Modification of highly dispersed silica with zirconium acetylacetonate

The chemisorption of Zr(acac)₄ and the formation of nanoparticles of ZrO₂ on the surface of silica were studied by IR spectroscopy, thermogravimetry, thermal and X-ray phase analysis. The composition was established and the hydrolytic and thermal properties of ≡SiOZr(acac)₃ groups were investigated. __________ Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 44, No. 3, pp. 191–195, May/June, 2008.     

One-step synthesis of highly dispersed gold nanocrystals on silica spheres

Highly dispersed gold nanocrystals decorating silica spheres were prepared from HAuCl4 and NaOH via a deposition-precipitation (DP) process, in which the isoelectric point (IEP) of the substrate was adjusted during sphere synthesis by interaction of the surface with ammonia molecules. Through the systematic variation of pH (4-8), reaction temperature (65-96 degrees C), and time (10-30 min), a superior product with small (2-5 nm), homogeneously distributed gold crystals was obtained at pH 7 and a reaction temperature of 96 degrees C. These materials will offer enhanced performance as catalysts and contrast enhancers in biomedical imaging.     

Synthesis of mesoporous silica nanobamboo with highly dispersed tungsten carbide nanoparticles

By controlling the interaction between cationic surfactant micelles and ammonium metatungstate during the formation of mesoporous silica structure, highly dispersed tungsten carbide (WC) nanoparticles of 2.0 nm in diameter on mesoporous silica nanospheres were synthesized at lower concentration of ammonium metatungstate. With additional ammonium metatungstate, a novel mesoporous silica nanobamboo structure was formed with bimodal size-distributed WC nanoparticles, in which 2.0 nm WC was homogeneously distributed in nanobamboo's mesoporous silica wall and those with larger diameter (10.0-20.0 nm) were only formed on the nanobamboo's inner surface and at its internodes. The mesoporous silica nanobamboo also had a very high tensile strength due to its bamboo-like structure.     

Adsorption properties of highly dispersed silica with a partially hydrophobic surface

Highly dispersed silica samples with different degrees of substitution of silanol groups by trimethylsilyl groups are obtained by the gas-phase modification method. The adsorption of vitamins B1, B6, and E on initial and modified silica samples is studied. It is shown that the modified adsorbents with degrees of substitution of silanol groups up to 40% exhibit higher affinity to vitamin molecules; in this case, adsorption properties of the modified silica samples depend on the nature of the adsorbate and the number of grafted groups.     

The adsorption of amino acids on the surface of highly dispersed silica

The adsorption of arginine, histidine, lysine, and ornithine on the surface of highly dispersed silica from aqueous solutions was studied as a function of pH. The equilibrium constants of the formation of surface complexes were calculated using the Stern model for the electrical double layer. It was shown that the possibility of adsorption of amino acids on the silica surface is determined by the presence of additional basic groups in their molecules.Translated from Kolloidnyi Zhurnal, Vol. 66, No. 6, 2004, pp. 733–738.Original Russian Text Copyright © 2004 by Vlasova, Golovkova.     

Microwave-induced synthesis of highly dispersed gold nanoparticles within the pore channels of mesoporous silica

Highly dispersed gold nanoparticles have been incorporated into the pore channels of SBA-15 mesoporous silica through a newly developed strategy assisted by microwave radiation (MR). The sizes of gold are effectively controlled attributed to the rapid and homogeneous nucleation, simultaneous propagation and termination of gold precursor by MR. Diol moieties with high dielectric and dielectric loss constants, and hence a high microwave activation, were firstly introduced to the pore channels of SBA-15 by a simple addition reaction between amino group and glycidiol and subsequently served as the reduction centers for gold nanoparticles. Extraction of the entrapped gold from the nanocomposite resulted in milligram quantities of gold nanoparticles with low dispersity. The successful assembly process of diol groups and formation of gold nanoparticles were monitored and tracked by solid-state NMR and UV-vis measurements. Characterization by small angle X-ray diffraction (XRD) and transmission electron microscopy (TEM) indicated that the incorporation of gold nanoparticles would not breakup the structural integrity and long-range periodicity of SBA-15. The gold nanoparticles had a narrow size distribution with diameters in the size range of 5-10 nm through TEM observation. The average particles size is 7.9 nm via calculation by the Scherrer formula and TEM measurements. Nitrogen adsorption and desorption isotherms gave further evidence that the employed method was efficient and gold nanoparticles were successfully incorporated into the pore channels of SBA-15.     

Identification of different structures of chromium trioxide supported on highly dispersed silica by photoluminescence

The intensity ratio of the two lines in the excitation spectra of photoluminescence of CrO₃ supported on silica depends on the chromium content and on catalyst treatment. Because of the characteristic dependence the excitation line at 410 nm is related to monochromate while the other line centered at 490–540 nm is due to di- or polychromates.

---

CrO₃, , . 410 , 490–530 - - .

     

Thioether moiety functionalization of mesoporous silica films for the encapsulation of highly dispersed gold nanoparticles

Highly dispersed gold nanoparticles within mesoporous thin films (MTFs) have been synthesized through a newly developed controllable strategy, in which (1,4)-bis(triethoxysilyl)propane tetrasufide (BPTS) organosiloxane coupling agent was co-assembled with tetraethyl orthosilicate (TEOS) to form organic groups functionalized mesoporous composite films followed with oxidization, ion-exchange with Au(en)₂Cl₃ (en: 1,2-ethanediamine) compound and calcination under hydrogen/nitrogen mixing atmosphere. Small-angle X-ray diffraction (XRD) characterization indicated that up to 10 mol% of BPTS could be incorporated into mesoporous hybrid films, and that would not breakup the structural integrity and long-range periodicity. The loaded gold nanoparticles were uniformly distributed due to the molecular level homogenous mixing of the BPTS precursor with TEOS, and its concentration could be controlled via the original ratio of BPTS to TEOS. The nanoparticles had a narrow size distribution with diameters in the size range of 3-7 nm through transmission electron microscopy (TEM) observation and underwent a slight size increase with the higher gold load level. An overall increase in the absorption intensity, a red shift of absorption peak, together with a comparatively narrower bandwidth could be observed at higher gold concentration within composite films from UV-vis spectra. Wide-angle XRD, TEM, X-ray photoelectron spectroscopy (XPS) and UV-vis spectra characterizations all agreed on the fact that the gold loading level could be controlled by the amount of BPTS in the starting sol for preparing MTFs.     

The adsorption of biogenic amines on the surface of highly dispersed silica from aqueous solutions

The adsorption of some biogenic amines (histamine, tryptamine, and tyramine) on the surface of highly dispersed silica from aqueous solutions is studied as a function of pH and ionic strength. It is established that biogenic amines in a protonated form interact with dissociated silanol groups of SiO₂ surface forming outer-sphere complexes. The constants of the formation of surface complexes are calculated.     

Adsorption of cinnamic and caffeic acids on the surface of highly dispersed silica from different solvents

The adsorption of cinnamic and caffeic acids on initial and partially silylated highly dispersed silica A-300 from polar (water-ethanol solution), low polar (chloroform and dichloroethane), and apolar (hexane and carbon tetrachloride) solvents is investigated. The dependence of adsorption on solvent polarity is established. It is disclosed that the dependences of the adsorption of cinnamic and caffeic acids on the degree of surface hydrophobization have different characters.     

Effect of supramolecular interactions with cationic surfactants on adsorption of flavonoids on highly dispersed silica surface

The effect of the cationic surfactants decamethoxine and miramistin on the physicochemical properties of the natural flavonoids quercetin and rutin is studied spectrophotometrically in the range of physiological pH values. It is established that the interaction with these cationic surfactants changes the spectral characteristics of the flavonoids in solutions and essentially increases their adsorption on the surface of highly dispersed silica as compared with their aqueous solutions. It is shown that the efficiency of flavonoid adsorption from decamethoxine and miramistin solutions is governed by solution pH, flavonoid hydrophobicity, and the nature of a cationic surfactant.     

Vibrational spectroscopy of dispersed silica: Aerosil

Conclusions A complex experiment has been carried out to examine the vibrational spectrum of Aerosil, and it has been found that the silanol group is the main active center of this type of dispersed silica. This fact conforms well with the previously advanced supposition that the structure of the core of silica is of a closed type in this case.The experimentally measured vibrational spectrum of the adsorbed water is practically completely described by a model in which one silanol center reacts with a water cluster. This agrees with the fact that chemical hydrophobic reactions take place on the surface of the usual commercial, i.e.,wet Aerosil. Since water is adsorbed as a cluster around one center, then in the presence of the usual 2. wt. % of water, a large part of the surface will be free of water and available for other reactions.It is natural that the above-considered simple models do not permit explanation of all the details of the observed spectra and a large amount of work will have to be carried out with more complicated models.Patrice Lumumba Peoples's Friendship University, Institute of Surface Chemistry, Ukrainian Academy of Sciences. Joint Institute of Nuclear Research. Translated from Zhurnal Strukturnoi Khimii, Vol. 33, No. 4, pp. 66–75, July–August, 1992.     

Methylsilylation of highly dispersed graphite surfaces

The chemisorption of hexamethyldisilazane on the surface of a highly dispersed graphite has been studied. It was shown that with increase in the reaction temperature, the amount of the grafted trimethysilyl groups increases. The characteristic features of the formation of the trimethylsilyl coating have been discussed on the basis of the data on the thermodesorption of water, carbon oxides and methane from graphite surfaces with mass-spectrometric monitoring.Deceased.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 28, No. 2, pp. 184–186, March–April, 1992.     

The effect of copper ions on adsorption of histamine and histidine on the surface of highly dispersed silica

The effect of copper ions on the adsorption of histamine and histidine on the surface of highly dispersed silica from aqueous solutions is studied. It is shown that the formation of complex particles in solution determines the character of adsorption of these biomolecules. The equilibrium constants of the formation of ternary surface complexes, where silanol groups of silica act as a ligand, are calculated. It is shown that, in such complexes, nitrogen atoms of either histamine or histidine enter into the inner coordination sphere of copper ion.     

The catalytic efficiency of Fe-containing nanocomposites based on highly dispersed silica in the reaction of CO2 hydrogenation

Research on Chemical Intermediates - Oxide Ni(80)Fe(20)/SiO2, Co(93)Fe(7)/SiO2, and Ni(19)Co(77)Fe(4)/SiO2 nanocomposites (NCs) were prepared using highly dispersed silica. It was modified by...     

Adsorption of a cationic surfactant, miramistin, from aqueous solutions on the surface of highly dispersed silica

The adsorption of a universal antiseptic agent, the cationic surfactant miramistin, on the surface of highly dispersed silica has been studied. It has been shown that, when miramistin is adsorbed from acidic premicellar solutions, the main contribution to miramistin binding with the surface is made by hydrogen bonding between amide groups of surfactant molecules and silanol groups of silica, which is, at higher pH values, accompanied by ionic interaction between positively charged quaternary nitrogen atoms of miramistin and negatively charged dissociated silanol groups. In the case of adsorption from a micellar solution, an increase in the surface concentration of miramistin is almost independent of solution pH, because the second layer is predominantly formed due to hydrophobic interactions.     

Characterization of diene polymers. I. Infrared and NMR studies: Nonadditive behavior of characteristic infrared bands

Extinction coefficients of the characteristic infrared bands due to isomeric structural units were measured for polybutadiene and polyisoprene in CS₂ or CCl₄ solutions and were compared with the isomer composition determined by NMR. The NMR signal assignments were made on the basis of the spectra of deutero derivatives of the polymers. In the case of polyisoprene, linear relations were obtained between the extinction coefficients and the isomer contents determined by NMR for the absorption bands at 1385 cm^?1 (characteristic of trans-1,4 units), 1376 cm^?1 (cis-1,4 units), and 889 cm^?1 (3,4 units). However, for the absorption bands at 840 cm^?1 (characteristic of cis-1,4 and trans-1,4 units), isomerized polyisoprenes did not give such a linear relationship. In polybutadiene, the extinction coefficient for the atactic 1,2 units was found to be lower than that of the syndiotactic 1,2 unit. These experimental facts lead to the conclusion that additivity of the extinction coefficients does not always hold for diene polymers. The deviation from the linear relation may be associated with regular sequences of one isomeric conformation in the chain.     

Intensities of some group characteristic infra-red bands

Molar-intensity data have been obtained, both as peak extinction coefficients and as band areas, for several infra-red bands known to be characteristic of chemical groups. In view of the fact that many compounds are insoluble in spectroscopically suitable solvents, the substances were measured as solids in potassium bromide disks. The bands considered were CN stretching band in nitriles, the CO stretching band in esters, ketones, amides, acids and salts, the NO stretching bands in nitro compounds, and the SO stretching bands in sulphones, sulphonamides and sulphonic acids. About twenty compounds were examined in each case.The usefulness of such data in analysis and structural diagnosis has been considered. It was concluded that, provided the total area under the band, rather than the peak-extinction coefficient is used as the measure of intensity, reasonably constant intensity factors could be assigned to several of the above characteristic bands. The significance of this is that rough quantitative estimates of the concentrations of certain groups in material of unknown structure can be made, and that intensity measurements may be used to supplement structural diagnosis from band frequencies.     

Chemical modification of dispersed silica by pyrimidine derivatives

Results are given of the chemical modification of silicas containing and groups on their surface by pyridimidines in the gaseous phase. IR spectroscopy and field desorption mass spectrometric methods were used to obtain information on the structure of the surface compounds prepared. Possible reaction schemes are suggested. The high hydrolytic stability of some of the immobilized hydroxypyrimidines has been established.Translated from Teoreticheskaya i Éksperimental'naya Khimiya, Vol. 22, No. 4, pp. 495–499, July–August, 1986.