Glassy carbon electrode modified with nanoparticles of selected metal/metal oxides and single-walled carbon nanotubes for electro analysis of ascorbic acid and paracetamol
This thesis presents a research study on the novel electrochemical sensors based on single-walled carbon nanotube/nanoparticles for the voltammetric determination of ascorbic acid and paracetamol. The determination of ascorbic acid and paracetamol using bare electrodes have several limitations...
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| Format: | Thesis |
| Language: | English |
| Published: |
2015
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/71195/1/FS%202015%2081%20IR.pdf http://psasir.upm.edu.my/id/eprint/71195/ |
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| Summary: | This thesis presents a research study on the novel electrochemical sensors based on
single-walled carbon nanotube/nanoparticles for the voltammetric determination of
ascorbic acid and paracetamol. The determination of ascorbic acid and paracetamol
using bare electrodes have several limitations such as poor sensitivity and
reproducibility. Electrode modified by using a hybrid of both nanoparticles and singlewalled
carbon nanotubes (SWCNTs) could provide better sensitive and reproducibility
in the electrochemical determination of ascorbic acid and paracetamol.
The solid phase voltammetry of microparticles (SPVM) technique is applied for the
fabrication and characterization of the electrochemical sensors. SWCNTs and
metal/metal oxides-modified glass carbon electrodes (GCEs) were fabricated by a
mechanical attachment technique. SWCNT/tungsten/GCE, SWCNT/tungsten
oxide/GCE and SWCNT/zinc oxide/GCE were fabricated for the detection of ascorbic
acid. Electrochemical determination of paracetamol in a potassium dihydrogen
phosphate electrolyte solution was performed with SWCNT/zinc oxide/GCE and
SWCNT/nickel/GCE. The electrochemical behavior and electrocatalytic properties of
all the modified electrodes were characterized by using cyclic voltammetry (CV) and
electrochemical impedance spectroscopy (EIS). Nanocomposites of the selected
metal/metal oxide and SWCNT were examined by the UV-visible spectroscopy (UVVis),
scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer
(EDX).
When a SWCNT/nanoparticle was introduced as the mediator, current responses
toward ascorbic acid in the potassium dihydrogen sulphate electrolyte solution
dramatically increased in comparison to the bare GCE. In the cyclic voltammetric
analysis, the enhancement factors were 2.5, 3.5, and 2.0 for the SWCNT/WO3/GCE,
SWCNT/W/GCE and SWCNT/ZnO/GCE, respectively. In the application of
electrodes immobilized with a nanocomposite for ascorbic acid determination, the
SWCNT/WO3/GCE, SWCNT/W/GCE and SWCNT/ZnO/GCE displayed a sensitivity
of 14.6, 23.8, 13.7 mA M-1 and a detection limit of 5.1, 1.9, 21.0 M, respectively.
Cyclic voltammetry studies indicated that the oxidation of ascorbic acid at all the modified electrodes was a diffusion controlled process. The effect of pH was
investigated and the optimal pH was obtained: pH 2 (SWCNT/WO3/GCE), 2.5
(SWCNT/W/GCE), and 4-5 (SWCNT/ZnO/GCE) when 0.1 M potassium dihydrogen
phosphate solution was used. The activation energy (Ea) of the electrocatalytic reaction
was found to be 3.43, 1.02 and 3.81 kJ mol-1 corresponding to SWCNT/WO3/GCE,
SWCNT/W/GCE and SWCNT/ZnO/GCE, respectively using a temperature study.
The electrochemical method was assessed with a repeatability study, and relative
standard deviation (RSD) values of 5.3%, 3.5% and 3.8% were obtained for
SWCNT/WO3/GCE, SWCNT/W/GCE and SWCNT/ZnO/GCE, respectively. All the
modified electrodes were used for ascorbic acid recovery determination in real
samples, with excellent recovery rates of near 100% with RSD ranging from 2.0-6.5%.
The peak current response of paracetamol obtained at the SWCNT/ZnO/GCE and
SWCNT/Ni/GCE were significantly better than that of a bare GCE, with the
enhancement factors of 4 and 5, respectively. The improved current response of
modified electrodes is attributed to the unique structure and physicochemical
properties of SWCNT and nanoparticles. In the determination of paracetamol using
cyclic voltammetry, a linear current response was observed for the concentration range
of 0.05 to 0.50 mM. The SWCNT/ZnO/GCE and SWCNT/Ni/GCE displayed a
sensitivity of 42.5, 63.8 mA M-1 and a detection limit of 0.32, 0.12 M, respectively
Redox reactions of paracetamol at the SWCNT/ZnO/GCE and SWCNT/Ni/GCE were
controlled by both diffusion and adsorption. Both modified electrodes had higher
oxidation peak currents at lower pH.
The reproducibility of the developed method in paracetamol detection was assessed.
Relative standard deviations of 5.5% and 5.6% were obtained for SWCNT/ZnO/GCE
and SWCNT/Ni/GCE, respectively in the repeatability study. Both modified
electrodes show excellent results for detecting paracetamol in real life samples with a
RSD of 1.9%. Scanning electron micrographs indicate the porous and uneven
distribution of nanocomposites on the modified electrode surfaces. The particle size of
nanocomposite was found to be bigger after electroanalysis. From the UV-Vis
analysis, a decrease in band gap energy was discovered when a SWCNT was
introduced to the nanoparticles. This could have improved the electrical conductivity
of the nanocomposite and therefore enhance the electrocatalytic activity. It was
indicated in the EIS analysis that the charge transfer resistance of the
SWCNT/ZnO/GCE is higher compared to other modified electrodes.
In conclusion, several electrochemical sensors were fabricated and characterized on
the voltammetric determination of ascorbic acid and paracetamol. The results
demonstrated that SWCNT and selected metal/metal oxide are superior electrode
materials. The electroanalytical method is a simple, fast, low cost and sensitive
approach for the detection of ascorbic acid and paracetamol. The results indicate that
the modified electrodes based on SWCNT and selected metal/metal oxides can be
applied for the routine qualitative and quantitative determination of ascorbic acid or
paracetamol. |
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