E. M. Pakhlov

National Academy of Sciences of Ukraine, Kievo, Kyiv City, Ukraine

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Publications (53)71.7 Total impact

  • [Show abstract] [Hide abstract]
    ABSTRACT: Fumed silica, initial alumina blend, after mechanochemical activation (MCA), and fumed binary silica/alumina (SA) were studied using infrared spectroscopy, X-ray diffraction (XRD), ultrasoft X-ray emission (USXE) spectroscopy (giving emission bands Si Lα, Al Lα and O Kα related to valence electron transfer onto core levels) and quantum chemistry. The MCA influence on nanoparticle characteristics (sizes, electronic structure) increases with increasing alumina content in the blends due to stronger abrasive effect of alumina nanocrystallites (snagging a surface layer of nanoparticles during MCA) than non-crystalline silica nanoparticles. A difference in Si Lα, Al Lα and O Kα affected by MCA increases with increasing alumina content. It is greater for the top peak of the upper valence band (UVB) than for a lower energy peak in the bottom of the UVB. These spectral changes suggest redistribution of electron density between Si, Al and O atoms depending on alumina content, material type and treatment conditions. The main difference in the properties of the SA blends and binary SA is due to distribution of Si atoms in alumina phase and Al atoms in silica phase in fumed SA (which is amorphous at CAl2O3 ≤ 30 wt.%) in contrast to the SA blends with practically separated silica and alumina nanoparticles.
    Journal of Non-Crystalline Solids 01/2014; 403:30–37. · 1.72 Impact Factor
  • Colloids and Surfaces A Physicochemical and Engineering Aspects 01/2014; 456:261–272. · 2.11 Impact Factor
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    ABSTRACT: Unmodified pyrogenic silica PS300 and partially silylated nanosilica samples at a degree of substitution of surface silanols by trimethylsilyl (TMS) groups ΘTMS=27.2% and 37.2% were studied to elucidate features of the interfacial behavior of water adsorbed alone, or co-adsorbed with methane, hydrogen, or trifluoroacetic acid (TFAA). In the aqueous suspension modified PS300 at ΘTMS=37.2% forms aggregates of 50-200nm in size and can bind significant amounts of water (up to ∼5g/g). Only 0.5g/g of this water is strongly bound, while the major fraction of water is weakly bound. The presence of surface TMS groups causes the appearance of weakly associated water (WAW) at the interfaces. The adsorption of methane and hydrogen onto TMS-nanosilica with pre-adsorbed water (hydration degree h=0.05 or 0.005g/g) increases with increasing temperature. In weakly polar CDCl3 medium, interfacial water exists in strongly (SAW, chemical shift δH=4-5ppm) and weakly (δH=1-2ppm) associated states, as well as strongly (changes in the Gibbs free energy -ΔG>0.5-0.8kJ/mol) and weakly (-ΔG<0.5-0.8kJ/mol) bound states. WAW does not dissolve TFAA but some fraction of SAW bound to TMS-nanosilica surface can dissolve TFAA.
    Journal of Colloid and Interface Science 01/2014; 434:28–39. · 3.17 Impact Factor
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    ABSTRACT: Two sets of hybrid polyurethane-poly(2-hydroxyethyl methacrylate) semi-interpenetrating polymer networks - nanooxide composites with 0.25 or 3 wt% nanosilica or nanoalumina functionalised with OH, NH2 or CH=CH2 groups were prepared. Combined atomic force microscopy, infrared spectroscopy, thermally stimulated depolarisation current, differential scanning calorimetry and creep rate spectroscopy analysis of nanostructure and properties of the composites was performed. The pronounced dynamic heterogeneity and the strong impact of oxide additives, basically suppression of the dynamics and temperature-dependent increasing modulus of elasticity, were observed. The effects correlated with either interfacial interactions (for silica) or nanostructure (for alumina). Low oxide content strongly affected the matrix due to formation of the peculiarly cross-linked, via double covalent hybridisation of three components, structure of nanocomposites.
    RSC Advances 05/2013; · 3.71 Impact Factor
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    ABSTRACT: This paper focuses on the investigation of nanooxide composites SiO2/TiO2/X (X = SnO2, NiO) synthesized by controlled low�temperature hydrolysis of TiCl4, SnCl4 (followed by thermal treatment of some samples) on nanosilica surface (specific surface area 300 m2/g) and by thermolysis of Ni(NO3)2 ⋅ 6H2O at 600°C. The effect of the nature and concentration of a doping agent on the phase composition of the com� posites and their physicochemical properties is determined. The properties of the synthesized systems are examined by means of XRD analysis, nitrogen adsorption, potentiometric titration, and photon correlation spectroscopy.
    Protection of metals and physical chemistry of surfaces 01/2013; 49(49):541-547. · 0.69 Impact Factor
  • Applied Surface Science 10/2012; · 2.54 Impact Factor
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    XIII Ukrainian —Polish Symposium on Theoretical and Experimental Studies of Interface Phenomena and their Technological Applications, Ukraine; 09/2012
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    ABSTRACT: A series of photocatalysts based on silica (nanoparticulate) supported titania, ceria, and ceria/zirconia were synthesized and characterized by a variety of techniques including surface area measurements, X-ray diffraction, Fourier transform infrared spectroscopy, zeta potential, surface charge density, and photocatalytic behavior toward methylene blue decomposition. Thermal treatment at 600 °C increases the anatase content of the titania based catalysts detected by XRD. Changes in the infrared spectra before and after thermal treatment indicate that at low temperature there are more SiOTi bonds than at high temperature. As these bonds break upon heating the SiO2 and TiO2 separate, allowing the TiO2 anatase phase to form. This results in an increased catalytic activity for the thermally treated samples. Nearly all titania based samples exhibit a negative surface charge density at pH 7 (initial pH of photocatalytic studies) which aids adsorption of methylene blue. The crystallinity of ceria and ceria/zirconia based catalysts are in some cases limited, and in others non-existent. Even though the energy band gap (Eg) can be lower for these catalysts than for the titania based catalysts, their photocatalytic properties are inferior.
    Applied Surface Science 06/2012; 258(17):6288–6296. · 2.54 Impact Factor
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    ABSTRACT: C/AST/PEG nanocomposites with fumed AST (89 wt % Al2O3, 10 wt % SiO2, 1 wt % TiO2), activated carbon, and poly(- ethylene glycol), PEG, were prepared in a wide range of PEG and C/AST (1 : 9) contents. Thermal transitions (mainly in a PEG phase) were investigated by differential scanning calorimetry. The dynamic behavior was investigated by thermally stimulated depolarization current and dielectric relaxation spectroscopy. The PEG crystallinity degree decreases in the nanocomposites, in particular at CPEG � 40 wt %. A significant fraction of amorphous polymer is immobilized at a filler surface making no contribution to the glass transition, whereas the rest exhibits a lower glass transition temperature, when compared with bulk polymer, because of loosened molecular packing of the chains. Several relaxations arising from the polymer matrix, the filler, and their combination were identified and analyzed. The segmental a-relaxation of the PEG matrix was found to become faster in the nanocomposites.
    Journal of Applied Polymer Science 04/2012; · 1.40 Impact Factor
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    ABSTRACT: Morphological characteristics of CuO- and NiO-doped silica/titania nanocomposites are analyzed using atomic force microscopy and low-temperature nitrogen adsorption. The different types of pores (nano-, meso- and macropores) in the powder composites are modeled as voids between spherical nanoparticles packed in random aggregates. It is shown that specific surface area, total pore volume, average pore radius, incremental pore size distribution and changes in relationships between these characteristics of the composites reveal a non-linear behavior depended on the presence of the dopants. The textural and atomic force microscopy investigations suggest that processes of aggregation differ from each other depending on the type of doping oxide. Fractal dimension, estimated according to Frenkel-Halsey-Hill equation using the adsorption branch, has values about 2.50–2.60 and indicates the aggregate formation.
    Chemistry, Physics and Technology of Surface. 01/2012; 3(4):386-394.
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    ABSTRACT: SiO2/TiO2/CuO composites have been synthesized by deposition technique using low temperature hydrolysis of TiCl4 and thermolysis of Cu(CH3CO2)2 · H2O at silica A-300 surface. The properties of the samples have been explored by means of XRD, nitrogen adsorption, potentiometric titration, and photon correlation spectroscopy. As the results indicate, there are both anatase and some amount of rutile formed at CCuO = 1 wt. %. A gradual shift of the point of zero charge (from pH = 3.48 to 6.60) has been observed with increasing CuO content.
    Хімія, фізика та технологія поверхні. 01/2012; 3(2):172-177.
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    ABSTRACT: Nanosilicas (A-50, A-300, A-500)/activated carbon (AC, SBET=1520m2/g) composites were prepared using short-term (5min) mechanochemical activation (MCA) of powder mixtures in a microbreaker. Smaller silica nanoparticles of A-500 (average diameter dav=5.5nm) can more easily penetrate into broad mesopores and macropores of AC microparticles than larger nanoparticles of A-50 (dav=52.4nm) or A-300 (dav=8.1nm). After MCA of silica/AC, nanopores of non-broken AC nanoparticles remained accessible for adsorbed N2 molecules. According to ultra-soft X-ray emission spectra (USXES), MCA of silica/AC caused formation of chemical bonds Si–O–C; however, Si–C and Si–Si bonds were practically not formed. A decrease in intensity of OKα band in respect to CKα band of silica/AC composites with diminishing sizes of silica nanoparticles is due to both changes in the surface structure of particles and penetration of a greater number of silica nanoparticles into broad pores of AC microparticles and restriction of penetration depth of exciting electron beam into the AC particles.
    Applied Surface Science 01/2011; 258(3):1115-1125. · 2.54 Impact Factor
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    ABSTRACT: Interfacial interactions and dynamics were studied in silica and alumina core-poly(vinyl pyrrolidone) (PVP) shell nanoparticles with different shell thicknesses starting from 1-2 nm (monolayer); their geometry and structural organization were comprehensively characterized by several techniques. Far- and mid-IR spectroscopy, combined with DSC activation analysis of the glass transition, allowed to register hydrogen bonding and Lewis/Brønsted interactions, and the multi-modal glass transition dynamics in PVP nanoshells, as well as their interrelationship. For PVP monolayer, only a few “abnormal” modes constituted glass transition which covered the temperature range from 80 to 230 °C, with varying the activation energy by an order of magnitude.
    Macromolecular Symposia 11/2010; 296(1):541 - 549.
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    ABSTRACT: The characteristics of composites with PEG (35kDa) - nanooxides (fumed silica A-300, SBET=342m2/g, and alumina/silica/titania (AST) at oxides content of 22, 28, and 50wt%, respectively, SBET=38m2/g) were studied depending on PEG content (CPEG=100, 90, 80, 40, and 20wt%) at different temperatures and various hydration using Fourier transform infrared (FTIR) spectroscopy, photon correlation spectroscopy (PCS), differential scanning calorimetry (DSC), thermally stimulated depolarization current (TSDC), and dielectric relaxation spectroscopy (DRS) methods. In the aqueous suspensions the secondary particle (aggregates of primary particles) size distribution corresponds to larger particles for PEG/AST than PEG/A-300. For composite powders (0.3-3wt% of water) with well distributed macromolecules (according to the FTIR spectra) the relaxation characteristics (temperature of relaxation maxima, activation energy of relaxation, glass transition temperature and activation energy) show that overall interaction is stronger for PEG/A-300 but local interaction in the adsorption layer is stronger for PEG/AST because of much greater SBET of A-300 (first effect) and stronger Brønsted acid sites in AST (second effect). © 2010 Elsevier B.V.
    Colloids and Surfaces A Physicochemical and Engineering Aspects 05/2010; 360(1):220-231. · 2.11 Impact Factor
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    ABSTRACT: Interfacial interactions, chain dynamics, and glass and melting transitions were studied in well-defined core-shell nanoparticles with amorphous silica or crystalline alumina cores and noncrystallizable poly(vinyl pyrrolidone) (PVP) or crystallizable poly(ethylene glycol) (PEG) shells. Varying particle composition caused regular changes in the shell thickness from 1 to 2 nm (monomolecular layer) up to 90 nm. Far- and mid-IR spectroscopy allowed us to register hydrogen bonding and, tentatively, Lewis/Brønsted (LB) interfacial interactions as well as changes in the dynamics and conformational state of the polymer chains as a function of the nanoshell thickness. Their most pronounced peculiarities were found for the monomolecular polymer layers. The LB interactions were stronger with the alumina substrate than silica. DSC analysis was performed, and the data obtained were in agreement with the spectroscopic data. Unlike the bulk polymer, the PVP monolayer was characterized with an extraordinarily large dynamic heterogeneity within the glass transition while broadening the transition range and varying the activation energy by an order of magnitude. The PEG monolayer adsorbed on silica was totally amorphous, whereas a highly crystalline one with the anomalously thin lamellae, down to 3 nm thick, was adsorbed on an alumina surface, presumably as a result of the quasi-heteroepitaxial crystallization process.
    Langmuir 04/2010; 26(13):10968-79. · 4.38 Impact Factor
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    ABSTRACT: Polyurethane-poly(2-hydroxyethyl methacrylate) semi-IPN-silica nanocomposites with low content (0.25 and 3 wt%) of differently functionalized 3-D fumed silica nanoparticles were studied using a combined AFM/DSC/CRS approach over the −100 to 160°C range. The pronounced heterogeneity of the PHEMA and PU glass transitions’ dynamics and the effects of considerable suppression of dynamics and increasing elastic properties by silica additives were shown. It was caused by formation of peculiarly cross-linked structures due to “double hybridization,” in particular via selective covalent bonding of the silica surface, functionalized by ‒OH, ‒NH2 or ‒CH˭CH2 groups, with the matrix constituents. The silica dispersion remained unchanged in these nanocomposites; therefore the relationships between interfacial interactions and dynamics/modulus behavior could be followed.
    Journal of Macromolecular Science Part B 01/2010; 49(1):18-32. · 0.63 Impact Factor
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    ABSTRACT: Adsorption modification of nanosilica allows effective regulation of its physicochemical, structural–mechanical, pharmacological, and biological properties thus broadening its field of application. Liquid-phase methods used for this purpose have several substantial drawbacks mainly of a technological and ecological character. Therefore a new effective and ecologically safe method was developed for adsorption modification of nanosilica with non-volatile organic compounds (bioactive compounds, polymers). The process is carried out in fluidized state in gaseous dispersion medium with the solvent atmosphere. The developed method allows one to achieve a defined degree of surface coverage and to conserve initial dispersity of silica required.
    12/2009: pages 169-177;
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    ABSTRACT: Morphological, structural, and adsorptive characteristics of such fumed oxides as alumina, silica, composite silica/alumina and alumina/silica/titania were studied using a variety of experimental methods. Heating of nanooxides caused several processes resulting in the temperature dependent structural changes of the materials because of changes in the amounts of intact and dissociatively adsorbed water not only at the surface of the nanoparticles but also in their volume that lead to changes in the oxide matrix structure. These processes dependent on the composition of nanooxides are much stronger for nanosilica than for alumina or composite oxides. The morphology of primary nanoparticles is more stable on different treatments than the structure of secondary and ternary particles. The amounts of water adsorbed onto the nanooxides from air correspond to the amounts of water strongly bound (unfrozen at T < 273 K) to the oxide surfaces in aqueous suspensions.Graphical abstractHeating history can strongly affect many physicochemical properties of nanooxides, because of changes in the amounts of intact and dissociatively adsorbed water at the surface of nanoparticles and in their volume.
    Powder Technology. 01/2009; 195(3):245-258.
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    ABSTRACT: 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.
    Journal of Colloid and Interface Science 12/2008; 330(1):125-37. · 3.17 Impact Factor
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    ABSTRACT: 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.
    Journal of Colloid and Interface Science 08/2008; 323(1):6-17. · 3.17 Impact Factor

Publication Stats

154 Citations
71.70 Total Impact Points

Institutions

  • 1995–2010
    • National Academy of Sciences of Ukraine
      • O. O. Chuiko Institute of Surface Chemistry
      Kievo, Kyiv City, Ukraine
  • 2004
    • University of Brighton
      • School of Pharmacy and Biomolecular Sciences
      Brighton, ENG, United Kingdom
  • 2003
    • Maria Curie-Sklodowska University in Lublin
      • Faculty of Chemistry
      Lublin, Lublin Voivodeship, Poland
  • 1993
    • Ukrainian Academy of Agrarian Sciences
      Kievo, Kyiv City, Ukraine