Sensitivity and stability of conducting polymers and copper-based metal organic framework for optical ammonia gas sensor
Optical approaches for ammonia (NH3) gas sensing are contemplated as a reliable alternative to the conventional chemiresistive gas sensing techniques. Absorbance-based sensor by using white light were developed by using gasochromic materials, namely conducting polymers and copper-based metal-o...
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| Format: | Thesis |
| Language: | English |
| Published: |
2022
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| Subjects: | |
| Online Access: | http://psasir.upm.edu.my/id/eprint/99744/1/ITMA%202022%202%20IR.pdf http://psasir.upm.edu.my/id/eprint/99744/ |
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| Summary: | Optical approaches for ammonia (NH3) gas sensing are contemplated as a reliable
alternative to the conventional chemiresistive gas sensing techniques. Absorbance-based
sensor by using white light were developed by using gasochromic materials, namely
conducting polymers and copper-based metal-organic framework. Conducting polymers
can be considered as the ideal material to be used as a single-component optical NH3 gas
sensor at room temperature. Recent interest in metal-organic frameworks has risen
significantly, owing to their high surface area and porosity, as well as the inherent
convenience of sculpting to design selected coordination sites for gas adsorption. Hence,
a copper-based metal-organic framework, HKUST-1, has been chosen as a potential type
of MOF for the intrinsic optical NH3 gas sensor. The optical sensing performance of
three different types of electropolymerised conducting polymers namely polyaniline
(PANI), poly(3,4-ethylenedioxythiophene) (PEDOT) and polypyrrole (PPy), towards
NH3 gas were evaluated. On the basis of the former study, bilayers and copolymers
containing electropolymerised PEDOT and PANI were further probed in order to attain
the desired NH3 sensing outputs from both materials. Characterisations of the samples
were carried out using Raman spectroscopy, Fourier transform infrared spectroscopy
(FTIR), and field emission scanning electron microscopy (FESEM) where functional
group identifications of the corresponding samples and their morphological analysis
were identified.. PEDOT exhibited the highest sensitivity (9.03/%) towards NH3 gas
comparing to PANI and PPy with the detection limit of 2.73 ppm, which is in agreement
with their respective conductivity trends. The order of the bilayers and the presence of
acid dopant on the fabrication of the sensing platform produced different absorbance
responses upon exposure to NH3 gas. The gasochromic behaviour of PANI and PEDOT
during the adsorption of NH3 gas was closely related to the changes in the oxidation state
which have simultaneously altered the colour intensity of the respective sensing layer.
Meanwhile, in contrast to the in-situ works, a long-term sensitivity performance of
conducting polymers and metal-organic frameworks coated on side-polished plastic
optical fibre (SP-POF) was presented. Long-term sensitivity of HKUST-1, PANI in protonated (emeraldine salt, ES) and deprotonated state (emeraldine base, EB) to the
high concentration of NH3 gas was performed. ES-EB composite has exhibited higher
NH3 sensitivity to the sole ES and ES-(HKUST-1) with minimal loss of sensitivity. ES-EB coated SP-POF has exhibited minimal sensitivity loss to NH3 gas throughout the test
duration with a 7.8% decrease followed by ES (28.1%) and ES-(HKUST-1) (50.86%).
Of all developed samples in this work, PEDOT has exhibited the highest sensitivity to
NH3 gas(9.03/%) while PANI (EB) has exhibited shortest response and recovery time to
1% NH3 gas, at room temperature. Also, incorporation of EB in the ES-coated SP-POF
composite has significantly reduce the loss of sensitivity to NH3 gas. |
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