Papers by Author: Akrajas Ali Umar

Abstract: Conducting polymers are excellent host materials for nanoparticles of metals and semiconductors. PANI-Ag-Co nanocomposite was prepared by chemical oxidative polymerization of aniline monomer in the presence of nitric acid. PANI-Ag-Co thin films were deposited on the glass substrate using spin-coating technique. The films were characterized by UV-Vis spectroscopy, XRD, AFM and TEM to analyze the internal structure and surface morphology. The performance of the sensor was conducted using I–V measurement to obtain the changes in the current before and after the incubation with E. coli bacteria in water. In UV-visible absorbance bands, a single peak appears at 421.6 nm in each band indicating the Ag-Co alloy nanoparticles were formed. The peaks in the XRD patterns show the crystals are oriented along (111) planes for Ag while (200) plane for Co. AFM images indicate the surface roughness of the PANI-Ag-Co films decreases when the concentration of Co increased. TEM image shows spherical shaped of Ag-Co alloy particles with diameter in the range of 6 – 10 nm. I–V measurements show that the current change of the films increased when incubated in E. coli. The sensitivity on E. coli increases as we increase the Co concentration. PANI-Ag-Co nanocomposite thin films can be explored further for microbial sensor application in future study.

Abstract: The nanocomposite of polyaniline (PANI) and bimetallic nanoparticles of silver and iron were prepared by the oxidative polymerization of aniline and the reduction process of bimetallic compound with the presence of nitric acid and PVA. The nanocomposite thin films in various compositions were deposited using spin-coating technique. The films were characterized by UV-visible spectroscopy to study the optical and structural properties. The microphotograph from TEM image shows the nanospherical of Ag-Fe alloy particles in 5 – 25 nm diameter size. The sensitivity performance was tested using I-V measurement to obtain the changes of resistivity before and after the incubation with E. coli bacteria in water. UV-visible absorption bands show the single absorbance peak at 422 – 424 nm in each band indicating the Ag-Fe alloy nanoparticles form. I-V characteristic shows the sample which contains Fe-rich Ag-Fe alloy performed high sensitivity on E. coli.

Abstract: Localized surface plasmon resonance (LSPR) peak wavelength of nanostructures metallic materials, such as gold and silver, is very sensitive to the dielectric environment of the materials; hence widely used as sensors to detect various types of chemicals. In this study, high - yield gold nanoplates ca. 63% have been grown on the quartz substrate using the seed - mediated growth method. The grown gold nanoplates exhibit variety of shapes such as triangular, hexagonal, truncated hexagonal and flat rod. The LSPR spectrum of Au nanoplates sample has two absorption bands; centring at 543 nm and 710 nm, which are associated with transverse SPR (t-SPR) and longitudinal SPR (l-SPR) respectively. The intensities and peaks position of these two bands were found to linearly change with the concentration of boric acid solutions.

Abstract: One-dimensional ZnO semiconductor nanomaterials have been attracting increasing attention due to their outstanding properties, which are different from bulk materials. ZnO has a direct band gap of 3.37 eV and large exciton binding energy hence its nanowires and nanorods have been regarded as one of the most promising materials for nanoscale electronic and optoelectronic devices such as ultraviolet laser diodes, optical detectors and gas sensor. ZnO nanowires and nanorods have been successfully synthesized by various techniques such as evaporation, sputtering and pyrolysis. In this paper we report the preparation of nanorod arrays of ZnO on ITO glass substrates which were pre-coated with ZnO nanoparticles by using low temperature chemical solution method and the result was compared with microwave hydrolysis process. The morphology and structure of ZnO nanorod arrays were investigated using field emission scanning electron microscopy (FESEM) and X-ray diffraction (XRD). The ZnO nanorod arrays with a diameter of 40-70 nm were successfully synthesized. In microwave hydrolysis method, the diameter, density and surface roughness was found to depend on the microwave power. The microwave method is far superior in producing ZnO nanostructure growth.

Abstract: Composite of TiO₂ nanowire and Cu₂O nanocube has been prepared. TiO₂ nanowire with ~240nm in thickness and 20 nm in length were synthesized by using liquid phase deposition(LPD) method at 50°C for 4h on ITO substrate. The anatase phase of TiO₂ nanowire was obtained by annealing the samples at 400°C for 1hin air. The Cu₂O nanocubes were prepared by the reduction of Cu²⁺ions with ascorbic acid in the present of trisodium citrate and sodium dodecilsulfat (SDS) surfactant under an alkaline condition. The SDS addition was added with various concentrations namely 10 mM, 18 mM, and 26 mM during the Cu₂O preparation for spin-coated onto TiO₂ nanowire at 3000 rpm for 30s. An optical property of TiO₂ Nanowire - Cu₂O Nanocube has been characterized by UV-Vis spectroscopy.The original TiO₂ nanowire has single absorption peak at 318 nm, but it was shifted to 321 nm as Cu₂O/SDS addition. A new peak at 440 nm was as the Cu₂O nanocube absorption spectra. The Cu₂O nanocube addition to the TiO₂ nanostructure film caused increase in the optical absorption of the system in the region 400 – 800 nm. We also studied the absorption properties of the hybrid system when Cu₂O nanocube preparation under SDS condition. It was that found the increase in the SDS concentration has caused the optical absorption of the hybrid in this region decreased. This is believed due to the decrease of Cu₂O nanocube size as the SDS concentration increase. This could be due to change in the TiO₂ nanowire-Cu₂O nanocube hybrid-structure. This cooperate may find use in photoelectrochemical application.

Abstract: Solvent controlled synthesis of tin oxide nanocatalysts were prepared via the hydrothermal method. To study the effect of solvent on the particle size of tin oxide and their catalytic efficiency on photodegradation of environmental hazardous materials, the synthesis was carried out at different concentrations of solvent (isoamyl alcohol) keeping all other reaction conditions constant. The nanoparticles were characterized by FourierTransmission Infrared Spectroscopy, Scanning Electron Microscopy, Transmission Electron Microscopy, X-ray Diffraction and Thermogravimetric analysis. Prepared nanoparticles were applied as nanocatalyst under UV-visible light for the photodegradation of methyl green,which is an abundant organic pollutant of industrial waste water. Photodegradation activities of the nanocatalysts were measured in three different ways, i. pseudo first order rate constant, “k”. ii. percentage degradationand iii. degradation rate. Effect of solvent was quantitatively explained in term of double sphere model of ion-ion interaction. Degradation of pollutants was also monitored by High Performance Liquid Chromatography.

Abstract: A simple technique of seed-mediated growth has successfully been performed to grow gold nanoplates onto solid substrates. The growth of gold nanoplates have been carried out attemperature of 28-30°C in the presence of a binary surfactant mixture: CTAB (cetyl trimethyl ammonium bromide) and PVP (poly-vinylpyrrolidone) with their various concentrations. Characterizations of the samples have been carried out by using UV-Vis spectroscopy, XRD and FESEM.UV-Vis spectra showed that the gold particles have grown with a various geometrical forms, such as spherical and others. XRD results informed that the presence of two peaks at 2θ: 38.195^o and 44.393^o indicated the gold nanoplates, with their crystal orientation of (111) and (200). FESEM images showed the edge-length size of nanoplates was dominated in the range of 11nm to 50 nm, with various morphologies of nanoplates, such as hexagonal,truncated hexagonal, triangular, square and spherical shapes.

Abstract: This paper reports an attempt to develop an optical sensor system to detect Bisphenol A (BPA) in water based on plasmonic property of Gold Nanoparticles (GNPs). Spherical GNPs of the average size of ca. 31±7 nm were grown on quartz substrate using seed mediated growth. An optical sensor system was setup, comprises a tungsten lamp light source, a duplex fiber optic probe, a spectrometer and a sensor chamber. Detection of BPA was done by comparing the Localized Surface Plasmon Resonance (LSPR) spectra of the GNPs film immersed in the deionised water and in BPA solutions by varying the concentration of BPA solutions from 58 mg/L to 0.003 ng/L. The LSPR spectra of GNPs sample were very sensitive to the presence of BPA where the shifted of their peaks position and the changed of their intensities are increases with the concentration of the BPA solutions.

Abstract: This paper reports a study on plasmonic properties of gold nanoparticles to detect the presence of formaldehyde solution in water. Gold nanoparticles were grown on substrates by the seed mediated growth method. A sensor system was setup, comprises a light source, a dual arm fibre optic probe, a spectrometer and sensor chamber. The detection of formaldehyde was done by comparing the Localized Surface Plasmon Resonance (LSPR) spectra of gold nanoparticles samples immersed in the deionised water and formaldehyde solution. It was observed that the peak position LSPR spectra of nanogold samples and their intensity were change by the presence formaldehyde. The difference between resonance peak intensity of LSPR spectra gold nanoparticles sample in formaldehyde solution and water can be used as sensing sensitivity parameter of the sensor. It was found that the sensing sensitivity is increase with the size of nanoparticles until it reach the optimum particles size.

Abstract: Electronic nose is a device that attempts to mimic the living being smell system for detection of particular gases or volatile compounds. This paper reports the development of an optical electronic nose using Fe (III) based metalloporphyrins Langmuir-Blodgett thin films as sensing elements for discriminating four volatiles, 2-propanol, acetone, cyclohexane and ethanol. A multilayer feed forward neural network was developed to classify the input vectors from these two sensors. After the network being trained 100 times and introduced to blind samples, it was found that there are three fault decision for propanol, two for acetone, five for cyclohexane and one four ethanol, during 50 times being recognized to the samples.