V. A. Tertykh

Preparation and properties of organomineral adsorbent obtained by sol–gel technology

Organomineral nanocomposite material has been obtained by sol–gel method through in situ formation of inorganic network in the presence of organic polymer. The most common silica precursor tetraethoxysilane (TEOS) and polysaccharide chitosan solution were used for the sol–gel transformations. The obtained chitosan–silica nanocomposite has been characterized by the physicochemical methods such as differential scanning calorimetry–thermogravimetry–mass spectrometry, Fourier transform infrared spectroscopy–thermogravimetry, elemental analysis, nitrogen adsorption/desorption isotherms, scanning electron microscopy, Fourier transform infrared spectroscopy to determine possible interactions between silica and chitosan macromolecules. Thermal destruction and products from gaseous phase in atmosphere of air and nitrogen were studied. It was found that introducing chitosan in silica network drastically change behavior of polymer during heat treatment in inert atmosphere. Adsorption of microquantities of Zn(II), Cu(II), Fe(III), Cd(II) and Pb(II) cations from the aqueous solutions by the obtained composite has been studied in comparison with the chitosan beads, previously cross-linked with glutaraldehyde. The adsorption capacity and kinetic sorption characteristics of the composite material were estimated. The obtained data were analyzed using the Langmuir and Freundlich isotherms, and the characteristic parameters for each isotherm were determined.

Effect of aerosil on the hydrothermal modification of porous structure of silica gel adsorbents

Abstract The effect of pyrogeneous silica (aerosil) on hydrothermal treatment (HTT) of narrow and mesoporous silica gels possessing various sizes of primary globules was studied. The HTT process was carried out in the autoclave at 200°C (6 h) in the liquid and gaseous phases. In the systems studied, aerosil was in the form of mechanical mixture with silica gel or constituted a separate phase in the aqueous suspension form. It was stated that the presence of pyrogeneous silica during the hydrothermal modification of silica gels affects the size of their specific surface area, average pores size and curves of pores volume distribution based on their radii. The extent of observed changes depends on the porous structure of initial adsorbents. The investigations show that it is possible to transfer the silica mass through the gaseous phase during the hydrothermal treatment. It was also pointed out that intensity of silica mass transfer observed during the hydrothermal modification in the gaseous phase does not differ from the mass transfer in the liquid phase systems. It was observed that for both modified silica gels relative efficiencies of the hydrothermal treatment are similar. This makes it possible to predict the extent of structural changes in the silica matrix, for silica gels of different porous structure, under the similar hydrothermal treatment conditions.

Electrokinetic Properties of the Pristine and Oxidized MWCNT Depending on the Electrolyte Type and Concentration

Electrostatic stabilization is reduced in its efficiency in an electrolyte-containing environment. The effect of electrolyte concentration is mostly described as negative factor for dispersion stabilization. Usually, zeta potential and physical stability decrease at increasing electrolyte concentration. The purpose of the present study was to measure the surface properties of nanotubes in aqueous solution of monovalent electrolytes at different concentration. Characteristics such as size distribution, surface chemistry, surface charge, and dispersability in aqueous phase have been identified. Hydrodynamic size and zeta potential in aqueous multiwalled carbon nanotube (MWCNT) suspensions were determined at different pH with the desired concentrations of electrolyte of the cationic group (NaCl, KCl, CsCl) and the anionic group (NaClO4). The correlations between the response of the surface functionality of pristine and oxidized multiwalled carbon nanotubes and electrical double layer (EDL) forming at different ionic environments in the vicinity of a nanotube surface were determined. The nanotube dispersion stabilization was found to be more affected by ion size and pH medium then electrolyte concentration. The data obtained confirms the predominant role of surface reactions. The most stable dispersion of nanotubes was achieved in KCl electrolyte solution at less negative charge of the surface.

The Reduction of Gold Nanoparticles in the Surface Layer of Modified Silica

Silicas with deposited hydridepolysiloxane layers were used for the in situ preparation of gold nanoparticles by the reduction of metal ions from a solution of chloroauric acid. The metal-containing silicas obtained were characterized by X-ray powder diffraction, transmission electron microscopy, and UV, IR, and laser correlation spectroscopy.

Covalent Attachment of Some Phenol Derivatives to the Silica Surface by Use of Single-stage Aminomethylation

The reaction conditions and component ratios were established for the attachment of 4-(2-pyridylazo)resorcinol (PAR), 1-(2-pyridylazo)-2-naphthol (PAN) and 8-hydroxyquinoline (8-HQ) to the silica surface by means of a single-stage Mannich reaction. The modified sorbents that were synthesized were characterized by an adsorption method, and DRIFT and UV spectroscopies. The concentrations of PAR, PAN and 8-HQ grafted to the silica surface that were attained were 2.8×10−5, 8.5×10−5 and 2.7×10−4 mol g−1, respectively.

Adsorption of V(V), Mo(VI) and Cr(VI) Oxoanions by Chitosan–Silica Composite Synthesized by Mannich Reaction

Immobilization of chitosan on modified silica surface has been carried out by aminomethylation (Mannich reaction). The obtained chitosan–silica (CSS) composite was characterized by the Fourier transform infrared spectroscopy, specific surface area and pore diameter. The concentration of chitosan in the composite was determined by the thermogravimetric method. The effects of various parameters, such as pH, contact time, initial concentration of the metal on the adsorption of V(V), Mo(VI) and Cr(VI) oxoanions by the CSS composite were investigated in comparison with the initial components: chitosan, amino-containing silica and silica. The maximum adsorption capacities of composite with respect to V(V) and Mo(VI) oxoanions at pH 2.5 were 1.6 and 1.5 mmol/g, respectively, and 0.5 mmol/g towards Cr(VI) in the neutral medium.

Magnetic Resonance and Optical Study of Carbonized Silica Obtained by Pyrolysis of Surface Compounds

The carbonized silica (SiO2:C) nanopowders were prepared by chemical modification of fumed silica (aerosil) by phenyltrimethoxysilane followed by thermal annealing at temperature in range of 500-800 °C in nitrogen flow. Their magnetic properties were investigated by electron paramagnetic resonance (EPR) in the temperature range from 4.2 K to 292 K. The initial and annealed SiO2:C samples revealed carbon (C) related defects. The carbon related radicals (CRR) in annealed SiO2:C nanopowders with g-factors 2.0042, 2.0039 were attributed to the oxygen (O)-centered CRR and C-centered CRR with a nearby O heteroatom, respectively. The EPR data were compared with infrared (IR) and photoluminescence (PL) data. It was found that the position of the PL band depends on the type of CRR formed after sample annealing. The PL with maximum intensity at 440 nm was found for the sample annealed at 500°C in which O-centered CRR was observed while in the sample annealed at 600°C in which C-centered CRR with a nearby O heteroatom was observed and graphite-like amorphous C clusters were appeared the peak of the PL band was shifted to the 510-520 nm.

Synthesis and Application of Metal-Containing Silicas

Gold nanoparticles were obtained by in situ reduction with silicon hydride groups grafted to the silochrom C-120 and aerosil A-300 silica surface. Such gold-containing silicas have been applied for hydrogen oxidation.

Immobilization of Optically Active Olefins on the Silica Surface by Combined Hydrosilylation and Sol–gel Technology

By means of hydrosilylation reactions between functional olefins and triethoxysilane in the presence of Speiers catalyst and sol-gel transformations of the reaction products, a number of optically active and complexing alkenes (quinine, quinidine, cinchonine, cinchonidine, alprenolol, N-allylrhodanine and hemin) were immobilized on the surface of silica. The structures of the compounds formed and the nature of their bonding with the surface were studied by DRIFT and NMR spectroscopies. The concentrations of olefins anchored to the surface layer of the silica matrix were estimated by UV spectroscopy.

A New Route for Preparation of Hydrophobic Silica Nanoparticles Using a Mixture of Poly(dimethylsiloxane) and Diethyl Carbonate

Organosilicon layers chemically anchored on silica surfaces show high carbon content, good thermal and chemical stability and find numerous applications as fillers in polymer systems, thickeners in dispersing media, and as the stationary phases and carriers in chromatography. Methyl-terminated poly(dimethylsiloxanes) (PDMSs) are typically considered to be inert and not suitable for surface modification because of the absence of readily hydrolyzable groups. Therefore, in this paper, we report a new approach for surface modification of silica (SiO2) nanoparticles with poly(dimethylsiloxanes) with different lengths of polymer chains (PDMS-20, PDMS-50, PDMS-100) in the presence of diethyl carbonate (DEC) as initiator of siloxane bond splitting. Infrared spectroscopy (IR), elemental analysis (CHN), transmission electron microscopy (TEM), atomic force microscopy (AFM), rotational viscosity and contact angle of wetting were employed for the characterization of the raw fumed silica and modified silica nanoparticles. Elemental analysis data revealed that the carbon content in the grafted layer is higher than 8 wt % for all modified silicas, but it decreases significantly after sample treatment in polar media for silicas which were modified using neat PDMS. The IR spectroscopy data indicated full involvement of free silanol groups in the chemisorption process at a relatively low temperature (220 °C) for all resulting samples. The contact angle studies confirmed hydrophobic surface properties of the obtained materials. The rheology results illustrated that fumed silica modified with mixtures of PDMS-x/DEC exhibited thixotropic behavior in industrial oil (I-40A), and exhibited a fully reversible nanostructure and shorter structure recovery time than nanosilicas modified with neat PDMS. The obtained results from AFM and TEM analysis revealed that the modification of fumed silica with mixtures of PDMS-20/DEC allows obtaining narrow particle size distribution with uniform dispersity and an average particle size of 15–17 nm. The fumed silica nanoparticles chemically modified with mixtures of PDMS-x/DEC have potential applications such as nanofillers of various polymeric systems, thickeners in dispersing media, and additives in coatings.