Rabab Khalid Sendi

Physico-chemical characteristics of ZnO nanoparticles-based discs and toxic effect on human cervical cancer HeLa cells

In this study, we investigated physico-chemical properties of zinc oxide nanoparticles (ZnO NPs)-based discs and their toxicity on human cervical cancer HeLa cell lines. ZnO NPs (80 nm) were produced by the conventional ceramic processing method. FESEM analysis indicated dominant structure of nanorods with dimensions 100-500 nm in length, and 20-100 nm in diameter. The high content of ZnO nanorods in the discs probably played significant role in toxicity towards HeLa cells. Structural defects (oxygen vacancies and zinc/oxygen interstitials) were revealed by PL spectra peaks at 370-376 nm and 519-533 nm for the ZnO discs. The structural, optical and electrical properties of prepared sample have influenced the toxicological effects of ZnO discs towards HeLa cell lines via the generation of reactive oxygen species (ROS), internalization, membrane damage, and eventually cell death. The larger surface to volume area of the ZnO nanorods, combined with defects, stimulated enhanced toxicity via ROS generation hyd...

Borosilicate Frit Addition Impact on the Structure and Electric Behavior of ZnO Nanoparticle-Based Varistors

In this study, ZnO-Bi2O3-Mn2O3 varistors fabricated from the nanoparticle size of ZnO powder and doped with borosilicate frit were prepared via the conventional ceramic processing method. The influence of different borosilicate frit concentrations (0-3.0 mol%) on the sintering, microstructure enhancement, and nonlinear behavior of the ZnO-Bi2O3-Mn2O3 system was investigated. Results show that the borosilicate frit was liquefied to improve the density of the ceramic during sintering and found to have significant effects on the ZnO varistors, especially on enhancing grain growth even at a low doping concentration of only 0.5% mol. The strong solid-state reaction in the varistor made from 20 nm ZnO powder during sintering may be attributed to the high surface area of the 20 nm ZnO nanoparticles. X-ray diffraction analysis indicated that the addition of borosilicate frit to the ZnO-Bi2O3-Mn2O3 varistor system results in the formation of Zn4O(BO2)6 during sintering if too much borosilicate frit was added (over 0.5% mol). Borosilicate frit doping also significantly influenced the electrical properties of the varistor with a marked drop in the breakdown voltage from 545 V to 188 V with increase of borosilicate frit doping concentration. The resistivity also experienced a dramatic drop from 535.7 kΩ.cm to 133.5 kΩ.cm with increase of borosilicate frit doping contents. Therefore, borosilicate frit doping can be used to control the structural properties and breakdown voltage of ZnO-Bi2O3-Mn2O3 varistor system fabricated from 20 nm ZnO powder.

Effects of frit addition on the surface morphology and structural properties of ZnO-Bi2O3-Mn2O3 discs

ZnO-Bi2O3-Mn2O3 discs were prepared using conventional ceramic processing method and sintered at 1000°C. The different percentages of frit on the ZnO-Bi2O3-Mn2O3 discs were 0.0%, 0.5%, 1.0% and 3.0%. From FESEM observation, the grain structure and grain growth were more uniformly constructed and well distributed. Frit addition was found to cause a big drop in the average grain size from 4.59 µm to 2.76 µm even with an addition of 0.5 mol%. The Si and Al content in the frit recipe might have played a role as inhibiting agents in grain growth during sintering. RAMAN intensity and phase shifting were not affected by frit addition except at 3 mol%. Frit addition did not affect the formation of secondary phases. Frit addition below 3 mol% in ZnO-Bi2O3-Mn2O3 varistor discs can be used as a method in controlling grain size without affecting other properties.

A Comparative Study between the Effects of Oxidizing and Reducing Atmospheres on the Properties of ZnO-Bi2O3-Mn2O3 Varistor Fabricated from Micro and Nanoparticles Size of ZnO

Zinc oxide-based varistors are semiconductor ceramics. Their excellent nonlinear electrical behaviors are induced from their grain boundaries and depend on their microstructural characteristics. From a theoretical aspect, finer primary particles with narrow size distributions provide better electrical and optical properties. Thus, these properties are related to the morphology and size of ZnO grains. In this study, ZnO-Bi2O3-Mn2O3 varistors fabricated from ZnO micro-and nanoparticle powders are prepared via conventional ceramic processing. The effects of ZnO particle size and different annealing ambients on the properties of ZnO varistors are also investigated. The strong solid-state reaction during sintering may be attributed to the high surface area of the 20 nm ZnO nanoparticles that promote strong surface reaction. The annealing process also improves grain crystallinity, as shown in the decrease in intrinsic compressive stress based on the X-ray diffraction lattice constant and full-width at half-maximum (FWHM) data. The reduced particle size significantly influences the electrical properties, showing a sharp drop in the breakdown voltage. Thus, the ZnO nanoparticles can be used to manufacture of varistors with superior properties and lower breakdown voltage compared with commercial ones.

In vitro cytotoxicity tests of ZnO‐Bi2O3‐Mn2O3-based varistor fabricated from ZnO micro and nanoparticle powders on L929 mouse cells

The present study investigated the cytotoxicity of ZnO‐Bi2O3‐Mn2O3-varistors. To this effect, ZnO‐Bi2O3‐Mn2O3 varistors fabricated from ZnO micro-and nanoparticle powders are prepared via conventional ceramic processing method. The effects of ZnO particle size on the properties of ZnO varistors are also investigated. The strong solid-state reaction during sintering may be attributed to the high surface area of the 20 nm ZnO nanoparticles that promote strong surface reaction. The intensity of XRD peaks reflected the high degree of crystallinity of the ZnO nanoparticles. However, the width of the peaks in case of ZnO nanoparticles has increased due to the quantum size effect. The cytotoxicity evaluation of ZnO varistor was conducted on mouse connective tissue fibroblast cells (L929) using Trypan Blue Exclusion Assay analysis. The results show that the four types of varistor samples lead to cellular mitochondrial dysfunction, morphological modifications and apoptosis at the various concentration range and th...

Structural, Optical and Antibacterial Properties of ZnO Commercial Powder Grades

We investigated the structural, optoelectronic and antibacterial properties of two commercial ZnO powder namely White (rubber grade) and Pharma (pharmaceutical grade) in order to study the correlation between the structural-optical property and the antibacterial efficacy. Transmission electron microscopy (TEM) micrographs showed rod-like morphology for the Pharma specimen and grainular shape for the White sample. X-ray diffractometry (XRD) results confirmed the superior crystallinity of the Pharma powder and photoluminescence (PL) data also showed higher UV photocatalysis of the Pharma powder if compared to that of White powder. Using the broth macrodilution method to determine the antibacterial activity of ZnO specimens, we discovered the Pharma grade exhibited stronger inhibition (80-98%) on the growth of Escherichia Coli (E. coli) especially for the ZnO suspension concentration of 10-20 mM. We believe that the superior crystallinity and stronger photocatalysis of the rod-like Pharma powder could have generated much more reactive oxygen species (OH-, H2O2 and O22-) than that of White sample resulting in the higher growth inhibition of E.coli. This work also highlights the impact of rod-like primary particles of Pharma powder in exhibiting good antibacterial efficacy if compared to the grainular particles of White powder and this observation justifies the usage of ZnO Pharma powder in pharmaceutical and healthcare products.

Analysis of Stress and Strain in ZnO Nanoparticle-Bi2O3-Mn2O3 Varistor Ceramics at Different Annealing Temperatures

The stress and lattice constants in zinc oxide (ZnO) nanoparticles play a major role in determining the distortions that occur in the crystal during the preparation of the sample as a result of exposure to several factors, such as external strain, temperature, pressing, and structural defects (oxygen vacancies and zinc/oxygen interstitials). 20 nm zinc oxide nanoparticles were used to make high-density ZnO discs doped with Bi2O3 and Mn2O3 via uniaxial pressing at 4 ton/cm2 and sintering at 1200 °C for 1 h. Structural, elemental, and optical characterizations were then performed on the samples using various techniques. High-oxygen thermal annealing significantly affected the varistor, particularly in enhancing the growth of the grain even at a low annealing temperature (400 °C). The strong solid-state reaction during annealing may be attributed to the high surface area of the 20 nm ZnO nanoparticles that exhibited a strong surface reaction even at low annealing temperatures. The annealing treatment also improved the grain crystallinity, as shown by the transition of the intrinsic compressive stress to tensile stress based on the XRD lattice constant and full-width at half-maximum data. Therefore, high-oxygen thermal annealing can be used as a new technique in controlling the stress in ZnO nanoparticle-Bi2O3-Mn2O3 based varistors with improved structural and optical properties.

Density impact of doped ZnO discs on the structural, electrical and optical properties in the ohmic region

The influence of different densities of doped ZnO discs on their structural, electrical and optical properties has been studied in this work by measuring the average grain size, resistivity, critical frequency, critical capacitance and energy band gap as functions of density. The microstructure of ZnO material has been investigated by a combination of X-ray diffractometry (XRD) and analytical electron microscopy (SEM, EDX). Doped ZnO has a large number of grains and grain boundaries, which are observed to be very disordered. Every sample has a different densities depending on the different grain size, which had a major effect on the properties of ZnO. There are also a considerable number of pores which depend on the size and the shape of grains. The voltage (V) against the current (I) curves, revealed a high linear (ohmic) relationship, mainly in sample B4, which represented the highest density value (5.486 g/cm3), highest resistivity value (0.46 GΩ.cm), and maximum capacitive critical frequency (48.23 MHz). However, the critical capacitance value (1.21 nF) decreased at a higher density, which could be due to the high traps. The photoluminescent measurements showed that the doped ZnO had a strong ultraviolet emission at around 381nm and a weak red emission around 650 nm. The results from PL spectroscopy revealed the band gap energy of ZnO (ranged from 3.25 eV to 3.29 eV), which increased gradually with density, depending on the grain boundaries barrier.The influence of different densities of doped ZnO discs on their structural, electrical and optical properties has been studied in this work by measuring the average grain size, resistivity, critical frequency, critical capacitance and energy band gap as functions of density. The microstructure of ZnO material has been investigated by a combination of X-ray diffractometry (XRD) and analytical electron microscopy (SEM, EDX). Doped ZnO has a large number of grains and grain boundaries, which are observed to be very disordered. Every sample has a different densities depending on the different grain size, which had a major effect on the properties of ZnO. There are also a considerable number of pores which depend on the size and the shape of grains. The voltage (V) against the current (I) curves, revealed a high linear (ohmic) relationship, mainly in sample B4, which represented the highest density value (5.486 g/cm3), highest resistivity value (0.46 GΩ.cm), and maximum capacitive critical frequency (48.23 MH...

Impact of high-oxygen thermal annealing on the structural, optical and electrical properties of ZnO discs made from 20-nm ZnO nanoparticles

20-nm nanoparticles of zinc oxide (ZnO) were used to make high-density ZnO discs by uniaxial pressing at 4 ton/cm2 pressure and sintering at 1200 °C for 1 hour. High-oxygen thermal annealing performed on the ZnO discs was found to have a profound impact especially enhanced grain growth even at a low annealing temperature of only 400 °C. Moreover, we observed a unique secondary growth of ZnO nanoparticles and growth of multilayer grains that have not been reported elsewhere. The strong solid state reaction during annealing was probably attributed to the high surface area of the 20-nm ZnO nanoparticles that promoted strong surface reaction even at low annealing temperatures. The ZnO discs have been found to contain a very high concentration of structural defects (oxygen vacancies and zinc/oxygen interstitials) that was indicated by the dominant and broad visible photoluminescence (PL) emission in the green band with peaks at (519 - 533) nm, and it was found that this visible emission was greatly increased a...

Post-Growth Annealing Effects on the Photoluminescence of ZnO Nanoparticle-Based Discs

The luminescence of ZnO exhibits a band-edge UV emission peak and a broad emission in the blue-green-red regions associated with the deep level defects as well as the oxygen vacancies and zinc interstitials in the discs. The mechanism of the defect is attributed to the electronic transitions from near conduction band-edge to the deep level acceptors and transitions from the deep donor levels to the valence band. In this study, post-growth annealing was conducted to investigate the mechanism involved in the visible luminescence of ZnO nanoparticle discs prepared. Post-growth thermal annealing can be applied as a new technique in controlling the optical properties of ZnO discs.