Muhammad Aftab Akram

Uniaxial Drawing of Graphene-PVA Nanocomposites: Improvement in Mechanical Characteristics via Strain-Induced Exfoliation of Graphene.

Polyvinyl alcohol (PVA)-stabilized graphene nanosheets (GNS) of lateral dimension (L) ~1xa0μm are obtained via liquid phase exfoliation technique to prepare its composites in the PVA matrix. These composites show low levels of reinforcements due to poor alignment of GNS within the matrix as predicted by the modified Halpin-Tsai model. Drawing these composites up to 200xa0% strain, a significant improvement in mechanical properties is observed. Maximum values for Young’s modulus and strength are ~×4 and ~×2 higher respectively than that of neat PVA. Moreover, the rate of increase of the modulus with GNS volume fraction is up to 700xa0GPa, higher than the values predicted using the Halpin-Tsai theory. However, alignment along with strain-induced de-aggregation of GNS within composites accounts well for the obtained results as confirmed by X-ray diffraction (XRD) characterization.

Arrays of ZnO/CuInxGa1-xSe2 nanocables with tunable shell composition for efficient photovoltaics

Arrays of one-dimensional (1D) nanostructure are receiving much attention for their optoelectronic and photovoltaic applications due to their advantages in light absorption, charge separation, and transportation. In this work, arrays of ZnO/CuInxGa1−xSe2 core/shell nanocables with tunable shell compositions over the full range of 0u2009≤u2009xu2009≤u20091 have been controllably synthesized. Chemical conversions of ZnO nanorods to a series of ZnO-based nanocables, including ZnO/ZnSe, ZnO/CuSe, ZnO/CuSe/InxGa1−x, ZnO/CuSe/(InxGa1−x)2Se3, and ZnO/CuInxGa1−xSe2, are well designed and successfully achieved. Composition-dependent influences of the CuInxGa1−xSe2 shells on photovoltaic performance are investigated. It is found that the increase in indium content (x) leads to an increase in short-circuit current density (JSC) but a decrease in open-circuit voltage (VOC) for the ZnO/CuInxGa1−xSe2 nanocable solar cells. An array of ZnO/CuIn0.67Ga0.33Se2 nanocables with a length of ∼1u2009μm and a shell thickness of ∼10u2009nm exhibits a ba...

Environment friendly template-free microwave synthesis of submicron-sized hierarchical titania nanostructures and their application in photovoltaics

A simple low-temperature microwave synthesis of hierarchical nanostructures (HNSs) of titania in DI water is reported. A great advantage of the reported method is the production of submicron-sized HNSs without any surfactant or hydrofluoric acid. The hierarchical morphology provides huge surface area for maximum exposure for light-driven reactions, and the 3D folding morphology allows further scattering of light to obtain its maximum utilization. FESEM, TEM, XRD, BET surface area measurement, UV/VIS and Raman spectroscopy were utilized to understand the structures. The mechanism of formation of nanostructures is also discussed. The nanostructures were employed in dye-sensitized solar cells for performance comparison.

Reaction Time and Film Thickness Effects on Phase Formation and Optical Properties of Solution Processed Cu2ZnSnS4 Thin Films

Copper-zinc-tin-sulfide (Cu2ZnSnS4 or CZTS) is a promising p-type semiconductor material as absorber layer in thin film solar cells. The sulfides of copper and tin as well as zinc and sulfur powders were dissolved in hydrazine. The effect of chemical reaction between precursor species, at room temperature, was assessed for 6 to 22xa0h. For 22xa0h reaction time, the effect of spin coated film thickness on the resulting composition, after annealing under N2 flow at 500xa0°C for 1xa0h, was investigated. The morphology, composition, and optical properties of the annealed films were determined by means of x-ray diffraction, scanning electron microscope, and spectrophotometer studies. It was found that, for less than optimal reaction time of 22xa0h or film thickness below 1.2xa0µm, other ternary phases namely Cu4SnS4, Cu5Sn2S7, and ZnS co-exist in different proportions besides CZTS. Formation of phase-pure CZTS films also exhibited a tendency to minimize film cracking during annealing. Depending on the processing conditions, the band gap (Eg) values were determined to be in the range of 1.55 to 1.97xa0eV. For phase-pure annealed CZTS film, an increase in the Eg value may be attributed to quantum confinement effect due to small crystallite size.

Microwave Augmented Fabrication and Evaluation of CNT-Reinforced Nanohydroxyapatite

Bioactive CNT reinforced hydroxyapatite nano-composite is synthesized by in-situ precipitation for use in load bearing orthopedic applications. Microwaves augment the synthesis, enhance the reaction rate, and institute energy savings. Heat and acid treated purified CNTs in microwaves are functionalized and dispersed in calcium nitrate tetrahydrate. Diammonium hydrogen phosphate is incorporated in calcium ion solution to furnish the required Ca:P ratio. Refluxing of the precursor solution is accomplished under microwaves. XRD shows the phase purity and crystallinity, FTIR spectroscopy indicates the fucntionalization of CNTs and SEM analysis depicts the nanoporous nanomorphology of synthesized powder. TGA measures the thermal endurance of product, showing good CNTs retention at high temperatures (1100°C) in nitrogen ambient, otherwise they get oxidized in air in that temperature range. CNT reinforced sintered biomaterial exhibits excellent consolidation and a Vicker hardness increment of 30%. The relation of between mechanical properties and sintering time is correlated by SEM.

Effect of Ethane-1,2-Diamine on Growth of ZnO Nanorods and Cyclohexane Sensing by Current-Voltage Characteristics Investigations

The growth of vertically aligned ZnO Nanorods arrays using Zinc Nitrate hexahydrate and Hexamethylene Tetramine (HMTA), by Chemical Bath Deposition on Silicon Wafer was investigated. The growth is conducted under influence of Ethane-1,2-diamine, the amine based enhancer was evaluated based on three different ratios (1:0.5, 1:1, 1:1.5) of enhancer to the precursor (Zinc Nitrate and HMTA). The effect different ratios of enhancers on morphology aspect ratio and crystallinity of the as grown Nanorods were studied under Scanning electron microscope (SEM) and X-ray powder diffraction (XRD). Electrical Properties such as current–voltage characteristics were investigated, its correlation to the morphology and aspect ratio of the Nanorods in the presence of 100μL-500μL of Aromatic Compound Cyclohexane and at different applied voltages.

Fabrication of Cellulose Acetate/Cellulose-HA Composite Films for Bone Fixation

Bone is a rigid and constantly remodeling organ, a type of tissue which provides support and protects organs in the body, and together they form the skeleton [1]. Materials generally used for implants bear tissue rejection and produce toxins on degradation [2]. Our objective is to synthesize a biocompatible composite of Hydroxyapatite (HA) and Cellulose using Cellulose Acetate as a matrix which mimics the properties of natural bone that can be used for bone replacements. Bone is composed of calcium phosphate (HA) and collagen, which gives bone desired properties [3]. Hydroxyapatite is the inorganic mineral found in the bone and is preferred due to its mechanical properties, biocompatibility, slow degradation in physiological environment and bioactivity [4]. Cellulose, structural component in plants is similar in properties to collagen therefore the properties of cellulose [4], HA and cellulose acetate are exploited to achieve our results. The experimental procedure is divided into two major steps; extraction of cellulose microfibers (CMF) from cotton followed by dispersion of cellulose and HA in cellulose acetate then casting membranes of the composite.

Synthesis and Characterization of MoS2/TiO2 Nanocomposites for Enhanced Photocatalytic Degradation of Methylene Blue under Sunlight Irradiation

2D nanosheets/ nanoparticles based MoS2/TiO2 nanocomposites were prepared in different weight compositions which were further employed to investigate photocatalytic degradation of methylene blue. Anatase TiO2 powder was prepared via sol-gel reflux method using titanium tetraisopropoxide as Ti precursor. MoS2/TiO2 nanocomposites were prepared by in situ addition of exfoliated MoS2 (2D-nanosheets) in different weight ratios of 0.1%, 0.5%, 1%, 2% and 5% in TiO2 sol. Surface morphology, phase analysis, optical properties were studied using SEM, XRD, UV-Vis spectroscopy respectively. SEM results showed that TiO2 nanoparticles were completely adsorbed over the surface of MoS2 sheets as reflux synthesis was employed. Efficient charge carrier separation was achieved which reduced recombination, and hence, enhanced photo-degradation of methylene blue was observed. The hetero-structures showed less operation time in sunlight for photodegradation of methylene blue and a highest rate constant was observed by 2 wt.% loading of MoS2 on TiO2. These composites can also be used commercially as they show promising results.