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Manganese oxides were synthesized during 40 min at 140 ºC via Microwave-Assisted Hydrothermal (MAH) method and treated at different temperatures in order to evaluate the phase evolution using structure refinement (Rietveld method). The samples obtained were heat treated at temperatures defined by means of thermal analysis (160 ºC, 480 ºC, 715 ºC, 870 ºC, 920 ºC and 1150 ºC) and analyzed by X-Ray Diffractometry (XRD), X-Ray Fluorescence (XRF), Fourier Transform Infrared (FTIR) spectroscopy, Raman scattering, UV-Vis absorption and Scanning Electron Microscopy (SEM). Structural characterizations allowed to identify five distinct phases: α-MnO2, Mn3O4, Mn5O8, Na2Mn5O10 and Na4Mn9O18 with weight percentages dependent on the heat treatment. The hausmannite structure (average crystallite size ranging from 28.9 nm to 99.1 nm) is present in all samples and go through various oxidation and reduction processes from 160 ºC to 1150 ºC without any major variation in the lattice parameters. Chemical characterizations identifies the presence of Na+ ions in all samples, either as substitution defects or as components of specific crystalline structures (Na2Mn5O10 and Na4Mn9O18), showing that the synthesized manganese oxides works as Na+ intercalation compounds, important materials for energy storage devices optimization. The results presented enables a better interpretation of the thermal and structural characteristics of manganese oxides synthesized via MAH.

The present work demonstrates the microwave-assisted synthesis of two different structural morphologies containing nickel oxide nanoparticles (NiO NPs) embedded in nitrogen (N) and sulfur (S) co-doped reduced graphene oxide (NS-rGO) nanosheets. The synthesized NiO anchored on NS-rGO nanosheets (NS-rGO-NiO composites) and NiO covered by NS-rGO nanosheets (NS-rGO:NiO composites) were used as an application in electromagnetic interference (EMI) shielding effectiveness (SE). The EMI SE studies reveal that NS-rGO:NiO composites show improved performance as compared to NS-rGO-NiO composites. In NS-rGO:NiO composites, the covered surface of NiO NPs by conducting NS-rGO nanosheets helps to improve the EMI SE application. The synthesized composite materials were extensively characterized using various techniques including scanning electron microscopy, energy dispersive X-ray spectroscopy, X-ray diffraction, thermogravimetric analysis, Raman spectroscopy, and X-ray photoelectron spectroscopy. Binding energy of N/S ...

Made available in DSpace on 2022-04-29T08:32:04Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Glass-ceramic materials were obtained by heat treatment (960°C for 2, 4, and 6 hs) of glasses with CaCO3 47.50 wt%-TiO2 23.75 wt%-SiO2 23.75-Al2O3 5.00 wt% formulation produced by the melt-quenching technique (melting at 1650°C and subsequent annealing at 650°C). The materials' structural characterization and crystallization kinetics (Kissinger method) indicate the presence of CaTiO3, CaSiO3, and CaTiSiO5 crystalline phases with activation energies 217, 281, and 446 kJ/mol, respectively. The structure refinement (Rietveld method) suggests metastability for the CaSiO3 and CaTiSiO5 phases as a function of the heat treatment time. The increase in time favors CaTiO3 crystallization, from 62.97 wt%, in the 2 hs treated sample, to 79.21 wt%, in the 6 hs treated sample. EDS and microstructure analyses confirm the glass-ceramic production and indicate segregation of the CaTiO3 phase for longer heat treatment times. Universidade Estadual Paulista (UNESP) Faculdade de Ciências e Tecnologia Departamento de Física Universidade Estadual Paulista (UNESP) Faculdade de Ciências Departamento de Química Universidade Estadual Paulista (UNESP) Faculdade de Ciências e Tecnologia Departamento de Física Universidade Estadual Paulista (UNESP) Faculdade de Ciências Departamento de Química

Made available in DSpace on 2021-06-25T11:14:28Z (GMT). No. of bitstreams: 0 Previous issue date: 2021-01-01 Since the optical and electrical properties of organic thin films devices depend on their supramolecular arrangement and the molecular chemical structure, the understanding of such characteristics is essential for the optimization of these devices. In this study, we determine the supramolecular arrangement of thin films produced using the Langmuir-Schaefer (LS) technique and explain how its supramolecular arrangement is affected by the molecular chemical structure using two perylene derivatives: bis-butylimide (BuPTCD) and bis-phenethylimide (PhPTCD). The optical absorption measurements reveal that both films grow homogeneously and indicate that the presence of H aggregates (forbidden emission) is higher for BuPTCD LS film than for PhPTCD LS film. Atomic force microscopic analysis shows that the PhPTCD LS film is rougher than the BuPTCD film. In addition, FTIR analyses indicate that both films have head-on molecular organization. XRD patterns reveal that both the BuPTCD LS film and the PhPTCD LS film are crystalline, but that crystallinity is more prevalent in the BuPTCD LS film. Thus, the results show that the difference presented in the chemical structures leads the films to have different supramolecular arrangements, with consequences for their optical properties. School of Technology and Applied Sciences São Paulo State University (UNESP) School of Technology and Applied Sciences São Paulo State University (UNESP)

Eu-doped 1, 3 and 5 % CaZrO3 red-emitting phosphors were synthesized for the first time using the microwave-assisted hydrothermal method followed by heat treatment at 1200 °C. After the crystallization, the orthorhombic CaZrO3 and the non-stoichiometric cubic Ca0.15Zr0.85O 1.85 phases were identified for all samples, and the portion of the non-stoichiometric phase increases as the Eu3+ concentration increases. The excitation spectra of the phosphors display Eu3+ f-f excitation bands (namely at 395 nm and 464 nm) and the Eu3+→O2- charge transfer band at 250 nm, confirming that the CaZrO3 host acts as sensitizer for the Eu3+ luminescence. Likewise, the emission spectra feature the typical Eu3+ emission within the red spectral region, displaying CIE color coordinates of (0.642; 0.332), (0.663; 0.330) and (0.668; 0.327) for the 1, 3 and 5 % doped samples, respectively, indicating high emission color purity. By using Eu3+ as spectroscopic probe, the high-resolution selective emission spectra (14 K) confirm that Eu3+ replaces Ca2+ and Zr4+ local sites in both CaZrO3 and the Ca0.15Zr0.85O1.85 phases. Finally, the high absolute emission quantum yield of the 3 %-doped phosphor found at 393 nm (0.29 ± 0.03) confirms its potential application as red-emitting phosphor, especially in rapid identification of latent fingerprints, security ink or as red-emitting coating of near-UV LEDs for WLED applications.