Palladium-coated nanocomposite on tapered optical fiber for hydrogen sensing applications
Gaseous pollutants such as hydrogen gas (H2) are present in daily human activities and have been studied extensively due to their high explosive and widespread use in many fields. A common H2 gas detector is electrically based. Although these electrical or conductometric sensors attain high sensi...
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Format: | Thesis |
Language: | English |
Published: |
2022
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Subjects: | |
Online Access: | http://psasir.upm.edu.my/id/eprint/104054/1/FK%202022%2097%20IR.pdf |
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Summary: | Gaseous pollutants such as hydrogen gas (H2) are present in daily human activities and
have been studied extensively due to their high explosive and widespread use in many
fields. A common H2 gas detector is electrically based. Although these electrical or
conductometric sensors attain high sensitivity, they suffer from drawbacks, including
poor selectivity, high operating temperature, and susceptibility to electromagnetic
interference, which the optical-based sensor can improve. Optical fiber sensors offer
advantages over electrical sensors in certain aspects, such as their compact size, the
ability to work in harsh environments, and the ability for remote and distributed sensing.
However, H2 detection with optical fibers has not been fully explored.
Nanotechnology-enabled chemical sensors have been increasingly used to enhance the
sensing performance compared to the conventional sensors toward target analytes owing
to their high surface area. The sensing layer based on nanostructures has been identified
to work at low temperatures with high sensitivity. Therefore, this research project aims
to design and comprehensively analyze optical fiber-based H2 gas sensors by
incorporating different nanocomposite coatings as sensing layers. This study uses
tapered multimode silica fiber (MMF) sensors as a transducing platform. The tapering
process is essential to improve the sensitivity to the environment through the interaction
of the evanescent field over the area of the tapered surface area. The tapered area is
coated with a sensor layer which is also an essential factor affecting the sensor's
performance. The influence of nanostructures’ morphology and roughness on the sensing
performance were also studied in this Ph.D. research.
The nanostructured materials investigated are graphene oxide (GO), polyaniline (PANI),
and molybdenum trioxide (MoO3). These nanomaterials were combined as a
nanocomposite sensing layer to enhance the H2 detection. A noble metal, palladium (Pd),
was selected as a catalyst to split hydrogen ions. The novel nanocomposites of Pd/GO,
Pd/PANI/GO, and Pd/MoO3/PANI were dropped cast on the tapered optical fiber for sensing analysis. Combining these materials as nanocomposite adds up the functionality
to enhance the high surface area to volume ratio to effectively miniaturize and improve
the sensing properties of the developed sensors. In this context, nanocomposite materials
promote effective H2 gas sensing peculiarity and allow the developed sensors to be
operational at low temperatures. Micro-nano characterization techniques such as
FESEM, EDX, AFM, and XRD were utilized to obtain detailed structural properties of
these nanostructures and fundamentally understand their functions concerning optical
sensor performance.
The response of the sensors towards H2 gas was measured at concentrations of 0.125%
- 2.00% using optical absorbance change within the wavelength range of 550-850 nm at
different temperatures. The sensor performance was evaluated regarding response time,
recovery time, sensitivity, repeatability, and stability at different temperatures.
The developed H2 sensors using tapered optical fiber coated with Pd/GO, Pd/PANI/GO,
and Pd/MoO3/PANI nanocomposite operated at different temperatures are the first of its
kind according to the author’s knowledge. The Pd/GO nanocomposite-based sensor
demonstrated higher sensitivity of about 33.22/vol% compared to Pd/PANI/GO and
Pd/MoO3/PANI nanocomposite, where the sensitivity is about 10.43/vol% and
16.81/vol%, respectively. The response and recovery time of the developed sensors
based on Pd/GO, Pd/PANI/GO, and Pd/MoO3/PANI nanocomposite recorded were 48 s,
60 s, and 90 s, and their recovery times were 420 s, 190 s, and 230 s, respectively.
Overall, the developed sensor based on Pd/GO nanocomposite showed excellent
sensitivity, higher response time, selectivity, and long-term stability compared to
Pd/PANI/GO and Pd/MoO3/PANI nanocomposite-based sensors. |
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