Sawsan Dagher

Influence of reactant concentration on optical properties of ZnO nanoparticles

Abstract Zinc oxide (ZnO) nanoparticles have been prepared by wet chemical method from zinc acetate. Particle size was controlled by adjusting the reactant concentration. The size of nanoparticles was investigated using ultraviolet–visible absorption spectra and photoluminescence spectra. The present nanoparticles exhibit non-linear optical behaviour with blue shift of the wavelengths as the particle size decreases. Furthermore, yellow emission is observed in ambient air while it disappears in the presence of nitrogen gas and gets substituted by blue violet emissions. While the blue violet emissions are familiar and likely to be attributed to electronic transitions from localised states (e.g. shallow donor states on Zn interstitials ‘Zni’) or the conduction band edge to the valence band, the yellow emission in the absence of nitrogen remains unclear. Our results of the present investigation suggest that the bubbling with nitrogen should fill the oxygen vacancies, substitute the oxygen interstitials, passivate the dangling bonds and introduce shallow acceptor states, which allow electronic transitions with shorter wavelengths (i.e. blue violet emissions). In the absence of nitrogen, surface defects such as oxygen interstitials and Zn(OH)2 and possibly other point defects become again active and induce deep acceptor states of ∼1 eV above the valence band edge, which allow electronic transitions of longer wavelength (i.e. yellow emission). Our results are compared to several available experimental data and first principle calculations in order to support our claims and conclusions.

Dye and Nanoparticles-Sensitized Solar Cells

The performance of dye sensitized and nanoparticles sensitized solar cells are presented in this study. Three types of natural extracts (black cherry, hibiscus and saffron) were utilized as sensitizers. The performance of the solar cells as a function of the natural sensitizer was studied for the hibiscus. The performance of nanoparticles sensitized solar cells based on PbS/CdS nanoparticles was also studied. The effect of CdS nanoparticles thickness on the performance was investigated. The power conversion efficiencies (Eff.) for the devices made with natural extracts, saffron, hibiscus and black cherry was 0.17, 0.45 and 0.54 %, respectively. The (Eff.) of the hibiscus dye sensitized solar cells were improved from 0.45 to 1.37 % with increasing the dye concentration from 1X to 4X. While the obtained (Eff.) of PbS/CdS nanoparticles devices were increased from 0.089 to 3.2 % with increasing the CdS layer deposition cycles from 1 to 7 under Air Mass (AM) 1.5 Global (G) solar illumination, which indicates higher (Eff.) with increasing the CdS thickness.

Microfluidics Based Magnetophoresis: A Review

Magnetophoresis, the manipulation of trajectory of micro-scale entities using magnetic forces, as employed in microfluidic devices is reviewed at length in this article. Magnetophoresis has recently garnered significant interest due to its simplicity, in terms of implementation, as well as cost-effectiveness while being efficient and biocompatible. Theory associated with magnetophoresis is illustrated in this review along with different sources for creating magnetic field gradient commonly employed in microfluidic devices. Additionally, this article reviews the state-of-the-art of magnetophoresis based microfluidic devices, where positive- and negative-magnetophoresis are utilized for manipulation of micro-scale entities (cells and microparticles), employed for operations such as trapping, focusing, separation, and switching of microparticles and cells. The article concludes with a brief outlook of the field of magnetophoresis.

Bilirubin detoxification using different phytomaterials: characterization and in vitro studies

Background Activated carbon (AC) is a common adsorbent that is used in both artificial and bioartificial liver devices. Methods Three natural materials – date pits of Phoenix dactylifera (fruit), Simmondsia chinensis (jojoba) seeds, and Scenedesmus spp. (microalgae) – were used in the present investigation as precursors for the synthesis of AC using physical activation. The chemical structures and morphology of AC were analyzed. Then, AC’s bilirubin adsorption capacity and its cytotoxicity on normal liver (THLE2) and liver cancer (HepG2) cells were characterized. Results Compared with the other raw materials examined, date-pit AC was highly selective and showed the most effective capacity of bilirubin adsorption, as judged by isotherm-modeling analysis. MTT in vitro analysis indicated that date-pit AC had the least effect on the viability of both THLE2 and HepG2 cells compared to jojoba seeds and microalgae. All three biomaterials under investigation were used, along with collagen and Matrigel, to grow cells in 3D culture. Fluorescent microscopy confirmed date-pit AC as the best to preserve liver cell integrity. Conclusion The findings of this study introduce date-pit-based AC as a novel alternative biomaterial for the removal of protein-bound toxins in bioartificial liver devices.

Analysis of dielectrophoresis based 3D-focusing in microfluidic devices with planar electrodes

This article models a dielectrophoresis based approach for achieving 3D focusing, of micro-scale objects, in microfluidic devices. The microfluidic device employs four planar electrodes; two electrodes each on the top and bottom surface of the microchannel and each slightly protrude into the microchannel. Each electrode establishes electric field with the neighboring electrode on the same and opposite surfaces. The dielectrophoretic force pushes the micro-scale objects both the directions transverse to the flow direction to achieve the desired 3D focusing. The developed model accounts for various forces such as that associated with inertia, sedimentation, drag, and dielectrophoresis. Finite difference method is used for calculating the electric field and dielectrophoretic force as well as the displacements of micro-scale objects in the microchannel. Several geometric and operating parameters influence the trajectory of micro-scale objects. There exists a threshold voltage beyond which there is no increase in levitation height.

Heterojunction Solar Cell Based on p-type PbS Quantum Dots and Two n-type Nanocrystals CdS and ZnO

Heterojunction solar cells based on PbS quantum dots (QDs) were prepared at room temperature via spin coating method. The PbS QDs were synthesized, characterized and utilized in p-n heterojunction solar cell structure. The effect of combining two different n-type nanoparticles on the solar cell photovoltaic performance was studied. The solar cells were characterized under 1 sun illumination (irradiation of 1,000 W/m2). The optimum solar cell by depositing PbS QDs layer onto ZnO/CdS nanoparticles layers exhibits a short-circuit current of 1.36 mA/cm2, open circuit voltage of 127 mV, and power conversion efficiency of 1.21 %, representing efficiency improvement more than 3 and 5 orders of magnitude compared with the case of employing only one n-type nanoparticles ZnO and CdS, respectively.

Bowing Character in Wurtzite ZnO-Based Ternary Alloys

The existence and origins of the bandgap bowing character in the wurtzite ZnO-based ternary alloys are theoretically investigated. The tight-binding method with minimal sp3 basis set is used to calculate the band structures, density of electronic states, and constituent charge states of both common-cation ZnO1−xSx and common-anion Zn1−xMgxO ternary alloys. The experimental data show that a well-pronounced bowing effect is induced in the common-cation case, whereas there is no apparent bowing effect in the common-anion case. The present investigation indicates that the bowing effect in the former case may result from competition between anions trapping charge made available by cations. The disappearance of this competition, in the case of common-anion alloys, eliminates the possibility of bowing, thus leading to the observed linear behavior. Furthermore, the electronegativity and its discrepancy between the two anion types are expected to play a dominant role in the magnitude of the bowing parameter. The excellent fit between our theoretical results and the available photoluminescence data support this model.