Production of MgAl/layered double hydroxide microspheres and investigation of the volumetric heat transfer coefficient in spray drying
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ABSTRACT:
SUBMITTER: Silva Neto L
PROVIDER: S-EPMC11035054 | biostudies-literature | 2024 Apr
REPOSITORIES: biostudies-literature
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Project description:This study aimed to evaluate the synthesis of MgAl/LDH from the drying process perspective, evaluating the influence of temperature (75-90 °C) and time (16-20 h) in the drying process. The synthesis was performed, maintaining a ratio of 2:1 of Mg/Al, and the drying was conducted according to a 22 experimental design: four axial points and three repetitions at the central point. The surface area and pore diameter ranged from 4.09 to 18.55 m2/g and 12.50 to 24.46 nm. Fourier transform infrared (FTIR) analysis indicated the drying-caused variation of the LDH typical bands intensities. Scanning electron microscopy (SEM) images showed the tendency of the increase of agglomeration with the temperature elevation. The drying parameters' influence was evident for X-ray diffraction (XRD) analysis observing the crystallite size increment, from 13.10 to 38.94 nm, and basal spacing variation, from 7.52 to 7.64 Å. The statistical models for growing crystal and reduction of the basal spacing were physically consistent but with low values of R 2. The drying time and temperature had a considerable influence on the chemical, physical, structural, and morphological properties of LDH.
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Project description:The combination of layered double hydroxides (LDH) with graphene oxide (GO) enables the formation of nanohybrids with improved properties. This work focuses on the structural and catalytic properties of Ce-containing MgAl LDH-GO composites bearing different concentrations of GO in the range of 5-25 wt.%. The synthesis of the composites was performed by co-precipitating the LDH phase in the presence of GO, while their characterization was performed using XRF, XRD, DRIFT, Raman, SEM, nitrogen adsorption-desorption, and acidity-basicity measurements. The LDH-GO composites, showing redox, basic, and acid catalytic functions, were tested in two different types of organic transformations: (i) Knoevenagel condensation and (ii) one-pot cascade oxidation-Knoevenagel condensation. (i) The cinnamic acid was synthesized by the Knoevenagel condensation of benzaldehyde with diethylmalonate. The composites showed catalytic performances in strong contrast to neat LDH or GO, suggesting a synergistic interaction between the two components. During Knoevenagel condensation, the catalytic activity increased with the GO content in the hybrids up to 15 wt.% and decreased afterwards. (ii) 2-Benzoyl-3-phenylacrylonitrile was synthesized by the aerobic oxidation of benzyl alcohol followed by the Knoevenagel condensation with benzoyl acetonitrile using three different non-polar solvents, i.e., toluene, benzene, and mesitylene. The conversion of benzyl alcohol was higher for the hybrid materials compared to the individual components but decreased with the increase of the graphene oxide concentration.
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Project description:Layered double hydroxides (LDHs) usually aggregate irregularly and hardly redisperse in water. Moreover, the affinity of LDHs is poor for organic compounds. In this study, three different core-shell composites, i.e. CMS@MgAl-LDH, CMS@NiAl-LDH, and CMS@ZnAl-LDH, were synthesized by direct fabrication of LDH nanoplatelets onto carbon microspheres (CMS) for the removal of the adsorbed 2,4-dichlorophenoxyacetic acid (2,4-D). The CMS@LDH composites show good water-dispersity due to the 3D hierarchical sphere structure and high affinity for 2,4-D due to the organic carbon cores that possess abundant hydrophobic compounds. It was found that the adsorption process was rapid, and the time required to reach the sorption equilibrium was within 100 min. The theoretical DFT calculation analysis suggested that the adsorption of 2,4-D on the CMS@LDH composites was dominated by π-π interactions, ion-exchange, and hydrogen bonding. The core-shell CMS@LDH composites can serve as a promising adsorbent that offers a rapid and effective adsorption capacity for the removal of 2,4-D in an aqueous solution.
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Project description:Phase-pure ZnMn2O4 nanopowders and their aggregated microsphere powders for use as anode material in lithium-ion batteries were obtained by a simple spray drying process using zinc and manganese salts as precursors, followed by citric acid post-annealing at different temperatures. X-ray diffraction (XRD) analysis indicated that phase-pure ZnMn2O4 powders were obtained even at a low post-annealing temperature of 400 °C. The post-annealed powders were transformed into nanopowders by simple milling process, using agate mortar. The mean particle sizes of the ZnMn2O4 powders post-treated at 600 and 800 °C were found to be 43 and 85 nm, respectively, as determined by TEM observation. To provide practical utilization, the nanopowders were transformed into aggregated microspheres consisting of ZnMn2O4 nanoparticles by a second spray drying process. Based on the systematic analysis, the optimum post-annealing temperature required to obtain ZnMn2O4 nanopowders with high capacity and good cycle performance was found to be 800 °C. Moreover, aggregated ZnMn2O4 microsphere showed improved cycle stability. The discharge capacities of the aggregated microsphere consisting of ZnMn2O4 nanoparticles post-treated at 800 °C were 1235, 821, and 687 mA h g-1 for the 1st, 2nd, and 100th cycles at a high current density of 2.0 A g-1, respectively. The capacity retention measured after the second cycle was 84%.
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Project description:A method of microalgae-templated spray drying to develop hierarchical porous Fe3O4/C composite microspheres as anode materials for Li-ion batteries was developed. During the spray-drying process, individual microalgae serve as building blocks of raspberry-like hollow microspheres via self-assembly. In the present study, microalgae-derived carbon matrices, naturally doped heteroatoms, and hierarchical porous structural features synergistically contributed to the high electrochemical performance of the Fe3O4/C composite microspheres, enabling a discharge capacity of 1375 mA·h·g-1 after 700 cycles at a current density of 1 A/g. Notably, the microalgal frameworks of the Fe3O4/C composite microspheres were maintained over the course of charge/discharge cycling, thus demonstrating the structural stability of the composite microspheres against pulverization. In contrast, the sample fabricated without microalgal templating showed significant capacity drops (up to ~40% of initial capacity) during the early cycles. Clearly, templating of microalgae endows anode materials with superior cycling stability.
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