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Your search keyword '"Najeh, I."' showing total 20 results
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20 results on '"Najeh, I."'

13. Production and characterization of carbon-vanadium nanocomposites

Author

Ministère de l’Enseignement Supérieur et de la Recherche Scientifique (Tunisie), Montes Morán, Miguel Ángel [0000-0002-8791-5582], Jeidi, H., Ahmed, W., Najeh, I., Chouiref, L., Montes Morán, Miguel Ángel, Gomes, H. L., Mir, L. El, Ministère de l’Enseignement Supérieur et de la Recherche Scientifique (Tunisie), Montes Morán, Miguel Ángel [0000-0002-8791-5582], Jeidi, H., Ahmed, W., Najeh, I., Chouiref, L., Montes Morán, Miguel Ángel, Gomes, H. L., and Mir, L. El

Abstract

Carbon-vanadium nanocomposites were prepared by sol–gel route after incorporating vanadium pentoxide nanopowder in carbon matrix based on resorcinol–formaldehyde xerogel, followed by thermal treatment. The resulting samples were characterized by different techniques, namely X-ray diffraction, Fourier transform infrared spectroscopy, RAMAN spectroscopy, Scanning electron microscopy, and electrical analysis. The X-ray diffraction analysis carried out on our samples that exhibits the pyrolysis temperature brings out the crystal phase change from V2O5 phase to V2O3 phase, also the presence of graphite phase in the samples, and the appearance of vanadium carbide V8C7 phase in sample pyrolyzed at 1000 °C. The Fourier transform infraredspectra are characterized by the appearance of peaks at 997, 792, and 559 cm−1corresponding to V–O stretching modes. RAMAN analysis shows the presence of characteristic peaks of vanadium oxide and the D and G bands characteristic of graphite. The Scanning electron microscopy graphs indicate the presence of macroporous carbon enriched by vanadium oxide in nanofibres shape. In addition, in an interesting way, the obtained material presents a percolation phenomenon in the temperature zone from 600 to 800 °C where the behavior of the material changes from insulator state to conductor one as a function of pyrolysis temperature. For that, the electrical analyses were carried out for the sample prepared at 650 °C. The dc conductance indicates a thermally activated process. The ac conductance shows a semiconductor–metal behavior change at 200 K. Indeed, the transfer of charge carriers is dominated by the correlated barrier hopping conduction model in the prepared material for measurement temperatures below 200 K. The impedance analysis shows a non-Debye relaxation phenomenon in the system. An electrical equivalent circuit has been proposed for the analysis of the impedance results and the determination of the fundamental parameters of the circuit at

Published
2022

14. Synthesis and characterization of microporous carbon matrix enriched by MnO2 nanoparticles.

Author

Ahmed, W., Jeidi, H., Najeh, I., Dahman, H., Silva, J. P. B., Moreira, J. Agostinho, Pereira, M., Gomes, M. J. M., and Mir, L. El

Subjects
TEMPERATURE effect, NANOPARTICLES, DIELECTRIC properties, GRAPHITIZATION, MANGANESE dioxide, ELECTRIC conductivity, MANGANESE oxides, NANOPOROUS materials
Abstract

Nanocomposites (RF/MnO2) based on resorcinol–formaldehyde (RF) as carbon matrix and manganese oxide nanoparticles (MnO2) as incorporated material were elaborated by a sol–gel method. The effect of pyrolysis temperature was studied using different characterization techniques. Firstly, the Raman results show two strong peaks referred to G and D bands of carbon and an additional one related to MnO2. Also, it reveals a change in the degree of graphitization when the temperature increases. This result suggests also the successful incorporation of the MnO2 into the matrix, which was confirmed by the FTIR analysis. Then, dc measurement proves that the behavior of the nanocomposite changed from insulator to metallic one when the pyrolysis temperature increased from 600 to 1000 °C passing through a sudden transition explained by a percolation phenomenon. The X-ray diffraction confirms the previous results concerning the temperature effect. More than this, it proves that the nanocomposites are partially crystallized with the appearance of the graphite structure, the manganese dioxide (MnO2), the manganese oxide (MnO), and the metallic manganese (Mn) at high pyrolysis temperature. The scanning electronic microscope (SEM) images depict the porous structure of the RF matrix. Finally, the electrical behavior and dielectric properties were in good agreement with the other results; they confirm the effect of the pyrolysis temperature on the electrical conductivity and the dielectric loser. The properties of the obtained nanoporous conducting carbon/manganese nanocomposite can be adjusted by the pyrolysis temperature which makes this material promising for many technological applications. [ABSTRACT FROM AUTHOR]

Published
2022
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20. Role of annealing temperature on electrical and optical properties of ZnO nanoparticles for renewable energy applications.

Author

Omri, K., Bettaibi, A., Najeh, I., Rabaoui, S., Khirouni, K., and El Mir, L.

Subjects
THERMISTORS, COLD (Temperature), THERMAL stresses, TEMPERATURE control, THERMAL properties
Abstract

Hexagonal wurtzite ZnO nanoparticles prepared by sol-gel technique followed by thermal treatment at different temperatures. The structural properties showed that the ZnO nanoparticles exhibit hexagonal wurtzite structure. The dielectric constant, loss tangent and ac conductivity were studied as a function of frequency and annealing temperature. All the dielectric parameters show dispersion and decrease with increase in annealing temperature. The optical band gap of our samples varied between 3.34 and 3.21 eV with increasing annealing temperature. The obtained results reveal that the as synthesized samples are promising for potential applications in the renewable energy devices. [ABSTRACT FROM AUTHOR]

Published
2016
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