The design and synthesis of a series of theophylline derivatives containing 1,2,3-triazole moieties are presented. The corrosion inhibition activities of these new triazole-theophylline compounds ...were evaluated by studying the corrosion of API 5 L X52 steel in 1 M HCl medium. The results showed that an increase in the concentration of the theophylline-triazole derivatives also increases the charge transference resistance (
) value, enhancing inhibition efficiency and decreasing the corrosion process. The electrochemical impedance spectroscopy under static conditions studies revealed that the best inhibition efficiencies (approx. 90%) at 50 ppm are presented by the all-substituted compounds. According to the Langmuir isotherm, the compounds
and
analysed exhibit physisorption-chemisorption process, with exception of the hydrogen
, bromo
and iodo
substituted compounds, which exhibit chemisorption process. The corrosion when submerging a steel bar in 1 M HCl was studied using SEM-EDS. This experiment showed that the corrosion process decreases considerably in the presence of 50 ppm of the organic inhibitors. Finally, the theoretical study showed a correlation between E
, hardness (
), electrophilicity (W), atomic charge and the inhibition efficiency in which the iodo
substituted compound presents the best inhibitor behaviour.
► Trace metal toxicity in Tourist beaches of Acapulco in Mexico. ► Presence of metals above permissible limit. ► Anthropogenic input of metals in tourist beaches.
A survey on the metal concentrations ...(As, Ba, Cd, Co, Cr, Cu, Fe, Mn, Ni, Pb, Sr, V, Zn) in beach water and sediments is reported from the tourist destination of Acapulco city on the Pacific coast of Mexico. The concentration of dissolved trace metals (DTMs) in beach water and acid leachable trace metals (ALTMs) in sediments indicated that they are anthropogenic in nature due to the increased tourist activities in the crowded beach locations. The statistical analysis indicates Fe and Mn play a major role as metal scavengers in both the medium (water and sediment) and the higher value of other metals is site specific in the study area, indicating that they are transported from the local area. Comparison results suggest that the beach water quality has deteriorated more than the sediments and special care needs to be taken to restore the beach quality.
In this work, the effect of the exact exchange in hybrid functionals based on one parameter is explored over the electronic structure of
Ti
2
O
3
,
V
2
O
3
,
Cr
2
O
3
,
Fe
2
O
3
,
MnO
,
SiO
2
,
GeO
2
..., and
SnO
2
, such that oxides with different nature are included in this data set. Structural parameters and magnetic states of these oxides are reproduced according to experimental information, which are discussed in the context of the exact exchange inclusion. Several exchange-correlation functionals are considered to reach this goal, two of them, HSE06 and B1WC, which were designed ad hoc to study metal oxides are contrasted with hybrid exchange-correlation functionals that contain a fraction (
α
) of the exact exchange, like PBE0. Thus, in this work, hybrid functionals where
α
is varied systematically provide a linear relationship between band gap and
α
, which gives one way to match the theoretical band gap with experimental information. If this optimum
α
is used to predict cell parameters or bulk modulus, then the corresponding results are close to experimental data. For the systems considered in this work, all-electron calculations were performed using a periodic ab initio code, which uses Gaussian localized basis set functions for the expansion of Bloch orbitals by linear combinations of atomic orbitals.
Thin films of IZO:Ga transparent conducting oxide (TCO) material have been deposited onto glass substrates, using RF magnetron sputtering under different conditions. Film thicknesses varying from 179 ...to 472 nm, an average Ga/(Ga + Zn + In) atomic ratio value of 1.3%, and In/Zn atomic ratios from 0.55 to 1.05, were obtained. It has been determined that as the In/Zn atomic ratio increases, the resistivity of the films decreases from 1.30 to 0.83 mΩ cm. A single hexagonal c-axis oriented IZO:Ga pure phase has been obtained. The average transmittance of the IZO:Ga film is ca. 80% for all position in the 400–700 nm wavelength region. FE-SEM images show that the IZO:Ga film exhibit a void-free surface with a rough morphology, containing round shape hexagons nanostructures with sizes between 100 and 200 nm. In this work, the electrochemical behavior (stability and electron transfer properties), and photoelectrochemical characteristics of IZO:Ga thin film samples have been examined. The electrochemical stability behavior has been examined by using electrochemical cyclic voltammetry (CV) technique in an acidic aqueous electrolyte, and compared to the behavior of two commercial TCOs on glass substrates (i.e.: ITO and FTO). The effect of IZO:Ga resistivity on the electrochemical performance was also examined by CV. It has been found that the standard electron transfer rate constant of hexacyanoferrate ion diminished at the less electrical conductive IZO:Ga sample (ko = 6.27 × 10−5 cm s−1) compared to the more conductive one (ko = 1.43 × 10−4 cm s−1). Photoresponse and photoelectrochemical properties IZO:Ga thin films have been evaluated in 0.1 M Na2S + 0.1 M Na2SO3 aqueous electrolyte, and under AM1.5G (100 mW cm−2) illumination. All of the IZO:Ga thin film samples demonstrate a typical anodic photocurrent response confirming their n-type conductivity behavior, with photocurrent values as high as 4 μA/cm2 at anodic potential bias. These results provide useful insights into the behavior of this TCO material and serve as a starting point for the selection of appropriate substrate materials for evaluating novel electrocatalysts, photoelectrodes and optoelectronic devices. As a case study, ZnO nanorods arrays vertically oriented to the substrate plane, exhibiting 200 nm of average diameter, were electrochemically grown onto these synthesized substrates with encouraging novel results.
•IZO:Ga transparent conducting oxide thin films deposited by RF sputtering.•Electrochemical stability determined by cyclic voltammetry.•Electron transfer kinetics onto film samples was examined.•Effect of film resistivity on the electrochemical properties.•Photoelectrochemical properties were evaluated.
Large-area vertically orientated and high-density ZnO nanorod arrays (NRAs) have been electrochemically grown directly onto IZO:Ga thin film transparent conductive oxide (TCO) substrates. For the ...sake of comparison, ZnO NRAs have also been electrodeposited onto conventional TCO/glass substrates (F-doped SnO2 (FTO) and Sn-doped In2O3 (ITO). The morphological and structural properties of the resulting ZnO NRAs have been studied. The nucleation and growth mechanism (NGM) that governs the electrochemical growth of these ZnO nanostructures onto these TCO substrates were investigated, demonstrating that the IZO:Ga thin film triggers the orientated and structured growth of ZnO nanorods. ZnO nanorods of ca. 225 nm, 256 nm and 259 nm in diameter and ZnO NRAs densities values of 2.05 × 108 cm−2, 2.27 × 108 cm−2 and 7.83 × 108 cm−2 have been obtained when deposited onto these FTO, ITO and IZO:Ga thin film substrates, respectively. NGM study results indicate that onto FTO and ITO after an initial current decay (following a Cottrell law), a 3D instantaneous nuclei formation limited by lattice incorporation takes place. Whereas onto the IZO:Ga substrate, at the early stages a new contribution 3D instantaneous nucleation under diffusion control, appeared, revealing that these densely packed IZO:Ga nanocrystals may act as homo-epitaxial nucleation sites.
In this work, 11 members of a 1,3,2,4‐dithiadiphosphetane 2,4‐disulfides family are analyzed from a theoretical point of view. These reagents are involved in thionation processes, where the first ...step implies the breaking bond between sulfur and phosphorus atoms to destroy the P2S2 ring, which is characteristic of these compounds. Thus, we estimate this breaking bond by analyzing the Gibbs energy over several temperatures, concluding that 3 of the most representative reagents of this family (Belleau, Davy, and Lawesson) are dissociated to yield 2 symmetrical species, for temperatures less than 400 K. This estimation, in gas phase, is reasonably good with respect to experimental information where these 3 reagents react at temperatures below 383 K. These 3 reagents present the lowest dissociation energies for several temperatures due to enthalpic and entropic contributions. Reagents and their monomers were analyzed by using the density functional theory framework to show that among the studied reagents, 3 of them exhibit similar behavior between themselves and correspond to the most used reagents in experimental thionation processes. For the separated species, the density functional theory chemical reactivity predictors indicate that the phosphorus atom has the biggest response when the system accepts electrons and sulfur atoms have the biggest response when the system gives electrons. This result is totally in accord with experimental suggestions for this kind of processes.
The P2S2 ring involved in thionation reagents is studied by using the density functional theory, which indicates that entropic contributions are needed to predict the corresponding dissociation energy. Among 11 thionation reagents, our theoretical method predicts that the Belleau, Lawesson and Davy reagents are dissociated below 400 K, in agreement with experimental information. According to the atoms in molecules approach, such a dissociation energy is related to the electron density found in the center of the P2S2 ring.
This study explored the relationship between investor sentiment (extracted from the StockTwits social network), the S&P 500 Index and gold returns. We investigated bilateral causality between gold ...prices and S&P 500 prices, the power of investor sentiment and gold returns to predict S&P 500 returns, and the influence of gold returns on S&P 500 volatility. We also considered whether the influence of sentiment varies according to the user's degree of experience. We considered the sentiment of messages that mentioned the S&P 500 Index and that users posted between 2012 and 2016. Granger causality analysis, ARIMA models and GARCH models were used for predicting S&P 500 Index returns and S&P 500 volatility. We observed a causal relationship between gold price and the S&P 500 Index. Our results also suggest that sentiment and gold returns predict S&P 500 Index returns. Finally, we observed that gold returns influence S&P 500 volatility and that the sentiment of experienced users affects S&P 500 returns.
•There is a bilateral causality between gold price and S&P 500.•Investor sentiment and gold returns can predict S&P 500 returns.•Gold returns influence the volatility of S&P 500 returns.•Sentiment from experienced investors influences S&P 500 returns.
In this work, 11 adducts with hydrogen bonds were studied by using the B3LYP exchange-correlation functional of the Kohn−Sham approach and the Møller−Plesset second-order perturbation theory MP2. ...With both approaches, the geometry of each adduct was optimized with the aug-cc-pVTZ basis set. The binding energies of the considered systems, found by the MP2 method, range from 1.2 to 8.3 kcal/mol. By using the atoms in molecules (AIM) analysis and the electron localization function (ELF) we found that the critical points positions characteristic of hydrogen bonds obtained by AIM and ELF are very similar each other. Besides, we found a linear correlation between the critical points positions found by AIM and those obtained by ELF with the B3LYP method and also with the MP2 method. The slope of such a linear relationship was close to 1 and the y-intercept close to 0.
A detailed analysis of the electronic structure and charge distribution around the trigonal site of Li-doped polyacetylene is reported using finite chain and periodic descriptions of the polymer. ...Atoms-in-molecules (AIM) analysis is done to characterize the nature of the bond between Li and the polymer backbone through the location of the bond critical points and computation of the total charge on the atomic basins around the doping site. We find that the Li atom donates practically one electron to the π-system, in accordance with the classical Su–Schriffer–Heeger model. However, despite that the Li atom is equidistant from the three closest C atoms in the geometric soliton, a single Li–C bond critical point is found. The AIM quantitative analysis of the electronic density reveals that the Li+ ion is immersed into the polymer π-cloud in a way that resembles a metallic bonding interaction.
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