Uno Mäeorg's research while affiliated with University of Tartu and other places
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Publications (139)
Silicone is often used in environments where water repellency is an advantage. Contact with water promotes the adhesion of microorganisms and biofilm formation. Depending on the application, this may increase the possibility of food poisoning and infections, the material's degrading appearance, and the likelihood of manufacturing defects. The preve...
Shungite is used in water filters that remove Escherichia coli from water. The mechanism and spectrum of the antibacterial activity of shungite are not precisely known. In this study, shungite and its dried water extract were characterized by means of X-ray diffraction, X-ray fluorescence and iodometry. The dried residue of the water extract of shu...
Transition metal-containing nitrogen-doped carbon catalysts for the electrochemical oxygen reduction reaction (ORR) were prepared from inexpensive biomass - rapeseed press cake; cobalt and/or iron salts and dicyandiamide were employed as metal and nitrogen sources. After acid treatment, the catalysts showed excellent electrocatalytic ORR activity i...
The present study considers TiC-derived carbon (CDC) and its partially oxidized derivative (ox-red-CDC) as potential electrode materials for pH-neutral aqueous electrolytes. The CDC was converted to ox-red-CDC by a modified Hummers’ method involving back-reduction with hydrogen at 800 °C. Oxidation degraded the graphitic CDC structures, as shown by...
Even though enehydrazide moiety is present in many pharmaceuticals, there is currently no straightforward method available for preparing cyclic enehydrazides, which could be valuable building blocks in anticancer research. Herein, we report how electronic effects and ring size influence the direction and yield of Ru catalytic carbon–carbon double b...
The kinetics of the platinum‐catalyzed dehydrocondensation reaction for five different mono‐alcohols and water is studied in order to identify the ones with the highest effectiveness in releasing gaseous H2 from the SiH groups of poly(methylhydrosiloxane) (PMHS). Our results show that the most common logic rules of alcohol reactivity do not apply...
Fluorescent nanoparticles (FNPs) have been widely used in chemistry and medicine for decades, but their employment in biology is relatively recent. Past reviews on FNPs have focused on chemical, physical or medical uses, making the extrapolation to biological applications difficult. In biology, FNPs have largely been used for biosensing and molecul...
We investigated the distribution of the Nd³⁺ impurity centers over five Ca²⁺ positions in the β-Ca3(PO4)2 lattice (space group R3c) using low-temperature site-selective laser spectroscopy and fluorescence kinetics measured by double spectral selection in combination with the results of periodic density functional theory (DFT) calculations.
Site-sel...
Construction of road embankments in peatlands commonly involves replacement of the peat with a fill-up soil of an adequate load-bearing capacity. This usually requires a lowering of the water level, turning a peatland from a carbon sink to a source of greenhouse gases. Thus, alternatives are sought that are less costly in both economic and ecologic...
In this study, two compounds (melamine phosphate and hexachlorocyclotriphosphazene) were used as nitrogen and phosphorus precursors to dope silicon carbide-derived carbon (SiCDC) with nitrogen and phosphorus moieties. The successful heteroatom doping was confirmed by X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy/energy-dis...
This article presents a method that efficiently enables us to identify differences in the composition of water clusters. The Fourier transform infrared (FTIR) spectra in the O–H stretching region 2500 cm⁻¹ to 4000 cm⁻¹ of apple juice, raspberry juice, lyophilized water from apples (apple water), and lyophilized water from raspberry juice (raspberry...
It is highly desirable to synthesise heteroatom-doped carbon-based materials in an environmentally friendly and simple way, which possess good electrocatalytic activity towards the oxygen reduction reaction (ORR). Therefore, in this study, we focused on comparing sulphur and nitrogen co-doped graphene-based materials prepared using simple synthesis...
Glyphosate is the most widespread herbicide and its global use is steadily increasing. Although glyphosate is considered to have low toxicity, its wide application has raised concerns about its effects on human health. The extensive use of glyphosate has risen a need of its continuous monitoring in drinking and surface waters to assure in accordanc...
A biomorphic microporous carbon is of a great interest in many applications, including energy storage, due to the cheap and “green” precursor materials. The macroscopic texture of carbon, which copies that of biologic precursor, benefits an access to the micropores. In this study, the novel wood-origin carbide-derived carbon (wCDC) was prepared by...
The soft sensors and electronic skin concept often relies on composites based on an elastomer (like PDMS) with some conducting fillers (like carbon nanotubes). In this paper, the ambient moisture sensitivity of MWCNT/PDMS composite multimodal mechanical sensors is demonstrated and tested in both resistance and capacitance measurements. In addition...
Modifications of pore size distribution and structural order of nanoporous carbide-derived carbon (CDC) materials with variety of surface areas and pore sizes were investigated using physical activation by etching with water vapour. Variable etching duration was used to explore the activation impact on the pore size distribution and the adsorption...
Double bond isomerization by in situ generated ruthenium hydride catalyst in 6- to 9-membered hydrazine heterocycles including an endocyclic N–N bond was investigated. Based on the results of the experiments, a conclusion was made that the generation of resonance-stabilized enehydrazides is generally favored, but in some cases, the reaction pathway...
Simple and modified synthesis route for preparation of Fe-N/C type oxygen reduction reaction (ORR) catalysts has been worked out and discussed. The significant effect of the N precursor chemical composition on the ORR activity in 0.1 M KOH and 0.1 M HClO4 electrolyte solutions has been demonstrated. The half-wave potential values increased in the f...
Liquid phase deposition polymerization (LPDP) is a recently reported method suitable for preparation of the conducting polymer poly(3,4-ethylenedioxythiophene) (PEDOT), with some similarities to vapor phase polymerization except the polymer film growth at the gas-solid boundary is replaced with growth at the liquid-solid interfacial layer. Film gro...
Hydrophobic silica aerogel powder and hollow glass microspheres (HGM) were used as fillers for an epoxy adhesive to improve its thermal insulator properties. At 50 wt% of HGM content, the thermal conductivity of the HGM/epoxy composite decreased from 0.182 W/m.K to 0.104 W/m.K. The aerogel/epoxy composite, on the contrary, showed a slight increase...
Triboelectric generators (TEGs) are devices that convert mechanical energy to electrical energy through triboelectric charging of different material surfaces at periodic contact. Typically, such devices consist of two dielectric contacting layers with electrodes attached on the non-contacting sides but alternatively, one material can simultaneously...
Of numerous species belonging to the medicinally important genus Hypericum, only H. perforatum L. and H. maculatum Crantz grow widely in Estonia. A comparative biochemical systematics study of hypericins, hyperforins and other phenolics within Hypericum spp. growing in Estonia was performed. For comprehensive metabolomic investigation, 42 samples o...
A 4-step route for the synthesis of novel phthalimide protected hydrazine heterocycles that include a C˭C double bond in the cycle was developed. Phthalimide protected Boc-hydrazine was used as a starting material, which was alkylated with bromoalkenes in mild conditions. Further steps involved Boc-deprotection and second alkylation with bromoalken...
Recently, ionic liquids (ILs) have been recognized to have significant potential as precursors or reaction media in nanolithography and MEMS component technologies. In this work, we demonstrate straightforward fabrication of positioned and well-defined microscale structures by electron beam (e-beam) irradiation of two different ILs: 1-hexyl-3-methy...
![Fig. 3. 1 H-NMR spectrum of TiO 2-MTICl in [THTP][DEHP] (P-IL 2 ).](profile/Marta-Berholts/publication/317116810/figure/fig3/AS:570406128291841@1513006826345/1-H-NMR-spectrum-of-TiO-2-MTICl-in-THTPDEHP-P-IL-2_Q320.jpg)
The lubricating performance of two oils (base oil PAO and synthetic motor oil denoted as 5w40) was clarified by doping them with phosphonium-based ionic liquids (P-ILs) and a mixture of P-ILs and metal oxide nanoparticles. The nanoparticles were synthesized by heating titanium tetrabutoxide and 1-methyl-3-(triethoxysilylpropyl)imidazolium chlorideb...
2-Bromo-5-(2-bromo-2-nitrovinyl)furan (G1 or Furvina) is an antimicrobial with a direct reactivity against thiol groups. It is active against Gram-positive and Gram-negative bacteria, yeasts and filamentous fungi. By reacting with thiol groups it causes direct damage to proteins but, as a result, is very short-living and interconverts into an array...
In this paper, a novel but simple deformation sensor concept is introduced together with the required electronics design to run it. The evaluated prototype sensors showed linear response to both elongation and bending for many hours of repetitive deformations, while still remaining simple and low cost. Thanks to the Wheatstone bridge setup used to...
We report the mechanical performance of α-FeOOH nanowire reinforced poly(vinyl alcohol) (PVA) composite nanofiber mat, fabricated using straightforward aqueous processing methods. Goethite (α-FeOOH) nanocrystals have a high elastic modulus and –OH rich surface, ensuring strong interactions with hydrophilic polymers and effective reinforcement. Need...
The influence of lignocellulosic nanofibers (LCNF) additive on the inherent mechanical properties of submicron electrospun poly(vinyl alcohol) (PVA) fibers is reported. LCNF with a diameter of 25±15 nm and a length of 220±90 nm obtained from hemp shives were dispersed in aqueous PVA solutions to produce homogeneous nanocomposite fibers with 0, 5, a...
Mechanism of an efficient and easily applicable catalytic system for the copper(I)-catalyzed azide-alkyne cycloaddition (CuAAC) reaction, consisting of phosphane-ligated CuI carboxylates and apolar/aprotic solvent was investigated by means of 1H NMR reaction monitoring techniques, isotope exchange studies, and DFT calculations (at the M06L/6-311++G...
Tin oxide is considered to be one of the most promising semiconductor oxide materials for use as a gas sensor. However, a simple route for the controllable build-up of nanostructured, sufficiently pure and hierarchical SnO2 structures for gas sensor applications is still a challenge. In the current work, an aqueous SnO2 nanoparticulate precursor so...
Sufficient stability of conductive polymers is crucial for allowing widespread application of these materials. Poly(3,4-ethylenedioxythiophene) (PEDOT) has a relatively high conductivity and transparency among conductive polymers. In this study, the stability of PEDOT thin films prepared by vapor phase polymerization was investigated at elevated te...
This research was conducted to develop a method for the establishment of changes in absorbance that occurs in the OH stretching vibration region 2,500-4,000 cm⁻¹ of FT-IR transmission spectra of water and juices. With the methodology described in this paper, a signal-to-noise ratio was obtained, which allows to measure the reproducibly of the FT-IR...
The polymerizable monomer of 1-(6-hydroxyhexyl)-3-methylimiadazolium bromide ionic liquid (IL) was synthesized. The thin layer chromatography tests were conducted at each step to verify the reactions. It was observed that the ionic liquid compound formed after 48 hours though confirmed the presence of starting materials. A high viscous transparent...
The synthesis of polymerizable ionic liquid (PIL) is a challenging objective and has drawn an intense attraction for its uniqueness such as mechanical durability, excellent ionic conductivity and low glass transition temperature (Tg) which lead to employ in electrospinning process and other emerging technology for its potential application in vario...
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 l...
Glyphosate (N-phosphonomethylglycine) is the most widely used non-selective postemergence herbicide for weed and vegetation control. The need for monitoring glyphosate levels in environmental samples and agricultural products proceeds from its extensive use due to the unregulated application and contradictory information about its toxicity on livin...
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 evaluat...
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 optimi...
Water is inherently a simple substance, but from Aristotle's time until today it raises a lot of questions. Living cells are about eighty per cent water. Organisms consist essentially of liquid water, which fulfils a lot of functions and should never be considered just an inert diluent. The unique properties of water are of fundamental relevance fo...
This work describes synthesis of CH2-skipped alternating piperazine-pyridine cycles with azide end-group starting from piperazine, 1-methylpiperazine and pyridine-2,6-dicarboxylic acid. This compound can be used to enhance binding efficiency by shielding repulsion between negatively charged phosphate groups in DNA-oligonucleotide hybridization tech...
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...
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.
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 tetr...
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...
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...
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 qualit...
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...
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.
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, X...
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 th...
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...
In the current invention a method for the preparation of an oxide material was described that involves bringing the sol onto the substrate, the gelation of the solution and thermal treatment of the gel. Alkoxides are used as precursor materials for the sol preparation and substrate free structures are employed for the manufacturing of the oxide mat...
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-ethy...
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 brom...
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 effec...
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 woo...
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 surf...
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 e...
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 spontane...
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 imidazol...
Three different azobenzene derivatives (azobenzene diazonium tetrafluoroborate, Fast Garnet GBC sulphate salt and Fast Black K salt) were covalently attached to glassy carbon (GC) electrodes by electrochemical grafting. The grafting of GC surfaces was controlled by varying the number of potential cycles during the modification procedures. The prese...
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 e...
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 me...
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-aminophen...
In the present work, it is shown that carbon nanotube-doped transition metal oxides are potential candidates for use as ceramic transparent electrode materials. Used carbon nanotubes (CNT-s) are synthesized by using chemical vapor deposition (CVD) method. Electrodes in shape of fibers are obtained via inexpensive and low temperature sot-gel method....
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 CeO...
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),...
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....
Ionic Polymer Metal Composites (IPMCs) are soft electroactive polymer materials that bend in response to the voltage stimulus (1 - 4 V). They can be used as actuators or sensors. In this paper, we introduce two new highly-porous carbon materials for assembling high specific area electrodes for IPMC actuators and compare their electromechanical perf...
Ionic polymer metal composites (IPMCs) are electroactive material devices that bend at low applied voltage (1–4 V). Inversely, a voltage is generated when the materials are deformed, which makes them useful both as sensors and actuators. In this paper, we propose two new highly porous carbon materials as electrodes for IPMC actuators, generating a...
Preparation of mechanically deboned meat (MDM) enables a more economical use of animal products and reduction of the amount of biological wastes. On the other hand, enhanced lipid oxidation causes concerns about safety and quality of MDM. There is no information about the actual chemical structure and possible health impact of these oxidation produ...
A new efficient technique for Boc introduction into hydrazines and amines is reported. The substrate is stirred in molten di-(tert-butyl)dicarbonate without any solvent. The method requires neither DMAP nor other catalyst. The scope of the method is demonstrated using several hydrazines and amines.
A novel method for the synthesis of cyclic hydrazine derivatives is reported. The new method for the generation of nitrogen-containing heterocycles is based on a polyanion strategy. The described method provides a convenient access to cyclic hydrazine derivatives, which are extensively used in drug industry and agriculture. The advantages and limit...
The electrochemical reduction of oxygen on glassy carbon (GC) electrodes modified with in situ generated diazonium cations of anthraquinone (AQ) has been studied using the rotating disk electrode (RDE) technique. The electrografting of the GC electrodes was carried out in two different media: in acetonitrile and in an aqueous acidic solution (0.5M...