Current Innovations in Chemical and Materials Sciences Vol. 5

This chapter revisits the review in expanded form of “Hydrothermal Synthesis of Vanadium Oxide Microstructures with Mixed Oxidation States” which summarizes many vanadium oxide micro and nano structures displaying different morphologies and V⁴⁺ / V⁵⁺ rates, most of the synthetic procedures are related to sol – gel synthesis executed with different V⁵⁺ oxide precursors namely V₂O₅, VO(OCH₂CH₃)₃, NH₄VO₃ and VOCl₃ in presence of different organic molecules, most of them acting as templates under self – assembled processes depending on their distinctive features, like surfactants (amphiphilic molecules), reducing agents and coordination ligands, under certain chemical parameters and conditions such as pH, concentration, stoichiometry, water / solvent rate at specific temperatures, which usually leads to different routes like layered intercalation compounds nanocomposites, semi or complete reduced vanadium oxide systems or coordinated systems directed under different building blocks that are predominant in the environmental chemical system. Once the first stage is completed hydrothermal treatment takes place and many processes occurred under higher temperature, pressure changes and time frame reactions, the resultant products display magnificent 1 – D, 2 – D and 3 – D morphologies, with different oxidations states rates and most of these structures are based in different structural vanadium oxides lattices that are able to withstand each system, like V₇O₁₆^2-, V₂O₄, V₆O₁₁ and V₄O₉^2-. This chapter focuses on the chemical stages that take place in previous and subsequent to hydrothermal treatment stages and analyses the possible redox reactions and species that could potentially display a major role in the formation of these intricate structures for the purpose of understanding the characteristic for future applications in many technological fields.

Present work deals with the preparation of some Pyrazole derivative salts which was prepared by using different kinds of aldehydes and hydrazine derivatives by using alkoxide as a base and using the 1, 3- dicarbonyl compound like ethyl acetoacetate at room temperature. Pyrazole containing molecules possess a wide range of biological activities such asantibacterial, antifungal, antiviral, anticancer, antidiabetic, anti-inflammatory, estrogen receptor agonists, etc. In recent years one pot three component synthesis has been taken a greater importance as it synthesize the most important pyrazole and its different kinds of derivative in just a single step. The reaction mixture was stirred on magnetic stirrer for about 10 to 20 minutes till colour change is observed and then product is separated by using organic solvents. The product obtained was converted to sodium salt ofPyrazole derivative by base hydrolysis. The entire synthesized compound was tested for their antibacterial activity against the Gram-positive and Gram-negative strains of bacteria. Amongst all synthesized compounds sodium 3-(3,4-dimethoxyphenyl)-5-methyl-1-phenyl-1H-pyrazole-4-carboxylate were found to be more potent as antibacterial Staphylococcus aureus and Bacillus subtilisagents. Whereas compound sodium 5-methyl-3-(3-nitrophenyl)-1H-pyrazole-4-carboxylate was more active against antibacterial Escherichia coli and Proteus vulgaris as antibacterial agent. The investigation of antibacterial screening data revealed that most of the tested compounds showed moderate to good antibacterialactivity.

The development of semipolar/nonpolar structures was lagged behind the development of polar structures. In this study, several nonpolar (11\(\bar{2}\) 0) a-plane GaN films were grown on semipolar (1\(\bar{1}\)02) r-plane sapphire substrates using various buffer layers within a low-pressure metal organic chemical vapor deposition system. The structural properties of nonpolar a-plane GaN films were intensively investigated by the X-ray diffraction and Raman scattering measurements. A set of buffer layers were adopted from a GaN layer to a composite layer containing a multiple AlN layer and an Al composition graded AlGaN layer, the full width at half maximum of the X-ray rocking curves measured along the [0001]- and (10\(\bar{1}\)0) -directions of a-plane GaN were reduced by 35% and 37%, respectively. It was also found that an order of magnitude reduction in the basal-plane stacking faults (BSFs) density can be reduced by the heterogeneous interface introduced with the composite buffer layer together. Moreover, the in-plane strains along c- and m-directions were increased from -0.326% and 0.121% to -0.388% and 0.288% when the buffer layer was changed from GaN to AlN, while they were further reduced to -0.107% and 0.137% when the buffer layer was replaced by the composite layer. A BSFs density as low as 2.95×10⁴ cm^-1, and a pit-free surface morphology were achieved for the a-plane GaN film grown with the composite buffer layer, which is promising for the development of nonpolar GaN-based devices in the future. This work provides promising insights for the development of nonpolar GaN-based LEDs with high-bandwidth for optical communications and microdisplays in the future.

The present work studies europium-ion spectroscopic features in solid solutions based on silicate-tungstates Ca₂La_6.8Eu_1.2Si_5.6W_0.4O_26.4 and Ca₈Eu₂Si₃W₃O₂₆ microcrystalline powders with the crystal structure of silicate apatite and scheelite respectively. Spectroscopy is the field of study that measures and interprets the electromagnetic spectra that result from the interaction between electromagnetic radiation and matter as a function of the wavelength or frequency of the radiation. In simpler terms, spectroscopy is the precise study of color as generalized from visible light to all bands of the electromagnetic spectrum. Spectroscopy, primarily in the electromagnetic spectrum, is a fundamental exploratory tool in the fields of astronomy, chemistry, materials science, and physics, allowing the composition, physical structure and electronic structure of matter to be investigated at the atomic, molecular and macro scale, and over astronomical distances. The spectroscopic features were studied by means of photoluminescence spectroscopy and X-ray excited luminescence at temperatures 4.6, 90 and 295 K. In Ca₂La_6.8Eu_1.2Si_5.6W_0.4O_26.4 only intensive luminescence was observed, which was characterized by a set of ⁵D₀ \(\rightarrow\) ⁷F_J dominant intraconfigurational transitions for Eu³⁺ ion. In Ca₈Eu₂Si₃W₃O₂₆, both ⁵D₀  \(\rightarrow\) ⁷F_J intraconfigurational transitions for Eu³⁺ ion and wide 430 nm emission band corresponding to host self-trapped exciton (STE) emission are observed. This STE emission band is reabsorbed by the f – f absorption of Eu³⁺ ions by means of energy transfer from host to Eu³⁺. The asymmetry coefficient which characterizes the shape of the emission spectrum of Eu³⁺ ions strongly depends on the energy of exciting photons. The Eu³⁺ ion might occupy two nonequivalent crystallographic sites. Some features of this phenomenon were discussed.

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Contamination of water with toxic substances due to rapid urbanization has become a worldwide cause of concern. Among these substances, arsenic occupies the topmost position in the priority list of hazardous substances given by ATSDR. Hence in the present study in order to eliminate the extra step of oxidizing As(III) in the process of arsenic removal by adsorption, a composite of acid-functionalized nanoporous carbon (Af-NPC) with MnO₂ nanoparticles was synthesized. Nanoporous carbon (NPC) structures synthesized from grass clippings mown at the yard were acid-functionalized and coated with manganese oxide nanoparticles at room temperature. The synthesized composite was characterized by FTIR, XRD, BET, TEM, TGA and XPS. Characterization results showed the formation of an acid-functionalized nanoporous carbon/MnO₂ (Af-NPC/MnO₂) composite which was amorphous in nature. Af-NPC/MnO₂ was further explored for the removal of As(III) and As(V) from the aqueous medium. Effects of factors such as pH, contact time, initial concentration and interfering ions on the adsorption of arsenic by Af-NPC/MnO₂ were studied in detail. The mechanism of adsorption was also studied using experimental data determined. The kinetic study indicated that removal of arsenic followed pseudo-second-order kinetics and the experimental equilibrium data fitted better in the Langmuir isotherm model with maximum monolayer adsorption capacity of 8.85 mg/g and 9.43 mg/g for As(III) and As(V), respectively. The removal rate of arsenic was found to be very fast compared to other adsorbents. The results of this study imply that Af-NPC/MnO₂ is an efficient adsorbent for the removal of As(III) and As(V) from an aqueous medium.

The evolution of nanofluids is important for improving the thermal conductivity of base fluids. The influence of thermal radiation and stratification on the magnetohydrodynamic micropolar nanofluid flow through a shrinking sheet with the prescribed heat flux on the surface is examined. The main aim of this study is to examine the effects of magnetohydrodynamics(MHD), microrotation, thermal radiation, magnetic field, and the Cattaneo-Christov heat flux law. The magnetic field pattern, characteristics of heat source, thermal radiation, and the dispersion of volume fraction having an impact on the effectiveness of nanoparticles’ heat and mass transfer rates. By using boundary layer estimations and similarity substitutions, the partial differential system is transformed into a set of nonlinear differential equations and solved by using the variational finite element procedure. A MATLAB program is developed to assess parametric simulations for skin friction factor, microrotation, fluid velocity, rate of heat transfer, and thermal properties of nanoparticles for the Glariken formulation. It is observed that the temperature field declined due to increasing values of the thermal stratification, and the heat transfer rate accelerated. The proposed optimal results revealed that the skin friction factor is enhanced efficiently by exerting suction and magnetohydrodynamic impact. There is a strong corelation between the two sets of results, which shows that the finite element method used here is accurate.

Modern high-performance tire treads are presently commonly reinforced with silica as rubber fillers because they raise key tire performance criteria such as lower rolling resistance and higher wet grip compared to carbon black-filled rubber. The present work aims at a synergistic effect of silica with different additional fillers in order to shift tire performance with respect to wet grip and rolling resistance for safety and fuel savings, respectively towards a better abrasion resistance, all characterized by the dynamic mechanical properties of the vulcanized compounds. The use of small amounts of secondary fillers or hybrid fillers in silica-reinforced tire tread compounds has the potential to improve tire performance further. In the present work, two secondary fillers: organoclay nanofiller and N134 carbon black were added to silica-based natural rubber compounds at a proportion of silica/secondary filler of 45/10 phr. The compounds were prepared with variable mixing temperatures based on the procedure commonly used for silica-filled NR systems. The results of Mooney viscosity, Payne effect, cure behavior and mechanical properties imply that the silica hydrophobation and coupling reaction of the silane coupling agent between the silica and elastomer are significantly enhanced by organoclay due to an effect of its modifier: an organic ammonium derivative. This modifier has an effect on scorch safety and cure rate. The compounds where carbon black was added as a secondary filler do not show this improvement. They give inferior filler dispersion compared to the pure silica-filled compound, attributed to an inappropriate high mixing temperature and the large specific surface area of the carbon black used. The dynamic mechanical properties indicate that organoclay as a secondary filler has the potential to improve the wet traction and rolling resistance of a tire tread, while the use of carbon black in silica-filled NR does not change these properties.