Sami S. Habib

Antimicrobial activity of metal oxide nanoparticles against Gram-positive and Gram-negative bacteria: a comparative study

Background Nanomaterials have unique properties compared to their bulk counterparts. For this reason, nanotechnology has attracted a great deal of attention from the scientific community. Metal oxide nanomaterials like ZnO and CuO have been used industrially for several purposes, including cosmetics, paints, plastics, and textiles. A common feature that these nanoparticles exhibit is their antimicrobial behavior against pathogenic bacteria. In this report, we demonstrate the antimicrobial activity of ZnO, CuO, and Fe2O3 nanoparticles against Gram-positive and Gram-negative bacteria. Methods and results Nanosized particles of three metal oxides (ZnO, CuO, and Fe2O3) were synthesized by a sol–gel combustion route and characterized by X-ray diffraction, Fourier-transform infrared spectroscopy, and transmission electron microscopy techniques. X-ray diffraction results confirmed the single-phase formation of all three nanomaterials. The particle sizes were observed to be 18, 22, and 28 nm for ZnO, CuO, and Fe2O3, respectively. We used these nanomaterials to evaluate their antibacterial activity against both Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive (Staphylococcus aureus and Bacillus subtilis) bacteria. Conclusion Among the three metal oxide nanomaterials, ZnO showed greatest antimicrobial activity against both Gram-positive and Gram-negative bacteria used in this study. It was observed that ZnO nanoparticles have excellent bactericidal potential, while Fe2O3 nanoparticles exhibited the least bactericidal activity. The order of antibacterial activity was demonstrated to be the following: ZnO > CuO > Fe2O3.

High-energy ball milling technique for ZnO nanoparticles as antibacterial material

Nanoparticles of zinc oxide (ZnO) are increasingly recognized for their utility in biological applications. In this study, the high-energy ball milling (HEBM) technique was used to produce nanoparticles of ZnO from its microcrystalline powder. Four samples were ball milled for 2, 10, 20, and 50 hours, respectively. The structural and optical modifications induced in the ‘as synthesized’ nanomaterials were determined by X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), and photoluminescence emission spectra (PL). SEM and TEM results show a gradual decrease in particle size from around 600 to ∼30 nm, with increased milling time. The initial microstructures had random shapes, while the final shape became quite spherical. XRD analysis showed ZnO in a hexagonal structure, broadening in the diffracted peaks and going from larger to smaller particles along with a relaxation in the lattice constant c. The value of c was found to increase from 5.204 to 5.217 Å with a decrease in particle size (600 to ∼30 nm). PL result showed a new band at around 365 nm, whose intensity is found to increase as the particles size decreases. These remarkable structural and optical modifications induced in ZnO nanoparticles might prove useful for various applications. The increase in c value is an important factor for increasing the antibacterial effects of ZnO, suggesting that the HEBM technique is quite suitable for producing these nanoparticles for this purpose.

Nanocrystalline Ba0.97Ca0.03SO4:Eu for ion beams dosimetry

Nanoparticles of Ba0.97Ca0.03SO4:Eu have been irradiated by 48 MeV Li3+, 75 MeV C6+, and 90 MeV O7+ ion beams with a fluence range of 1×109−1×1013 ion/cm2. The thermoluminescence (TL) glow curves along with the response curves of this nanophosphor have been investigated and compared with those of the corresponding microcrystalline samples. TL glow curve of the nanophosphor exposed to γ-rays has also been included in the letter with the aim of reporting some of the comparative measurements. The glow curves of the ion-beam irradiated nanomaterials are similar in their shapes to those induced by gamma rays, with a shift in the peak positions to the higher temperature side by around 30 K. The TL intensity of the ion-beam irradiated nanomaterials is found to decrease, while going from low to high atomic number (Z) ions (i.e., Li3+→O7+). Similar trend was also observed in the linearity of the TL response curves. The response curve of Li ion irradiated nanomaterials is sublinear in the whole range of studied flu...

Effect of Composition on Electrical and Optical Properties of Thin Films of Amorphous GaxSe100−x Nanorods

We report the electrical and optical studies of thin films of a-GaxSe100−x nanorods (x = 3, 6, 9 and 12). Thin films of a-GaxSe100−x nanorods have been synthesized thermal evaporation technique. DC electrical conductivity of deposited thin films of a-GaxSe100−x nanorods is measured as a function of temperature range from 298 to 383 K. An exponential increase in the dc conductivity is observed with the increase in temperature, suggesting thereby a semiconducting behavior. The estimated value of activation energy decreases on incorporation of dopant (Ga) content in the Se system. The calculated value of pre-exponential factor (σ0) is of the order of 101 Ω−1 cm−1, which suggests that the conduction takes place in the band tails of localized states. It is suggested that the conduction is due to thermally assisted tunneling of the carriers in the localized states near the band edges. On the basis of the optical absorption measurements, an indirect optical band gap is observed in this system, and the value of optical band gap decreases on increasing Ga concentration.

Nanoparticles of K2Ca2(SO4)3:Eu as effective detectors for swift heavy ions

The modification of thermoluminescence (TL) and photoluminescence (PL) properties of K2Ca2(SO4)3:Eu nanoparticles by swift heavy ions (SHI), irradiation is studied. Pellets form of the nanomaterials were irradiated by 48 MeV Li3+, 75 MeV C6+, and 90 MeV O7+ ion beams. The fluence range is 1×109−1×1013 ions/cm2. The modification in TL glow curves of the nanomaterials irradiated by Li3+, C6+, and O7+ ion beams are essentially similar to those induced by γ-ray irradiation. These glow curves have single peaks at around 427 K with a small variation in their positions by around ±3 K. The TL intensity of the ion beams irradiated nanomaterials is found to decease, while going from low to high atomic number (Z) ions (i.e., Li3+→O7+). The TL response curve of the pellets irradiated by Li3+ ions is linear in the whole range of studied fluences. The curves for C6+ and O7+ irradiated samples are linear at lower fluences (1×109–1×1012 ion/cm2) and then saturate at higher fluence. These results for the nanomaterials are...

Nanorods of LiF:Mg,Cu,P as Detectors for Mixed Field Radiations

Nanocrystalline powder of LiF: Mg,Cu,P phosphor has been synthesized by the chemical coprecipitation technique. Shape and size of these nanomaterials were observed by transmission electron microscope and atomic force microscope. The particles are of rod shapes having diameters from 50 to 80 nm and lengths varying within the range 0.4-0.7 mum. Pellets of these nanorods were irradiated by 48 MeV7Li3+ ions at different fluences in the range 1times1011-1times1014 ions/cm2 (with corresponding doses in the range 0.679-679 kGy) and their thermoluminescence (TL) properties have been studied. The TL glow curves are observed to have prominent peaks at around 588 K along with smaller one at around 410 K. The TL intensity of the former is found to increase with increasing the fluence, while that of the latter decreases. These behaviors are in contrast with those of the peaks induced by 137Cs gamma-rays. This modification in case of irradiation by ion beam has been attributed to the change in population of the luminescent/trapping centers due to the use of highly energetic ions. From these results, it is suggested that the nanorods of LiF:Mg,Cu,P might be used as detectors for mixed fields radiations such as space radiations.

Molecular gelation of ionic liquid–sulfolane mixtures, a solid electrolyte for high performance dye-sensitized solar cells

Cyclohexanecarboxylic acid-[4-(3-tetradecylureido)phenyl]amide is an efficient gelator to solidify ionic liquid electrolytes. In this paper we apply this low molecular weight gelator to solidify the newly prepared sulfolane based ionic liquid electrolyte. This solid electrolyte is successfully applied as an electrolyte for dye sensitized solar cells. This solid electrolyte is thermo-reversible, upon heating it will become a liquid and at room temperature it will solidify, facilitating the cell filling by the electrolyte. Applying this solid electrolyte we obtained 7.8% power conversion efficiency under simulated AM 1.5 full sunlight intensity. The devices with liquid and solid electrolytes were analysed by electrochemical impedance spectroscopy to explain the differences in the photovoltaic performance. These cells were also measured under outdoor conditions at Jeddah, Saudi Arabia to explore the feasibility of practical applications of this electrolyte.

Electrical transport properties of thin film of a-Se87Te13 nanorods

We have studied the electrical transport properties of thin film of a-S87Te13 nanorods. Initially, the glassy alloy of S87Te13 is prepared by melt-quenching technique. The amorphous nature of this alloy is verified by using X-ray diffraction technique. The nanorods of a-S87Te13 are synthesised on a glass substrate under an ambient gas (Ar) atmosphere using physical vapour condensation system. The morphology and microstructure of these nanorods are studied using scanning electron microscopy and transmission electron microscopy. The temperature dependence of dc conductivity for these nanorods is also studied over a temperature range of 500–100 K. On the basis of the temperature dependence of dc conductivity, the conduction mechanism in these nanorods is investigated. The results reveal that the thermally activated process is responsible for the transport of carriers in the temperature range 500–300 K. While the conduction takes place via variable range hopping (VRH) for temperature region 300–100 K. It is therefore, suggested that three-dimensional Motts variable range hopping (3D VRH) is the conduction mechanism responsible for the transport of charge carriers in the temperature region 300–100 K. Various Motts parameters such as density of states, degree of disorder, hopping distance and hopping energy are estimated on the basis of best fitting to our experimental data for Motts 3D VRH model.

Ag/ZnO nanoparticles thin films as visible light photocatalysts

Silver (Ag) and zinc oxide (ZnO) nanoparticles were simultaneously deposited on a glass substrate using the radio frequency (RF) sputtering technique at different substrate temperatures. Detailed characterization of the co-sputtered Ag/ZnO thin films was performed by X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM) and X-ray photoelectron spectroscopy (XPS). The as synthesized thin films were tested using UV-Vis diffuse reflectance spectroscopy to evaluate their optical properties. The obtained SEM results show a uniform dispersion of Ag nanoparticles within the ZnO matrix. These nanoparticles have average particle size of 20 nm. The optical band gap value was calculated from UV transmission spectra of Ag/ZnO thin films deposited at various substrate temperatures. This value was observed to be in the visible light range (i.e., 2.7–3.1 eV), which is much smaller than that of pure ZnO (3.37 eV). The photocatalytic activity of the produced thin films was evaluated through visible light photodegradation of 2-chlorophenol (2-CP) which has been used as a pollutant model in water. The synthesized thin films showed enhanced visible light photocatalytic efficiency towards 2-CP degradation at elevated substrate temperature and retained their catalytic efficiency with only 8% loss in efficiency after four reuse cycles. Kinetic parameters involved in the degradation process were investigated by applying a pseudo-second-order kinetic model.

Synthesis and characterization of nano- and microcrystalline cubes of pure and Ag-doped LiF

Lithium fluoride (LiF) produced in single crystals and doped with proper activators is a highly sensitive phosphor used in several applications such as integrated optics, colour centre laser and radiation dosimetry. In this work, we have developed a new synthetic chemical co-precipitation route for the synthesis of well-crystallized micro- and nanocrystalline cubes of pure and silver (Ag)-doped LiF. The as-synthesized samples were characterized by x-ray diffraction (XRD), scanning electron microscopy, absorption spectrum, photoluminescence (PL) and Raman spectroscopy. Size of the produced cubes could be controlled in the range 10 µm–50 nm by varying the solvent : co-solvent ratio. Micro-sized cubes could be grown in the presence of water as a solvent, while ethanol, which acts as a co-solvent, is found to be effective in reducing the size to the nanoscale. XRD results show complete crystalline structures in a griceite phase. The PL result of pure nanocubes exhibits a broad band in the range 370–550 nm, while that doped with Ag shows a prominent band at 420 nm. Raman spectra of the pure and Ag-doped LiF samples display several bands located in the range 80–236 cm−1. These results show that pure nanocubes of LiF have active colour centres without irradiation, which could be enhanced/modified by Ag dopants. This implies that these nanocubes might be useful in the development of optical devices.