Tutton K2Zn(SO4)2(H2O)6 salt: Structural-vibrational properties as a function of temperature and ab initio calculations

In this work, a thorough study of Tutton K2Zn(SO4)2(H2O)6 crystal was performed. Structural, electronic, vibrational, and thermal properties were analyzed and discussed. Calculations based on the density functional theory (DFT) were performed to provide a correct assignment of vibration modes (90 active Raman and 93 active IR), and analyses of band structure and density of states. Powder X-ray diffraction (PXRD) at 300 K showed that the Tutton crystallizes in monoclinic symmetry with space group P21/a. An electronic bandgap of 4.66 eV, typical of insulating material, was estimated by band structure calculation. The thermal analysis in the 300-700 K range by coupled TG-DTA thermogram revealed two endothermal events and one exothermal. Such events were investigated by PXRD and Raman spectroscopy as a function of temperature, where three phase changes associated with dehydration and crystallization were observed. The new phase structures were determined by the Le Bail and Rietveld methods. The thermal-structural findings suggest that the K2Zn(SO4)2(H2O)6 Tutton can be considered a promising thermochemical compound for residential heat storage devices due to a low onset for the dehydration temperature (≈327 K) and a high enthalpy of dehydration (77.4 kJ/ mol H2O).

Synergistic effects between acidity and the crystalline phases of thermally activated layered Zn hydroxide nitrate on the methanolysis of acidic soybean oils

Layered hydroxyl salts (LHS) is a promising catalyst in the field of methanolysis (transesterification and esterification reactions) of oil feedstocks. The catalytic activity of the catalyst can be enhanced with heat treatment. The present study investigated the relationship between thermal stability of the layered Zn hydroxide nitrate (ZHN), their acid-base properties, and the catalytic conversion of oil feedstocks to methyl ester. The solid, predominantly acidic catalyst was prepared at various temperatures (70-170 °C) and tested for the acidic/basic properties using the Hammett indicators and titration method followed by functional group analysis using FTIR, crystallization using X-ray diffraction, and surface morphology using SEM. The combination of various characterization techniques gave an insight into the changes in the phases of the layered Zn hydroxide nitrate catalysts upon thermal treatment. Major phase changes occurred at temperatures somewhat above 80, and 140 °C. The catalysts were extensively studied to understand the underlying effects on the FAME yields obtained from catalytic conversion of oleic acid spiked soy bean oil (a model of an acidic oil feedstock) into methyl esters. The results of the optimization reactions reaffirmed the effect of the phase changes when the highest FAME yield was observed from two activated samples namely, Zn5_80 and Zn5_140. The optimized reactions condition of catalytic conversion of SO containing 10% OA at 5 °C/min heating rate, 3 wt % catalyst concentration, 30:1 methanol to oil molar ratio, reaction time of 100 °C for 2 h gave 92% FAME yield when Zn5_140 was used as the catalyst. The detected of the single phase of Zn₅(OH)₈(NO₃)₂ in Zn5_80, Zn₅(OH)₈(NO₃)₂ and ZnO in Zn5_140 (2-phase system), including Zn₅(OH)₈(NO₃)₂, Zn₃(OH)₄(NO₃)₂, and ZnO in Zn5_170 (3-phase system), suggested all three phases contributes to the high catalytic activity in methanolysis of the acidic oils. Both Zn5_140 and Zn5_170 gave a comparably high FAME yields based on statistical analyses. This study ascertained the synergistic effects of the high acidity (>0.4 mmol/g) and the dominant active phases of the thermally treated layered Zn hydroxide nitrate on the high catalytic activity that favours esterification of acidic oil feedstocks.

Phase changes of tris(glycinato)chromium(III) monohydrate crystal systematically studied by thermal analyses, XRPD, FTIR, and Raman combined with ab initio calculations

Tris(glycinato)chromium(III) monohydrate [Cr(C₂H₄NO₂)₃·H₂O] crystals were grown through the slow solvent evaporation method. The crystals were studied by Fourier transform infrared (FTIR) and Raman spectroscopy at room temperature. The assignments of vibration modes were performed using the Density Functional Theory (DFT). Thermal analyses (TGA, DTA, and DSC), X-ray diffraction (XRD), and Raman were used to study the phase changes on the crystals under high- and low-temperature conditions. Temperature-dependent XRPD measurements were carried out in the interval of 473-12 K. Several changes were observed in the patterns, like the appearance of new peaks and the disappearance of peaks occurring within 373-393 K due to water loss. In addition, the Raman measurements were performed in the 423-10 K interval. Several changes on the inter and intramolecular vibration bands during the cooling, such as decreasing bands' intensities, the appearance of vibration modes, and discontinuities on the modes' behavior, were observed. These spectral modifications occurred at about 370 K and within 120-220 K, thus, confirming that the crystals undergo two phase changes, one being structural and the other one conformational, respectively, at high- temperature and low-temperature conditions. Finally, thermal investigations corroborated the structural and vibrational results under high temperatures.

Studies on the sonochemical polymorphism of Sb2O3 on activated graphite for the electrochemical determination of imipramine

This work reports the simultaneous sonochemical activation of graphite and sonohydrolysis of antimony chloride (SbCl₃) in the alkaline medium. The experiments conducted by bath sonicator operated at 37 kHz of frequency and a maximum power of 150 W. The simple sonohydrolysis of SbCl₃ alone produced an orthorhombic phase of Sb₂O₃, whereas, it produced mixed phases of cubic and orthorhombic Sb₂O₃ when introduced with graphite. Herein, the activated graphite (aGR) provides the best support to the growth of cubic phase. This cubic Sb₂O₃ is grown only on the graphite basal planes, which confirmed by scanning electron microscope. Moreover, the phase changes have identified by the X-ray diffraction, Raman and X-ray photoelectron analysis. The prepared aGR-Sb₂O₃ composite has applied to the electroanalytical studies of anti-depressant drug imipramine (IMP). The results showed that aGR-Sb₂O₃ revealed better activity than Sb₂O₃; the reasons are discussed comprehensively. Furthermore, aGR-Sb₂O₃ exhibited comparable analytical results for the determination of IMP.