Wee Tee Tan

Preparation and characterization of polypyrrole/graphene nanocomposite films and their electrochemical performance

A one-step electrochemical process had been employed to synthesize nanocomposite films of polypyrrole/graphene (PPy/GR) by electrochemical polymerisation on indium tin oxide (ITO) from an aqueous solution containing pyrrole monomer, graphene oxide (GO) nanosheets and sodium p-toluenesulfonate (NapTS). The X-ray diffraction (XRD) patterns showed that the typical peak of GO at 9.9o was missing from the nanocomposite’s diffraction pattern, suggesting that the GO had been stripped off of its oxygenous groups after the reaction. We postulated that a nanocomposite film was produced through a layer-by-layer deposition based on field emission scanning electron microscope (FESEM) images. The Raman spectroscopy profiles exhibited that the D/G intensity ratio (ID/IG) of PPy was not altered by the inclusion of GO due to the low concentration of the material used. However, the concentration was sufficient to increase the specific capacitance of the nanocomposite by 20 times compared to that of pure PPy, reflecting a synergistic effect between PPy and GR, as analysed by a three-electrode electrochemical cell. The electrochemical performance of the nanocomposites was affected by varying the deposition parameters such as concentrations of pyrrole and GO, scan rate, deposition time and deposition potential.

Anodization Parameters Influencing the Growth of Titania Nanotubes and Their Photoelectrochemical Response

TiO2 nanotubes (TNTs) were fabricated by electrochemical oxidation of Ti foil in a standard two-electrode cell-containing NH4F. The effects of bath temperature, voltage ramp prior to constant voltage held during anodization and present of complexing agent on the crystalline phase, nanotube growth, and dimensional change of TNT were investigated using XRD and FESEM. The results show that tube length decreases with bath temperature attributed to faster chemical dissolution rate at high temperature. However, nanotubes growth rate was enhanced by ~260% with the addition of EDTA as the complexing agent. Meanwhile, the nanotubes diameter was found to be proportionally dependent on bath temperature but independent of the voltage ramp and addition of EDTA. Photoelectrochemical response under illumination was enhanced by using the calcined TNT and is strongly affected by its dimensional changes. Thus, desired properties of TNT can be obtained by tuning the electrochemical condition for a wide-range application.

Solubilities of trace copper and lead species and the complexing capacity of river water in the Linggi River Basin

Chemical forms of copper and lead in river water of the Linggi River Basin have been fractionated into ASV labile, moderately labile, slowly labile, and inert metal species, based on a previously proposed scheme. Free (hydrated) metal ions were identified by a potentiometric method using an ion selective electrode. Speciation results showed that the soluble copper and lead species occurred mainly in the moderately labile and slowly labile fractions. The speciation results are primarily interpreted in terms of organic interaction due to agricultural based and light industries, and urban discharges. The measured metal complexing capacity (MCC) of the samples reveals consistency of the results with the nature of the discharge. MCC correlates reasonably well with the value from the permanganate test on the river water. In general, the speciation pattern was found to be consistent with the findings of other workers.

Effect of Water Content on Structural and Photoelectrochemical Properties of Titania Nanotube Synthesized in Fluoride Ethylene Glycol Electrolyte

In this work, the effect of water content from < 1 to 100 vol% on the electrochemical anodization of titanium in ethylene glycol-based electrolyte was investigated. The samples were characterized using X-ray diffraction (XRD) and their dimensional change was monitored by field emission scanning electron microscopy (FE-SEM). It was found that the microstructure and morphology of TiO2 varies dramatically with the water content. Nanotubes become less ordered with increasing water content up to 50 vol%. At 75 vol% water, only porous structure could be observed. Most importantly, at fixed applied voltage, smoother but relatively longer tubes can be grown with lower water content. Varying water content has no effect on the crystalline phase of the resulted nanotubes. However, the intensity of anatase (101) peak increases with increasing water content, indicating better crystallinity of samples. Nanotubes obtained in 50 vol% water exhibit the highest photoresponse when tested using linear sweep photovoltammetry due to enhanced microstructure and crystallinity.

Electrocatalytic Study of Paracetamol at a Single-Walled Carbon Nanotube/Nickel Nanocomposite Modified Glassy Carbon Electrode

A rapid, simple, and sensitive method for the electrochemical determination of paracetamol was developed. A single-walled carbon nanotube/nickel (SWCNT/Ni) nanocomposite was prepared and immobilized on a glassy carbon electrode (GCE) surface via mechanical attachment. This paper reports the voltammetry study on the effect of paracetamol concentration, scan rate, pH, and temperature at a SWCNT/Ni-modified electrode in the determination of paracetamol. The characterization of the SWCNT/Ni/GCE was performed by cyclic voltammetry. Variable pressure scanning electron microscopy (VPSEM) and energy dispersive X-ray (EDX) spectrometer were used to examine the surface morphology and elemental profile of the modified electrode, respectively. Cyclic voltammetry showed significant enhancement in peak current for the determination of paracetamol at the SWCNT/Ni-modified electrode. A linear calibration curve was obtained for the paracetamol concentration between 0.05 and 0.50 mM. The SWCNT/Ni/GCE displayed a sensitivity of 64 mA M−1 and a detection limit of 1.17 × 10−7 M in paracetamol detection. The proposed electrode can be applied for the determination of paracetamol in real pharmaceutical samples with satisfactory performance. Results indicate that electrodes modified with SWCNT and nickel nanoparticles exhibit better electrocatalytic activity towards paracetamol.

Effect of Electrolyte Concentration on the Morphology and Photoelectrochemical Response of Titania Nanotubes Prepared by Electrochemical Anodisation

In this work, the effect of NH4F concentration on the formation, dimensions and photoelectrochemical response of titania nanotubes produced by anodisation of Ti in ethylene glycol has been investigated. The results showed that a minimum amount of 0.25 wt.% NH4F is needed for the formation of uniform and ordered nanotubes in viscous ethylene glycol. Self-organized nanotubes can be synthesized in the concentration range of 0.250.7 wt.%; with a higher fluoride concentration leads to severe etching of the tube tops resulting in a grassy-like appearance. Varying the concentration of NH4F has no effect on the tube diameter and wall thickness. However, nanotubes length increases gradually by increasing the NH4F concentration with preferred growth along the c-axis. Thermal annealing at 500 °C transforms the amorphous nature of as-formed nanotubes into pure anatase phase. Photoelectrochemical response of nanotubes was tested with linear sweep photovoltammetry. It was found that microstructures, crystallinity and geometry of the nanotubes are important factors influencing the photoresponse.

Morphology and Dimensions Controlled of Titania Nanotubes in Mixed Organic-Inorganic Electrolyte

The formation of self-organized and highly ordered Titania nanotubes was achieved by anodisation of Ti in a mixture of water-ethylene glycol electrolyte. Control over the dimensions and morphology of nanotubes was successfully established by changing the anodisation voltage, the ammonium fluoride (NH4F) concentration and the anodisation time. A threshold voltage of 5 V is required for nanotube formation. Collapsed tubes were formed by applying electrochemical etching at high fluoride concentration. This study also showed that the nanotube lengths ranging from 0.5 to 2.6 μm could be formed by controlling the voltage applied and fluoride concentration with preferred growth along the c-axis.