Omolola E. Fayemi

Porphyrins as Corrosion Inhibitors for N80 Steel in 3.5% NaCl Solution: Electrochemical, Quantum Chemical, QSAR and Monte Carlo Simulations Studies

The inhibition of the corrosion of N80 steel in 3.5 wt. % NaCl solution saturated with CO2 by four porphyrins, namely 5,10,15,20-tetrakis(4-hydroxyphenyl)-21H,23H-porphyrin (HPTB), 5,10,15,20-tetra(4-pyridyl)-21H,23H-porphyrin (T4PP), 4,4′,4″,4‴-(porphyrin-5,10,15,20-tetrayl)tetrakis(benzoic acid) (THP) and 5,10,15,20-tetraphenyl-21H,23H-porphyrin (TPP) was studied using electrochemical impedance spectroscopy (EIS), potentiodynamic polarization, scanning electrochemical microscopy (SECM) and scanning electron microscopy (SEM) techniques. The results showed that the inhibition efficiency, η% increases with increasing concentration of the inhibitors. The EIS results revealed that the N80 steel surface with adsorbed porphyrins exhibited non-ideal capacitive behaviour with reduced charge transfer activity. Potentiodynamic polarization measurements indicated that the studied porphyrins acted as mixed type inhibitors. The SECM results confirmed the adsorption of the porphyrins on N80 steel thereby forming a relatively insulated surface. The SEM also confirmed the formation of protective films of the porphyrins on N80 steel surface thereby protecting the surface from direct acid attack. Quantum chemical calculations, quantitative structure activity relationship (QSAR) were also carried out on the studied porphyrins and the results showed that the corrosion inhibition performances of the porphyrins could be related to their EHOMO, ELUMO, ω, and μ values. Monte Carlo simulation studies showed that THP has the highest adsorption energy, while T4PP has the least adsorption energy in agreement with the values of σ from quantum chemical calculations.

Phthalocyanine Doped Metal Oxide Nanoparticles on Multiwalled Carbon Nanotubes Platform for the detection of Dopamine

The electrocatalytic properties of metal oxides (MO = Fe3O4, ZnO) nanoparticles doped phthalocyanine (Pc) and functionalized MWCNTs, decorated on glassy carbon electrode (GCE) was investigated. Successful synthesis of the metal oxide nanoparticles and the MO/Pc/MWCNT composite were confirmed using UV-Vis, EDX, XRD and TEM techniques. Successful modification of GCE with the MO and their composite was also confirmed using cyclic voltammetry (CV) technique. GCE-MWCNT/ZnO/29H,31H-Pc was the best electrode towards DA detection with very low detection limit (0.75 μM) which compared favourably with literature, good sensitivity (1.45 μA/μM), resistance to electrode fouling, and excellent ability to detect DA without interference from AA signal. Electrocatalytic oxidation of DA on GCE-MWCNT/ZnO/29H,31H-Pc electrode was diffusion controlled but characterized with some adsorption of electro-oxidation reaction intermediates products. The fabricated sensors are easy to prepare, cost effective and can be applied for real sample analysis of dopamine in drug composition. The good electrocatalytic properties of 29H,31H-Pc and 2,3-Nc were related to their (quantum chemically derived) frontier molecular orbital energies and global electronegativities. The better performance of 29H,31H-Pc than 2,3-Nc in aiding electrochemical oxidation of DA might be due to its better electron accepting ability, which is inferred from its lower ELUMO and higher χ.

Metal Oxide Nanoparticles/Multi-walled Carbon Nanotube Nanocomposite Modified Electrode for the Detection of Dopamine: Comparative Electrochemical Study

Electrochemical properties and sensor application of multi-walled carbon nanotubes (MWCNTs), doped with metal oxides [(MO=nickel oxide (NiO), zinc oxide (ZnO) and iron oxide (Fe3O4)] nanoparticles was investigated using FTIR, XRD, UV-vis spectroscopy, Raman spectroscopy, TEM, SEM, EDX, and cyclic voltammetry techniques. Electrochemical oxidation of dopamine on a glassy carbon electrode (GCE) modified with multi-walled carbon nanotubes doped with metal oxides (GCE/MWCNT/NiO, GCE/MWCNT/ZnO, GCE/MWCNT/Fe3O4) was examined by cyclic voltammetry, EIS and square wave voltammetry in 0.1 M phosphate buffer solution PBS at pH 7. The results were compared with those obtained on bare GCE, GCE/MWCNT and MO GCE modified electrodes (GCE/NiO, GCE/ZnO, GCE/Fe3O4). All electrodes were conditioned at potential of 0.2V (vs Ag/AgCl, sat’d KCl) in DA solution for EIS experiment. It was found that the multi- walled carbon nanotubes improve remarkably the reactivity of NiO, ZnO and Fe3O4 for dopamine oxidation. The GCE/MWCNT/NiO, GCE/MWCNT/ZnO, GCE/MWCNT/Fe3O4 electrodes exhibited good linear properties in the concentration range from 4 × 10-5 μM to 6.25 μM for the quantitative analysis of dopamine (DA) with a limit of detection of 7.99 × 10-12 M, 3.742 × 10-7 M and 1.386 × 10-6 M respectively. The limit of detection of GCE/MWCNT/NiO was better than the other two nanocomposites modified electrodes. The interference study also revealed no AA interference signal at AA concentration 1000 times that of DA. The DPV techniques give well distinct peaks for the DA and AA and a wider separation potential. The prepared electrode exhibited satisfactory stability and long shelf life when stored at ambient conditions. It has been demonstrated that the GCE/MWCNT/NiO modified electrode can be successfully used for the assay of dopamine in some real samples.

Some Phthalocyanine and Naphthalocyanine Derivatives as Corrosion Inhibitors for Aluminium in Acidic Medium: Experimental, Quantum Chemical Calculations, QSAR Studies and Synergistic Effect of Iodide Ions

The effects of seven macrocyclic compounds comprising four phthalocyanines (Pcs) namely 1,4,8,11,15,18,22,25-octabutoxy-29H,31H-phthalocyanine (Pc1), 2,3,9,10,16,17,23,24-octakis(octyloxy)-29H,31H-phthalocyanine (Pc2), 2,9,16,23-tetra-tert-butyl-29H,31H-phthalocyanine (Pc3) and 29H,31H-phthalocyanine (Pc4), and three naphthalocyanines namely 5,9,14,18,23,27,32,36-octabutoxy-2,3-naphthalocyanine (nPc1), 2,11,20,29-tetra-tert-butyl-2,3-naphthalocyanine (nPc2) and 2,3-naphthalocyanine (nP3) were investigated on the corrosion of aluminium (Al) in 1 M HCl using a gravimetric method, potentiodynamic polarization technique, quantum chemical calculations and quantitative structure activity relationship (QSAR). Synergistic effects of KI on the corrosion inhibition properties of the compounds were also investigated. All the studied compounds showed appreciable inhibition efficiencies, which decrease with increasing temperature from 30 °C to 70 °C. At each concentration of the inhibitor, addition of 0.1% KI increased the inhibition efficiency compared to the absence of KI indicating the occurrence of synergistic interactions between the studied molecules and I− ions. From the potentiodynamic polarization studies, the studied Pcs and nPcs are mixed type corrosion inhibitors both without and with addition of KI. The adsorption of the studied molecules on Al surface obeys the Langmuir adsorption isotherm, while the thermodynamic and kinetic parameters revealed that the adsorption of the studied compounds on Al surface is spontaneous and involves competitive physisorption and chemisorption mechanisms. The experimental results revealed the aggregated interactions between the inhibitor molecules and the results further indicated that the peripheral groups on the compounds affect these interactions. The calculated quantum chemical parameters and the QSAR results revealed the possibility of strong interactions between the studied inhibitors and metal surface. QSAR analysis on the quantum chemical parameters obtained with B3LYP/6-31G (d,p) method show that a combination of two quantum chemical parameters to form a composite index provides the best correlation with the experimental data.

Silver Nanoparticles Mediated by Costus afer Leaf Extract: Synthesis, Antibacterial, Antioxidant and Electrochemical Properties

Synthesis of metallic and semiconductor nanoparticles through physical and chemical routes has been extensively reported. However, green synthesized metal nanoparticles are currently in the limelight due to the simplicity, cost-effectiveness and eco-friendliness of their synthesis. This study explored the use of aqueous leaf extract of Costus afer in the synthesis of silver nanoparticles (CA-AgNPs). The optical and structural properties of the resulting silver nanoparticles were studied using UV-visible spectroscopy, scanning electron microscopy (SEM), transmission electron microscopy (TEM) and Fourier transform infra–red spectrophotometer (FTIR). TEM images of the silver nanoparticles confirmed the existence of monodispersed spherical nanoparticles with a mean size of 20 nm. The FTIR spectra affirmed the presence of phytochemicals from the Costus afer leaf extract on the surface of the silver nanoparticles. The electrochemical characterization of a CA-AgNPs/multiwalled carbon nanotubes (MWCNT)-modified electrode was carried out to confirm the charge transfer properties of the nanocomposites. The comparative study showed that the CA-AgNPs/MWCNT-modified electrode demonstrated faster charge transport behaviour. The anodic current density of the electrodes in Fe(CN)6]4−/[Fe(CN)6]3− redox probe follows the order: GCE/CA-Ag/MWCNT (550 mA/cm2) > GCE/MWCNT (270 mA/cm2) > GCE (80 mA/cm2) > GCE/CA-Ag (7.93 mA/cm2). The silver nanoparticles were evaluated for their antibacterial properties against Gram negative (Escherichia coli, Klebsiella pneumonia, Pseudomonas aeruginosa) and Gram positive (Bacillus subtilis and Staphylococcus aureus) pathogens. The nanoparticles exhibited better inhibition of the bacterial strains compared to the precursors (leaf extract of Costus afer and silver nitrate). Furthermore, the ability of the nanoparticles to scavenge DPPH radicals at different concentrations was studied using the DPPH radical scavenging assay and compared to that of the leaf extract and ascorbic acid. The nanoparticles were better DPPH scavengers compared to the leaf extract and their antioxidant properties compared favorably the antioxidant results of ascorbic acid. The green approach to nanoparticles synthesis carried out in this research work is simple, non-polluting, inexpensive and non-hazardous.

Zinc Oxide Nanocomposites of Selected Polymers: Synthesis, Characterization, and Corrosion Inhibition Studies on Mild Steel in HCl Solution

Nanocomposites of ZnO and some selected polymers, namely, poly(ethylene glycol), poly(vinylpyrrolidone), and polyacrylonitrile, were synthesized and characterized using Fourier transform infrared (FTIR) spectroscopy, ultraviolet–visible (UV–vis) spectroscopy, thermogravimetric analysis (TGA), and transmission electron microscopy (TEM) techniques. The FTIR and UV–vis spectra confirmed the successful formation of the polymer nanocomposites. TGA results revealed that the synthesized polymer nanocomposites are more thermally stable than the polymers alone. ZnO nanoparticles were about 50–75 nm in size, assumed a rodlike shape, and got embedded in the polymer matrices, as revealed by TEM images. Corrosion inhibition potentials of the synthesized ZnO/polymer nanocomposites were investigated for mild steel in 5% HCl solution using potentiodynamic polarization (PDP), linear polarization resistance, and electrochemical impedance spectroscopy measurements. The results showed that each ZnO/polymer nanocomposite inhibits mild steel corrosion in 5% HCl solution better than the respective polymer alone. The nanocomposites, according to PDP studies, behaved as a mixed-type inhibitor. The predominant mode of adsorption of the nanocomposites to a mild steel surface was found to be mixed type, and the adsorption process obeys the Langmuir adsorption isotherm model. Scanning electron microscopy images also revealed the protective attributes of the ZnO/polymer nanocomposites for mild steel in 5% HCl solution.

Electrochemical Detection of Phenanthrene Using Nickel Oxide Doped PANI Nanofiber Based Modified Electrodes

A nickel oxide doped polyaniline nanofibers PANI-NiO based electrochemical sensor was constructed for detection of phenanthrene. Successful synthesis of PANI-NiO nanocomposite was confirmed with techniques such as SEM, XRD, EDX, FTIR, and UV-visible spectroscopy. The electrocatalytic oxidation of phenanthrene on PANI-NiO on modified glassy carbon electrode GCE-PANI-NiO was studied using cyclic voltammetry, square wave voltammetry, and impedance spectroscopy and discussed. Results showed that detection of phenanthrene was enhanced by the nanostructure of PANI-NiO film. The square wave voltammetry analysis shows a very low detection limit of 0.732 pM for phenanthrene with the linear range of 7.6 pM–1.4 × 10−11 M. The Tafel value of 227 mVdec−1 suggests adsorption of phenanthrene oxidation intermediates on the GCE-PANI-NiO electrode. The GCE-PANI-NiO modified electrodes gave better performance towards phenanthrene in terms of current response, oxidation potential, current recovery, stability, and resistance to electrode fouling effects.

Electrocatalysis of Lindane Using Antimony Oxide Nanoparticles Based-SWCNT/PANI Nanocomposites

This work describes the chemical synthesis of antimony oxide nanoparticles (AONPs), polyaniline (PANI), acid functionalized single-walled carbon nanotubes (fSWCNTs), and the nanocomposite (AONP-PANI-SWCNT) as catalyst for the trace detection of lindane. Successful synthesis of the nanomaterials was confirmed by Fourier transform infrared (FT-IR) spectroscopy, ultraviolet-visible (UV-Vis) spectroscopy, x-ray diffraction (XRD) spectroscopy, and scanning electron microscopy (SEM). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) were used for investigating the electrochemical behavior of the modified electrodes in the ferrocyanide/ferricyanide ([Fe(CN)6]4−/[Fe(CN)6]3−) redox probe. GCE-AONP-PANI-SWCNT exhibited faster electron transport properties as well as higher electroactivity as compared to bare-GCE, GCE-AONPs, GCE-PANI, and GCE-SWCNT electrodes. Electrocatalytic studies further showed that GCE-AONP-PANI-SWCNT modified electrode was stable (after 20 scans) with only a small current drop in lindane (0.57%). The GCE-AONP-PANI-SWCNT electrode with low detection limit of 2.01 nM performed better toward the detection of lindane as compared to other studies in literature. The GCE-AONP-PANI-SWCNT electrode is highly selective toward the detection of lindane in the presence of various organic and inorganic interfering species. Real sample analysis of river water and tap water samples using the developed sensor gave satisfactory percentage recoveries therefore confirming the potential of the proposed sensor for practical application.

Antimicrobial and Wound Healing Properties of Polyacrylonitrile-Moringa Extract Nanofibers

A simple and cost-effective material composed of polyacrylonitrile nanofibers containing different concentrations of moringa (MR) leaf extracts was fabricated for antimicrobial properties and wound dressing. The fabricated materials were characterized by scanning electron microscopy, thermal gravimetric analysis, and Fourier transmission infrared spectroscopy. The antibacterial sensitivity of the developed polyacrylonitrile-moringa extract nanofibers was evaluated against Staphylococcus aureus and Escherichia coli by the agar diffusion method. A pronounced antibacterial activity was observed with the increase in the incorporated moringa leaf extract concentration within the polyacrylonitrile-moringa extract nanofibers against the bacterial strains. The best antibacterial sensitivity was observed for nanofibers containing 0.5 g of moringa leaf extract which had an inhibitory zone of 15 mm for E. coli and 12 mm for S. aureus. Furthermore, the cost-effective and biodegradable nanofibrous polyacrylonitrile–moringa extract nanofiber was also used to conduct further studies regarding wound dressing. The result reveals that the increase in the concentrations of moringa leaf extract influenced the healing properties of the material. For days 1, 4, and 7 of the wound dressing experiment, the % wound closure of the rat was the highest for the nanofiber containing 0.5 g of moringa leaf extract (35, 87, and 95%, respectively) compared to the positive control medical gauze (29, 75, and 93%, respectively).

Electrochemical properties of nanoporous based materials doped with metal oxide nanoparticles for potential application as sensors

T current study was aimed to use CNF as strength enhancer of two naturally superabsorbents (SAPs) i.e., Acrylic Acid (AA) and Carboxymethyl Cellulose (CMC) based SAPs. The results showed that increasing the CNF content may be resulted in decreasing the Swelling Capacity (SC) of the produced SAPs. The produced SAPs showed excellent swelling capacity in comparison to sodium polyacrylate based SAPs and due to biodegradable and non-toxic properties can be replaced with aforementioned SAPs. The Ionic Sensitivity (IS) of all produced SAPs was investigated and resulted in increased and decreased IS with increasing the CMC and CNF content respectively. Centrifuged swelling resulted sufficient strength of the SAPs based on AA during the water absorption due to increasing CNF addition. Additionally, the antibacterial test also studied and the results showed that SAPs based on AA containing chitosan had bactericidal property against Escherichia coli whereas CMC based SAPs exhibited no antibacterial property versus aforesaid bacteria............................................................................................................................ VI TABLE OF CONTENTS ......................................................................................................... IX LIST OF SELECTED SYMBOLS .................................................................................... XXXI LIST OF TABLES ........................................................................................................... XXXII CHAPTER 1 .............................................................................................................................. 1 1.0 SENSOR .............................................................................................................................. 2 1.1 CLASSIFICATION OF SENSORS ...................................................................................... 2 1.1.1 Chemical sensors .................................................................................................... 2 1.1.2 Biosensors ............................................................................................................... 4 1.2 APPLICATION OF ELECTROCHEMICAL SENSORS ........................................................... 5 1.2.1 Detection of drugs .................................................................................................. 6 1.2.2 Detection of pesticides ............................................................................................ 6 1.3 PROBLEM STATEMENT ................................................................................................ 6 1.4 AIM AND OBJECTIVES .................................................................................................. 8 CHAPTER 2 ............................................................................................................................ 10 2 LITERATURE REVIEW ................................................................................................ 10 2.1 NANOTECHNOLOGY .................................................................................................. 11 2.1.1 Classification of Nanomaterials ........................................................................... 11