Emmanuel Iheanyichukwu Iwuoha

A Fumonisins Immunosensor Based on Polyanilino-Carbon Nanotubes Doped with Palladium Telluride Quantum Dots

An impedimetric immunosensor for fumonisins was developed based on poly(2,5-dimethoxyaniline)-multi-wall carbon nanotubes doped with palladium telluride quantum dots onto a glassy carbon surface. The composite was assembled by a layer-by-layer method to form a multilayer film of quantum dots (QDs) and poly(2,5-dimethoxyaniline)-multi-wall carbon nanotubes (PDMA-MWCNT). Preparation of the electrochemical immunosensor for fumonisins involved drop-coating of fumonisins antibody onto the composite modified glassy carbon electrode. The electrochemical impedance spectroscopy response of the FB1 immunosensor (GCE/PT-PDMA-MWCNT/anti-Fms-BSA) gave a linear range of 7 to 49 ng L−1 and the corresponding sensitivity and detection limits were 0.0162 kΩ L ng−1 and 0.46 pg L−1, respectively, hence the limit of detection of the GCE/PT-PDMA-MWCNT immunosensor for fumonisins in corn certified material was calculated to be 0.014 and 0.011 ppm for FB1, and FB2 and FB3, respectively. These results are lower than those obtained by ELISA, a provisional maximum tolerable daily intake (PMTDI) for fumonisins (the sum of FB1, FB2, and FB3) established by the Joint FAO/WHO expert committee on food additives and contaminants of 2 μg kg−1 and the maximum level recommended by the U.S. Food and Drug Administration (FDA) for protection of human consumption (2–4 mg L−1).

Application of a Bismuth-Silver Nanosensor for the Simultaneous Determination of Pt-Rh and Pd-Rh Complexes

The present work describes the development of an electrochemical sensor for the simultaneous determination of Pd-Rh and Pt-Rh complexes using a bismuth-silver bimetallic nanofilm modified glassy carbon electrode. The electrochemical sensor was prepared by drop-casting bismuth-silver bimetallic nanoparticles on to glassy carbon electrode surfaces. The HRTEM microscopy and UV-Vis spectroscopy results of the bismuth-silver nanoparticles were compared with other work in literature. The developed nanosensor exhibited a linear working range of 0.4 - 1.4 ng/L for Pd-Rh and 0.8-1.2 ng/L for Pt-Rh DMG complexes, respectively. Very low detection limits (S/N = 3) of 0.19 ng/L for Pd (II), 0.2 ng/L Pt (II) and 0.22 ng/L for Rh (III) were obtained and the sensor was successfully applied to environmental samples.

An Amperometric Cytochrome P450-2D6 Biosensor System for the Detection of the Selective Serotonin Reuptake Inhibitors (SSRIs) Paroxetine and Fluvoxamine

Paroxetine is the second most prescribed selective serotonin reuptake inhibitor (SSRI) antidepressant drug, characterized by extensive inter-individual variation in steady state plasma concentrations resulting in drug toxicity amongst patinets. A nanopolymeric biosensor for studying the biotransformation of paroxetine is presented. The bioelectrode system consists of cytochrome P450-2D6 enzyme encapsulated in nanotubular poly (8-anilino-1-napthalene sulphonic acid) electrochemically deposited on gold. The biosensing procedure involved the determination of the extent of modulation of fluvoxamine responses to the P450-2D6 enzyme electrode after incubation in paroxetine standard solutions. Paroxetine inhibited the activity of cytochrome P450-2D6 (CYP2D6) resulting in a decrease in the fluvoxamine signal of the biosensor. The biosensor gave a linear analytical response for the paroxetine in the interval 0.005 and 0.05 μM, with a detection limit of 0.002 μM and a response time of 30 s. Electrochemical Michaelis–Menten kinetics of the reversible competitive inhibition of the fluvoxamine responses of the biosensor by 0, 0.05 and 0.1 μM paroxetine gave apparent Michaelis–Menten constant (KMapp) values of 1.00 μM, 1.11 μM and 1.25 μM, respectively. The corresponding value for the maximum response, IMAX was 0.02 A. The dissociation constant, KI, value evaluated from Dixon analysis of the paroxetine modulation data was estimated to be-0.02 μM while Cornish-Bowden analysis confirmed the competitive inhibitory characteristics of the enzyme.

Electrochemical Studies on Novel LiMnPO4 Coated with Magnesium Oxide-Gold Composite Thin Film in Aqueous Electrolytes

Abstract. Pristine LiMnPO4 and LiMnPO4/Mg-Au composite cathode materials were synthesized and their electrochemical properties interrogated using voltammetric, spectroscopic and microscopic techniques. The composite cathode exhibited better reversibility and kinetics than the pristine LiMnPO4. This was demonstrated in the values of the diffusion coefficient (D) and the charge and discharge capacities determined through cyclic voltammetry. For the composite cathode, D = 2.0 x 10-9 cm2/s while the pristine has a D value of 4.81 x 10-10 cm2/s. The charge and discharge capacities of LiMnPO4/Mg-Au at 10 mV/s were 259.9 mAh/g and 157.6 mAh/g, respectively. The corresponding values for pristine LiMnPO4 were 115 mAh/g and 44.75 mAh/g, respectively.. A similar trend was observed in the results obtained from electrochemical impedance spectroscopy measurements. These results indicate that LiMnPO4/Mg-Au composite has better conductivity and will facilitate faster electron transfer and better electrochemical performance than pristine LiMnPO4.

Iron-Gold Coated-LiMn2-XO4 Nanowire High Power Cathode System Probed by Spectroscopic and Microstructural Analysis

The migration of lithium (Li) ions in electrode materials affects the rate performance of rechargeable Li ion batteries. Therefore, the application of LiMn2O4, whichis an appealing cathode material in high power systems, requires fast electron transfer kinetics which is possible through the use of nanostructured morphologies and conductive material. Nanowires offer the advantage of a large surface to volume ratio, efficient electron conducting pathways and facile strain relaxation. In this study, LiMn2O4 nanowires with cubic spinel structure were synthesized by using a α-MnO2 nanowire-template-based method. LiMn2O4 nanowires have diameters less than 10 nm and lengths of several micrometers. Fe-Au nanoparticles were synthesized and used as coating material to improve both the catalytic activities and stability of the LiMn2O4 nanowires. The Li[Fe0.02Au0.01]Mn1.97O4 nanowires with modified architecture effectively accommodates the structural transformation during Li+ ion charge and discharge. Hence, the Li[Fe0.02Au0.01]Mn1.97O4 nanowire cathode system shows outstanding stability and enhanced electrocatalytical properties. Microstructural analysis of Li[Fe0.02Au0.01]Mn1.97O4 linked its composition and processing to its properties and performance. High resolution transmission electron microscope (HR-TEM) of the nanomaterial showed good crystallinity which contributed towards good reversibility. XRD analysis revealed a pure cubic spinel structure without any impurities. Structural information provided by Raman and solid state spectroscopy further corroborated these findings. The improved rate and cycling performance is related to the conductive particles infused within the nanowires which make up the electrode.

Bimetallic Nanocomposites of Palladium (100) and Ruthenium for Electrooxidation of Ammonia

Symmmetrically oriented Pd (100) and its bimetallic Pd (100)Ru electrocatalysts were chemically synthesized and their conductive properties employed in the electrochemical oxidation of ammonia. Electrochemical data based on EIS, SWV and CV revealed that the Pt/Pd (100)Ru electrode showed a better conductivity and higher catalytic response towards the electrooxidation of ammonia compared to Pt/Pd (100) electrode. This was demonstrated by the EIS results where Pt/Pd (100)Ru gave a charge transfer resistance (Rct) of 48.64 Ω, high exchange current and lower time constant (5.2738 x 10-1A and 3.2802 x 10-7 s /rad) values while the Pt/Pd (100) had values of 173.2 Ω, 1.4811 x 10-1A and 4.8321 10-7 s /rad. The drastic drop in Rct highlights the superiority of the Pt/Pd (100)Ru over the Pt/Pd (100) and confirms that facile interfacial electron transfer processes occur on the Pt/Pd (100)Ru electrode during the electrocatalytic ammonia oxidation. Investigations through voltammetry revealed that the Pt/Pd (100)Ru had a higher peak current density and a shift in potential to more negative values at ≈ -0.2 V and ≈ -0.4 V. The EASA value of Pt/Pd (100)Ru was found to be 119.24 cm2 whereas Pt/Pd (100) had value of 75.07 cm2. The high electrochemically active surface area of Pd (100)Ru at 119.24 cm2 compared to the 75.07 cm2 for Pd (100) strengthened this observation in performance between the two catalysts for ammonia electrooxidation.

A Novel Polyaniline Nanocomposite with Doping Effects of Poly(Methyl Methacrylate) and TiO2 Nanoparticles

Polyaniline (PANI) is a globally investigated conductive polymer with a variety of applications in various fields due to its ease of synthesis and modification. One method of enhancing the physico-chemical properties and processability of PANI is the incorporation of polymers and nanoparticles to form composite and hybrid materials with new features. This study reports the electrochemical synthesis of a polyaniline nanocomposite that incorporates titanium dioxide nanoparticles (TiO2) and poly (methyl methacrylate) (PMMA). The significant effects of PMMA and TiO2 nanoparticles on structural, morphological, optical and electrochemical properties of native polyaniline were investigated using Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM), energy dispersive X-ray (EDX) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, cyclic voltammetry (CV) and square wave voltammetry (SWV). The formation and deformation of relevant peaks observed from the FTIR spectra confirm the intrusion of PMMA and TiO2 into PANI while the voltammetric results show that the incorporation of both dopants significantly enhanced the electroactivity of PANI in a neutral pH medium.

Spectro-Electrochemical of Detection Anthracene at Electrodeposited Polyamic Acid Thin Films

Polyamic acid (PAA) thin films were prepared by electrodepositing PAA onto indium tin oxide (ITO) electrode and characterized using electrochemical methods (cyclic voltammetry, square wave voltammetry), Ultraviolet Visible spectroscopy and Ultraviolet Visible/Spectro-electrochemistry (UV/vis Spectro-electrochemistry). The electrodeposited PAA thin films were observed to have two redox couples with a formal of 118 mV and 274 mV. The diffusion coefficient (De) determined from cyclic voltammetry was found to be 7.9x10-6 cm2/s and provide a measure of how fast charge is transported through the thin film. PAA showed a broad absorption peak at 214 nm due to the carbonyl chromophores within the polymer and shoulder peak at 293 nm from a quinoid-type chromophore. The calculated band gap of 4.23 eV suggested the polymer was optically transparent between 300 nm to 800 nm. This indicated that the PAA thin films has emerged as a very promising and cost effective alternative material to ITO with good transparent and conductive properties. PAA thin films were further applied for the detection of anthracene. The analytical response of anthracene was studied at the ITO/PAA using spectro-electrochemistry. The characteristic analytical absorbance signal for anthracene was clearly identified at 375 nm when ITO/PAA electrode was polarised at -800 mV (vs Ag/AgCl). The calibration curve for anthracene showed a linear response from 4.95x10-4 to 1.15x10-2 M. The ITO/PAA showed a low detection limit of (0.0068 g/L) and high sensitivity for anthracene, making it a suitable platform for spectro-electrochemical analysis of polycyclic aromatic hydrocarbons.

Anilino-Functionalized Graphene Oxide Intercalated with Pt Metal Nanoparticles for Application as Supercapacitor Electrode Material

Nanostructured anilino-functionalized reduced graphene oxide intercalated with Pt metal nanoparticles was successfully synthesized. Graphene oxide nanosheets were synthesized using a modified Hummers method with simultaneous in-situ functionalization with aniline and ionic Pt reduction and dispersion through sonication. The nanomaterial was characterised with FTIR, UV-visible, SEM, TEM, EDX, XRD and Raman spectroscopy to ascertain surface, chemical, elemental and crystalline properties, composite structures, size, morphology and successful entrapment of metal nanoparticles while the electro-conductivity of the nanomaterial was interrogated using CV. The graphene oxide was successfully functionalized with aniline with new peaks belonging to the N-H and C-N group being present and calculated band gaps of 5.35 eV and 4.39 eV which are attributed to functionalization of graphene oxide. The functionalized graphene oxide was successfully loaded with platinum nanoparticles as TEM revealed that the Pt particles are spread out on the graphene sheets and when magnified a uniform distribution of the nanoparticles can be observed. The material (functionalized graphene oxide loaded with platinum nanoparticles) was used in the design of an asymmetric supercapacitor cell using 6M KOH aqueous electrolyte. On testing by galvanostatic charge/discharge, a high specific capacitance value of 605 F/g with a corresponding energy and power densities of 0.021kWh/Kg and 0.372kW/Kg respectively, were obtained.

Synthesis and Characterization of Green Tea Stabilized Iron Nanocatalysts for Brymothymol Blue (BTB) Degradation

Iron nanoparticles (FeNPs) were prepared from the green tea extracts at different temperatures through green synthesis procedure and characterized by various physicochemical techniques like UV-Visible spectroscopy, FTIR Spectroscopy, energy dispersive X-ray spectrometry (EDS), X-ray diffraction and high resolution tunneling microscopy (HRTEM) and the results confirmed the synthesis of polydisperse and stable FeNPs by the tea extracts. The catalytic activity of FeNPs was investigated using a common environmental pollutant BTB often used in textile industries for dyeing purposes. In these tests, catalytic degradation of BTB with FeNPs at a 10 μL or 30 μL concentration was done in the presence of 2% hydrogen peroxide. Results show no BTB degradation in the absence of the FeNPs. However, a 38% and 68% degradation of BTB was realized in the presence of 10μL and 30 μL FeNPs respectively indicating that the iron nanocatalysts were responsible for the dye degradation. The BTB degradation kinetics was found to follow pseudo-first order kinetics with rate constants at the two catalyst concentrations being 0.023 min-1 and 0.063 min-1 respectively.