Investigation of the reaction mechanism and kinetics of production of anhydrous sodium metaborate (NaBO2) by a solid-state reaction

In this study, the solid-state reaction mechanism and kinetics were investigated for production of anhydrous sodium metaborate (NaBO₂), an industrially and technologically important boron compound. To assess the kinetics of solid-state production of NaBO₂, the chemical reaction between borax (Na₂B₄O₇) and sodium hydroxide (NaOH) was investigated by use of the thermal analysis techniques thermogravimetry (TG) and differential thermal analysis (DTA). DTA curves obtained under non-isothermal conditions at different heating rates (5, 10 and 20 °C/min), revealed five endothermic peaks corresponding to five solid-state reactions occurring at 70, 130, 295, 463, and 595 °C. The stages of the solid-state reaction used for production NaBO₂ were also analyzed by XRD, which showed that at 70 and 130 °C, Na₂B₄O₇ and NaOH particles contacted between the grains, and diffusion was initiated at the interface. However, there was not yet any observable formation of NaBO₂. Formation of NaBO₂ was initiated and sustained from 295 to 463 °C, and then completed at 595 °C; the product was anhydrous NaBO₂. Activation energies (E _a) of the solid-state reactions were calculated from the weight loss based on the Arrhenius model; it was found that in the initial stages of the solid-state reaction E _a values were lower than in the last three steps.     

The uranium recovery from aqueous solutions using amidoxime modified cellulose derivatives. IV. Recovery of uranium by amidoximated hydroxypropyl methylcellulose

Amidoxime modified hydroxypropyl methylcellulose (HPMC) films (HPMC-g-AO) were used for the recovery of uranium from aqueous solutions by a complexation process. The adsorption experiments were carried out by immersion of a certain amount of films in UO₂ ²⁺ solutions (resultant pH 4.1) ranging in concentration from 100 to 1,000 ppm. The effect of temperature (25–50 °C) on the adsorption capacity of HPMC-g-AO was investigated at the optimized time. The adsorption kinetics and the thermodynamics as well as the adsorption capacity of HPMC-g-AO films were investigated. The adsorption capacity was found as 765 mg UO₂ ²⁺/g dry film. The kinetic and the thermodynamic parameters (i.e. activation energy, enthalpy, entropy and Gibbs free energy) for the interaction of UO₂ ²⁺ with HPMC-g-AO were calculated based on known basic relations. The results showed that adsorption occurred through strong electrostatic interactions with an enthalpy of ?36.5 kJ/mol. The desorption of UO₂ ²⁺ were investigated using different desorption agents such as EDTA, HCl, NaHCO₃, and NaOH. After the 2 weeks treatment period, the highest desorption yield were found as 23 % with NaHCO₃.     

An inverse coefficient problem for a quasilinear parabolic equation with periodic boundary and integral overdetermination condition

In this paper, the inverse problem of finding the time‐dependent coefficient of heat capacity together with the solution periodic boundary and integral overdetermination conditions is considered. Under some natural regularity and consistency conditions on the input data, the existence, uniqueness, and continuous dependence upon the data of the solution are shown. Some considerations on the numerical solution for this inverse problem are presented with an example. Copyright © 2014 John Wiley & Sons, Ltd.     

Metallo Phthalocyanines bearing 2‐Isopropyl‐6‐methylpyrimidin‐4‐yloxy Substituents: Synthesis,Characterization, Aggregation Behavior,Antioxidant and Antibacterial Activity,and Electronic Properties

A novel phthalonitrile derivative bearing 2‐isopropyl‐6‐methylpyrimidin‐4‐yloxy substituents at peripheral positions was synthesized by a nucleophilic substitution reaction. Metallophthalocyanines were obtained from the reaction of the novel phthalonitrile with metal Zn, Cu, Co, and Ni salts. The characterization of the compounds was performed using elemental analysis as well as UV/Vis, FT‐IR, and ¹H‐NMR spectroscopy. The aggregation behaviors of phthalocyanine complexes were also investigated. These metallophthalocyanines do not show any aggregation behavior between 10^–4–10^–6 M concentration range in THF. The antioxidant activities of the synthesized compounds were evaluated using three different tests: 2, 2‐diphenyl‐1‐picrylhydrazyl (DPPH) radical scavenging, metal chelating activity, and reducing power assays. All the compounds exhibited various antioxidant activities. In addition, antimicrobial activity of the compounds was tested over four gram positive and two gram negative bacteria. Moreover, the ground‐state geometries of the complexes were optimized using density functional theory (DFT) methods at B3LYP/6‐31G(d, p) level in order to obtain information about the 3D arrangements and electronic structure.     

Nitro Derivatives of Parabanic Acid as Potential Explosives: A Theoretical Study

This work deals with certain parabanic acid (PA) derivatives because they possess great calculated density (>1.8 g · cm^–3) and high content of nitrogen (26 %). Computed ballistic properties of eight different parabanic acid derivatives are presented. The structures were optimized at the B3LYP/6‐31G(d, p) level. The calculated data for PA are found to be compatible with the experimental X‐ray data. The detonation performance analyses were done using empirical Kamlet‐Jacobs equations. Additionally, detonation products were assigned and power index were calculated. All the compounds considered are powerful candidates for high energy materials.     

Simultaneous determination of seven phthalic acid esters in beverages using ultrasound and vortex‐assisted dispersive liquid–liquid microextraction followed by high‐performance liquid chromatography

A sensitive, rapid, and simple high‐performance liquid chromatography with UV detection method was developed for the simultaneous determination of seven phthalic acid esters (dimethyl phthalate, dipropyl phthalate, di‐n‐butyl phthalate, benzyl butyl phthalate, dicyclohexyl phthalate, di‐(2‐ethylhexyl) phthalate, and di‐n‐octyl phthalate) in several kinds of beverage samples. Ultrasound and vortex‐assisted dispersive liquid–liquid microextraction method was used. The separation was performed using an Intersil ODS‐3 column (C₁₈, 250 × 4.6 mm, 5.0 μm) and a gradient elution with a mobile phase consisting of MeOH/ACN (50:50) and 0.2 M KH₂PO₄ buffer. Analytes were detected by a UV detector at 230 nm. The developed method was validated in terms of linearity, limit of detection, limit of quantification, repeatability, accuracy, and recovery. Calibration equations and correlation coefficients (> 0.99) were calculated by least squares method with weighting factor. The limit of detection and quantification were in the range of 0.019–0.208 and 0.072–0.483 μg/L. The repeatability and intermediate precision were determined in terms of relative standard deviation to be within 0.03–3.93 and 0.02–4.74%, respectively. The accuracy was found to be in the range of –14.55 to 15.57% in terms of relative error. Seventeen different beverage samples in plastic bottles were successfully analyzed, and ten of them were found to be contaminated by different phthalic acid esters.     

Corrosion prevention of mild steel in acidic medium by 2-Pyrrolidin-1-yl-1,3-thiazole-5-carboxylic acid: Theoretical and experimental approach

The inhibition efficiency of 2-Pyrrolidin-1-yl-1,3-thiazole-5-carboxylic acid (PTCA) against mild steel (MS) corrosion was investigated in acidic solution by using quantum chemical calculations based on Density Functional Theory (DFT) method and electrochemical measurements. The electrochemical impedance spectroscopy (EIS), potentiodynamic, potential zero charge (pzc) analysis and electrochemical noise (EN) measurements at various concentrations (from 0.1 to 10 mM) and immersion times were utilized in experimental part. The surface analysis was achieved scanning electron microscope (SEM) and contact angle measurements in the absence and presence of 10 mM PTCA. According to DFT results, PTCA exhibited 3.737 eV band gap and 8.130 Debye dipole moment which were a signal of potentially convenient corrosion inhibitor properties. PTCA has a remarkable corrosion inhibition capability to mild steel, which inhibited both anodic and cathodic corrosion rates, relying on it's physically adsorption on the metal solution interface and protection ability was increased with increasing PTCA concentration. The obtained adsorption equilibrium constant was 11.11 × 10³ M^-1 and calculated standard free energy of adsorption was ?33.03 kJ mol^?1. The determined activation energy values were 55.58 kJ mol^?1 and 96.86 kJ mol^?1 in 0.5 M HCl in the absence and presence of 10 mM PTCA, respectively. PTCA demonstrated a strong inhibition efficiency of 98.3%, after 168 h immersion, according to the EIS results. As a consequently, we recommend that PTCA is a convenient inhibitor in 0.1 M HCl for mild steel protection against corrosion.     

Asymmetrically tetra-substituted phthalocyanine derivatives: synthesis,photophysical and photochemical properties

Transition Metal Chemistry - The syntheses of highly soluble asymmetrically substituted metal free and zinc phthalocyanine derivatives bearing three 4-(4-(5-phenyl-1,3,4-oxadiazol-2-yl)phenoxy) and...     

Development of a Diamond Nanoparticles-based Nanosensor for Detection and Determination of Antiviral Drug Favipiravir

This study developed a nanosensor for the detection and determination of favipiravir, a presumed drug that has potential therapeutic efficacy in treating COVID-19 patients, from tablets and serum samples. This nanosensor was obtained by adding the optimum amount of diamond nanoparticles into carbon paste. For the determination of favipiravir adsorptive stripping differential pulse (AdSDPV) and adsorptive stripping square wave voltammetry (AdSSWV) were used. Limit of detection values were found as 4.83×10⁻⁹ M and 2.44×10⁻⁷ M for bulk and 5.18×10⁻⁸ M and 4.38×10⁻⁸ M for serum samples using AdSDPV and AdSSWV, respectively. Recovery studies made of the tablet and serum produced satisfactory results.     

Multi‐crystalline silicon solar cells with metal‐assisted nano‐texturing using HNO3 as hole injection agent

In this study, metal‐assisted etching (MAE) with nitric acid (HNO₃) as a hole injecting agent has been employed to texture multi‐crystalline silicon wafers. It was previously proven that addition of HNO₃ enabled control of surface texturing so as to form nano‐cone shaped structures rather than nanowires. The process parameters optimized for optically efficient texturing have been applied to multi‐crystalline wafers. Fabrication of p‐type Al:BSF cells have been carried out on textured samples with thermal SiO₂/PECVD‐SiN_x stack passivation and screen printed metallization. Firing process has been optimized in order to obtain the best contact formation. Finally, j_sc enhancement of 0.9 mA/cm² and 0.6% absolute increase in the efficiency have been achieved. This proves that the optimized MAE texture process can be successfully used in multi‐crystalline wafer texturing with standard passivation methods.

J –V curves and SEM images of the nano and iso‐textured samples. j_sc enhancement of 0.9 mA/cm² together with 0.6% absolute efficiency gain was observed on nano‐textured samples.