Frontiers in Chemical Research
Volume:2 Issue: 1, Winter and Spring 2020

Two novel univariate calibration methods, namely the extended ratio subtraction method (EXRSM) and the simultaneous ratio subtraction method (SRSM) were employed for the simultaneous determination of catechol (CT) and hydroquinone (HQ) in synthetic binary mixtures. The precision, accuracy, and specificity of these methods were statistically compared to those obtained from the derivative method (as a univariate calibration method), and the principal component regression (PCR) and the partial least squares (PLS) methods (as two multivariate calibration methods). Comparison of the results showed that there was no significant difference between the proposed methods. The main advantages of the proposed methods are that, unlike the other analytical methods, it is not necessary to use expensive apparatus and chemicals, and that they can be easily performed using a simple spectrophotometer that is available in all quality control labs. The developed methods were successfully applied for the simultaneous determination of CT and HQ with different ratios in tap water as the real sample.

Stabilization of polypropylene (PP) against thermal oxidation during its melt processing and service life, due to its susceptibility to oxidation, is of great importance from both scientific and industrial points of view. The present work was devoted to synthesize a new antioxidant for polypropylene through esterification reaction between thymolphthalein and stearic acid. The occurrence of the reaction was confirmed by Fourier transform infrared (FT-IR) spectroscopy, size exclusion chromatography and melting point measurements. The reaction product was proved to be a mixture of thymolphthalein mono- and di-stearate. It was also shown that the esterification of thymolphthalein, in addition to lowering its polarity, lessens its melting point significantly from 246 to 186 °C, hence, helping the synthesized additive to be mixed with the polymer more favorably in comparison to thymolphthalein. Differential scanning calorimetry demonstrated that the new additive improves stability of the polymer in melt state, significantly. Moreover, oven ageing experiments revealed that the additive stabilizes the polymer against oxidation outstandingly in solid state and its efficiency is comparable to that of SONGNOX 1010, which is a powerful commercially used antioxidant for the polymer.

Stabilization of polypropylene (PP) against thermal oxidation, due to the susceptibility of this commodity polymer to oxidation, is of great importance from both scientific and industrial points of view. The present work aimed at preparing a new polymeric antioxidant for polypropylene, which has no tendency toward migration from the polymer. Accordingly, a diacid (phenylmalonic acid), which has a labile hydrogen atom and can act as a hydrogen donor antioxidant, was polymerized with 1,4-phenylenediamine to render a polyamide. Occurrence of the reaction was confirmed by FT-IR spectroscopy, differential scanning calorimetry (DSC), gel permeation chromatography and thermogravimetric analysis (TGA). The synthesized polyamide was melt-mixed with PP and its uniform distribution in the matrix was verified by the yellowness index measurements. Oxidation onset temperature and oxidative induction time of the samples using DSC proved that the additive enhances stability of the polymer remarkably in melt state. However, its stabilization efficiency is not as outstanding as that of SONGNOX 1010; a conventional antioxidant for PP. But oven ageing experiments followed by FT-IR spectroscopy revealed that the synthesized antioxidant amends thermo-oxidative stability of the polymer in solid state with an eminent efficiency which is even better than that of SONGNOX 1010. Furthermore, its remarkable stabilization activity was proved by DPPH method. Finally, the synthesized polyamide’s potential, as an efficient antioxidant for PP, especially in the long-term stabilization, was assigned to the presence of the two different hydrogen donor groups, i.e. allylic and amine hydrogen atoms, in the molecular structure of the new antioxidant.

Dye effluents are among the most persistent sources of pollution of water bodies and aquatic life. Notable dyes with known carcinogenic effects at low concentrations include azo reactive dyes. The present investigation is focused on the photocatalytic degradation of representative commercial azo dyes using zinc oxide (ZnO). The findings of this research show that ZnO irradiated with ultraviolet (UV) radiation is more effective at degrading C .I. Reactive Yellow 145, C .I. Reactive Blue 194 and C.I. Reactive Red 194 as compared to the sunlight irradiated ZnO. The crystallinity, surface morphology and band gap energy of the ZnO were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) image and UV-Visible absorption spectroscopy respectively. The ZnO has a hexagonal wurzite structure with a band gap of 3.17 eV. The degradation profile was found to decrease with increasing initial dye concentration. The degradation efficiency of the respective dyes under UV and sunlight irradiation was found to be 90% and 85% for CIRY145; 88% and 82% for CIRB194; 96% and 90% for CIRR194. Optimum degradation pH values of 6.9, 7.2 and 6.2 were also recorded for CIRY145, CIRB and CIRR194, respectively, and the general degradation profile was found to follow first order kinetics. Gas chromatographic studies of the degradation reaction intermediates also showed that the degradation profile is time-dependent and all potentially carcinogenic intermediates were degraded into smaller environmentally friendly products such as oxalic acid and acetic acid.

A batch adsorption method for the removal of methyl orange and phenolphthalein from aqueous media onto muscovite clay has been assessed and proven to be successful. The adsorption studies were performed at 303, 323 and 343 K. Factors such as temperature and pH were evaluated. Equilibrium adsorption for all the adsorbates was attained after 30 minutes. Investigation of the adsorption isotherm at 303 K using the Langmuir and Freundlich isotherm models showed that the adsorption of both indicators obey the Langmuir isotherm model with monolayer adsorptive capacities of 13.00 and 2.48 mg/g for methyl orange and phenolphthalein, respectively. The pseudo-second-order kinetic model best describes both adsorption processes with R2 > 0.99 and negative activation energies indicating physisorption processes. Assessment of the thermodynamic parameters showed that although the adsorption processes were endothermic (ΔH values of +8.77 kJ/mol and +15.62 kJ/mol for methyl orange and phenolphthalein respectively) over the range of temperatures studied, the relatively high entropy changes (+38.05 kJ/(molK) and +52.52 kJ/(molK) for methyl orange and phenolphthalein respectively) gave an overall negative change in Gibbs free energy making the processes spontaneous. Generally, the adsorption of both dyes was found to increase steadily within the pH range of 3.3 to 7.0 but decreased drastically from pH = 8.0 to 10.0, a phenomenon which can be attributed to electrostatic repulsion between anionic sites on the dyes and negatively charged active sites on the surface of the adsorbent.

Fuel cells are promising alternatives in power generation. Direct ethanol fuel cells (DEFCs) offer significant advantages due to the comparatively safe handling, non-toxicity and renewability of ethanol as well as its high power density. Development of the efficient catalysts for ethanol electroxidation has attracted great attention and represents one of the major challenges in electrocatalysis. This work investigates ethanol electrooxidation on Cu-BDC MOF catalyst-modified electrodes. The catalysts are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive spectroscopy (EDS), cyclic voltammetry (CV) and chronoamperometry (CA) techniques. The Cu-BDC MOF catalyst shows significantly improved catalytic activity and high durability for ethanol electrooxidation.