Interfacial behavior of polar and nonpolar frozen/unfrozen liquids interacting with hydrophilic and hydrophobic nanosilicas alone and in blends.

HYPOTHESIS: Various nanosilica characteristics depend on hydrophobization strongly affecting interfacial phenomena. Is it possible to prepare hydrophilic samples with hydrophobic silica (AM1) alone and in blends with hydrophilic one (A-300)? It can be done with addition of a small amount of water to the powders which then are mechanically treated. EXPERIMENTS: Nanosilicas were characterized using adsorption, desorption, microscopic, spectroscopic, and quantum chemistry methods. 1H NMR spectroscopy and cryoporometry were applied to AM1 and AM1/A-300 blends wetted and mechanically treated. Wetted blends were studied with additions of n-decane and chloroform-d. FINDINGS: The powders wetted at h = 0.3-3.0 g of water per gram of dry solids have increased bulk density. Samples are in gel-like state at h = 4-5 g/g. Water interaction energy with nanoparticles nonmonotonically depends on h (maximal at h = 3 g/g). Upon mechanical treatment of wetted blends (h < 1.5 g/g), separated AM1 structures are absent. At greater h values, blend reorganization occurs to form AM1 aggregates covered by A-300 shells. Organics can displace water from mesovoids toward narrower pores inaccessible for larger molecules or into larger voids to reduce the contact area between immiscible liquids. Freezing point depression caused by confined space and dissolution effects is affected by the blend organization.

Zeta Potential of Beta Zeolites: Influence of Structure, Acidity, pH, Temperature and Concentration.

Measurements of the zeta potential of solid heterogeneous supports are important for preparation of metal supported catalysts and for shaping zeolites into extrudates. In the current work, different types of heterogeneous support materials such as SiO2, Al2O3, and a range of beta zeolites of different silica- to-alumina ratio were analysed. It was observed that parameters such as temperature, pH and acidity significantly affect the zeta potential. In several instances, depending on the materials' acidity and microstructure, maxima in zeta potential were observed. The solid materials were thoroughly characterized using XRD, SEM, EDX, TEM, nitrogen physisorption, Al-NMR and FTIR with pyridine before zeta potential measurements.

Nanooxide/Polymer Composites with Silica@PDMS and Ceria-Zirconia-Silica@PDMS: Textural, Morphological, and Hydrophilic/Hydrophobic Features.

SiO2@PDMS and CeO2-ZrO2-SiO2@PDMS nanocomposites were prepared and studied using nitrogen adsorption-desorption, Fourier transform infrared spectroscopy (FT-IR), scanning electron microscopy (SEM), measurements of advancing and receding contact angles with water, and microcalorimetry. The pore size distributions indicate that the textural characteristics change after oxide modification by poly(dimethylsiloxane) (PDMS). Composites are characterized by mainly mesoporosity and macroporosity of aggregates of oxide nanoparticles or oxide@PDMS nanoparticles and their agglomerates. The FT-IR spectra show that PDMS molecules cover well the oxide surface, since the intensity of the band of free silanols at 3748 cm-1 decreases with increasing PDMS concentration and it is absent in the IR spectrum at C PDMS ≥ 20 wt% that occurs due to the hydrogen bonding of the PDMS molecules to the surface hydroxyls. SEM images reveal that the inter-particle voids are gradually filled and aggregates are re-arranged and increase from 20 to 200 nm in size with the increasing polymer concentration. The highest hydrophobicity (contact angle θ = 140° at C PDMS = 20-40 wt%) is obtained for the CeO2-ZrO2-SiO2@PDMS nanocomposites. The heat of composite immersion in water shows a tendency to decrease with increasing PDMS concentration.

Synthesis, Structural, and Adsorption Properties and Thermal Stability of Nanohydroxyapatite/Polysaccharide Composites.

A series of composites based on nanohydroxyapatite (nHAp) and natural polysaccharides (PS) (nHAp/agar, nHAp/chitosan, nHAp/pectin FB300, nHAp/pectin APA103, nHAp/sodium alginate) was synthesized by liquid-phase two-step method and characterized using nitrogen adsorption-desorption, DSC, TG, FTIR spectroscopy, and SEM. The analysis of nitrogen adsorption-desorption data shows that composites with a nHAp: PS ratio of 4:1 exhibit a sufficiently high specific surface area from 49 to 82 m2/g. The incremental pore size distributions indicate mainly mesoporosity. The composites with the component ratio 1:1 preferably form a film-like structure, and the value of S BET varies from 0.3 to 43 m2/g depending on the nature of a polysaccharide. Adsorption of Sr(II) on the composites from the aqueous solutions has been studied. The thermal properties of polysaccharides alone and in nHAp/PS show the influence of nHAp, since there is a shift of characteristic DSC and DTG peaks. FTIR spectroscopy data confirm the presence of functional groups typical for nHAp as well as polysaccharides in composites. Structure and morphological characteristics of the composites are strongly dependent on the ratio of components, since nHAp/PS at 4:1 have relatively large S BET values and a good ability to adsorb metal ions. The comparison of the adsorption capacity with respect to Sr(II) of nHAp, polysaccharides, and composites shows that it of the latter is higher than that of nHAp (per 1 m2 of surface).

Properties of Water Bound in Hydrogels.

In this review, the importance of water in hydrogel (HG) properties and structure is analyzed. A variety of methods such as ¹H NMR (nuclear magnetic resonance), DSC (differential scanning calorimetry), XRD (X-ray powder diffraction), dielectric relaxation spectroscopy, thermally stimulated depolarization current, quasi-elastic neutron scattering, rheometry, diffusion, adsorption, infrared spectroscopy are used to study water in HG. The state of HG water is rather non-uniform. According to thermodynamic features of water in HG, some of it is non-freezing and strongly bound, another fraction is freezing and weakly bound, and the third fraction is non-bound, free water freezing at 0 °C. According to structural features of water in HG, it can be divided into two fractions with strongly associated and weakly associated waters. The properties of the water in HG depend also on the amounts and types of solutes, pH, salinity, structural features of HG functionalities.

Silica-Supported Titania-Zirconia Nanocomposites: Structural and Morphological Characteristics in Different Media.

A series of TiO2-ZrO2/SiO2 nanocomposites were synthesized using a liquid-phase method and characterized by various techniques, namely, nitrogen adsorption-desorption, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, high-resolution transmission electron microscopy, and photon correlation spectroscopy (PCS). It was revealed that the component ratio and calcination temperature affect the phase composition of nanocomposites. Composites TiZrSi1 (TiO2:ZrO2:SiO2 = 3:10:87) and TiZrSi2 (10:10:80) calcined at 1100 °Ð¡ demonstrate the presence of t-ZrO2 crystallites in TiZrSi1 and ZrTiO4 phase in TiZrSi2. The samples calcined at 550 °Ð¡ were amorphous as it was found from XRD data. According to the Raman spectra, the bands specific for anatase are observed in TiZrSi2. According to XPS data, Zr and Ti are in the highest oxidation state (+4). Textural analysis shows that initial silica is mainly meso/macroporous, but composites are mainly macroporous. The particle size distributions in aqueous media showed a tendency of increasing particle size with increasing TiO2 content in the composites.

Solid-phase extraction of explosive nitramines on macroreticular polymers modified by freezing with water or acetone.

A novel approach is proposed to modify the porous structure and surface properties of the polymers used in solid-phase extraction. The approach involves soaking in water or acetone, followed by freezing in liquid nitrogen (77.4 K) and was employed for two polymeric materials: Amberlite XAD-7 and Amberlite XAD-16. Variations in the surface properties of the adsorbents were justified by the action of acetone and water as solvents affecting the textural and other characteristic of the materials. The initial and treated adsorbents were used in extraction of explosive nitramines from aqueous samples. The performed modifications of the polymer texture allow us to increase the recovery rate as compared with the initial adsorbents. The results were justified by the swelling of fragments of the polymers and by the additional process of sorption of nitramines. The results indicate that polymeric adsorbents can be easily modified by the soaking/freezing process and the materials can be achieved that prove usefulness for the effective separation of explosive nitramines from aqueous samples.

Evaluation of adsorption and desorption steps in the solid-phase extraction of explosives using carbon/silica gel nanocomposites.

New series of carbon/silica gel nanocomposites, carbosils, prepared by the carbonization of starch bound to silica gel, and carbosils additionally silylated with octadecyldimethylchlorosilane were synthesized. These materials were applied as adsorbents in the solid-phase extraction of explosive nitrate esters and nitroaromatics from aqueous solutions. The adsorption and desorption steps were evaluated separately. It was found that both the molecular properties of explosives (dipole moments, orbital energies, solvation effects) and textural properties influenced by carbon deposits or octadecyl moieties have a large impact on the recovery rates. It was shown that the composites with moderate content of carbon deposits or with the highest amounts of carbon deposits and additionally silylated can be used as materials tailored for extraction of explosives from the aqueous solutions.

Effects of the surroundings and conformerisation of n-dodecane molecules on evaporation/condensation processes.

The evaporation/condensation coefficient (ß) and the evaporation rate (γ) for n-dodecane vs. temperature, gas pressure, gas and liquid density, and solvation effects at a droplet surface are analysed using quantum chemical density functional theory calculations of several ensembles of conformers of n-dodecane molecules in the gas phase (hybrid functional ωB97X-D with the cc-pVTZ and cc-pVDZ basis sets) and in liquid phase (solvation method: SMD/ωB97X-D). It is shown that ß depends more strongly on a number of neighbouring molecules interacting with an evaporating molecule at a droplet surface (this number is estimated through changes in the surface Gibbs free energy of solvation) than on pressure in the gas phase or conformerisation and cross-conformerisation of molecules in both phases. Thus, temperature and the surrounding effects at droplet surfaces are the dominant factors affecting the values of ß for n-dodecane molecules. These values are shown to be similar (at reduced temperatures T/Tc < 0.8) or slightly larger (at T/Tc > 0.8) than the values of ß calculated by the molecular dynamics force fields (MD FF) methods. This endorses the reliability of the previously developed classical approach to estimation of ß by the MD FF methods, except at temperatures close to the critical temperature.

Comparison of adsorption affinity of polyacrylic acid for surfaces of mixed silica-alumina.

The influence of solution pH (in the range 3-9) on the adsorption of polyacrylic acid (PAA) on the mixed silica-alumina surface (SA-3: SiO2 97 %-Al2O3 3 % and SA-96: SiO2 4 %-Al2O3 96 %) was investigated. The following methods were applied in experiments: spectrophotometry, viscosimetry, potentiometric titration, and microelectrophoresis, which enable determination of adsorbed amount of the polymer, thickness of its adsorption layers, surface charge density, and zeta potential of solid particles in the presence and absence of PAA, respectively. The obtained results indicate that rise of solution pH causes the decrease of PAA adsorption and the increase of its adsorption layer thickness on surfaces of both solids. Moreover, significantly higher adsorption of polyacrylic acid was obtained on the SA-96 surface. This is a result of more favorable electrostatic interactions occurring between the adsorbing polymer chains and the SA-96 surface and formation of a greater number of adsorbate-adsorbent connections through hydrogen bridges.

Molecular-level understanding of the carbonisation of polysaccharides.

Understanding of both the textural and functionality changes occurring during (mesoporous) polysaccharide carbonisation at the molecular level provides a deeper insight into the whole spectrum of material properties, from chemical activity to pore shape and surface energy, which is crucial for the successful application of carbonaceous materials in adsorption, catalysis and chromatography. Obtained information will help to identify the most appropriate applications of the carbonaceous material generated during torrefaction and different types of pyrolysis processes and therefore will be important for the development of cost- and energy-efficient zero-waste biorefineries. The presented approach is informative and semi-quantitative with the potential to be extended to the formation of other biomass-derived carbonaceous materials.

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.

Cryogels: morphological, structural and adsorption characterisation.

Experimental results on polymer, protein, and composite cryogels and data treatment methods used for morphological, textural, structural, adsorption and diffusion characterisation of the materials are analysed and compared. Treatment of microscopic images with specific software gives quantitative structural information on both native cryogels and freeze-dried materials that is useful to analyse the drying effects on their structure. A combination of cryoporometry, relaxometry, thermoporometry, small angle X-ray scattering (SAXS), equilibrium and kinetic adsorption of low and high-molecular weight compounds, diffusion breakthrough of macromolecules within macroporous cryogel membranes, studying interactions of cells with cryogels provides a consistent and comprehensive picture of textural, structural and adsorption properties of a variety of cryogels. This analysis allows us to establish certain regularities in the cryogel properties related to narrow (diameter 0.4100 µm) with boundary sizes within modified life science pore classification. Particular attention is paid to water bound in cryogels in native superhydrated or freeze-dried states. At least, five states of water - free unbound, weakly bound (changes in the Gibbs free energy-ΔG<0.5-0.8 kJ/mol) and strongly bound (-ΔG>0.8 kJ/mol), and weakly associated (chemical shift of the proton resonance δ(H)=1-2 ppm) and strongly associated (δ(H)=3-6 ppm) waters can be distinguished in hydrated cryogels using (1)H NMR, DSC, TSDC, TG and other methods. Different software for image treatment or developed to analyse the data obtained with the adsorption, diffusion, SAXS, cryoporometry and thermoporometry methods and based on regularisation algorithms is analysed and used for the quantitative morphological, structural and adsorption characterisation of individual and composite cryogels, including polymers filled with solid nano- or microparticles.

Textural characteristics of model and natural bone tissues and interfacial behavior of bound water.

Water, as a probe liquid bound in model systems (highly disperse hydroxyapatite - protein composites as a model of the main components of bones) and rat bone tissues healthy and affected by osteoporosis occurred due to experimental Alzheimer's disease (EAD), has been investigated using low-temperature (1)H NMR spectroscopy, NMR cryoporometry, TG/DTG/DTA, DSC, and TG and DSC thermoporometry. The textural characteristics of these intact systems cannot be studied using the standard adsorption methods, but the cryoporometry and thermoporometry methods give these characteristics. The (1)H NMR spectra of water bound in model and natural bone tissues include signals, which can be assigned to strongly associated (typical) water (SAW, chemical shift of proton resonance δ(H)=5-6 ppm) and weakly associated (atypical) water (WAW) at δ(H)=1-2 ppm. Contributions of SAW and WAW give information on textural organization of both model and natural bones. The influence of such co-adsorbates as HCl, CDCl(3), CD(3)CN, C(6)D(6), and (CD(3))(2)SO on the interfacial behavior and clustering of bound water depends on their polarity, amounts of components, and textural and structural features of the materials analyzed with the (1)H NMR spectroscopy and cryoporometry methods. According to the NMR cryoporometry data, the EAD causes an increase in nanoporosity of the bone tissues. The total porosity and the specific surface area of biostructures (accessible for water molecules and estimated using NMR cryoporometry and TG thermoporometry methods with a model of cylindrical pores) are larger for the EAD sample. Weakly polar chloroform-d has a significant influence on the organization of water in the bone tissue, and this effect is greater for the EAD sample as more porous material.

Post-synthesis surface-modified silicas as adsorbents for heavy metal ion contaminants Cd(II), Cu(II), Cr(III), and Sr(II) in aqueous solutions.

To analyze the influence of silica surface modification and confined space effects on specific interactions of divalent and trivalent metal cations with surface functionalities, three different high surface area silicas with different pore size distributions were modified with the following organosilanes: 3-aminopropyltriethoxysilane, N-(2-aminoethyl)-3-aminopropyltriethoxysilane, 3-(trimethoxysilylpropyl)diethylenetriamine, N-(triethoxysilylpropyl)ethylenediaminetriacetic acid (EDTrA), and 3-(2,4-dinitrophenylamino)propyltriethoxysilane. The silicas were characterized by N(2) adsorption and reflectance FTIR spectroscopy before and after surface modification. N(2) adsorption and pore size distributions showed an increase in the pore width for all EDTrA-modified silicas, opposite to what occurred with the other organosilanes. Adsorption isotherms of Cd(II), Cr(III), Cu(II), and Sr(II) obtained from aqueous solutions were compared and analyzed by silica type, organosilane functional group, and metal adsorbed. Reflectance FTIR spectroscopy was used to probe the acetate functionality in EDTrA as a function of adsorbed metal content. A band shift to higher energy for Cr(III) on the wide pore silica studied indicated that the interaction with the acetate groups can be probed in this manner. In general, the wider pore distribution silica provided larger adsorption maxima, whereas the narrower pore distribution silica provided more favorable ΔG because of stronger binding of the cations. Cr(III) and Cu(II) exhibited larger adsorption maxima compared to Cd(II) and Sr(II), with the grafted organosilanes studied since the first cations have a greater charge/radius ratio than the second ones that provide a greater binding energy.

Activated carbons and carbon-containing poly(vinyl alcohol) cryogels: characterization, protein adsorption and possibility of myoglobin clearance.

Adsorption of myoglobin (Mb), bovine serum albumin (BSA) and γ-globulin (GG) onto activated carbons (ACs) with different pore size distributions, and poly(vinyl alcohol) (PVA) monolithic cryogels containing AC particles was studied. The highest initial rate of Mb adsorption was observed for AC having the largest specific surface area (1939 m(2) g(-1)) and pore volume (1.82 cm(3) g(-1)). The adsorption kinetics of proteins was characterized by a bimodal shape of the distribution f(D) function of an effective diffusion coefficient. Adsorption isotherms of Mb and GG were of Freundlich type within the studied range of equilibrium concentrations (10-150 µg mL(-1)). The distributions of free energy of protein adsorption were bimodal and reflected both interactions with carbon surfaces and self-association of proteins. Adsorbed amounts of Mb were the highest among the proteins studied (up to 700 mg g(-1) carbon), which was attributed to the higher fraction of pores accessible for Mb. Incorporation of carbon particles into PVA-based cryogel resulted in macroporous monolithic composite materials (AC-PVA) exhibiting good flow-through properties. Scanning electron microscopy of the composites showed macroporous aggregates of carbon particles held together by films and bridges of PVA. The rates of adsorption and adsorbed amounts of proteins on AC-PVA were reduced compared to the pristine carbon and depended on the carbon content in the composites. Nevertheless, adsorption of Mb on AC-PVA took place even in the presence of 500-fold higher concentration of BSA. This indicated a possibility of Mb clearance from blood plasma using the PVA-carbon monoliths.

Composites with macroporous poly(vinyl alcohol) cryogels with attached activated carbon microparticles with controlled accessibility of a surface.

A set of glutaraldehyde (GA) cross-linked poly(vinyl alcohol)/activated carbon (PVA/GA/AC) composites prepared in the form of monolithic rods using a cryogelation technique and studied using adsorption, mercury porosimetry, scanning electron microscopy (SEM), and quantum chemistry methods display porosity similar to that of PVA/GA cryogel at a high GA content (content ratio GA/AC = 1 and GA/PVA = 0.2). GA cross-linked PVA multilayer coverage is an effective barrier for adsorption on AC particles. Variations in surface chemistry (AC initial and oxidized in air at 300 °C for 12 h) and content (14-62.5%w/w) of ACs in PVA/GA/AC composites relatively weakly affect their textural characteristics at a high GA content (specific surface area S(BET) < 120 m²/g, pore volume V(p) < 0.35 cm³/g). However, PVA/GA/AC composite rods formed with a lower concentration of GA (content ratio GA/AC = 1/6 and GA/PVA = 1/10) have significantly greater S(BET) (∼500 m²/g) and V(p) (>0.55 cm³/g) values because of improved accessibility of the AC surface. This provides better adsorption of methylene blue as a probe compound.

Driving forces of conformational changes in single-layer graphene oxide.

The extensive oxygen-group functionality of single-layer graphene oxide proffers useful anchor sites for chemical functionalization in the controlled formation of graphene architecture and composites. However, the physicochemical environment of graphene oxide and its single-atom thickness facilitate its ability to undergo conformational changes due to responses to its environment, whether pH, salinity, or temperature. Here, we report experimental and molecular simulations confirming the conformational changes of single-layer graphene oxide sheets from the wet or dry state. MD, PM6, and ab initio simulations of dry SLG and dry and wetted SLGO and electron microscopy imaging show marked differences in the properties of the materials that can explain variations in previously observed results for the pH dependent behavior of SLGO and electrical conductivity of chemically modified graphene-polymer composites. Understanding the physicochemical responses of graphene and graphene oxide architecture and performing selected chemistry will ultimately facilitate greater tunability of their performance.

pH-driven physicochemical conformational changes of single-layer graphene oxide.

Single-layer graphene oxides (SLGOs) undergo morphological changes depending on the pH of the system and may account for restricted chemical reactivity. Herein, SLGO may also capture nanoparticles through layering and enveloping when the pH is changed, demonstrating potential usefulness in drug delivery or waste material capture.

Morphological and chemical features of nano and macroscale carbons affecting hydrogen peroxide decomposition in aqueous media.

Chemical and structural factors of carbon materials affect their activity in adsorption and surface reactions in aqueous media. Decomposition of hydrogen peroxide studied is a probe reaction for exploring parameters of carbons that might be involved, such as specific surface area, nitrogen and oxygen doping and conformational changes. To date, a detailed comparison of the behavior of carbon nanoscale (Carbon Nanotubes, CNT, Single Layer Graphene Oxide, SLGO) with macroscale (Activated carbons, AC) materials in this reaction has not been forthcoming. Herein, we demonstrate that on their first cycle, ACs in doped and undoped forms outperform all nanoscale carbons tested in the H(2)O(2) decomposition. Among the nanocarbons, nitrogen-doped CNT exhibited the highest activity in this reaction. However, subsequent recycling of each carbon, without chemical regeneration between uses, reveals SLGO exhibits greater reaction rate stability over an extended number of cycles (n>8) than other carbons including nitrogen-doped CNT and ACs. The effects of pH, temperature and concentration on the reaction were analyzed. Quantum-chemical modeling and reaction kinetics analysis reveal key processes likely involved in hydrogen peroxide decomposition and show evidence that the reaction rate is linked to active sites with N-and O-containing functionalities.