Uno Mäeorg

University of Tartu, Dorpat, Tartu, Estonia

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Publications (87)196.37 Total impact

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    ABSTRACT: Corrosion inhibition of metallic substrates is an important and crucial step for great economical as well as environmental savings. In this paper, we introduce an extra thin effective corrosion inhibitive material having layered structure designed for protection and functionalization of Ti Grade 5 alloy substrates. The coating consists of a first layer made of thin graphene nanoplatelets, on top of which a multilayer Al2O3 and TiO2 films is applied by low-temperature atomic layer deposition. The amorphous structure of the metal oxide films was confirmed by micro-Raman and X-ray diffraction analysis. Corrosion inhibition ability of the prepared coatings was analyzed by open circuit potential, potentiodynamic plot and by voltammetric analysis, in aqueous potassium bromide solution. The open circuit potential of the graphene-metal oxide coated substrate showed much passive nature than bare substrate or graphene coated or only metal oxide coated substrates. The localized corrosion potential of the graphene-metal oxide coated, only metal oxide coated, and bare substrates were found 5.5, 3.0, and 1.1 V, respectively. In addition, corrosion current density values of the graphene-metal oxide and only metal oxide coated substrates showed much more passive nature than the bare and graphene coated substrates. Long immersion test in the salt solution further clarified the effective corrosion inhibition of the graphene-metal oxide coated substrate. The analyzed results reflect that the graphene-metal oxide films can be used to prepare better and effective corrosion inhibition coatings for the Ti Grade 5 alloy to increase their lifetime.
    Full-text · Article · Sep 2015 · Journal of Nanoscience and Nanotechnology
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    ABSTRACT: Synthesis of important heterocyclic hydrazine derivatives N-aminopyrrolidine, N-aminopiperidine, and N-aminoazepane from hydrazine hydrate and dihalogenides were examined and optimized. These heterocyclic hydrazine derivatives were used in condensation reactions with six different monosaccharides to form corresponding hydrazones. Biological evaluations of these novel compounds, which are simple acyclic nucleoside analogs, were done. L-Arabinose N-aminoazepane hydrazone showed minor anti-HIV activity, giving a starting point for further structural modifications. (Chemical Equation Presented).
    No preview · Article · Jun 2015 · Synthetic Communications
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    ABSTRACT: The aim of the present study was to investigate a novel composite as lubricant additive for metal wear parts, composing of protic ionic liquid and functionalized copper oxide nanoparticle composite. A simple and an easy-to-modify synthesis method for the preparation of thiol covered copper oxide nanoparticles was developed. A long process of optimization of reaction parameters was carried out that resulted in preparing non-agglomerated oil dispersible copper oxide nanoparticles with an estimated average diameter of 60 nanometers based on SEM measurements. Novel protic ionic liquid, which dissolves in oil was synthesized. Lubricant tribological experiments with the standardized four-ball-method were conducted with 15 kg. The addition of 3% ionic liquid and 0.5% copper oxide nanoparticles to base oil reduced the wear up to 35% compared to base oil without any additives, while 1% of protic IL reduced wear up to 47%. In addition, the novel type lubricant additive has many advantages and can also widen the range of applications, e.g. wider temperature range and preserved functionality at harsh conditions where oil-based lubricants fail. © 2015, Kauno Technologijos Universitetas. All rights reserved.
    No preview · Article · Apr 2015
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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.
    Full-text · Article · Jan 2015 · Open Chemistry
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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.
    Full-text · Article · Oct 2014 · Physical Chemistry Chemical Physics
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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.
    No preview · Article · Sep 2014 · Materials Science and Engineering C
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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).
    Full-text · Article · Jul 2014 · Ceramics International
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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.
    No preview · Article · Jun 2014 · Journal of Solid State Electrochemistry
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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
    No preview · Article · Apr 2014 · Journal of Polymer Science Part B Polymer Physics
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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.
    Full-text · Article · Apr 2014 · RSC Advances
  • 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.
    No preview · Article · Apr 2014 · Heterocycles
  • 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.
    No preview · Article · Jan 2014 · Organometallics
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    ABSTRACT: A new approach for functionalising oxidised MWCNTs using hydroxylated imidazolium bromide via esterification reaction is reported. The bromide anion of a functionalised MWCNTs was exchanged with bis(trifluoromethanesulfonyl) imide (TFSI) through a metathesis reaction to improve its solubility in the IL medium. Composite was characterized with IR, XPS, EDX and TGA analysis, which clearly confirmed that the MWCNTs were functionalized with IL. For potential application as lubricant, the tribological properties of the IL-functionalised MWCNTs (MWCNT-IL) were also evaluated. It was confirmed that even low concentrations of MWCNT-IL composite in ILs causes a significant improvement in the anti-wear and friction properties.
    No preview · Article · Jan 2014 · MRS Online Proceeding Library
  • 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.
    No preview · Article · Jan 2014 · Proceedings of the Estonian Academy of Sciences
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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.
    No preview · Article · Jan 2014 · RSC Advances
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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.
    No preview · Article · Nov 2013
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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.]
    No preview · Article · Nov 2013 · Synthetic Communications
  • 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.
    No preview · Article · Jun 2013 · Organic Letters
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    ABSTRACT: Gas sensor material was prepared by encapsulation of functionalized single-walled carbon nanotubes (SWCNT) into a gas-permeable polymer poly(1-trimethylsilyl-1-propyne) (PTMSP). A phenylhydrazino group was used for the functionalization of SWCNTs to improve their solubility and compatibility with polymers. Syntheses were carried out in aqueous surfactant solutions and in pure phenylhydrazine without surfactant. Two different temperatures (24 and 50°C) and two surfactants (sodium dodecyl sulfate and tricaprylmethylammonium chloride — Aliquat®336) were compared. Functionalized SWCNTs were characterized by X-ray photoelectron (XPS), Raman and Fourier transform infrared (FTIR) spectroscopy. Analyses showed that the synthesis at higher temperature in pure phenylhydrazine resulted in the highest functionalization yield. Phenylhydrazine itself proved to be a good solvent for SWCNTs. The functionalized nanotubes were soluble in organic solvents that under the same conditions were appropriate solvents for polymers. The sensitivity of functionalized SWCNT-PTMSP thin film composite to NO2 gas at room temperature was significantly higher than that of the similar sensor material containing the pristine SWCNTs.
    No preview · Article · Jun 2013 · Central European Journal of Chemistry
  • 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).
    No preview · Article · Apr 2013 · Carbohydrate research

Publication Stats

1k Citations
196.37 Total Impact Points


  • 2000-2015
    • University of Tartu
      • • Institute of Physics
      • • Institute of Chemistry
      • • Department of Organic Chemistry
      Dorpat, Tartu, Estonia
  • 2010
    • Utrecht University
      • Division of Organic Chemistry and Catalysis
      Utrecht, Utrecht, Netherlands
  • 1996-2000
    • Uppsala University
      • Department of Medical Biochemistry and Microbiology
      Uppsala, Uppsala, Sweden