Electrochemical Fabrication and Characterization of p-CuSCN/n-Fe2O3 Heterojunction Devices for Hydrogen Production

[EN] p-CuSCN/n-Fe2O3 heterojunctions were electrochemically prepared by sequentially depositing alpha-Fe2O3 and CuSCN films on FTO (SnO2:F) substrates. Both alpha-Fe2O3 and CuSCN films and alpha-Fe2O3/CuSCN heterojunctions were characterized by field emission scanning electron microscopy (FESEM), energy-dispersive X-ray spectroscopy (EDX), and X-ray diffraction (XRD). Pure crystalline CuSCN films were electrochemically deposited on alpha-Fe2O3 films by fixing the SCN/Cu molar ratio in an electrolytic bath to 1:1.5 at 60 degrees C, and at a potential of -0.4 V. The photocurrent measurements showed increased intrinsic surface states or defects at the alpha-Fe2O3/CuSCN interface. The photoelectrochemical performance of the alpha-Fe2O3/CuSCN heterojunction was examined by chronoamperometry and linear sweep voltammetry techniques. The alpha-Fe2O3/CuSCN structure exhibited greater photoelectrochemical activity compared to the alpha-Fe2O3 thin films. The highest photocurrent density was obtained for the alpha-Fe2O3/CuSCN films in 1 M NaOH electrolyte. This strong photoactivity was attributed to both the large active surface area and the external applied bias, which favored the transfer and separation of the photogenerated charge carriers in the alpha-Fe2O3/CuSCN heterojunction devices. The flatband potential and donor density were maximal for the heterojunction. These results suggest a substantial potential to achieve heterojunction thin films in photoelectrochemical water splitting applications. (c) 2017 The Electrochemical Society. All rights reserved.This work was supported by the Ministry of High Education and Scientific Research (Tunisia), Ministerio de Economia y Competitividad (ENE2016-77798-C4-2-R) and Generalitat Valenciana (Prometeus 2014/044).Bouhjar, F.; Ullah, S.; Mollar García, MA.; Marí, B.; Bessais, B. (2017). Electrochemical Fabrication and Characterization of p-CuSCN/n-Fe2O3 Heterojunction Devices for Hydrogen Production. Journal of The Electrochemical Society. 164(13):936-945. https://doi.org/10.1149/2.1431713jes9369451641

Hydrothermal synthesis of nanostructured Cr-doped hematite with enhanced photoelectrochemical activity

[EN] Using the easily applicable hydrothermal method Cr-doped hematite thin films have been deposited polycrystalline on conductive glass substrates. The hydrothermal bath consisted of an aqueous solution containing a mixture of FeCl3.6H(2)O and NaNO3 at pH = 1.5. The samples were introduced in an autoclave and heated for a fixed time at a fixed temperature and then annealed in air at 550 degrees C. The concentration of the incorporated Cr atoms (Cr4+ ions) was controlled by varying the concentration of the Cr(ClO4)(3) precursor solution, varied from 0% to 20%. All samples followed morphological and structural studies using field-emission scanning electron microscopy, high-resolution transmission electron microscopy and X-ray diffraction. Chronoamperometry measurements showed that Cr-doped hematite films exhibited higher photoelectrochemical activity than the undoped films. The maximum photocurrent density and incident photon conversion efficiencies (IPCE) were obtained for 16 at.% Cr-doped films. This high photoactivity can be attributed to both the large active surface area and increased donor density caused by Cr-doping in the alpha-Fe2O3 films. All samples reached their best IPCE at 400 nm. IPCE values for 16 at.% Cr-doped hematite films were thirty times higher than that of undoped samples. This high photoelectrochemical performance of Cr-doped hematite films is mainly attributed to an improvement in charge carrier properties. (C) 2017 Elsevier Ltd. All rights reserved.This work was supported by the Ministry of Higher Education and Scientific Research, Tunisia and Ministerio de Economia y Competitividad (ENE2016-77798-C4-2-R) and Generalitat Valenciana (Prometeus 2014/044).Bouhjar, F.; Mollar García, MA.; Chourou, M.; Marí, B.; Bessais, B. (2018). Hydrothermal synthesis of nanostructured Cr-doped hematite with enhanced photoelectrochemical activity. Electrochimica Acta. 260:838-846. https://doi.org/10.1016/j.electacta.2017.12.049S83884626

Electrodeposited Cr-Doped alpha-Fe2O3 thin films active for photoelectrochemical water splitting

[EN] Polycrystalline hematite (alpha-Fe2O3) Chromium (Cr)-doped thin films were electrodeposited on fluorine-doped tin oxide-coated glass substrates. The electrodeposition bath comprised an aqueous solution containing FeCl3 center dot 6H(2)O, NaCl, and H2O2.Chromium was added to the electrolyte at such a proportion that the Cr/(Cr + Fe) ratio remained within the 2-8 at. % range. The as-deposited films were subsequently annealed in air at 650 degrees C for 2 h. The structure and morphological characteristics of the undoped and Cr-doped alpha-Fe2O3 thin films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and UV-Vis spectroscopy. Cr doping led the main XRD lines to shift to lower angles, which mostly resulted from substituting Fe3+ for Cr4+ ions that leads to alpha-Fe2O3 lattice contraction. The SEM observations showed that the roughness and aspect of surfaces changed with the Cr doping level. The photoelectrochemical (PEC) performance of the alpha-Fe2O3 films was examined by chronoamperometry and linear sweep voltammetry techniques. The Cr-doped films exhibited greater photoelectrochemical activity than the undoped alpha-Fe2O3 thin films. The highest photocurrent density was obtained for the 8% Cr-doped alpha-Fe2O3 films in 1 M NaOH electrolyte. All the samples achieved their best IPCE at 400 nm. The IPCE values for the 8 at.% Cr-doped hematite films were 20-fold higher than that of the undoped sample.This Cr-doped hematite films 'excellent photoelectrochemical performance was mainly attributed to improved charge carrier properties. Such high photoactivity was attributed to the large active surface area and increased donor density caused by increasing the Cr doping in the alpha-Fe2O3 films. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.This work was supported by the Ministry of High Education and Scientific Research (Tunisia), the Ministry of Economy and Competitiveness (Spain) (ENE2016-77798-C4-2-R) and the Generalitat Valenciana (Prometeus 2014/044).Bouhjar, F.; Derbali, L.; Marí, B.; Bessais, B. (2020). Electrodeposited Cr-Doped alpha-Fe2O3 thin films active for photoelectrochemical water splitting. International Journal of Hydrogen Energy. 45(20):11492-11501. https://doi.org/10.1016/j.ijhydene.2019.10.215S1149211501452

Electrodeposited chromium-doped alpha-Fe2O3 under various applied potential configurations for solar water splitting

[EN] In this work, high quality hematite (alpha-Fe2O3) Chromium (Cr)-doped thin films have been synthesized via electrodeposition technique, on fluorine-doped fin oxide-coated glass substrates, under various applied potential configurations [cyclic voltammetry (CV), linear sweep voltammetry (LSV) and - 0.5 V]. Chromium was added to the electrolyte at such a proportion that the Cr/(Cr + Fe) ratio remained within 8%. The as-deposited films were subsequently annealed in air at 650 degrees C for 2 h. Our novel study highlights the effect of using variable potential approaches during the film preparation on the properties of Cr-alpha-Fe2O3 deposited films. The prepared thin films were analyzed by X-ray diffraction, Raman spectroscopy, scanning electron microscopy, UV-Vis absorption and photoelectrochemical (PEC) analysis. XRD revealed that samples are crystallized in Cr-Fe2O3 cubic structure with a crystalline orientation in the plane (1 1 1) and a clear improvement of the crystallinity and size crystallite of the Cr-Fe2O3 deposited using CV process. SEM micrographs showed that the morphology grains were three-sided pyramid-shaped, expanding with increase of the crystallinity. The calculated band gap values are 2.18, 2.23 and 2.20 eV, respectively for - 0.5 V, LSV, CV. The Cr-Fe2O3 films synthesized in this study showed high PEC activity with very low carrier density in comparison with the conventionally electrodeposited films. This Cr-doped hematite films 'excellent photoelectrochemical performance was mainly attributed to improved charge carrier properties. Such high photoactivity was attributed to the large active surface area and increased donor density caused by increasing the Cr doping in the alpha-Fe2O3 films.This work was supported by the Ministry of High Education and Scientific Research (Tunisia), the Ministry of Economy and Competitiveness (Spain) (ENE2016-77798-C4-2-R) and the Generalitat Valenciana (Prometeus 2014/044).Bouhjar, F.; Derbali, L.; Marí, B.; Bessais, B. (2020). Electrodeposited chromium-doped alpha-Fe2O3 under various applied potential configurations for solar water splitting. Results in Physics. 17:1-7. https://doi.org/10.1016/j.rinp.2020.102996S171

Crystal growth and design of various shapes of PbS micro and nanocrystals from a hydrothermal process

[EN] This paper reports on a systematic study highlighting dramatic morphological changes during the preparation of Lead Sulfide (PbS) by a hydrothermal process. PbS micro/nanostructures having different shapes and sizes were prepared via a simple hydrothermal reaction between lead acetate and a sulfur precursor (Thiourea (Tu) or Na2S). We show that the shapes of the PbS micro/nanostructures can be tuned by varying the process parameters, for instance the concentration of the precursors (lead acetate and Thiourea), the reaction time and the reaction temperature. The hydrothermal ? based PbS structures were characterized by Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), High-Resolution TEM (HRTEM) and X-Ray Diffraction (XRD). We succeeded synthesizing PbS crystallites having symmetric six- and eight-arms starfish-shaped dendrites by using Thiourea (Tu) as anionic precursor. The decrease of Tu concentration as low as 0.05 M switches the crystal morphology to irregular flower- and cubic ? like shapes, while the increase of the reaction time up to 6 h leads to the formation of mono-arms dendrites. The addition of Triethylamine (TEA) to Tu in the initial reaction blocks the growth of the six-arm starfish shaped PbS crystals and leads to the formation of octahedral and sub-spherical crystals. A morphological change from starfish dendrites to crystalline nanoparticles occurs by replacing Tu by Na2S as a sulfur precursor; this transition from dendrites to nanoparticles was attributed to the nature of the anionic precursorThis work was supported by the University of Tunis El Manar (Tunisia) and Ministerio de Economia y Competitividad (Grant Number PID2019-107137RB-C21), SpainJemai, S.; Hajjaji, A.; Baig, F.; Harabi, I.; Marí, B.; Bessais, B. (2021). Crystal growth and design of various shapes of PbS micro and nanocrystals from a hydrothermal process. Materials Characterization. 175:1-8. https://doi.org/10.1016/j.matchar.2021.111036S1817

Increase of magnetic and magnetoelectric properties in Co/Mn co-doped BiFeO3 multiferroic

International audienceCo and Mn co-doped BiFeO3 samples are successfully realized using a stirred hydrothermal route to form BiFe0.9CoxMn0.1-xO3 (for x=0.01, 0.03, 0.05, 0.07 and 0.09) system. Our data show that both the ferroelectric (TC) and antiferromagnetic (TN) transition temperatures increase especially TN varies by up to 23°C when changing from BiFe0.9Co0.01Mn0.09O3 to BiFe0.9Co0.09Mn0.01O3. Such strong TN enhancement is explained by Co ionic size which induces a chemical pressure by reducing the unit cell and consequently favor the exchange coupling between the magnetic moments carried by Fe/Co/Mn. Moreover, Co 3+ (d 6 electronic configuration) by replacing Fe (d 5) increases the magnetization reaching a value of 3.394 emu/g for BiFe0.9Co0.09Mn0.01O3, by favoring double exchange interactions. The direct magnetoelectric (ME) measurements on those samples show a significant increase of the ME coefficient with a value of 8.720 mV/(Oe.cm) for BiFe0.9Co0.05Mn0.05O3 i.e. up to 6 times higher than that of pure BiFeO3. For Mn-rich compositions, because of a parasitic Bi25FeO40 phase and high electric losses, no intrinsic ME coefficient could be measured

Synthesis and Characterization of TiO(2) Nanotubes (TiO(2)-NTs) Decorated with Platine Nanoparticles (Pt-NPs): Photocatalytic Performance for Simultaneous Removal of Microorganisms and Volatile Organic Compounds

International audienceThis work reports on the effect of TiO nanotubes (TiO-NTs), decorated wih platinum nanoparticles (Pt-NPs), on the removal of bacteria and volatile organic compounds (VOCs). The Pt-NPs were loaded onto the TiO-NTs using the electrodeposition method at four decoration times (100, 200, 300, and 600 s). The realized Pt-NPs/TiO-NTs nanocomposites were used for the degradation of cyclohexane, a highly toxic and carcinogenic VOC pollutant in the chemical industry. The achieved Pt-NPs/TiO-NTs nanocomposites were characterized using X-ray diffraction (XRD), photoluminescence (PL), diffuse reflectance spectroscopy (UV-Vis), and scanning (SEM) and transmission (TEM) electron microscopy. To understand the photocatalytic and antibacterial behavior of the Pt-NPs/TiO-NTs, simultaneous treatment of Escherichia coli and cyclohexane was conducted while varying the catalyst time decoration. We noticed a complete bacterial inactivation rate with 90% VOC removal within 60 min of visible light irradiation. Moreover, the Langmuir-Hinshelwood model correlated well with the experimental results of the photocatalytic treatment of indoor air

Large magnetoelectric response and its origin in bulk Co-doped BiFeO 3 synthesized by a stirred hydrothermal process

International audienceIn this work, we study the effect of Co-doping on the magnetoelectric (ME) response of multiferroic BiFeO3 (BFO) ceramics made of powder synthesized using a stirred hydrothermal method known to facilitate chemical reactions and favor good chemical homogeneity and particles size distribution. An unprecedented ME coefficient up to 11.3 mV/(Oe.cm) i.e. 8 times higher than pure BFO ceramic, measured with a direct method is achieved for 3–5% Co-doping which makes bulk Co-doped-BFO among the largest single-phase ME materials. We show that Co-doping can be seen as a chemical pressure i.e. a proxy hydrostatic pressure resulting into an increase of Néel antiferromagnetic temperature and especially a destabilization of the cycloidal magnetic modulation because of magnetoelastic coupling. By suppressing the cycloidal arrangement that we evidenced unambiguously by using low energy Raman spectroscopy, the linear ME effect is no more inhibited and can then take place explaining the large ME response. We argue that the combination of mechanical and chemical means during the stirred hydrothermal approach we used might be at the origin of such response by favoring Co-distribution and avoiding parasitic phases and therefore such a chemical route might be further explored in the future

Synthesis and characterization of multiferroic materials for the environment

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