characterized by three crystallographically different Q 3 Si positions (edge, near-edge and center of the ribbon, Figure 1), the 29 Si MAS NMR spectrum consisted of three well-resolved resonances at −92.0, −94.5 and −98.0 ppm (Figure 10a), stemming from Si centers located in the near-edge, center and edge positions, respectively [54][55][56]. A weak resonance at −85.9 ppm was attributed to surface Q 2 silanol groups [53].…”

Section: Ftir Spectroscopymentioning

confidence: 99%

Influence of Dry Milling on Phase Transformation of Sepiolite upon Alkali Activation: Implications for Textural, Catalytic and Sorptive Properties

et al. 2020

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Activation of natural sepiolite by means of grinding in a planetary mill followed by wet NaOH activation was studied for the purpose of endowing the product with enhanced basicity for potential catalytic/sorptive applications. Synthesized solids were characterized with X-ray powder diffraction (XRD), N2 adsorption/desorption, scanning electron microscopy (SEM), energy dispersive (EDX), atomic absorption (AAS), Fourier-transform infrared (FTIR) and 29Si magic angle spinning nuclear magnetic resonance (MAS NMR) spectroscopies. Surface basicity was determined by titration with benzoic acid. Grinding changed the pathway of sepiolite phase transformation upon NaOH treatment. The as-received sepiolite evolved to Na-sepiolite (loughlinite) with a micropore system blocked by nanocrystalline Mg(OH)2, while ground samples yielded magnesium silicate hydrate phase (MSH), with well-developed microporous texture. In unmilled sepiolite desilication involved preferential leaching of Si from the center of the structural ribbons, while in ground samples additional loss of Si from ribbon-ribbon corner linkages was observed. In all cases treatment with NaOH led to enhancement of surface basicity. Synthesized materials were tested as catalysts in a base-catalyzed aldol self-condensation of acetone and oxidation of cyclohexanone to ε-caprolactone, as well as CO2 sorbents. Catalytic trends depended not only on samples’ basicity, but also on texture and phase composition of the catalysts. Grinding combined with alkali activation proved a simple and effective method for boosting CO2-sorption capacity of sepiolite to the level comparable to amine-functionalized, acid-activated sepiolite sorbents.

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Nuclear Magnetic Resonance Spectroscopy

Cited by 9 publications

References 98 publications

Water Orientation in Smectites Using NMR Nutation Experiments

Water Orientation in Smectites Using NMR Nutation Experiments

Role of Clay Substrate Molecular Interactions in Some Dairy Technology Applications

Influence of Dry Milling on Phase Transformation of Sepiolite upon Alkali Activation: Implications for Textural, Catalytic and Sorptive Properties

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