en
Български
Direct mechanochemical synthesis of SrMoO4: structural and luminescence properties
In this study, the effects of ball milling conditions on the phase formation, symmetry of structural units and photoluminescence features of SrMoO4 were investigated. A stoichiometric mixture of SrCO3 and MoO3 in a molar ratio of 1 : 1 was subjected to intense mechanical treatment in air using a planetary ball mill by applying two milling speeds: 500 and 850 rpm. The obtained samples were characterized by X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), Raman spectroscopy, infrared (IR) spectroscopy, UV-vis (UV-vis) diffuse reflectance spectroscopy and photoluminescence (PL) spectroscopy. The fast synthesis (1 h milling time) of tetragonal SrMoO4 occurred at the higher milling speed of 850 rpm. A longer milling time (5 h) was needed to synthesize SrMoO4 at a lower milling speed of 500 rpm. The average crystallite sizes of the as-prepared samples were 25 and 20 nm at 500 and 850 rpm, respectively. SEM analysis revealed that the mechanochemically produced SrMoO4 sample contained a variety of particle shapes including hexagonal and polyhedral ones. Raman and IR spectroscopy results confirmed the formation of tetragonal SrMoO4. UV-vis absorption spectra showed one peak at 230 nm, and the calculated optical band gaps of SrMoO4 were 4.27 eV (5 h/500 rpm) and 4.34 eV (1 h/850 rpm). Photoluminescence (PL) spectra of both the samples exhibited blue emissions with a peak maximum at 400 (405) nm upon excitation at 325 nm wavelength. CIE coordinates of this mechanochemically synthesized SrMoO4 were located in the blue region with different positions.
Influence of Synthesis Conditions on the Capacitance Performance of Hydrothermally Prepared MnO2 for Carbon Xerogel-Based Solid-State Supercapacitors
In this study, the potential to modify the phase structure and morphology of manganese dioxide synthesized via the hydrothermal route was explored. A series of samples were prepared at different synthesis temperatures (100, 120, 140, and 160 ◦C) using KMnO4 and MnSO4·H2O as precursors. The phase composition and morphology of the materials were analyzed using various physicochemical methods. The results showed that, at the lowest synthesis temperature (100 ◦C), an intercalation compound with composition K1.39Mn3O6 and a very small amount of α-MnO2 was formed. At higher temperatures (120–160 ◦C), the amount of α-MnO2 increased, indicating the formation of two clearly distinguished crystal structures. The sample obtained at 160 ◦C exhibited the highest specific surface area (approximately 157 m2/g). These two-phase (α-MnO2/ K1.39Mn3O6)materials, synthesized at the lowest and highest temperatures, respectively, and containing an appropriate amount of carbon xerogel, were tested as active mass for positive electrodes in a solid-state supercapacitor, using a Na+-form Aquivion® membrane as the polymer electrolyte. The electrochemical evaluation showed that the composite with the higher specific surface area, containing 75% manganese dioxide, demonstrated improved characteristics, including 96% capacitance retention after 5000 charge/discharge cycles and high energy efficiency (approximately 99%). These properties highlight its potential for application in solid-state supercapacitors.
Supercapacitor Cell Performance with Bacterial Nanocellulose and Bacterial Nanocellulose/Polybenzimidazole Impregnated Membranes as Separator
Supercapacitors are advanced energy storage devices renowned for their rapid energy delivery and long operational lifespan, making them indispensable across various industries. Their relevance has grown in recent years due to the adoption of environmentally friendly materials. One such material is bacterial nanocellulose (BNC), produced entirely from microbial sources, offering sustainability and a bioprocess-driven synthesis. In this study, BNC was synthesized using a symbiotic microbial community. After production and purification, pristine BNC membranes, with an average thickness of 80 microns, were impregnated with an alkali-alcohol meta-polybenzimidazole (PBI) solution. This process yielded hybrid BNC/PBI membranes with improved ion-transport properties. The BNC membranes were then doped with a 6 M KOH solution, to enhance OH− conductivity, and characterized using optical microscopy, ATR FT-IR, XRD, CVT, BET analysis, and impedance spectroscopy. Both BNC and BNC/PBI membranes were tested as separators in laboratory-scale symmetric supercapacitor cells, with performance compared to a commercial Viledon® separator. The supercapacitors employing BNC membranes exhibited high specific capacitance and excellent cycling stability, retaining performanceover 10,000 charge/discharge cycles. These findings underscore the potential of BNC/KOH membranes for next-generation supercapacitor applications.
Water-Soluble Polyglycidol-Grafted Ladder Calix Resorcinarene Oligomers with Open Chain and Cyclic Topologies: Synthesis, Characteristics, and Biological Evaluation
Ladder oligomers containing calixarene skeletons in the main chain—calix[4]resorcinarene (CRA) ladder macromolecules with open chain and cyclic macromolecules with double ring-like (Noria-type) topologies—bring particular research attention as functional materials with various applications. However, there is still a remarkable lack of studies into the synthesis of fully water-soluble derivatives of these interesting macromolecules. Research on this topic would allow their bio-based research and application niche to be at least revealed. In the present study, a strategy for the synthesis of water-soluble polyglycidol-derivatized calix resorcinarene ladder oligomers with open chain and cyclic structures is introduced. A grafting from approach was used to build branched or linear polyglycidol chains from the ladder scaffolds. The novel structures were synthesized in quantitative yields and fully characterized by NMR, FTIR and UV–vis spectroscopy, gel permeation chromatography, MALDI-TOF mass spectrometry, analytical ultracentrifugation, and static light scattering to obtain the molar mass characteristics and composition. The biocompatibility and toxicity of the two polyglycidol-derivatized oligomers were investigated and the concentration dependence of the survival of three cell lines of human origin determined. The selective apoptosis effect at relatively low dissolve concentrations toward two kinds of cancerous cell lines was found.
Nanocomposite Perfluorosulfonic Acid/Montmorillonite-Na+ Polymer Membrane as Gel Electrolyte in Hybrid Supercapacitors
Solid-state supercapacitors with gel electrolytes have emerged as a promising field for various energy storage applications, including electronic devices, electric vehicles, and mobile phones. In this study, nanocomposite gel membranes were fabricated using the solution casting method with perfluorosulfonic acid (PFSA) ionomer dispersion, both with and without the incorporation of 10 wt.% montmorillonite (MMT). MMT, a natural clay known for its high surface area and layered structure, is expected to enhance the properties of supercapacitor systems. Manganese oxide, selected for its pseudocapacitive behavior in a neutral electrolyte, was synthesized via direct coprecipitation. The materials underwent structural and morphological characterization. For electrochemical evaluation, a two-electrode Swagelok cell was employed, featuring a carbon xerogel negative electrode, a manganese dioxide positive electrode, and a PFSA polymer membrane serving as both the electrolyte and separator. The membrane was immersed in a 1 M Na2SO4 solution before testing. A comprehensive electrochemical analysis of the hybrid cells was conducted and compared with a symmetric carbon/carbon supercapacitor. Cyclic voltammetric curves were recorded, and galvanostatic charge–discharge tests were conducted at various temperatures (20, 40, 60 °C). The hybrid cell with the PFSA/MMT 10 wt.% exhibited the highest specific capacitance and maintained its hybrid profile after prolonged cycling at elevated temperatures, highlighting the potential of the newly developed membrane.
Download