Roland Habchi

Enhanced photocatalytic performance of novel electrospun BN/TiO2 composite nanofibers

High activity boron nitride/titanium dioxide (BN/TiO2) composite nanofiber photocatalysts were synthesized for the first time via the electrospinning technique. The as-spun nanofibers with a controlled ratio of boron nitride nanosheets (BN) were calcined under air at 500 °C for 4 hours. Their morphological, structural and optical properties were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), energy-dispersive X-ray spectroscopy (EDX), BET surface area, Fourier-transform infrared (FTIR), Raman spectroscopy, UV-Visible spectrophotometry and room temperature photoluminescence (PL). The effect of loading different BN sheet amounts on the photocatalytic degradation of methyl orange (MO) was investigated. The results indicated that the presence of BN sheets improved the separation of the photo-induced electron–hole pairs in TiO2 and increased the band gap energy and the specific surface area compared to pure TiO2 nanofibers. BN/TiO2 (10 wt%) composite nanofiber photocatalytic activity is enhanced to 99% compared to 60% and 65% for P25 and TiO2 nanofibers, respectively. Thus, the BN/TiO2 composites significantly increase the UV light photo-response and improve the separation of photo-induced electron–hole pairs of TiO2.

Synthesis of novel ZnO/ZnAl2O4 multi co-centric nanotubes and their long-term stability in photocatalytic application

Based on the Kirkendall effect, novel double, triple and quadruple co-centric nanotubes of ZnO/ZnAl2O4 have been successfully fabricated by combining the two techniques of electrospinning and atomic layer deposition. The as-prepared samples were annealed at 900 °C under air. Their morphological, structural and optical properties were studied by Scanning Electron Microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), Energy-Dispersive X-ray spectroscopy (EDX), UV-visible spectrophotometry, Raman spectroscopy, photoluminescence (PL) and reflectance emission. The performances and long-term stability of these multi co-centric nanotubes for photocatalytic applications have been evaluated under the same conditions. As result, in the photodegradation of methyl orange (MO) under UV irradiation, the triple and quadruple co-centric nanotubes of ZnO/ZnAl2O4 exhibit a higher photodegradation efficiency (94% and 99%, respectively) in repeated and long-term applications compared to the pure ZnO which has very low long-term photocatalytic stability. Thus, the fact of coupling these two semiconductors ensured a high photocatalytic activity and long term stability.

Tunable properties of GO-doped CoFe2O4 nanofibers elaborated by electrospinning

Cobalt ferrite (CoFe2O4) one-dimensional nanofibers doped with graphene oxide (GO) were successfully synthesized for the first time via an electrospinning technique. The as-spun nanofibers were calcined at 600 °C for 3 h with a slow heating rate of 2 °C min−1. Their morphological and structural properties were studied by scanning electron microscopy (SEM), X-ray diffraction (XRD), Transmission Electron Microscopy, energy-dispersive X-ray spectroscopy (EDX), and Raman spectroscopy. All GO-doped CoFe2O4 fibers possessed a pure spinel structure. The average fiber diameter and grain size were influenced by the GO weight amount. The effect of the graphene oxide incorporation on the magnetic properties of the fibers was investigated by superconducting quantum interference device (SQUID) magnetometry. At room temperature, a slight enhancement of the saturation magnetization was detected while increasing the GO amount. Therefore, doping with GO is able to tune the magnetic properties of the CoFe2O4 fibers elaborated by the electrospinning technique.

Switching times variation of power MOSFET devices after electrical stress.

The switching performance of three power MOSFET devices with different oxide thicknesses is studied after several periods of electrical stress. The thickest oxide reveals a large accumulation of positive charges in the oxide bulk after small periods of stress. These charges affect the switching parameters by increasing the rise time and by decreasing the fall time. Larger periods of stress reduce the effect of positive charges by increasing the number of interface states. The threshold voltage is decreased by the effect of a positive oxide charge and increases with the appearance of interface states. All these phenomena are less observable as we reduce the oxide thickness.

A faster power MOSFET device with electrical stress treatment

Purpose – The aim of this paper is to provide some specific information on the effects of DC voltage stress on the current, rise time (Tr) and fall time (Tf), at switching between on and off state of power n‐MOSFET devices.Design/methodology/approach – A constant positive electrical stress voltage technique is used to study the devices in this work by giving the gate a positively bias with respect to source and a short circuit of the drain with the grounded source. Voltage stress is gradually increased by automatic 1 V step until it reaches the max tolerated value by the gate dielectric (70 V for device studied in this paper). Response of the device for electrical stress was measured for different doses (stress time).Findings – The experimental results show that the rise time increases the beginning of stress dose and then it almost stabilises with time, while fall time decreases at first and then starts to increase for higher stress time. The modification of the device switching time parameters were asso...

High photodegradation and antibacterial activity of BN–Ag/TiO2 composite nanofibers under visible light

To develop material with good photocatalytic properties for organic compound degradation and bacterial removal, we produced Ag/TiO2 and BN–Ag/TiO2 composite nanofibers that included controlled amounts of boron nitride (BN) nanosheets and silver (Ag). After annealing at 500 °C under air, we used scanning electron microscopy, transmission electron microscopy, Brunauer–Emmet–Teller analysis, X-ray diffraction, energy-dispersive X-ray spectroscopy, Raman spectroscopy, UV-visible reflectance spectroscopy and room temperature photoluminescence to investigate the morphological, structural and optical properties of all samples. The photocatalytic tests using methylene blue under visible light, in repeated and long-term applications, showed that the photodegradation activity of BN(5 wt%)–Ag(3 wt%)/TiO2 composite nanofibers was 17.2 and 2.3 times higher than that of pure TiO2 and Ag(3 wt%)/TiO2 nanofibers, respectively. In antibacterial tests using Gram-negative Escherichia coli, 3 hours of incubation with BN(5 wt%)–Ag(3 wt%)/TiO2 composite nanofibers killed all bacteria. These results indicate that the synthesized BN(5 wt%)–Ag(3 wt%)/TiO2 composite nanofibers can be considered to be a multifunctional material for photodegradation and antibacterial applications.

Evaluation of the electrical properties under extreme stress in photovoltaic solar modules

Purpose – The purpose of this paper is to discuss the effect of electric reverse stress currents on the performance of photovoltaic solar modules.Design/methodology/approach – The effect of a reverse introduced current as a function of time is studied on the I‐V and C‐V characteristics and parameters which were extracted and analyzed using numerical analysis based on a reliable double exponential model.Findings – The effect of an introduced reverse current for different periods simulated the effect of accumulated extreme reverse currents which may arise in solar cells and modules due to different reasons, causing dramatic changes in the shunt resistance as well as other characteristics, mainly when the time of the current application exceeded a certain limit.Originality/value – The paper contributes to the research on the damaging effects of reverse currents on the normal operation of the solar cells and modules.

Evolution of photovoltaic solar modules dark properties after exposition to electrical reverse stress current inducing thermal effect

Purpose – The purpose of this paper is to investigate the dark properties as a function of reverse current induced defects. Dark characteristics of solar modules are very essential in the understanding the functioning of these devices. Design/methodology/approach – Reverse currents were applied on the photovoltaic (PV) modules to create defects. At several time intervals, dark characteristics along with surface temperature were measured. Findings – Current-voltage (I-V) and capacitance-voltage (C-V) characteristics furnished valuable data and threshold values for reverse currents. Maximum module surface temperatures were directly related to each of the induced reverse currents and to the amount of leakage current. Microstructural damages, in the form of hot spots and overheating, are linked to reverse current effects. Experimental evidence showed that different levels of reverse currents are a major degrading factor of the performance of solar cells and modules. Originality/value – These results give a re...

Stabilization and encapsulation of magnetite nanoparticles

The goal is to stabilize magnetite nanoparticles (NPs) in order to prepare them for encapsulation and to obtain a core–shell structure. Magnetite NPs were obtained by a co-precipitation method and then treated with different stabilizing agents in order to get a full dispersion in an aqueous medium. The dispersed particles were then coated with silica using a TEOS solution. The samples were characterized by Raman spectroscopy, TEM, EDX analysis, and FTIR measurements. The particles are the basis of a core–shell structure where a potential polymer or drug could be anchored on the surface.

Interface defects detection and quantification on a Si/SiO2 structure

Purpose The purpose of this paper is to investigate and classify the defects on silicon-based power devices under extreme conditions. Design/methodology/approach Electrical characterization was performed on MOS devices to study their interface defects. The devices were subjected to a voltage or a current constraint to induce defects, and then measurements were done to detect the effects of those defects. Measurements include current voltage, capacitance and conductance characterization. The Hill–Coleman method was used to calculate the interface states density in each case. Findings It was found that most of the defects have energies within the upper band gap of the semiconductor. Originality value The method used in this paper allows the determination of any interface defects on a Si/SiO2 structure.