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 YPO sub(4) and YPO sub(4) times 0.8H sub(2)O 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.
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•Possible Nd3+ positions in β-tricalcium phosphate were calculated by DFT methods.•Two types of charge compensation have been identified in Nd3+ doped β –TCP.•Low-temperature site-selective laser ...spectroscopy of Nd3+ doped β -TCP was done.•The position of eight Nd3+ optical centers (OCs) in β -TCP lattice was determined.•Two types of OCs, Nd-Nd pairs and Nd-OH were identified by energy transfer probe.
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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-selective fluorescence excitation spectra of the Nd3+ ion were measured by fine tuning the laser wavelength in the spectral band of the 4I9/2(1) → 4G5/2(1,2) transitions and by fluorescence detection in the spectral band of the 4F3/2(1) → 4I9/2(1,2) transitions. The kinetics of nonradiatiative energy transfer from the 4F3/2(1) crystal field (CF) level was used to probe the local structure of Nd3+ sites. Theoretical modelling of the replacement of Ca2+ ions by Nd3+ ions with different charge compensation schemes was carried out. In the context of heterovalent substitution, hydrothermal synthesis conditions, and charge-balance mechanisms, two structural models of substitution have been proposed and thoroughly studied: substitution by a single Nd3+ ion accompanied by a trapped hydroxyl group, and substitution with a pair of Nd3+ ions. Numerical modeling of possible substitution scenarios calculated for a large number of combinations of cation-exchange sites in the lattice was carried out. The results obtained were classified according to the parameters of the accommodation of impurities and the energies of defect formation. The most favorable configurations of the distribution of impurity Nd3+ cations in the β-Ca3(PO4)2 lattice were predicted. By combining the “energy transfer probe” analysis and the results of the structural modeling, a relationship was found between the local geometry and the spectral and kinetic properties of luminescence of the Nd3+ optical centers. This allowed us to accurately determine the local structural geometries of eight experimentally detected the Nd3+ optical centers among the various possibilities in the distribution of the dopant ions over five cationic positions in β-Ca3(PO4)2. Six optical centers represent different types of Nd3+ - Nd3+ pairs, the formation of which is energetically favorable for charge compensation according to the 3Ca2+ → 2Nd3+ + ⎕ scheme, when one calcium position remains vacant. Two optical centers are single centers of the Nd3+ ion in which the charge is compensated by negatively charged hydroxyl ions intercalated during hydrothermal synthesis according to the scheme Ca2+→ Nd3+ + OH−. It was assumed that these pairs are located in several structural cavities free of PO4 tetrahedra.
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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 following order: C(SiC) < Fe + Urea/C < Fe + EDTA/C < Fe + DIPO/C ≤ Fe + Phen/C ≤ Fe + Bipyr/C in both electrolyte solutions studied. Molar ratio of Fe:N precursor and Fe content change in the Fe + Bipyr/C catalyst was found to be negligible. Noticeable change in ORR activity has been observed after acid treatment step of Fe + Bipyr/C. The 150-h durability tests demonstrated that in terms of the activity/stability ratio the Fe + Phen/C is the best ORR catalyst.
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•ORR activity strongly depends on the chemical composition of N precursor.•Novel 1,3-di(1H-imidazol-1-yl)-2-propanol based Fe-N/C catalyst for ORR•~150 h durability tests performed for Fe-N/C catalyst in 0.1 M HClO4 solution.•The durability test showed better stability for Fe + Phen/C.
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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 sol, which is free of organic contaminants and sorbed ions and is fully stable over time, was prepared in a highly reproducible manner from an alkoxide Sn(OR)4 just by mixing it with a large excess of pure neutral water. The precursor is formed as a separate liquid phase. The structure and purity of the precursor is revealed using XRD, SAXS, EXAFS, HRTEM imaging, FTIR, and XRF analysis. An unconventional approach for the estimation of the particle size based on the quantification of the Sn-Sn contacts in the structure was developed using EXAFS spectroscopy and verified using HRTEM. To construct sensors with a hierarchical 3D structure, we employed an unusual emulsification technique not involving any additives or surfactants, using simply the extraction of the liquid phase, water, with the help of dry butanol under ambient conditions. The originally generated crystalline but yet highly reactive nanoparticles form relatively uniform spheres through self-assembly and solidify instantly. The spheres floating in butanol were left to deposit on the surface of quartz plates bearing sputtered gold electrodes, producing ready-for-use gas sensors in the form of ca. 50 μm thick sphere-based-films. The films were dried for 24 h and calcined at 300 °C in air before use. The gas sensitivity of the structures was tested in the temperature range of 150-400 °C. The materials showed a very quickly emerging and reversible (20-30 times) increase in electrical conductivity as a response to exposure to air containing 100 ppm of H2 or CO and short (10 s) recovery times when the gas flow was stopped.
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 accordance with the set standards. Within the present study, we have developed a novel assay for the on-site detection of glyphosate by combining flow-through technology with the high specificity of immunorecognition. The proposed biosensing system was based on the detection of fluorescence signal generated by the quantitative replacement of glyphosate in antigen-antibody complex with IgY-type anti-glyphosate antibodies on microbeads by synthetic 5-carboxytetramethylrhodamine (5-TAMRA) conjugated glyphosate. The working range of this assay was in low millimolar range and the time required for glyphosate detection around 0.5 h. The applicability of the immunoassay for glyphosate detection in surface water was tested and the biosensor results were validated with high-performance liquid chromatography.
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 serve as both a contacting and an electrode material. In this work, we report the use of poly(3,4-ethylenedioxythiophene) (PEDOT) for TEG device were PEDOT film serves as both a contacting surface to PDMS and as an electrode. Two different PEDOT films were prepared on glass substrates by vapour-phase polymerization (VPP) and VPP combined with electropolymerization method and compared as TEG electrodes. Additionally, PEDOT/poly(1,6-hexanediol-co-citric acid) (PHC) composite films were prepared by using solution casting polymerization. These methods yielded PEDOT films with different morphology, surface roughness and conductivity. Best performance was demonstrated for the PEDOT film with the lowest surface roughness (1.88 nm RMS), prepared by VPP method, which generated peak current of 0.45 mA/m2 and power density of 95 W/m2, outperforming Sn doped In2O3 electrode approximately by threefold in the same experimental setup.
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•PEDOT serving as both contacting surface and electrode in TEG device.•Various kinds of PEDOT films were synthesized for TEG.•Chemical composition of PEDOT may have high influence on TEG performance.•PEDOT is a superior electrode material for TEG devices in conjunction with PDMS.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK, ZRSKP
Šungiidifiltreid on kasutatud Escherichia coli eemaldamiseks veest. Šungiidivee toimemehhanism ja toimespekter pole teada. Käesolev uuring kirjeldab šungiiti ja selle vesiekstrakti ...röntgendifraktsiooni, röntgenfluorestsentsi ja jodomeetria abil. Šungiidi vesiekstrakti kuivjääk sisaldas suhteliselt vähe süsinikku (28,1% kivimis vs 0,5% kuivjäägis), räni (23,9% vs 0,3%) ja kaaliumi (1,14% vs 0,05%) ning suhteliselt palju väävlit (1,6% vs 21,6%), rauda (1,4% vs 10%), alumiiniumi (2,1% vs 5%) ja niklit (0,02% vs 1,14%). Selgitati välja šungiidivee möju Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, Candida albicans, Streptococcus uberis ja Saccharomyces cerevisiae suhtes. Escherichia coli, Pseudomonas aeruginosa ja Streptococcus uberis ei olnud 24h inkubatsiooni 3:7 ekstraktis välja külvatavad. Staphylococcus aureus, Candida albicans ja Saccharomyces cerevisiae elasid inkubatsiooni šungiidivees üle vörreldavalt destilleeritud veega. Vee pH neutraliseerimine ei kaotanud bakteritsiidset toimet. Samas, toitainete juuresolekul ei ilmnenud šungiidiveel bakterivastast möju.
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8.
A route towards a new hydrazino-ormosil Põhako, K; Mäeorg, U; Saal, K ...
Journal of physics. Conference series,
12/2007, Volume:
93, Issue:
1
Journal Article
Peer reviewed
Open access
We have synthesized a new compound, 3-hydrazinopropyltrimethoxysilane, which can be applied in chemical modification of SiO2 surfaces. The synthesis route is rather simple, including only two major ...steps. The compound was analysed and confirmed by NMR and FTIR spectroscopy. The new silane can offer a sound alternative to aminosilanes, which are widely applied in several technologies as adhesion promoters.
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/mK to 0.104 W/mK. The aerogel/epoxy composite, on the contrary, showed a slight increase in its thermal conductivity, most probably due to the filling of aerogel pores with the epoxy adhesive. Furthermore, it was shown that adhesion values of epoxy composites increase with the addition of aerogel and decrease when HGM was used as the filler material. Realistic numerical finite element method simulations revealed an increase in thermal isolation properties for both HGM/epoxy and aerogel/epoxy composites. Key words: thermal insulator, epoxy composite, aerogel, hollow glass microspheres, adhesion, polymer testing methods and devices, finite element method.
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