CHARACTERISATION OF PEDOT AND ITS DERIVATIVES IN ELECTROCHEMICAL SENSING APPLICATIONS

The emergence of a new class of polymer, namely conducting polymers (CPs) in late 1970s, has attracted many hysicists, chemists and materials researchers to study them in depth due to the unique properties and broad applications of this material. Poly(3,4-ethylenedioxythiophene) (PEDOT) has been found to be the most chemically stable CP to date. The aim of this project was to characterise PEDOT and its derivatives for applications in ion sensing. In this work, PEDOT and its derivatives i.e. poly(3,4-propylenedioxythiophene) (PProDOT) and poly(3,3-dibenzyl-3,4-propylenedioxythiophene) (PDBPD) doped with perchlorate ( ClO-4) have been electrochemically synthesised on glassy carbon (GC) and indium-tin-oxide coated glass (ITO) electrodes in acetonitrile. PEDOTs were also prepared in aqueous solutions using perchlorate ( ClO-4) and chloride( Cl-) counterions as comparison. Scanning electron microscopy (SEM), atomic force microscopy (AFM), contact angle (CA) measurements and Raman spectroscopy have been used to characterise the physical properties of the polymer coated glassy carbon (GC) and ITO electrodes. PDBPD has shown to have the most compact morphology, roughest and least wettable surface. The electrochemical studies have shown that PEDOT has the highest capacitive current. The combination of this property and mixed electronic and ionic conductivity make the PEDOT suitable to be used as a solid contact (transducer) in all-solid-state ion-selective electrode (ASSISE). PEDOT doped with poly(sodium 4-styrenesulfonate) (PSS) was found to be superior to hyaluronic acid (HA) as a solid contact for ASS Ca2+-, K+- and Na+-selective electrodes. Measurements of Ca2+ and K+ upon plant stress using ion ion-selective microelectrodes have been demonstrated. Chiral electrodes based on electrodeposited PEDOT doped with chiral molecules (collagen, HA and hydroxypropyl cellulose) were shown to discriminate between (R)-(−)- and (S)-(+)-mandelic acid. The work carried out in this thesis has shown that PEDOT is one of the most versatile conducting polymers

Effect of catalysts and precursors in the synthesis of carbon nanotubes by catalytic chemical vapour deposition

Since the pioneering report of discovery of carbon nanotubes (CNTs) in 1991 by Iijima, scientists and researchers worldwide have carried out in depth investigations in this new family of carbon because of its myriad properties and potential applications. The synthesis of novel nanoscale material is the main target in current material science. This study investigates the effect of different types of cabon source and and catalyst on the type of CNTs formed via catalytic chemical vapour deposition (CCVD) method. Three types of carbon source i.e. acetylene, methane and ethanol were used for the synthesis of CNTs. The catalysts used in the synthesis of CNTs are monometallic, bimetallic and trimetallic derived from Fe, Co and Ni salts using wet impregnation method. The catalysts were characterized by scanning electron microscope (SEM) and energy-dispersive X-ray analysis (EDX). The analysis confirmed the presence of Fe, Co and Ni. The as-synthesized CNTs were characterized using SEM/field emission-scanning electron microscope (FE-SEM), EDX, Raman spectroscopy and transmission electron microscopy (TEM). This analysis also confirmed that all the prepared catalysts were active for the production of CNTs. SEM/FE-SEM analysis revealed different morphologies of CNTs were formed when different catalysts and carbon source were used. Raman spectra revealed that acetylene and methane precursor produced multi-walled carbon nanotubes (MWNTs) as indicated by the presence of G-band and D-band peaks. However, their structures were different depending on the catalysts used. Meanwhile, the presence of RBM peaks along with the G-band and D-band revealed that singlewalled carbon nanotubes (SWNTs) are produced using ethanol as the carbon source. TEM micrographs obtained confirmed that acetylene and methane produced MWNTs and ethanol produced SWNTs with diameter in the range of 14.74-34.59 nm, 10.19-37.61 nm and 0.96-2.52 nm, respectively. However, Fe/Al2O3 catalyst selectively produced double-walled carbon nanotubes (DWNTs) when ethanol was used as the carbon source. Generally, this research has been successful in producing various types of CNTs depending on the catalyst used and the carbon source selecte

A new approach for electrodeposition of poly (3, 4-ethylenedioxythiophene)/polyaniline (PEDOT/PANI) copolymer

In this study, poly (3, 4-ethylenedioxythiophene) (PEDOT) and polyaniline (PANI) based copolymer was synthesized by electrochemical oxidative polymerization using chronoamperometry technique. A new approach was used to perform the copolymerization process. The copolymer film was prepared at a potential obtained from the intercept point in the LSV of the both monomers. The electrodeposition was performed in solution containing 10mM of concentrations of each monomer and 0.1 M lithium perchlorate (LiClO4). The resulting conducting polymer films were characterized using scanning electron microscope (SEM), Raman spectroscopy and Fourier transform infrared (FTIR) to study the surface morphology, chemical properties and the presence of the functional groups of the conducting polymer films. The FTIR and Raman spectra proved the successful formation of the conductive polymers and copolymer onto the ITO glass. The electrochemical properties of the resultant polymer films were further analyzed using the cyclic voltammetry and electrical impedance spectroscopy

Electrodeposition of poly(3,4-ethylenedioxythiophene)/reduced graphene oxide/manganese dioxide for simultaneous detection of uric acid, dopamine and ascorbic acid

A simple and sensitive sensor of poly(3,4-ethylenedioxythiophene)/reduced graphene oxide/manganese dioxide modified glassy carbon electrode (PrGO/MnO2) was fabricated via cyclic voltammetry (CV) for simultaneous detection of uric acid (UA), dopamine (DA) and ascorbic acid (AA). The PrGO/MnO2 composite film possessed excellent electrocatalytic rate and high selectivity towards the oxidation of UA, DA and AA in 0.1 M PBS (pH 6.0). The peak potential separation (∆Ep) of AA-DA, AA-UA and DA-UA were 166, 312 and 146 mV, respectively. The detection limits of 1.00, 0.02 and 0.05 μM with a linear response of 1–800, 0.03–45 and 0.3–80 μM were obtained for AA, DA and UA, respectively. This sensor also showed an excellent stability (reproducibility and repeatability)

Designing an advanced electrode of mixed carbon materials layered on polypyrrole/reduced graphene oxide for high specific energy supercapacitor

A free-standing and flexible film is fabricated by layering multiwalled carbon nanotube/reduced graphene oxide/nanocrystalline cellulose composite on polypyrrole/reduced graphene oxide composite layer. The bilayer composite film is prepared by in-situ polymerization through a vacuum filtration method followed by a chemical reduction in the presence of hydrazine vapor and used as an electrode material for supercapacitor. The aggregation of multiwalled carbon nanotube and graphene oxide in the composite are addressed effectively by the support of nanocrystalline cellulose that favors ions movements in the composite. The symmetrical supercapacitor device developed in this study combines the features of pseudocapacitor and electrical double layer capacitor and delivers outstanding supercapacitive properties. As manifested by the electrochemical results, the device exhibits a high specific capacitance of 882.2 F g−1, remarkable cycling stability of ∼90% over 10,000 cycles, and high specific energy of 44.6 Wh kg−1 with a high specific power of 2889.9 W kg−1, which outperformed many other reported polypyrrole-based materials for supercapacitors. This makes the bilayer a promising candidate for future high performance energy storage devices

Effect of electropolymerization potential on the preparation of PEDOT/graphene oxide hybrid material for supercapacitor application

Conducting polymer poly(3,4-ethylenedioxythipohene) (PEDOT) hybrid with carbon-based material, graphene oxide (GO), was prepared for supercapacitor application. Different applied potentials were employed in order to study the effect of electropolymerization potential on PEDOT/GO thin film. Field emission scanning electron microscopy (FESEM) images showed that PEDOT/GO possessed more pronounced wrinkle paper-like sheet surface morphology as the potential increased from 1.0 to 2.0 V. Fourier transform infrared spectroscopy (FTIR) and Raman spectroscopy revealed that GO was successfully incorporated into PEDOT during electropolymerization. The cyclic voltammetry (CV) and galvanostatic charge-discharge (GCD) measurements revealed that the PEDOT/GO composite electropolymerized at the applied potential of 1.2 V exhibited a maximum specific capacitance of 115.15 F/g with energy density and power density of 13.60 Wh/kg and 139.09 W/kg, respectively at current density 0.3 A/g. The EIS result showed that the Rct decreased as the electropolymerization potential rose from 1 V to 1.2 V and increased when the electropolymerization further increased to 2 V due to a large electron transfer resistance that makes the rate of charge transfer becomes slower

Optimization of titanium dioxide decorated by graphene quantum dot as a light scattering layer for enhanced dye-sensitized solar cell performance

Titanium dioxide (TiO2) as a photoanode in dye-sensitized solar cells (DSSCs) has some drawbacks that reduce its photovoltaic performances i.e. low dye loading capacity and low light-harvesting efficiency. Therefore, TiO2 decorated by graphene quantum dot (GQD) as a light scatterer has been successfully fabricated via electrodeposition and drop-casting. The response surface methodology/central composite design was successfully utilized to optimize the preparation of photoanode with TiO2-GQD as a light scattering layer (LSL). A reduced quadratic model was successfully designed to predict the power conversion efficiency (PCE) accurately up to 97% with a 3% residual standard error. The TiO2-GQD LSL depicted a cluster of spherical nanoparticles on top of the photoanode that not only enhanced the light scattering effect but also improved the light-harvesting range from visible light to ultraviolet and near-infrared range. The resultant TiO2 nanoparticles with TiO2-GQD LSL showed vast enhancement of PCE up to 66% from 3.06% to 5.01% due to a good synergistic effect

Review-electrochemical detection of uric acid, dopamine and ascorbic acid

Uric acid (UA), dopamine (DA) and ascorbic acid (AA) exist in the human body as protein metabolism, neurotransmitter and antioxidant, respectively. The abnormal levels of UA, DA and AA could lead to certain diseases and it could be measured and determined using electrochemical sensors. UA, DA and AA have close oxidation potentials and cause overlapping peaks in electrochemical measurements. Researchers have been working on electrode modification by using different materials to overcome those challenges and improve their selectivity, sensitivity and limit of detection. This review aims to highlight the performance of modified electrochemical sensors for detection of UA, DA and AA individually or simultaneously

Quantitative measurement of amoxicillin in Ibuprofen tablets using UPLC

A novel quantitative analytical method for the determination of Penicillin contaminant, Amoxicillin in non-penicillin pharmaceutical drug product (Ibuprofen tablet 400 mg) has been developed and validated using Ultra performance liquid chromatography (UPLC). The extraction of amoxicillin from the drug tablets was carried out with bi-distilled water and the separation was achieved by making use of a BEH C18 column with particle size of 1.7 μm (100 mm × 2.1 mm). The isocratic run accomplished using phosphate buffer (pH 5.0): methanol (95:5, v/v) mixture as mobile phase run at a flow rate of 0.3 mL/min. The rapid, accurate and low cost UPLC method was proven to be suitable within the current good manufacturing practices (cGMP) of pharmaceutical ingredients. In addition, the validation of the developed method was conducted as per the ICH (International conference of harmonization) guidelines Q2 (R1). Further, the method was found to be linear in the range of (0.024–0.096 μg/mL for amoxicillin) with a correlation coefficient, R2 of 0.999 and net in terms of specificity, linearity, precision, accuracy, detection limit (DL), and quantitation limit (QL) are appeared to be satisfactory. The precision was assessed in terms of injections repeatability with a maximum %RSD of 1.8%, while the intermediate precision Day-1 with %RSD of 0.96 and the intermediate precision Day-2 with %RSD of 1.56 were observed. Thus, from the observation of satisfactory results for amoxicillin detection, the developed UPLC-based method can successfully be applied in the pharmaceutical quality control laboratories to fulfill the regulatory requirements

Capacitive enhancement of reduced titania nanotubes by reversed pulse electrodeposited Mn2O3 and Co3O4

Many attempts have been done to improve the capacitive performance of reduced titania nanotubes (R-TNTs) by incorporation of metal oxides via electrodeposition method. In this study, pulse reverse electrodeposition technique has been applied to deposit Mn2O3 and Co3O4 onto the R-TNTs as this technique has the ability to control the composition of targeted materials while at the same time helps in facilitating the uniformity of deposition and the size of the metal oxides onto the reduced nanotubes. Based on FESEM and TEM analyses, it is proven that both metal oxides were uniformly deposited without covering the nanotubes opening. Besides, Mn2O3 and Co3O4 with crystallite size of 13.6 nm and 12.4 nm were recorded in XRD analysis. Electrochemical analyses were performed to evaluate the capacitive performance of both deposited metal oxides. The CV profiles of both metal oxides showed similar patterns attributed to simultaneous charge-storage mechanisms of electric double-layer in R-TNTs and pseudocapacitance in the metal oxides. Galvanostatic charge-discharge showed Mn2O3/R-TNTs exhibits higher specific capacitance of 37.0 mF cm-2 compared to Co3O4/R-TNTs of 16.9 mF cm-2 at 0.1 mA cm-2. Moreover, these deposited samples also exhibit good electrochemical stability by retaining 87% of the initial capacity over 1000 cycles