SEARCH CONTENT

You are looking at 1 - 10 of 11,108 items :

  • Inorganic Chemistry x
  • Theoretical and Quantum Chemistry x
Clear All

Abstract

Water electrolysis is an environment-friendly process of producing hydrogen with zero-carbon emission. Herein, we studied the water vapor electrolysis using a proton-conducting membrane composed of graphene oxide (GO) nanosheets intercalated with cations (Al3+ and Ce3+). We examined the effect of cation introduction on the physical and chemical structures, morphology, thermal and chemical stabilities, and the proton conductivity of stacked GO nanosheet membranes by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), X-ray photoemission spectroscopy (XPS), Raman spectroscopy, atomic force microscopy (AFM), dynamic light scattering (DLS), thermogravimetric-differential thermal analysis (TG-DTA), and electrochemical impedance spectroscopy (EIS). Concentration cell measurements revealed that the cation-modified membranes are pure proton conductors at room temperature. The proton conductivity of a GO membrane was much improved by cation modification. The cation-modified GO membranes, sandwiched with Pt/C electrodes as the cathode and anode, electrolyzed humidified air to produce hydrogen at room temperature, indicating the feasibility of this carbon-based electrochemical device.

Abstract

Chemical names can be so long that, when a manuscript is printed, they have to be hyphenated/divided at the end of a line. Many names already contain hyphens, but in some cases, using these hyphens as end-of-line divisions can lead to illogical divisions in print, as can also happen when hyphens are added arbitrarily without considering the ‘chemical’ context. The present document provides guidelines for authors of chemical manuscripts, their publishers and editors, on where to divide chemical names at the end of a line, and instructions on how to avoid these names being divided at illogical places. Readability and chemical sense should prevail when authors insert hyphens. The software used to convert electronic manuscripts to print can now be programmed to avoid illogical end-of-line hyphenation and thereby save the author much time and annoyance when proofreading. The Recommendations also allow readers of the printed article to determine which end-of-line hyphens are an integral part of the name and should not be deleted when ‘undividing’ the name. These Recommendations may also prove useful in languages other than English.

FREE ACCESS
FREE ACCESS

Abstract

Various type of zeolites has been produced based on kaolinite and this study likewise utilized kaolin clay as raw material to synthesis zeolite A. Kaolin was in inactive state, therefore it was transformed to metakaolin through dehydroxylation at 800 °C for 4 h. The metakaolin as a source of silica and alumina was then utilized in the synthesis of zeolite A. After hydrothermal synthesis, the zeolite A was exchanged with different concentration of zinc nitrate solution. Zinc content in ion-exchanged zeolite A, ZnA was determined through AAS to calculate the ion exchange capacity. Higher concentration of zinc nitrate had higher zinc content and higher ion exchange capacity. Zeolite A and zinc-exchanged zeolite A were characterized under SEM, XRD and FTIR. Finally, zeolite A and zinc-exchanged zeolite A was used to investigate the antimicrobial properties against gram-negative bacteria, Escherichia coli and gram-positive bacteria Staphylococcus aureus. There was no antimicrobial activity for zeolite A yet zinc-ion–exchanged zeolite A showed inhibition zones around the samples for both the microorganisms.

Abstract

The opening of the S8 ring with the formation of linear sulfur oligomers in the presence of tri-n-butylmethylphosphonium dimethylphosphate is shown. The reaction products are separated and characterized with 1H, 13C, 31P, 17O NMR spectroscopy, HD-MS, MALDI spectroscopy and XRD. It is shown that dimethylphosphate-anion is active in the reaction, and the addition of sulfur atoms occurs via the oxygen atom of dimethylphosphate-anion. It is found that a mixture of products is formed, which differ in the number of sulfur atoms in the chain. The assumptions were made about the mechanism of interaction of sulfur with tri-n-butylmethylphosphonium dimethylphosphate.

Abstract

Risks of a false decision on conformity of the chemical composition of a multicomponent material or object due to measurement uncertainty are defined using the Bayesian approach. Even if the conformity assessment for each particular component of a material is successful, the total probability of a false decision (total consumer’s risk or producer’s risk) concerning the material as a whole might still be significant. This is related to the specific batch, lot, sample, environmental compartment, or other item of material or object (specific consumer’s and producer’s risks), or to a population of these items (global consumer’s and producer’s risks). A model of the total probability of such false decisions for cases of independent actual (‘true’) concentrations or contents of the components and the corresponding measurement results is formulated based on the law of total probability. It is shown that the total risk can be evaluated as a combination of the particular risks in the conformity assessment of components of the item. For a more complicated task, i.e. for a larger number of components under control, the total risk is greater. When the actual values of the components’ concentrations or contents, as well as the measurement results, are correlated, they are modelled by multivariate distributions. Then, a total global risk of a false decision on the material conformity is evaluated by the calculation of integrals of corresponding joint probability density function. A total specific risk can be evaluated as the joint posterior cumulative function of actual property values of a specific item lying outside the multivariate specification (tolerance) domain when the vector of measured values obtained for the item is inside this domain. The effect of correlation on the risk is not easily predictable. Examples of the evaluation of risks are provided for conformity assessment of denatured alcohols, total suspended particulate matter in ambient air, a cold/flu medication, and a PtRh alloy.

Abstract

Increasing demands to obtain chemicals via greener and more sustainable materials and processes introduces concepts that should be considered and applied from lab to larger scales. Obtaining bioactive chemicals from agro-industrial non-food biomass waste can combine benign techniques and bio-circular economy to reach this goal. After extraction, evaluating profitability and environmental impacts to decide whether separation – and to what extent – is necessary or not is indispensable. This could be integrated into an approach known as sufficiency, as an important criterion for sustainability. From this perspective, Brazil’s annual generation of 8 million tons of orange waste is relevant, since citrus waste has large amounts of high-value compounds, such as pectin, d-limonene and flavonoids. This case study aimed at developing and comparing green and sustainable analytical methods to obtain flavonoids from orange peel. Homogenizer, ultrasound and microwave-assisted extractions were employed using chemometric tools, considering time, sample/solvent ratio, temperature and ethanol concentration as variables to obtain extracts containing hesperidin, naringenin, hesperetin and nobiletin. The bioactive flavonoids were determined by high-performance liquid chromatography (HPLC-UV). Microwave extraction was the most efficient method for obtaining the majority of flavonoids studied, six times more for hesperidin. Moreover, orange waste from different farming models showed diverse chemical profiles showing the importance of this alternative in natural product resources.

Abstract

The isotopic composition and atomic weight of lead are variable in terrestrial materials because its three heaviest stable isotopes are stable end-products of the radioactive decay of uranium (238U to 206Pb; 235U to 207Pb) and thorium (232Th to 208Pb). The lightest stable isotope, 204Pb, is primordial. These variations in isotope ratios and atomic weights provide useful information in many areas of science, including geochronology, archaeology, environmental studies, and forensic science. While elemental lead can serve as an abundant and homogeneous isotopic reference, deviations from the isotope ratios in other lead occurrences limit the accuracy with which a standard atomic weight can be given for lead. In a comprehensive review of several hundred publications and analyses of more than 8000 samples, published isotope data indicate that the lowest reported lead atomic weight of a normal terrestrial materials is 206.1462 ± 0.0028 (k = 2), determined for a growth of the phosphate mineral monazite around a garnet relic from an Archean high-grade metamorphic terrain in north-western Scotland, which contains mostly 206Pb and almost no 204Pb. The highest published lead atomic weight is 207.9351 ± 0.0005 (k = 2) for monazite from a micro-inclusion in a garnet relic, also from a high-grade metamorphic terrain in north-western Scotland, which contains almost pure radiogenic 208Pb. When expressed as an interval, the lead atomic weight is [206.14, 207.94]. It is proposed that a value of 207.2 be adopted for the single lead atomic-weight value for education, commerce, and industry, corresponding to previously published conventional atomic-weight values.

Abstract

These recommendations are a vocabulary of basic radioanalytical terms which are relevant to radioanalysis, nuclear analysis and related techniques. Radioanalytical methods consider all nuclear-related techniques for the characterization of materials where ‘characterization’ refers to compositional (in terms of the identity and quantity of specified elements, nuclides, and their chemical species) and structural (in terms of location, dislocation, etc. of specified elements, nuclides, and their species) analyses, involving nuclear processes (nuclear reactions, nuclear radiations, etc.), nuclear techniques (reactors, accelerators, radiation detectors, etc.), and nuclear effects (hyperfine interactions, etc.). In the present compilation, basic radioanalytical terms are included which are relevant to radioanalysis, nuclear analysis and related techniques.