Rosari Saleh

Transition-metal-doped ZnO nanoparticles: synthesis, characterization and photocatalytic activity under UV light.

ZnO nanoparticles doped with transition metals (Mn and Co) were prepared by a co-precipitation method. The synthesized nanoparticles were characterized using X-ray diffraction, scanning electron microscopy, energy dispersive X-rays, Fourier transform infrared spectroscopy, electron spin resonance spectroscopy and diffuse reflectance spectroscopy. The photocatalytic activities of the transition-metal-doped ZnO nanoparticles were evaluated in the degradation of methyl orange under UV irradiation. ZnO nanoparticles doped with 12 at.% of Mn and Co ions exhibited the maximum photodegradation efficiency. The experiment also demonstrated that the photodegradation efficiency of Mn-doped ZnO nanoparticles was higher than that of Co-doped ZnO nanoparticles. These results indicate that charge trapping states due to the doping were the decisive factor rather than the average particle size and energy gap. Moreover the effect of pH values on the degradation efficiency was discussed in the photocatalytic experiments using 12 at.% Mn- and Co-doped ZnO nanoparticles.

Infrared absorption in a-SiC:H alloy prepared by d.c. sputtering

Abstract Infrared absorption and hydrogen effusion were measured on silicon rich a-SiC:H films deposited by d.c. sputtering. Hydrogen concentration was changed by hydrogen implantation. The results show that the shift of the SiH stretching absorption from 2000 to 2100 cm−1 with increasing carbon concentration is mainly due to hydrogen-related void formation. The absorption strength of SiH stretching and wagging absorptions are found to be independent of carbon concentration. The data suggest that both 720 and 780 cm−1 absorptions are due to CSi stretching vibrations with the 720 cm−1 absorption presumably related to HSiC groups. Under the deposition condition applied, these HSiC groups are the predominant sites for hydrogen and carbon incorporation.

Preparation, Characterization and Photocatalytic Activity of Multifunctional Fe3O4/ZnO/CuO Hybrid Nanoparticles

A series of copper oxide supported on Fe3O4/ZnO with molar ratio of Fe3O4:ZnO:CuO varies from 1:1:1 to 1:1:5 were prepared by sol-gel method. X-ray diffraction, field emission scanning electron microscope, energy-dispersive X-ray spectroscopy, UV-visible diffuse reflectance spectroscopy and vibrating sample magnetometer were used to characterize the as prepared Fe3O4/ZnO/CuO hybrid nanoparticles. The results show that Fe3O4/ZnO/CuO hybrid nanoparticles consist of cubic spinel Fe3O4, hexagonal wurtzite ZnO and monoclinic CuO. All prepared samples show ferromagnetic behavior. The photocatalytic activities of these hybrid nanoparticles under visible light irradiation were evaluated by the degradation of malachite green. The results revealed that hybrid nanoparticles exhibited higher photocatalytic activities than pure nanoparticles.

Synthesis of iron(II,III) oxide/zinc oxide/copper(II) oxide (Fe3O4/ZnO/CuO) nanocomposites and their photosonocatalytic property for organic dye removal

A facile sol-gel method was adopted to synthesize iron(II,III) oxide/zinc oxide/copper(II) oxide (Fe3O4/ZnO/CuO) nanocomposites with various CuO loadings at a low temperature. The prepared nanocomposites were characterized by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, energy-dispersive X-ray spectroscopy, UV-Vis spectroscopy, vibrating sample magnetometry, and Brunauer-Emmett-Teller (BET) surface area analyses. The photosonocatalytic properties of the nanocomposites were tested by methylene blue removal in aqueous solutions under the combination of UV or visible light and ultrasound. The catalyst with the lowest CuO loading exhibited the highest photosonocatalytic performance under UV light, while the fastest degradation under visible light was achieved at the highest CuO loading. Overall, the photosonocatalytic process with light and ultrasound irradiation led to more complete degradation compared to using light alone. According to the experiments performed with radical scavengers, the holes and OH radicals are the dominant oxidative species. The nanocomposites can be easily separated from the treated solution using an external magnetic field, and the samples remain very stable after 4 cycles. These results indicate that these materials have great potential for treating organic pollutants in wastewaters.

Dynamics of localized excitons and high-excitations effects in II–VI quantum wells and heterostructures

Abstract We investigate and discuss two aspects that are of importance for II–VI lasers, namely the dynamics of excitons and the high excitation processes capable to show optical gain. In the first case we concentrate on CdTe/ZnTe quantum wells, which exhibit an especially pronounced inhomogeneous broadening due to disorder. We investigate the relaxation of excitons under emission of optical and acoustic phonons. For the second topic we start with bulk II–VI compounds and proceed to thin layers, heterostructures and quantum wells, showing the excitonic effects are more important for II–VI laser materials as compared to the more established III–V compounds for the (infra)red, which are dominated by an electron-hole plasma.

Recombination at defects in amorphous silicon (a-Si:H)

Abstract Optical excitation with energy Ex = 1.16 eV was used to study the defect-related photoluminesce in a-Si:H. Light-induced electron spin resonance shows that both electrons and holes are generated in the band tails by defect absorption. The carriers appear to be created in a two-step process and cluster around the defects. The photoluminescence spectra display both the familiar intrinsic band near 1.3 eV and a defect-related band near 0.8 eV, the latter one being strongly enhanced compared with excitation with Ex above the optical gap (Ex > 1.8 eV). It is proposed that the defect bands in undoped, phosphorus- and boron-doped films originate from tunneling transitions of majority carriers from band-tail states into the respective predominating dangling-bond states (D0, D− or D+, in the dark). The influence of temperature and of the defect density on both emission bands is studied, the defects being generated by doping, electron bombardment and light exposure. The general behavior suggests that the tunneling transitition into the defect states in general is non-radiative. However, depending on the specific local configuration, this transition can occur radiatively as well.

Removal of Methylene Blue Dye Contaminant by Combination of Ultrasonic and Visible Light Irradiation Using Perovskite LaMnO3 Nanocatalyst

The applicability of LaMnO3 perovskite as nanocatalyst was investigated for removing of methylene blue as a model compound of organic pollutant under visible light and ultrasonic irradiation simultaneously. The LaMnO3 perovskite was synthesized by co-precipitation method and it was characterized in terms of morphological, structural, compositional, optical and magnetic properties. The detailed characterization confirmed that LaMnO3 perovskite had a single-phase orthorhombic structure with estimated crystallite size of 44 nm. UV-vis diffuse reflectance spectra showed a weak reflection with small band gap energy. The weak ferromagnetic behavior with a saturation magnetization of 3 emu/g was obtained at 1 Tesla. The photosonocatalytic showed significantly higher catalytic activity in decomposing methylene blue compared to that of sonocatalytic or photocatalytic alone. Radical scavenger experiments revealed that holes were the predominant oxidative species involved in the process.

Comparison of Catalytic Activities for Sonocatalytic, Photocatalytic and Sonophotocatalytic Degradation of Methylene Blue in the Presence of Magnetic Fe3O4/CuO/ZnO Nanocomposites

Fe3O4/CuO/ZnO nanocomposites with different molar ratio were synthesized using sol-gel method. The as-synthesized samples were characterized by X-ray diffraction (XRD), UV-visible spectroscopy, BET surface area analyszer, and Electron Spin Resonance (ESR). The sonocatalytic-photocatalytic-sonophotocatalytic activity of as-synthesized samples was investigated based on methylene blue degradation. Moreover, the role of active species was investigated using scavenger technique. The results showed that hole plays an important key role in sono-photo-sonophotocatalytic degradation of methylene blue.

Magnetic Composite Fe3O4/CuO/TiO2 Nanoparticles: Preparation, Characterization and Photocatalytic Activity

Magnetic composite Fe3O4/TiO2/CuO nanoparticles have been synthesized by sol-gel method at low temperature. The resultant composite nanoparticles coupled with different Cu contained by adjusting the molar ratio of CuO to (Fe3O4/TiO2) from 1:1 – 5:1. The structure, morphology and properties of nanoparticles were characterized using XRD, EDX, FESEM and VSM. The results showed that all composite nanoparticles consist of cubic spinel Fe3O4, anatase TiO2 and monoclinic CuO, have ferromagnetic properties. The photocatalytic performance was evaluated using methylene blue in aqueous solutions under UV and visible light irradiation. Among the composite Fe3O4/TiO2/CuO nanoparticles, the sample with the molar ratio of CuO to (Fe3O4/TiO2) = 5 : 1 exhibited the highest photocatalytic efficiency. Photocatalytic mechanism was investigated by measuring the photocatalytic degradation rate in the presence of scavenger. The results suggested that holes play the most important role in degradation of methylene blue.

Synthesis, Characterization and Catalytic Properties of Perovskite LaFeO3 Nanoparticles

Orthorhombic structure of rare earth perovskite-type oxide LaFeO3 nanoparticles with light absorption properties in the visible range was prepared by co-precipitation method. The prepared nanoparticles was characterized by several measurements such as X-ray diffraction, energy dispersive X-ray, field emission scanning electron microscope, diffuse reflectance spectroscopy, vibrating sample magnetometer and electron spin resonance spectroscopy. Methylene blue was taken as the model pollutant to evaluate its photocatalytic, sonocatalytic, photosonocatalytic degradation in the presence of LaFeO3 nanoparticles. The degradation of methylene blue followed the pseudo-first order model in all three processes. The observed rate constants indicate that the photosonocatalytic was faster than the respective individual. Radical scavenger experiments revealed that holes were the predominant oxidative species involved in all three processes.