Publications internationales
Résumé: It is indisputable that structural defects are pivotal in modulating the properties of materials. This study provides a comprehensive analysis of the structural, optical, and photoluminescence characteristics of V2O5, ZrO2, and ZrV2O7.These materials were chosen for their potential applications in various key technological domains. The XRD results revealed the formation of high-purity materials with no secondary phases. It was determined that ZrO2exhibits the most significant quantity of structural defects among the investigated materials. The variation in crystallite size as determined by XRD aligns with the variation in grain size observed through Scanning Electron Microscopy (SEM).The optical band gaps of V2O5, ZrO2, and ZrV2O7 were determined to be 2.27 eV, 5.19 eV, and 2.38 eV, respectively. X-ray Photoelectron Spectroscopy (XPS) analysis indicated the presence of constituent elements without any contaminants. A detailed examination of the photoluminescence (PL) emission characteristics in both UV–Vis and near-infrared (NIR) regions for all materials presented broad visible luminescence in the [450–650] nm range under UV excitation. Structural defects are crucial in determining the physico-chemical properties of materials. This is thoroughly examined for V2O5, ZrO2, and ZrV2O7.The infrared (IR) emission spectra, introduced for the first time in this study for V2O5, ZrO2, and ZrV2O7, are employed to elucidate the localization of structural defects within the band gap
Résumé: Ball milling was used in order to produce ZnONPs with different mean crystallite sizes and shapes. XRD, FTIR, SEM, and PL characterizations were used to determine milling time's effect on ZnONPS's structural, morphological, and optical properties. XRD-analysis showed a decrease in particle size (43 to 12 nm) and a change in the lattice parameter c, from 5.177 to 5.198 Å. SEM analysis showed the formation of aggregated particles, evenly distributed. PL results indicated the appearance of new bands, which are associated to the formation of defects. Moreover, it was showed that milled ZnONPs enhanced antibacterial activity by decreased minimum inhibitory concentration (MIC) values. Indeed, MIC of Serratia marcescens and Shigella were initially, i.e., at t=0 h, 1024 µg/mL but, after of milling, it decreases to 32 µg/mL and 64 µg/mL, respectively. On the other hand, the MICs of Staphylococcus-coagulase-negative and Staphylococcus-aureus-ATCC23 decreased from 128 µg/mL and 64 µg/mL to 4 µg/mL and 2 µg/mL, respectively, as a function of milling time. In general, ball milling shows significant promise for enhancing antibacterial activity. However, this requires the control and optimization of the physicochemical parameters involved in the different stages of this process, as well as the understanding of the mechanisms underlying it. This is the subject of future research, with the obligation to broaden the scope of these investigations to other nanomaterials obtained in multiple ways
Résumé: In this study, we report a facile hydrothermal synthesis of strontium-doped SnS nanoflowers that were used as a catalyst for the degradation of antibiotic molecules in water. The prepared sample was characterized using X-ray diffraction (XRD), scanning electron microscopy (SEM), and ultraviolet–visible absorption spectroscopy (UV–Vis). The photocatalytic ability of the strontium-doped SnS nanoflowers was evaluated by studying the degradation of metronidazole in an aqueous solution under photocatalytic conditions. The degradation study was conducted for a reaction period of 300 min at neutral pH, and it was found that the degradation of metronidazole reached 91%, indicating the excellent photocatalytic performance of the catalyst. The influence of experimental parameters such as catalyst dosage, initial metronidazole concentration, initial reaction pH, and light source nature was optimized with respect to metronidazole degradation over time. The reusability of the strontium-doped SnS nanoflowers catalyst was investigated, and its photocatalytic efficiency remained unchanged even after four cycles of use.
Résumé: For several decades, the use of antibiotics has led to the emergence of highly resistant human and animal pathogens, posing a significant threat to global health, food security, and economic progress. In the quest for alternatives to combat multidrug-resistant bacteria and yeasts, the utilization of nanoparticles materials has emerged as a promising avenue. In this research, we investigated the antimicrobial properties of Zn-Al-layered double hydroxide, synthesized through co-precipitation and subsequently calcined at temperatures of 400, 600, and 800°C. A total of 21 bacterial strains, including 15 clinical strains and 6 Gram-reference strains, along with one fungal strain, were subjected to testing. The synthesized materials underwent characterization using various techniques such as X-ray diffraction (XRD) spectroscopy, scanning electron microscopy (SEM), ultraviolet–visible spectroscopy, and fourier-transform infrared (FTIR) spectroscopy. The key findings indicate that the uncalcined Zn-Al-layered double hydroxide and the heterojunction ZnO-ZnAl2O4 calcined at 400°C and 600°C exhibited a minimum inhibitory concentration (MIC) of 0.125 μg/mL against the tested strains. The spinell ZnAl2O4 calcined at 800°C showed MICs ranging between 0.125 and 2 μg/mL, with a greater bactericidal effect on gram-negative bacteria (GNBs) such as Enterobacteriaceae and non-Enterobacteriaceae compared to Gram-positive bacteria. Consequently, the heterojunction ZnO-ZnAl2O4 demonstrated higher efficacy against Gram-positive bacteria. These findings highlight the potential of heterojunction ZnO-ZnAl2O4 and spinell ZnAl2O4 as mixed metal oxides derived from ZnAl-layered double hydroxide, offering promising alternatives to traditional antibiotics and suggesting their potential use as impregnating agents in matrices with a broad spectrum of specific antimicrobial activity.
Résumé: The determination of the band edge positions turns out to be of particular importance in different fields. We present a comparison of different approaches for the determination of the band edge alignment. For this purpose, we suggested studying the ZrO2|V2O5 heterojunction. The structural properties investigated by means of X-ray diffraction (XRD) revealed the formation of pure V2O5 with an orthorhombic structure. The resulting ZrO2, however, exhibits two different phases (monoclinic and tetragonal). Based on the absorption spectra, the near-band edges for V2O5, ZrO2, and ZrO2|V2O5 were found to be 2.07, 4.9, and 2.12 eV, respectively. The corresponding band gap values determined by the Tauc method were found to be 2.32, 5.16, and 2.35 eV, respectively. The down-conversion photoluminescence (PL) spectra of pure and junctioned materials are discussed in detail. The up-conversion in ZrO2 revealed its band gap value (∼5.14 eV), which is very close to the one obtained by the Tauc method (∼5.16 eV). The band gap alignment of the ZrO2|V2O5 heterojunction was determined using Sanderson method and experimentally using X-ray photoelectron spectroscopy (XPS). In this work, we propose an In-depth photoluminescence study for the confirmation of the type of heterojunction by probing the hydroxyl radical (HO•) production.
Résumé: In this work, Mg2+ doped ZnS nanoparticles were prepared by solvothermal method, using ethanol as solvent at 135 °C.The nanoparticles were characterized by XRD, SEM, UV–vis and PL. After doping, XRD revealed a reduction in lattice parameter, confirming Mg2+ substitution into the ZnS host lattice. The UV–vis study indicated that the incorporation of Mg2+ ions does not modify the band gap width of the nanoparticles. The PL spectra measured at 325 nm excitation wavelength, reveals that the photogenerated electrons of Zn0·9Mg0·1S have a slower recombination rate than ZnS nanoparticles. The XPS finding confirm that the chemical environment of the elements has been affected by the presence of the Mg2+. The Valence Band Maximum (VBM) was determined to be 0.2eV for ZnS and 1eV for Zn0·9Mg0·1S, respectively. These findings confirm the perturbation of electronic properties when Mg2+ is added to the ZnS. The photocatalytic ability was estimated through the degradation of tartrazine under natural-sunlight irradiation. Zn0.9Mg0.1S shows a high photocatalytic activity, compared to ZnS nanoparticles. The photocatalytic degradation was studied through different parameters, such as: the source of irradiation, the pH, the dye concentration, the catalyst concentration, and the recyclability. The degradation investigation shows that tartrazine is better oxidized at free pH = 6,7, with a dye concentration of 20 mg/L and a catalyst dosage of 1 g/L. Zn0.9Mg0.1S degraded 98% of tartrazine under natural-sunlight irradiation. In addition, the catalyst retained a good photo-degradation capacity, even after many treatment cycles. The scavengers study confirmed that the main active species responsible for the photocatalytic degradation of tartrazine were the oxidation groups (O2•-).
Résumé: Various concentrations of Mg2+ substitutional doped ZnS nanoparticles (Zn MgxS, x = 0, 0.02, 0.07, and 0.1) were prepared by adopting the solvothermal method, using ethanol as the solvent at 135°C. The obtained micro/nanoparticles were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and room temperature photoluminescence (PL) spectroscopy. XRD revealed the conservation of the host ZnS crystal phase after the substitution of Zn2+ by Mg2+ but was accompanied by a weak decrease of the lattice parameter. SEM analysis showed the formation of aggregated particles that were evenly distributed. PL spectra exhibited a near-band-edge (NBE) emission centered at 430 nm, and another band at 585 nm, related to sulfur defects; moreover, no shift occurred when x increased. To explain this finding, computational density functional theory (DFT) calculations were performed, revealing constant gap energy after substitution was maintained at the point G, whereas the density of stats of both CV and BV were reinforced near the band gap.
Résumé: A novel nickel oxide nanoparticles modified glassy carbon electrode was fabricated and used as a non enzymatic sensor for glucose determination. Aimed as promising alternative to conventional chemical methods, NiO-NPs were synthesized via a green synthetic approach using Nigella sativa Extract. NiO NPs were characterized using Fourier transfer infrared spectroscopy (FTIR), X-ray diffraction (XRD), transmission electron microscopy (TEM), and scanning electron microscopy with EDS profile. Electrochemical measurements were performed using cyclic voltammetry (CV) and Chrono-ammperometry (CA) in 0.1 M NaOH solutions, revealing a well defined redox couple of NiIII/NiII. The electrogenerated NiIII species on the electrode surface act as an excellent catalyst toward the glucose oxidation reaction. Our modified electrode presents good stability, short response time < 3 s, low detection limit around 3.2 µM, and two linear ranges of detection from 50 µM to 600 µM, and from 1 mM to 10 mM with sensitivity equal to 987.85 mA cm-2mM−1 and 170.85 mA cm-2mM -1 respectively.
Résumé: A surfactant-free hydrothermal technique was used to synthesize calcium (Ca2+) incorporated ZnS nanoparticles (ZnS:Ca). The structural, morphological, optical and microstructural properties of the produced nanoparticles are investigated by XRD, SEM, PL and XRF techniques, respectively. The XRD patterns revealed the preservation of the cubic phase after Ca2+ addition, and a decrease of the crystallite size. The SEM micrographs showed the formation of good shaped spherical particles, and evenly distributed. The ZnS:Ca photoluminescence emission bands were blue-shifted and broader than those of pristine ZnS. Finally, the photocatalytic activity of methylene orange (MO) was enhanced by Ca2+ incorporation. According to XRF measurements, the solubility limit of Ca2+ in ZnS lattice is found to be at 0.16% of Ca2+/Zn2+ mass ratio. This result can explain the saturation of the rate constant in the photocatalysis process.
Résumé: Green-synthesized NiO nanoparticles (NiONPS) have been developed using Nigella Sativa seeds extract as stabilizing agent. The pH of the solution has been modulated, by the addition of NaBH4. NiONPs have been characterized by XRD, FTIR, SEM and TEM. FTIR measurements and TEM images highlighted that NiONPs were surrounded by some biological compounds coming from the extract. The total reduction of 4-nitrophenol to 4-aminophenol corresponding to the catalytic activity of NiONPs was occurred at pH7, pH9 and pH11 in 60min, 10min and 45min respectively. These results revealed that the best catalytic activity is obtained at pH9 which is confirmed by electrocatalytical activity measurements where the resistance charge transfer corresponding is 53.7 Ω cm2 and the Warburg constant 0.0395Ωs-1/2 related a good ion diffusion, indicated consequently an increase number of electroactive sites. Thus, the carrier charges generated in the NiO mass can easily reach the surface which contribute to the reduction of 4-nitrophenol.