Electrocatalytic activity of BasoliteTM F300 metal-organic-framework structures

For the case of the commercially available metal-organic framework (MOF) structure Basolite^TM F300 or Fe(BTC) with BTC = benzene-1,3,5-tricarboxylate, it is shown that the Fe(III/II) electrochemistry is dominated by reductive dissolution rather than ion insertion (which in marked contrast is dominating the behaviour of Fe(III/II) open framework processes in Prussian blues). Solid Fe(BTC) immobilised onto graphite or platinum working electrodes is investigated and it is shown that well-defined and reversible Fe(III/II) reduction responses occur only on platinum and in the presence of aqueous acid. The process is shown to follow a CE-type mechanism involving liberation of Fe(III) in acidic media, in particular for high concentrations of acid. Effective electrocatalysis for the oxidation of hydroxide to O₂ (anodic water splitting) is observed in alkaline aqueous media after initial cycling of the potential into the reduction potential zone. A mechanism based on a MOF-surface confined hydrous iron oxide film is proposed.     

Ultraviolet-A induced changes in photosystem II of thylakoids: effects of senescence and high growth temperature

Ultraviolet-A (UV-A) radiation induced changes in photosystem II (PS II) of senescing leaves of wheat seedlings were investigated. UV-A radiation did not show any significant effect on the level of photosynthetic pigments. However, the decline in F(v)/F(m) and oxygen evolution rate indicated the damaging effect of the radiation on primary photochemistry of PS II. Modification at the Q(B)-binding site was inferred from the observed downshift of peak temperature of thermoluminescence (TL) B-bands. The UV-A induced changes in PS II of chloroplasts from senescing leaves were found to be synergistically accelerated by high growth temperature.     

Isoscalar giant monopole resonance for drip-line and super heavy nuclei in the framework of relativistic mean field formalism with scaling calculation

We study the isoscalar giant monopole resonance for drip-lines and super heavy nuclei in the framework of relativistic mean field theory with a scaling approach. The well known extended Thomas-Fermi approximation in the nonlinear σ-ω model is used to estimate the giant monopole excitation energy for some selected light spherical nuclei starting from the region of proton to neutron drip-lines. The application is extended to the super heavy region for Z=114 and 120, which are predicted by several models as the next proton magic numbers beyond Z=82. We compared the excitation energy obtained by four successful force parameters NL1, NL3, NL3*, and FSUGold. The monopole energy decreases toward the proton and neutron drip-lines in an isotopic chain for lighter mass nuclei, in contrast to a monotonic decrease for super heavy isotopes. The maximum and minimum monopole excitation energies are obtained for nuclei with minimum and maximum isospin in an isotopic chain, respectively.     

Multi-objective geometric programming problem with ∊-constraint method

In multi-objective geometric programming problem there are more than one objective functions. There is no single optimal solution which simultaneously optimizes all the objective functions. Under these conditions the decision makers always search for the most “preferred” solution, in contrast to the optimal solution. A few mathematical programming methods namely fuzzy programming, goal programming and weighting methods have been applied in the recent past to find the compromise solution. In this paper ?$?$-constraint method has been applied to find the non-inferior solution. A brief solution procedure of ?$?$-constraint method has been presented to find the non-inferior solution of the multi-objective programming problems. Further, the multi-objective programming problems is solved by the fuzzy programming technique to find the optimal compromise solution. Finally, two numerical examples are solved by both the methods and compared with their obtained solutions.     

OH···X (X = O, S) hydrogen bonding in thetrahydrofuran and tetrahydrothiophene

In this article, hydrogen bonding interaction between p-cresol (p-CR) and cyclic ether, tetrahydrofuran (THF) and thioether, tetrahydrothiophene (THT) has been investigated. Two-color resonantly enhanced two-photon ionization in conjunction with the fluorescence detected IR (FDIR) spectroscopy was used to record the changes in the OH stretching frequency in these complexes. The FDIR spectra showed existence of a single conformer of the p-CR·THF and two conformers of the p-CR·THT complex. With the help of computed IR spectra and atoms-in-molecules analysis, the two conformers of p-CR·THT were assigned as the complex of p-CR with THT (C(2))/THT (C(S)). The redshift of OH stretching frequency for the p-CR·THF complex was greater compared to those for the conformers of the p-CR·THT complex. The binding energies of the p-CR·THF and p-CR·THT complexes were computed to be 7.42 and 6.15 kcal/mole. These were of the same order as those for the acyclic analogs, diethylether (DEE), and diethylsulfide (DES), of the solvent molecules under investigation. Although the DEE and THF consist of same number of carbon atoms, the dispersion energy contribution was much higher (43%) for DEE than that for THF (30%). In the case of sulfur analogs, however, it was similar (~50%) in the case of both DES well as THT complexes. All the computed H-bond indicators for these two complexes nicely correlate with the observed redshift of the O-H stretch.     

Influence of the microstructure and its stability on the electrochemical properties of EMD produced from a range of precursors

The influence of the microstructure and the stable crystal structure on the electrochemical properties of the electrolytic manganese dioxide (EMD) produced from manganese cake (EMD_MC), low-grade manganese ore (EMD_LMO), and synthetic manganese sulfate solutions (EMD_SMS) is reported. X-ray diffraction, Fourier transform infrared spectroscopy, thermogravimetry/differential thermal analysis, field emission scanning electron microscopy (FESEM), and chemical analyses were used to determine the structural and chemical characteristics of the EMD samples. The charge–discharge profile was studied in 9 M KOH using a galvanostatic charge–discharge unit. All the samples were found to contain predominantly γ-phase MnO₂, which is electrochemically active for energy storage applications. FESEM images show that preparation method significantly influences surface morphology, shape, and size of the EMD particles. In almost all cases, nanoparticles were obtained, with spindle-shaped nanoparticles for EMD_MC, platy nanoparticles in the case of EMD_LMO, and anisotropic growth of tetra-branched star-like nanoparticles of EMD_SMS. These nanoparticles arrange themselves in a near net-like fashion, resulting in porosity of the flakes of EMD during electrochemical deposition. Thermal studies showed loss of structural water and formation of lower manganese oxides. The EMD_MC showed superior discharge capacity of ~280 mAh g^?1 as compared to EMD_LMO (275 mAh g^?1) and EMD_SMS (245 mAh g^?1).     

One-pot synthesis of phosphorylsuccinates and triphenylphosphanylidenesuccinates containing a thioamido group

Abstract

Stable substituted dialkyl phosphorylsuccinates were synthesized, as a mixture of two diastereoisomers, in high yields using one-pot reaction of dialkyl acetylenedicarboxylates, trialkyl phosphites, and thioamides in CH₂Cl₂ at room temperature. Using triphenylphosphine instead of phosphites, afforded stabilized triphenylphosphanylidenesuccinates. DFT calculations at B3LYP/6-31?+?G(d) level indicated that among four possible conformational diastereoisomers of dimethyl 2-(dimethoxyphosphoryl)-3-ethanethioamidosuccinate, the (2R,3S) and (2S,3S) diastereomers are the most stable forms.     

Zeolitic Imidazolate Framework (ZIF)‐Derived,Hollow‐Core,Nitrogen‐Doped Carbon Nanostructures for Oxygen‐Reduction Reactions in PEFCs

The facile synthesis of a porous carbon material that is doped with iron‐coordinated nitrogen active sites (FeNC‐70) is demonstrated by following an inexpensive synthetic pathway with a zeolitic imidazolate framework (ZIF‐70) as a template. To emphasize the possibility of tuning the porosity and surface area of the resulting carbon materials based on the structure of the parent ZIF, two other ZIFs, that is, ZIF‐68 and ZIF‐69, are also synthesized. The resulting active carbon material that is derived from ZIF‐70, that is, FeNC‐70, exhibits the highest BET surface area of 262 m² g^?1 compared to the active carbon materials that are derived from ZIF‐68 and ZIF‐69. The HR‐TEM images of FeNC‐70 show that the carbon particles have a bimodal structure that is composed of a spherical macroscopic pore (about 200 nm) and a mesoporous shell. X‐ray photoelectron spectroscopy (XPS) reveals the presence of Fe‐N‐C moieties, which are the primary active sites for the oxygen‐reduction reaction (ORR). Quantitative estimation by using EDAX analysis reveals a nitrogen content of 14.5 wt. %, along with trace amounts of iron (0.1 wt. %), in the active FeNC‐70 catalyst. This active porous carbon material, which is enriched with Fe‐N‐C moieties, reduces the oxygen molecule with an onset potential at 0.80 V versus NHE through a pathway that involves 3.3–3.8 e^? under acidic conditions, which is much closer to the favored 4 e^? pathway for the ORR. The onset potential of FeNC‐70 is significantly higher than those of its counterparts (FeNC‐68 and FeNC‐69) and of other reported systems. The FeNC‐based systems also exhibit much‐higher tolerance towards MeOH oxidation and electrochemical stability during an accelerated durability test (ADT). Electrochemical analysis and structural characterizations predict that the active sites for the ORR are most likely to be the in situ generated N? FeN₂₊₂/C moieties, which are distributed along the carbon framework.     

Molecular‐Level Understanding of Ground‐ and Excited‐State O?H⋅⋅⋅O Hydrogen Bonding Involving the Tyrosine Side Chain: A Combined High‐Resolution Laser Spectroscopy and Quantum Chemistry Study

The present study combines both laser spectroscopy and ab initio calculations to investigate the intermolecular O? H???O hydrogen bonding of complexes of the tyrosine side chain model chromophore compounds phenol (PH) and para‐cresol (pCR) with H₂O, MeOH, PH and pCR in the ground (S₀) state as well as in the electronic excited (S₁) state. All the experimental and computational findings suggest that the H‐bond strength increases in the S₁ state and irrespective of the hydrogen bond acceptor used, the dispersion energy contribution to the total interaction energy is about 10–15 % higher in the S₁ state compared to that in the S₀ state. The alkyl‐substituted (methyl; +I effect) H‐bond acceptor forms a significantly stronger H bond both in the S₀ and the S₁ state compared to H₂O, whereas the aryl‐substituted (phenyl; ?R effect) H‐bond donor shows a minute change in energy compared to H₂O. The theoretical study emphasizes the significant role of the dispersive interactions in the case of the pCR and PH dimers, in particular the C? H???O and the C? H???π interactions between the donor and acceptor subunits in controlling the structure and the energetics of the aromatic dimers. The aromatic dimers do not follow the acid–base formalism, which states that the stronger the base, the more red‐shifted is the X? H stretching frequency, and consequently the stronger is the H‐bond strength. This is due to the significant contribution of the dispersion interaction to the total binding energy of these compounds.     

Optical properties of ZnO nanoparticles synthesized by varying the sodium hydroxide to zinc acetate molar ratios using a Sol-Gel process

Material property dependence on the OH⁻/Zn²⁺ molar ratio of the precursor was investigated by varying the amount of NaOH during synthesis of ZnO. It was necessary to control the water content and temperature of the mixture to ensure the reproducibility. It was observed that the structural properties, particle size, photoluminescence intensity and wavelength of maximum intensity were influenced by the molar ratio of the precursor. The XRD spectra for ZnO nanoparticles show the entire peaks corresponding to the various planes of wurtzite ZnO, indicating a single phase. UV measurements show the absorption that comes from the ZnO nanoparticles in visible region. The absorption edge of these ZnO nanoparticles are shifted to higher energies and the determined band gap energies are blue shifted as the OH⁻/Zn² molar ration increases, due to the quantum confinement effects. The photoluminescence characterization of the ZnO nanostructures exhibited a broad emission band centred at green (600 nm) region for all molar ratios except for OH⁻/Zn²⁺ = 1.7 where a second blue emission around 468 nm was also observed. The photoluminescence properties of ZnO nanoparticles were largely determined by the size and surface properties of the nanoparticles.