V.V. Turov

Nuclear magnetic resonance studies of interfacial phenomena

Unmodified and Modified Silicas Interfacial Phenomena at a Surface of Nanosilica Silica gels, Aerogels, Silochrome, and Poly(methylsiloxane): Structural, Interfacial and Adsorption Characteristics, and Structure-Property Relationships Interfacial Phenomena at Surfaces of Structurally Ordered Silicas Thin Films and Other Moieties on Silica Supports Interfacial Phenomena at Surfaces of Mixed Oxides Mixed Nanooxides Porous Oxides as a Function of Morphology Structurally Ordered Oxides Nanocrystalline and Microcrystalline Materials Clays, Zeolites, and Other Natural Minerals Interfacial Phenomena at Surfaces of Carbon Materials Texture of Carbonaceous Materials and Chemical Shift of Adsorbed Molecules Activated Carbons Graphitized Carbons and Graphite Carbon Nanotubes Interfacial Phenomena at Carbon-Mineral Composites Carbon Blacks Carbonized Silicas and Mixed Oxides Interfacial Phenomena at Polymer Surfaces Natural Polymers: Cellulose, Starch, Chitosan, Hyaluronic Acid, and Others Synthetic Polymers Hydrogels and Cryogels Polymer-Nanooxide Systems Polymers in Confined Space of Pores Interactions of Biomacromolecules with Water, Organic Compounds, and Oxides, Polymers, and Carbon Adsorbents Proteins Proteins in Adsorbed State DNA Lipids Water Associated with Bio-Objects: Cells and Tissues Yeast Saccharomyces cerevisiae Cells Intracellular Water in Partially Dehydrated Bone Marrow Cells Freeze-Dried Bovine Gametes with Organic Additives Red Blood Cells Bone Tissue Muscular Tissues Intracellular Water and Cryopreservation Interaction of Seeds, Herbs, and Related Materials with Water and Nanooxides Recurring Trends in Adsorption, Spectroscopy, and Other Interfacial Experiments Methods Low-Temperature 1H NMR Spectroscopy Low-Temperature Nitrogen Adsorption Adsorption of Water and Organics Polymer and Protein Adsorption Infrared Spectroscopy Thermogravimetry Differential Scanning Calorimetry Auger Electron Spectroscopy Temperature-Programmed Desorption with Mass-Spectrometry Control Thermally Stimulated Depolarization Current Dielectric Relaxation Spectroscopy Ultraviolet-Visible Spectroscopy Rheometry Potentiometric Titration Photon Correlation Spectroscopy Adsorption of Metal Ions X-Ray Diffraction Raman Spectroscopy AFM, SEM, and TEM Quantum Chemistry Conclusions

Features of fumed silica coverage with silanes having three or two groups reacting with the surface

Abstract Fumed silicas modified by 3-methacryloyloxypropyltrimethoxysilane (MAPTMS), methacryloyloxymethylenemethyl diethoxysilane (MMDES), and 3-aminopropyltriethoxysilane (APTES) were studied by means of TPD-DTG, IR, 1 H NMR, electrophoresis, photon correlation spectroscopy, and theoretical methods. The modification of fumed silica by these silanes strongly changes the ζ (pH) potential and the particle size distribution in aqueous suspensions depending on the amounts and the structure of a modifier. MMDES gives the better results in comparison with its mixture with APTES or individual MAPTMS in order to reduce the particle (agglomerate) size of modified silica at the modifier concentrations over the 0.05–0.2 mmol/g range. Grafted silanes reduce the hydrophilic properties of silica depending on the pretreatment conditions. Bound MMDES diminishes the ζ potential in contrast to MAPTMS, which markedly magnifies negative ζ potential at pH>5 due to large amounts of residual SiOR groups hydrolysed in the suspensions.

Porous structure and water state in cross-linked polymer and protein cryo-hydrogels

The porous structure and the state of the water are two main factors which define the vast applications of hydrogels in the life science arena. The structural characterisation and water state in hydrogels produced by the cryogelation of poly(hydroxyethyl methacrylate) and gelatine were undertaken using different techniques. Images obtained using confocal laser scanning and multiphoton microscopies were analysed using ImageJ/Fiji software to estimate the total porosity, specific surface area and pore size and wall thickness distribution functions of each of the hydrogels. The hydration properties and structural characteristics of the nanopore component of the polymer and protein hydrogels were analysed using DSC, 1H NMR spectroscopy and cryoporometry and modelled using the PM6 quantum chemical method. The hydrogels produced by cryogelation were shown to have a large macropore volume, high pore interconnectivity and small specific surface area. The main portion of water was shown to be attributable to bulk water located within macropores. The relative amounts of bound water in the hydrogels were demonstrated to be small (<10 wt% of bulk water) making macroporous hydrogels an attractive system for biological applications. An understanding of the parameters studied here is important for the future engineering of cryogels for biological applications.

Behaviour of pure water and water mixture with benzene or chloroform adsorbed onto ordered mesoporous silicas

Structural characteristics of synthesized ordered mesoporous silicas MCM-41, MCM-48 and SBA-15 were studied using XRD, nitrogen adsorption and FTIR methods. Pure water and mixtures with water/benzene and water/chloroform-d adsorbed onto silicas were studied by 1H NMR spectroscopy with layer-by-layer freezing-out of bulk and interfacial liquids. Concentrated aqueous suspensions of MCM-48 and SBA-15 were studied by thermally stimulated depolarization current (TSDC) method. Benzene and chloroform-d can displace a portion of water to broad pores from the pore walls and from narrower pores, especially in the case of a large excess of an organic solvent. This process is accompanied by diminution of both interaction energy of water with an adsorbent surface and freezing temperature depression of adsorbed water. The effect of nonpolar benzene on pore water is much stronger than that of weakly polar chloroform-d. Modifications of the Gibbs-Thomson relation to describe the freezing point depression of mixtures of immiscible liquids confined in pores allow us to determine distribution functions of sizes of structures with unfrozen pore water and benzene.

Adsorption layers of water on the surface of hydrophilic, hydrophobic and mixed silicas

Abstract The 1 H NMR technique was used to study the hydration activity of hydrophilic (Aerosil A-300), methylated (MS) and mixed in a 5:1 ratio (MIX) silicas. It has been determined that the thickness of a layer of adsorbed water in an aqueous medium becomes higher for MS compared with that for A-300. The above phenomenon may be explained by polarization of the adsorbent particles. Hydrophobic and hydrophilic particles in the MIX sample are bound together by the strong electrostatic interactions. 1 H NMR spectra of adsorbed water are characterized by the appearance of a new signal having an anomalously low value of chemical shift (δ = 1 ppm), which may be caused by water molecules forming the surface-hydrated complex carrying a negative charge. The appropriate values of the free surface energy of adsorbents have been calculated.

Structural, textural and adsorption characteristics of nanosilica mechanochemically activated in different media

The structural, textural, and adsorption characteristics of mechanochemically activated (MCA) fumed silica A-300 as dry or water, ethanol, or water/ethanol-wetted powders (0.5 g of a solvent per gram of silica) in a ball mill for 1-6 h were studied in comparison with those of the initial powder. The MCA treatment enhances bulk density (ρ(b)) of the powder (from 0.045 g/cm(3) for the initial silica to 0.4 g/cm(3) for 6 h-MCA-treated water-wetted silica) depending on medium type and MCA time (t(MCA)). Stronger effects are observed for the MCA treatment of water-wetted silica than of dry or ethanol- or water/ethanol-wetted samples. The MCA treatment weakly affects the specific surface area (S(BET)). However, void (pore) size distribution, porosity, particle aggregation and size distribution in aqueous suspension, behavior of interfacial water, properties of poly(vinyl alcohol)/silica composites and adsorption of gelatin depend more strongly on the t(MCA) and ρ(b) values. Some of the observed changes in the characteristics (e.g., gelatin adsorption) depend on the ρ(b) value but are independent of the medium type used on the MCA. Other characteristics are nonlinear functions of both t(MCA) and ρ(b) values.

Adsorption of polar and nonpolar compounds onto complex nanooxides with silica, alumina, and titania.

Adsorption of low-molecular adsorbates (nonpolar hexane, nitrogen, weakly polar acetonitrile, and polar diethylamine, triethylamine, and water) onto individual (silica, alumina, titania), binary (silica/alumina (SA), silica/titania (ST)), and ternary (alumina/silica/titania, AST) fumed oxides was studied to analyse the effects of morphology and surface composition of the materials. Certain aspects of the interfacial phenomena dependent on the structural characteristics of oxides were analysed using calorimetry, (1)H NMR, and Raman spectroscopies, XRD, and ab initio quantum-chemical calculations. The specific surface area S(BET,X)-to-S(BET,N(2)) ratio (X is an organic adsorbate) changes from 0.68 for hexane adsorbed onto amorphous SA8 (degassed at 200 degrees C) to 1.85 for acetonitrile adsorbed onto crystalline alumina (degassed at 900 degrees C). These changes are relatively large because of variations in orientation, lateral interactions, and adsorption compressing of molecules adsorbed onto oxide surfaces. Larger S(BET,X)/S(BET,N(2)) values are observed for mixed oxides with higher crystallinity of titania or/and alumina phases in larger primary nanoparticles with greater surface roughness and hydrophilicity. Polar adsorbates can change the structure of aggregates of oxide nanoparticles that can, in turn, affect the results of adsorption measurements.

Structural and adsorption characteristics and catalytic activity of titania and titania-containing nanomaterials.

Morphological, structural, adsorption, and catalytic properties of highly disperse titania prepared using sulfate and pyrogenic methods, and fumed titania-containing mixed oxides, were studied using XRD, TG/DTA, nitrogen adsorption, (1)H NMR, FTIR, microcalorimetry on immersion of oxides in water and decane, thermally stimulated depolarization current (TSDC) and catalytic photodecomposition of methylene blue (MB). Phase composition and aggregation characteristics of nanoparticles (pore size distribution) of sulfate and pyrogenically prepared titania are very different; temperature dependent structural properties are thus very different. Catalytic activity for the photodecomposition of MB is greatest (per gram of TiO(2) for the pure oxide materials) for non-treated ultrafine titania PC-500, which has the largest S(BET) value and smallest particle size of the materials studied. However, this activity calculated per m(2) is higher for PC-105, possessing a much smaller S(BET) value than PC-500. The activity per unit surface area of titania is greatest for the fumed silica-titania mixed oxide ST20. Calcination of PC-500 at 650 degrees C leads to enhancement of anatase content and catalytic activity, but heating at 800 and 900 degrees C lowers the anatase content (since rutile appears) and diminishes catalytic activity, as well as the specific surface area because of nanoparticle sintering.

Interfacial Behavior of n-Decane Bound to Weakly Hydrated Silica Gel and Nanosilica over a Broad Temperature Range

The interfacial and temperature behavior of n-decane bound to weakly hydrated nanosilica A-400 (initial, heated, or compacted) or silica gel Si-60 was studied using low-temperature (1)H NMR spectroscopy applied to static samples that allowed us to observe signals only of mobile decane and unfrozen water molecules. For deeper insight into the phenomena studied, interactions of n-decane, 1-decanol, and water with a set of nanosilicas and silica gels were analyzed using DSC and thermoporometry. Both NMR and DSC results demonstrated that during heating of frozen samples at a heating rate of 5 K/min a portion of decane or decanol remained frozen at temperature higher than the freezing point of bulk liquid (Tf). For decane and decanol adsorbed onto silica gels Si-40, Si-60, and Si-100, the number, position, and intensity of freezing and melting peaks observed in the DSC thermograms over the 170-300 K range during cooling and heating of samples depended on the pore size distribution of silicas as well as on the amounts and type of adsorbates. The position of the main freezing peak of decane for all samples was close to Tf because the alkane amount was greater than the pore volume; i.e., a fraction of decane was bulk liquid. According to (1)H NMR data, a portion of decane, which was in a quasi-crystalline solid state characterized by fast molecular exchange (i.e., short transverse relaxation time) and not observed in the spectra, was greater than a portion of decane frozen at temperatures close to Tf during cooling that appears in the DSC endotherms of heated samples.

Structural features of polymer adsorbent LiChrolut EN and interfacial behavior of water and water/organic mixtures

The structural and adsorption characteristics of polymer adsorbent LiChrolut EN and the behavior of adsorbed water and water/organic mixtures were studied using adsorption, microcalorimetry, transmission and scanning electron microscopy, mass spectrometry, infrared spectroscopy, 1H NMR spectroscopy with layer-by-layer freezing-out of liquids (190-273 K), and thermally stimulated depolarization current method (90-265 K). This adsorbent is characterized by large specific surface area (approximately 1500 m2/g) and pore volume (0.83 cm3/g) with a major contribution of narrow pores (R<10 nm) of a complicated shape (long hysteresis loop is in nitrogen adsorption-desorption isotherm). The adsorbent includes aromatic and aliphatic structures and oxygen-containing functionalities and can effectively adsorb organics and water/organic mixtures. On co-adsorption of water and organics (dimethyl sulfoxide, chloroform, methane), there is a weak influence of one on another adsorbate due to their poor mixing in pores. Weakly polar chloroform displaces a fraction of water from narrow pores. These effects can explain high efficiency of the adsorbent in solid-phase extraction of organics from aqueous solutions. The influence of structural features of several carbon and polymer adsorbents on adsorbed nitrogen, water and water/organics is compared on the basis of the adsorption and 1H NMR data.