Influence of boron doping on characteristics of glucose based hydrothermal carbons

In this study, the influence of boron doping on structural and surface properties of carbon material synthesized by hydrothermal method was investigated, and the obtained results were compared with the previously published influence that boron has on characteristics of carbonized boron-doped hydrothermal carbons (CHTCB). Hydrothermal carbons doped with boron (HTCB), were obtained by hydrothermal synthesis of glucose solution with the different nominal concentrations of boric acid. It was found that glucose based hydrothermal carbon does not have developed porosity, and the presence of boron in their structure has insignificant influence on it. On the contrary, additional carbonization increases the specific surface area of the undoped sample, while the increase in boron content drastically decreases specific surface area. Boron doping leads to a decrease in the amount of surface oxygen groups, for both, hydrothermally synthesized and additionally carbonized material. Raman analysis showed that boron content does not affect the structural arrangement of HTCB samples, and Raman structural parameters show higher degree of disorder, compared to the CHTCB samples. Comparison of structural and surface characteristics of hydrothermal carbons and carbonized materials contributes to the study of the so far, insufficiently clarified influence that boron incorporation has on the material characteristics.

Synthesis of the new lost foam refractory coatings based on talc

This paper is focused on the preparation procedures, using talc-based filler to improve the rheologic properties of the lost foam refractory coatings. Talc, with grain size of 40 mm, was mechanically activated in a vibration mill over the following times: 10, 20 and 30 min. Depending on the time required for the mechanical activation, the change in the filler grain size and shape was analysed along their effects on the talc-filled lost foam coating dispersion ability and stability. In order to characterize the filler, the following methods were used: X-ray diffraction, scanning electron microscopy and optic microscopy. The coating compo-sition was tuned by choosing the suitable grain size and shape factor of the activated filler. In addition, different coating components (additives, solvent) were applied to alter the coating generation procedure. It was shown that the application of this type of the lost foam refractory coatings - water-based coatings - have a positive influence on quality of the aluminium alloy castings, which contributes to reducing the cost of cleaning and processing of the castings. Also, alcohol-based refractory coatings with talc-based activated fillers were tested and used to have the castings produced in the sand moulds.

Organophosphorous pesticide removal from water by graphene-based materials - only adsorption or something else as well?

The extensive use of pesticides requires innovative approaches to remediate these compounds from the environment. Carbon materials are traditionally used as adsorbents for removing pesticides, and the development of new families of carbon materials allows more advanced approaches in environmental applications. Using Density Functional Calculations, we have predicted chemical reaction between the S(O)=P moieties of organophosphates with point defects in graphene - single vacancies, Stone-Wales defects and epoxy-groups. The reaction was confirmed using Ultra High Performance Chromatography for two graphene oxide samples and dimethoate as a representative of organophosphates. The exact reaction mechanism is still elusive, but it is unambiguously confirmed that no selective oxidation of dimethoate to more toxic oxo-analog occurs. Presented results can help develop novel systems for irreversible conversion of organophosphates to non-toxic compounds without using aggressive chemical agents or external physical factors like UV radiation.

Unveiling the regioselective synthesis of antiviral 5-isoxazol-5-yl-2'deoxyuridines with a molecular electron density theory perspective

The regioselective synthesis of a potent antiviral sugar nucleoside isoxazole analogue from the [3+2] cycloaddition (32CA) reaction of aceto-nitrile-N-oxide (ANO) and acetyl-protected 5-ethynyl-2?-deoxyuridine (EDU) has been studied at MPWB1K/6-311G(d,p) level within the molecular electron density theory (MEDT) perspective. ANO is classified as a zwitterionic species devoid of any pseudoradical or carbenoid center from the electron localization function (ELF) analysis. The ortho regioisomer is energetically preferred over the meta one by the activation enthalpy of 21.7-24.3 kJ mol-1, suggesting complete regioselectivity in agreement with the experiment. The activation enthalpy increases from 53.9 kJ mol-1 in gas phase to 71.5 kJ mol-1 in water suggesting more facile reaction in low polar solvents. The minimal global electron density transfer (GEDT) at the TSs suggests non-polar character and the formation of new covalent bonds has not been started at the located TSs showing non-covalent intermolecular interactions from Atoms-in-Molecules (AIM) study and in the Independent Gradient Model (IGM) isosurfaces. The AIM analysis shows more accumulation of electron density at the C-C interacting region relative to the C-O one, and earlier C-C bond formation is predicted from the bonding evolution theory (BET) study.

Development of a method for derivatization of ethanolamines and its application to sand samples

Nitrogen mustards are dangerous and available blistering chemical warfare agents. In the presented study, six derivatization methods are compared for the analysis of degradation products of the most important blistering nitrogen mustards (ethyl diethanolamine, methyl diethanolamine and triethanolamine) by gas chromatography coupled with mass spectrometry. Five silylation methods (using BSTFA and BSA) and one trifluoroacetylation method (using TFAA) were tested. The derivatization reactions were performed in acetonitrile. As the method with optimal results, trifluoroacetylation by TFAA was selected. Analytes reacted with the corresponding reagent rapidly, quantitatively, with stable kinetics and at room temperature. Calibration curves for quantitative analysis of ethanolamines after TFAA derivatization were created. Correspond-ing detection limits varied between 9?10-3 and 7?10-5 mmol?dm-3 for the tested analytes. The developed method was applied for the analysis of ethanolamines after extraction from sand using acetonitrile. Limits of detection were 11.4 to 12.3 ?g of the analyte in 1 g of sand. It is encouraged to use the developed method in military deployable laboratories designated for rapid identification of chemical warfare agents and corresponding degradation products.

Urea as a complexing agent for selective removal of Ta and Cu in sodium carbonate based alumina CMP slurry

This work reports urea as a promising complexing agent in sodium carbonate (Na2CO3) based alumina slurry for chemical mechanical planarization (CMP) of tantalum (Ta) and copper (Cu). Ta and Cu were polished using Na2CO3 (1 wt.%) with alumina (2 wt.%) in the presence and absence of urea. The effect of slurry pH, urea concentration, applied downward pressure and platen rotational speed were deliberated and the outcomes were conveyed. Prior to the addition of urea, Ta removal rate (RR) was observed to enhance with pH from acidic to alkaline having maximum RR at pH 11. However, Cu RR decreases with increasing pH with minimum RR at pH 11. With the addition of urea in the slurry, Cu to Ta removal rate selectivity of nearly 1:1 is encountered at pH 11. The addition of urea boosts the Ta RR and suppresses Cu RR at the same time at 11 pH, as it adsorbs on the metal surface. Potentiodynamic polarization was conducted to determine the corrosion current (Icorr) and the corrosion potential (Ecorr). The electrochemical impedance spectroscopy (EIS) of both the metals was carried out in the proposed formulation and the obtained outcomes were elaborated.

Structural stability of biofilms produced from silkworm cocoon fibers

Biofilms were obtained from cocoons of the silkworm, Bombyx mori, involving the removal of sericin, extraction and solubilization of fibroin fibers, dialysis of fibroin dispersions and preparation of biofilms by the casting process. Biofilm transparency was verified by UV-Vis spectroscopy and thermal stability by thermogravimetric/differential scanning calorimetry (TG/DSC). Soon after preparation, the solidification of the fibroin solution prepared from the cocoons and extracted by the Ajisawa method was monitored until the biofilm stabilized, using Attenuated Total Reflectance-Fourier Transform Infrared spectroscopy (ATR FT-IR) as a function of time. The results showed that there is a change in the conformation from the silk I structure (?-helix) to silk II (?-sheet). In order to improve the characterization of the biofilms obtained by the Ajisawa method and LiBr solubilization of fibroin fibers, Raman spectroscopy was used to verify stabilization of the different possible molecular conformations for the fibers in these materials, by comparison with the cocoon spectra and those of the solid (freeze-dried hydrogel) precipitated by dialysis for 72 h. By comparing the Raman spectra of the biofilms in terms of the intensities of the broadened band characteristic of amide I, it was possible to assess the conformational changes in both materials based on possible transitions between ?-sheet conformations and flexible ?-helix and ?-turn structures. The results showed a dispersion of these conformations in the biofilms generated and in the solid freeze-dried hydrogel spectrum, and the ?-sheet conformation was found to be predominant. The TG and DSC curves showed that the materials with higher ?-sheet content exhibited higher thermal resistance. Thus, the data obtained further elucidate the properties of these materials which are widely used in various processes.

Synthetic route towards 1,2,3,4-tetrahydroquinoxaline/piperidine combined tricyclic ring system

The synthetic route toward novel tricyclic, nitrogen-containing system is disclosed. Three novel compounds possessing structural features of 1,2,3,4-tetrahydroquinoxaline and decahydropyrido[3,4-b]pyrazine are synthesized starting from readily available precursors in six or seven steps, of which the last three or four steps respectfully are diastereoselective. Key reaction steps include N-acylation, Hofmann rearrangement and ring-closing Buchwald-Hartwig reaction. Compounds trans-8, cis-12 and trans-12 are synthesized in order to prove that this novel, tricyclic system can be functionalized with various groups. Synthetic significance of this heterocyclic system lies in the possibility for the orthogonal functionalization of three different amino groups, allowing fine structural tuning.

Synthesis and properties of new fused pyrrolo-1,10-phenanthroline type derivatives

New fused pyrrolo-phenanthroline type derivatives were synthesized, in two steps, from 1,10-phenanthroline and evaluated for antimicrobial activity and fluorescence properties. Our synthetic approach involved a 3+2 dipolar-cycloaddition of some selected N-substituted 1,10-phenanthrolin-1-ium ylides, (m)ethoxycarbonyl and cyano (1,2-di)substituted acetylenes and alkenes, respectively. The structures of compounds were supported by analytical and spectroscopic data. Molecular structures of four compounds have also been also determined by monocrystal XRD analyses. All synthesized compounds were then evaluated for their potential antimicrobial activity against Staphylococcus aureus ATCC25923, Escherichia coli ATCC25922 and Candida albicans ATCC10231. Two of the compounds demonstrated good activity against the above tested strains.

Correlation between silane concentration and temperature operated toward conductivity of well-synthesized chitosan-fly ash composite membrane

Composite membrane is synthesized using well-synthesized chitosan as matrix crosslink with fly ash as filler and modified using 3-glicydyloxypro-pyltrimetoxy silane coupling agent. XRD analysis is carried out to characterize fly ash. While, FTIR characterization is conducted to determine the interaction between chitosan matrix and fly ash that has been modified using silane. The emergence of a new absorption at wave numbers 1118.64 cm-1 shows the inter-action between silane and fly ash. In addition, the widening of OH absorption shows that hydrogen bonds are formed between the silane and chitosan. The interaction is also demonstrated by the evenly distributed hills and valleys on AFM topography analysis. Characterizing the composite membrane with TGA analysis is done to determine thermal stability. While, proton conductivity of the composite membranes are measured using EIS. The highest conductivity values are obtained with the addition of 5 % silane concentration of 2.75x10-4 S cm-1 at room temperature, 3.995x10-4 S cm-1 at 40?C, and 3.909x10-4 S cm-1 at 60?C. On the contrary, measurements at 80?C, decomposition in all composite membranes occur. Thus, the crosslinked composite membrane chitosan - fly ash prepared by silane-crosslinking technique has potential to be applied with polymer electrolyte membrane fuel cell (PEMFC).