Uno Mäeorg

University of Tartu, Dorpat, Tartu County, Estonia

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Publications (75)136.2 Total impact

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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.
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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. · 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 & engineering. C, Materials for biological applications. 09/2014; 42C:538-545.
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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. · 2.09 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. · 3.71 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. · 3.71 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 01/2014; 18:1725–1733. · 2.23 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.
    Journal of Materials Research. 11/2013; 28(22).
  • 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; · 6.32 Impact Factor
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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. · 2.03 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; · 3.36 Impact Factor
  • physica status solidi (a) 12/2012; 209(12):2481-2486. · 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; 361:51–56. · 1.69 Impact Factor
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    ABSTRACT: In the present work, it is shown that carbon nanotube-doped transition metal oxides are potential candidates for use as ceramic transparent electrode materials. Electrodes in shape of fibers are obtained via inexpensive and low temperature sol-gel method. Fiber electrodes are characterised by SEM-FIB and rheological analizes. Due to extraordinary electrical and optical properties of CNT-s and good chemical and physical stability of metal oxide ceramics, resulting composites could be an interesting subject for industry.
    IOP Conference Series Materials Science and Engineering 08/2012; 38(1).
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    ABSTRACT: An efficient method for the synthesis of cyclic hydrazine derivatives starting from disubstituted hydrazines is reported. The method is based on the selective alkylation of hydrazine dianions with bromoalkenes and subsequent cyclization using Grubbs’ catalysts. The described method provides fast and easy access to the substrates for ring-closing metathesis and the corresponding heterocycles containing a hydrazine moiety. The scope and limitations of the new method are also demonstrated.
    Tetrahedron. 01/2012; 68(4):1011–1016.
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    ABSTRACT: The invention of electrospinning has solved the problem of producing micro- and nanoscaled metal oxide fibres in bulk quantities. However, until now no methods have been available for preparing a single nanofibre of a metal oxide. In this work, the direct drawing method was successfully applied to produce metal oxide (SnO2, TiO2, ZrO2, HfO2 and CeO2) fibres with a high aspect ratio (up to 10 000) and a diameter as small as 200 nm. The sol–gel processing includes consumption of precursors obtained from alkoxides by aqueous or non-aqueous polymerization. Shear thinning of the precursors enables pulling a material into a fibre. This rheological behaviour can be explained by sliding of particles owing to external forces. Transmission (propagation) of light along microscaled fibres and their excellent surface morphology suggest that metal oxide nanofibres can be directly drawn from sol precursors for use in integrated photonic systems.
    Science and Technology of Advanced Materials 06/2011; 12(3):034412. · 2.61 Impact Factor
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    ABSTRACT: The electrochemical response of 2,2′-azino-bis(3-ethylbenzothiazoline-6-sulfonic acid) diammonium salt (ABTS) on aryl-modified glassy carbon (GC) electrodes has been investigated. The electrochemical modification of GC surface with 4-nitrophenyl (NP) and 4-carboxyphenyl (CP) groups was performed using the diazonium reduction method. The 4-aminophenyl-modified GC electrodes were obtained by electroreduction of NP films. The surface coverage of aryl groups was altered by varying the number of potential scans during electrografting experiments. The electrochemical behaviour of ABTS was studied on bare and aryl-modified GC electrodes using cyclic voltammetry and the rotating disk electrode (RDE) methods. Electrochemical measurements were performed in acetate and phosphate buffers (pH=4–8) to study the effect of pH on the electron transfer process. The response of ABTS was independent of pH for bare GC and GC/NP electrodes (modified by 20 electrografting scans), whereas a slight pH-dependence was observed for other electrodes. The strongest blocking action was observed for the NP-modified GC electrodes of higher surface coverage and the lowest for reduced NP films (modified by a single electrografting scan).
    Journal of Electroanalytical Chemistry - J ELECTROANAL CHEM. 01/2011; 661(2):343-350.
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    ABSTRACT: A new method for the synthesis of 3-hydrazinopropyl trimethoxysilane is proposed. The method is relatively simple and is based on hydrosilylation like the synthesis of analogous aminosilanes. For drying allylhydrazine hydrate a new efficient silyl hydride base method is proposed. The product, a new hydrazino-ormosil (organically modified silicate), can be applied in chemical modification of SiO 2 surfaces, thus offering an alternative to aminosilane modification, which is widely applied in several surface coating technologies.
    Proceedings of the Estonian Academy of Sciences 01/2011; 60(1):64-68. · 0.37 Impact Factor
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    ABSTRACT: The 2,2,2-trichloroethoxycarbonyl (Troc) protecting group was efficiently removed from Troc-protected aliphatic and aromatic amines and also some Troc, Tos- and Troc, Ac-protected amines using activated mischmetal (MM). All reactions were performed by refluxing in dry tetrahydrofuran under an argon atmosphere and gave moderate to excellent yields. Several new compounds were synthesized, and new data about reactivity of Troc group were obtained.
    Synthetic Communications 11/2010; 40(22):3397-3404. · 1.06 Impact Factor
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    ABSTRACT: The scope of a set of recently reported hydrazine reagents has been explored with respect to arylation. Compounds of type R1NHNHCOR2 can be selectively arylated under very mild conditions using triarylbismuth diacetates.
    ChemInform 01/2010; 33(46).

Publication Stats

610 Citations
136.20 Total Impact Points


  • 1993–2014
    • University of Tartu
      • • Institute of Chemistry
      • • Institute of Physics
      • • Department of Pharmacology (ARFR)
      • • Department of Organic Chemistry
      Dorpat, Tartu County, Estonia
  • 1998
    • Uppsala University
      Uppsala, Uppsala, Sweden