Uno Mäeorg

University of Tartu, Dorpat, Tartu, Estonia

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Publications (85)191.09 Total impact

  • 04/2015; 21(2). DOI:10.5755/j01.mech.21.2.11723
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    ABSTRACT: Herein we report the study of the influence of synthesis conditions during the microwave-hydrothermal crystallization of freshly precipitated gels on the phase composition and morphology of the rare-earth doped yttrium orthophosphates nanoparticles. We characterize the nanoparticles of YPO4 and YPO4·0.8H2O using X-ray diffraction analysis, TEM, and FT-IR spectroscopy. Furthermore, we argue that for the given phase the degree of crystallinity and thus the sample morphology depend strongly on the synthesis conditions. We establish that the hexagonal hydrate phase can be obtained by means of microwave-hydrothermal method if one uses phosphate anion excess or adjusts pH of the reaction mixture. Also we show that the metastable hydrate phase is most likely stabilized by hydroxyl groups at elevated temperatures.
    Journal of Alloys and Compounds 03/2015; 639:415-421. DOI:10.1016/j.jallcom.2015.03.125 · 2.73 Impact Factor
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    ABSTRACT: Ionic liquid (IL) synergy with other materials may influence their properties significantly. Nevertheless, their advantageous liquid state turns out to be an impediment for applications in devices which need stable solid state shaping. In the current study we present a novel method where new siloxane functionalized IL acts as a modifier for carbon nanotubes (CNTs) and titanium alkoxide-CNT coated hybrid cotton fibers. This elaborated route carried out by interconnected and entangled ionic liquid, sol-gel and solid carbon nanotube networks opens up opportunities for functionalization of sol-gel materials with different shapes and sizes. The comparison of properties of IL, ionogel, ionogel/CNT mixture and titanium alkoxide coatings is performed. Ionogel-modified cotton fibers have increased hydrophobicity, linear density, breaking force and ultimate strength as compared to the uncoated cotton fibers. These properties are ensured even after washing threads with water. A uniformly coated CNT network around the fibers strengthens the material and increases its electric conductivity. New type of hybrids can be utilized in formulations which have UV-shielding and hydrophobic properties as well as for antibacterial properties. Characterization studies of the product were carried out by energy-dispersive X-ray spectroscopy (EDX), scanning electron microscopy (SEM), optical microscopy and infrared (IR) spectroscopy.
    Open Chemistry 01/2015; 13(1):279-286. DOI:10.1515/chem-2015-0031 · 1.33 Impact Factor
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    ABSTRACT: Using the energy transfer kinetics probe we found that –OH acceptors are distributed in the volume of the Nd3+:YPO4 nanoparticles as crystal structure defects or in the mesopores.
    Physical Chemistry Chemical Physics 10/2014; 16:26806-26815. DOI:10.1039/C4CP03774J · 4.20 Impact Factor
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    ABSTRACT: Thermally cross-linked glucose-containing electrospun gelatin meshes were studied as possible cell substrate materials. FTIR analysis was used to study the effect of glucose on cross-linking reactions. It was found that the presence of glucose increases the extent of cross-linking of fibrous gelatin scaffolds, which in return determines scaffold properties and their usability in tissue engineering applications. Easy to handle fabric-like scaffolds were obtained from blends containing up to 15% glucose. Maximum extent of cross-linking was reached at nearly 20% glucose content. Cross-linking effectively resulted in decreased solubility and increased resistance to enzymatic degradation. Preliminary short-term cell culture experiments indicate that such thermally cross-linked gelatin-glucose scaffolds are suitable for tissue engineering applications.
    Materials Science and Engineering C 09/2014; 42C:538-545. DOI:10.1016/j.msec.2014.05.075 · 3.09 Impact Factor
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    ABSTRACT: The preparation of ionogels by sol–gel processing has attracted much attention, because the final ceramic materials combine properties of both inorganic matrix (thermal and mechanical stability) and the ionic liquid (ionic conductivity). The aim of this study was to combine different imidazolium based ionic liquids (1-ethyl-3-methylimidazolium tetrafluoroborate [EMIM][BF4], 1-butyl-3-methyl imidazolium tetrafluoroborate [BMIM][BF4], 1-decyl-3-methylimidazolium tetrafluoroborate [DMIM][BF4] and 1-methyl-3-[3′-(triethoxysilyl)propyl]imidazolium chloride MTICl) with titanium(IV) butoxide to prepare homogenous hybrid fibers through aqueous sol–gel reaction. The study showed that ionic liquid miscibility with metal alkoxide plays an important role in the preparation of homogenous fibers. Unlike simple imidazolium salts functionalized ionic liquid was dispersed homogenously in fibers, but the main advantage is derived from its chemical structure. New stable ionic liquid can be involved in sol–gel processes through ethoxy groups and as a result it associates with titanium alkoxide network by covalent bonding providing non-leaking ceramic hybrid material. Indirect and direct characterization studies of the product were carried out by energy-dispersive X-ray spectroscopy (EDX), silicon-29 nuclear magnetic resonance spectroscopy (29Si NMR), scanning electron microscopy (SEM) and optical microscopies; also infrared spectra (IR) were recorded. Thermal analyses were performed by differential scanning calorimetry (DSC).
    Ceramics International 07/2014; 40(6):7729–7735. DOI:10.1016/j.ceramint.2013.12.114 · 2.09 Impact Factor
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    ABSTRACT: Anthraquinone groups were electrochemically grafted to glassy carbon (GC) electrodes via methylene linker to study the oxygen reduction reaction (ORR) in alkaline medium. Two different anthraquinone derivatives, 2- bromomethyl-anthraquinone or 2-chloromethylanthraquinone, were used to modify the GC electrode surface. Several modification conditions encompassing potential cycling and electrolysis at a fixed potential were employed in order to vary the surface concentration of MAQ groups (ΓMAQ) and to study the dependence of the O2 reduction behaviour on electrografting procedure. Cyclic voltammetry confirmed the presence of anthraquinone moieties attached to the GC electrode and ΓMAQ varied in the range of (0.5–2.4)×10−10 mol cm−2. Oxygen reduction was studied on MAQmodified GC electrodes of various surface coverage using the rotating disc electrode (RDE) and rotating ring-disc electrode (RRDE) methods. The RDE and RRDE results of O2 reduction reveal that GC/MAQ electrodes show rather similar electrocatalytic behaviour towards the ORR yielding hydrogen peroxide as the final product.
    Journal of Solid State Electrochemistry 06/2014; 18(6):1725–1733. DOI:10.1007/s10008-014-2392-4 · 2.23 Impact Factor
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    ABSTRACT: Transparent [90% transmittance at 550 nm at a sheet resistance (R-s) of 279 sq(-1)] poly(3,4-ethylenedioxythiophene) (PEDOT) films with electrical conductivities up to 1354 S cm(-1) are prepared using base-inhibited vapor phase polymerization at atmospheric pressure. The influence of reaction conditions, such as temperature and growth time, on the film formation is investigated. A simple and convenient two-electrode method is used for the in situ measurement of resistance, enabling to investigate the growth mechanism of polymer films and the influence of different parameters (relative humidity and the amount of oxidant) on the film growth. Low humidity exerts a detrimental effect on film growth and conductivity. In situ R-s measurements suggest that a large structural change occurs upon washing the PEDOT-oxidant film. (c) 2014 Wiley Periodicals, Inc. J Polym Sci Part B: Polym. Phys. 2014, 52, 561-571
    Journal of Polymer Science Part B Polymer Physics 04/2014; 52(8):561-571. DOI:10.1002/polb.23450 · 2.55 Impact Factor
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    ABSTRACT: While the popularity of the usage of room temperature microfluidic systems is booming in different technologies such as bio-technology, micro-scale chemistry, micro-printing and many others, systems applicable under high temperature and pressure are still remarkably under-developed. The main drawback of the existing systems is the inadequate quality of the available construction materials. In this work, extrusion of metal-oxo-alkoxide sol–gel precursors through the nozzle is utilized to produce the liquid thread that is allowed to self-transform into ceramic microtubes by a chemical curing process. The focus is on YSZ (8% Y2O3 stabilized ZrO2), which exhibits a stable 100% tetragonal phase nanocrystalline structure up to 1000 °C. These tubes have excellent mechanical characteristics and can withstand 1000 atm pressure inside the tubes. Owing to these and other physical, chemical and mechanical properties, there are many potential applications for these tubes, one example being that the high optical quality of the YSZ tubes could be useful for guiding of light. Ionic conductivity with no electronic component makes these tubes suitable for ionic membrane applications like solid oxide fuel cells (SOFCs) or corresponding gas sensors. Finally, we demonstrate a single-tube-based miniature plasma jet device potentially applicable as an ion source for local surface treatment or possibly as a micro plasma propulsion device for space applications.
    RSC Advances 04/2014; 4(34):17413-17419. DOI:10.1039/C4RA00621F · 3.84 Impact Factor
  • Oleg Lebedev · Uno Mäeorg
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    ABSTRACT: Aromatic-bridged bis(hydrazines) were found to be the main products in the reaction of hydrazine polyanions with α,α′-dibromo-o-xylene. It was confirmed that the reaction is driven by a metal–halogen exchange process. A three-step reaction mechanism is suggested.
    Organometallics 01/2014; 33(1):188-193. DOI:10.1021/om4009394 · 4.25 Impact Factor
  • Uno Mäeorg · Svetlana Tšupova
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    ABSTRACT: The synthesis of nitrogen containing heterocycles is of great importance in modern science, owing to their valuable biological properties, and endocyclic hydrazinocycles are no exception. There are methods that enable the transformation of amines to hydrazines, however the use of hydrazine derivatives and azo-compounds as starting materials is both logical and straightforward. In this review we aimed to summarize the methods that use simple hydrazines and azo-compounds for the synthesis of these heterocycles. We begin with simple stoichiometric alkylation of hydrazines and later on move to catalytic systems. Finally, we provide an overview of the advances in the field of azomethine imines chemistry.
    Heterocycles 01/2014; 88(1):129. DOI:10.3987/REV-13-SR(S)3 · 0.91 Impact Factor
  • Jaan Habicht · Uno Maeeorg
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    ABSTRACT: Coupling products of three major phenols appearing in the waste streams of shale oil production from kukersite oil shale were isolated and analysed using high-resolution mass spectrometry (HRMS). The pattern of water-soluble phenols in retorted kukersite semi-coke leachate changes quickly during weathering. The amount of phenols decreases, but the rate of disappearance is dissimilar for different constituents. Oxidation experiments with three major phenols (resorcinol, 5-methyl resorcinol, and 2,5-dimethylresorcinol) and their mixtures in pairs were performed in a reaction medium similar to semi-coke leachate. Reaction products were detected using silica gel thin layer chromatography (TLC) and isolated for further analysis by silica gel dry-column chromatography. The composition of primary reaction products was confirmed by nuclear magnetic resonance (NMR) spectroscopy. The primary coupling products of the studied resorcinols included the corresponding dimeric mono- and diquinones. Further coupling brought about the formation of water-insoluble products, which is the reason for the disappearance of resorcinols from the leachate.
    Proceedings of the Estonian Academy of Sciences 01/2014; 63(1):75. DOI:10.3176/proc.2014.1.10 · 0.37 Impact Factor
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    ABSTRACT: 5-Ethoxymethylfurfural (EMF) can be prepared from the corresponding halomethylfurfural and absolute ethanol in good yield. The use of significantly more affordable 96% ethanol results in formation of levulinic acid or its ester in considerable amount (up to 16%), which is difficult to separate from the desired EMF. In the present study we report that the addition of oil shale ash prevents the hydrolysis of the furan ring and enables the use of 96% ethanol with great success. The developed procedure is applicable to a wide range of aqueous alcohols, is operationally simple and utilizes an inexpensive basic ash, which is deposited in millions of tons per year. Notably, the basicity of the ash is decreased during the process, making its deposits less hazardous to the environment.
    RSC Advances 01/2014; 4:5689–5693. DOI:10.1039/c3ra46570e · 3.84 Impact Factor
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    ABSTRACT: In the present study, polymerizable ionic liquids (ILs), 1-[n-(methacryloyloxy)alkyl]-3-methylimidazolium bromides (n = 2, 6, 7, or 10), were synthesized in high yields. Moreover, the compounds obtained (n = 6, 7, or 10) were used in the preparation of composite materials comprising a polymerized IL matrix and a nonpolymerizable IL additive, 1-ethyl-3-methylimidazolium tetrafluoroborate ([EMIM][BF4]) in various proportions (up to 75% vol/vol of [EMIM][BF4]). The UV-radiation-initiated photopolymerization process was monitored in situ by measuring the resistivities of the mixtures. An increase in [EMIM][BF4] content in the composites led to an increase in the ionic conductivities of the materials while retaining their solid state at levels as high as 40% vol/vol of the [EMIM][BF4] content. The 40% vol/vol composites had conductivities of approximately 10−4 S/cm compared to the conductivities of 10−5 S/cm for the corresponding neat polymerized ILs. Above this [EMIM][BF4] content, the materials were sticky gels, and from 50% vol/vol onwards, entirely liquid.
    11/2013; 28(22). DOI:10.1557/jmr.2013.330
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    ABSTRACT: A new method for the synthesis of polymerizable ionic liquids bearing a methacrylate moiety was developed with the aim to avoid premature polymerization of synthesized compounds. Spacer length between the imidazolium cation and the polymerizable functional group varied from 2 to 10 carbon atoms. Different 1-(n-hydroxyalkyl)-3-methylimidazolium bromides and 1-[n-(methacryloyloxy)-alkyl]-3-methylimidazolium bromides were obtained with very good yields (more than 90%). [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications (R) for the following free supplemental resource: Full experimental and spectral details.]
    Synthetic Communications 11/2013; 43(21):2846-2852. DOI:10.1080/00397911.2012.745159 · 0.98 Impact Factor
  • Svetlana Tšupova · Uno Mäeorg
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    ABSTRACT: Palladium-catalyzed allylation of hydrazines using allyl alcohols is reported. This highly efficient protocol furnishes monoallylated hydrazines selectively, in 27-99% yields. Following an optimization of the reaction conditions and of the Pd-ligands, the allylations of both mono- and disubstituted hydrazines were investigated, as well as the effects of C2-substitution on the allylating agent. Of particular interest, a novel method for the selective monoallylation of monosubstituted hydrazines is demonstrated.
    Organic Letters 06/2013; 15(13). DOI:10.1021/ol4014798 · 6.32 Impact Factor
  • Aleksei Bredihhin · Uno Mäeorg · Lauri Vares
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    ABSTRACT: The influence of different parameters on the conversion of carbohydrates and biomass into the potential biofuel intermediate 5-bromomethylfurfural (BMF) has been studied. Our optimized conditions avoid the use of lithium salt additives, making this method cheaper and environmentally more benign compared to previously reported methods. Different wood species and their potential as a raw material in BMF and furfural production have also been evaluated. In addition, we report a very simple and efficient procedure for conversion of 5-hydroxymethylfurfural (HMF) into BMF or 5-chloromethylfurfural (CMF).
    Carbohydrate research 04/2013; 375C:63-67. DOI:10.1016/j.carres.2013.04.002 · 1.92 Impact Factor
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    ABSTRACT: An electrochemical study of Au electrodes electrografted with azobenzene (AB), Fast Garnet GBC (GBC) and Fast Black K (FBK) diazonium compounds is presented. Electrochemical quartz crystal microbalance, ellipsometry and atomic force microscopy investigations reveal the formation of multilayer films. The elemental composition of the aryl layers is examined by X-ray photoelectron spectroscopy. The electrochemical measurements reveal a quasi-reversible voltammogram of the Fe(CN)(6) (3-/4-) redox couple on bare Au and a sigmoidal shape for the GBC- and FBK-modified Au electrodes, thus demonstrating that electron transfer is blocked due to the surface modification. The electrografted AB layer results in strongest inhibition of the Fe(CN)(6) (3-/4-) response compared with other aryl layers. The same tendencies are observed for oxygen reduction; however, the blocking effect is not as strong as in the Fe(CN)(6) (3-/4-) redox system. The electrochemical impedance spectroscopy measurements allowed the calculation of low charge-transfer rates to the Fe(CN)(6) (3-) probe for the GBC- and FBK-modified Au electrodes in relation to bare Au. From these measurements it can be concluded that the FBK film is less compact or presents more pinholes than the electrografted GBC layer.
    ChemPhysChem 02/2013; 14(5). DOI:10.1002/cphc.201200934 · 3.36 Impact Factor
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    ABSTRACT: A technique of preparing microtube shape oxide structures by metal alkoxide gel sheet rolling is presented and discussed. Zr(OBu)(4) and Hf(OBu)(4) precursors have been used for self-formation of ZrO2 and HfO2 microrolls. The technique involves gelling the surface of concentrated sol, partition of gel film into segments by gel cracking and spontaneous rolling of obtained gel film segments. A phenomenological study of crack evolution in gel films has been conducted. The dependence of the thickness of formed gel film and rolling diameter on hydrolysis extent of metal alkoxide precursor and reaction time is reported. (C) 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
    physica status solidi (a) 12/2012; 209(12):2481-2486. DOI:10.1002/pssa.201228371 · 1.21 Impact Factor
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    ABSTRACT: The cluster crystals of Na2[SiF6] were obtained in the aqueous solutions of different methylalkylimidazolium (ethyl-, butyl- and decyl-) tetrafluoroborate ionic liquids (IL) in borosilicate glassware. It is demonstrated that sodium hexafluorosilicate crystalline compounds with good regularity and narrow size distribution containing dialkyl imidazolium ions between the hexagonal crystalline clusters interconnected to each other to a whole hexagonal aggregate can be obtained in large quantities. This characteristic phenomenon of crystallization of sodium hexafluorosilicate containing IL ions is reported for the first time. The mechanism of formation of various [RMIm]BF4–Na2[SiF6] microcrystalline morphologies and the influence of temperature on the growth kinetics are discussed. Crystallographic studies of the product were carried out by X-ray diffractometer (XRD), characterization by scanning electron microscopy (SEM) and optical microscopies; also infrared spectra (IR) were recorded. Thermal analysis were performed by differential scanning calorimetry–thermogravimetric analyzer (TGA–DSC). Presence of ionic liquid cations was confirmed by high resolution mass spectrometry (HRMS).
    Journal of Crystal Growth 12/2012; 361(1):51–56. DOI:10.1016/j.jcrysgro.2012.08.043 · 1.69 Impact Factor

Publication Stats

756 Citations
191.09 Total Impact Points

Institutions

  • 1993–2015
    • University of Tartu
      • • Institute of Chemistry
      • • Institute of Physics
      • • Department of Organic Chemistry
      Dorpat, Tartu, Estonia
  • 2010
    • Utrecht University
      • Division of Organic Chemistry and Catalysis
      Utrecht, Utrecht, Netherlands
  • 1998–2000
    • Uppsala University
      Uppsala, Uppsala, Sweden