Carbon nanotubes as fire gas sensors
Author(s)
Pearce, Ruth Elizabeth
Type
Thesis
Abstract
Multi walled carbon nanotubes (MWCNTs) possess properties that make them particularly
relevant for sensing applications in both the gas and liquid phase. This
study presents an evaluation of cheap readily available CVD grown MWCNTs for
use as fire gas sensors. Current fire detectors exploit heat and smoke detectors and
it is hoped that the inclusion of gas detectors will increase the speed and reliability
of detection.
In order to prepare a variety of different MWCNTs a range of CVD synthesis were
employed including an injected catalyst method where MWCNTs grew in dense
mats from quartz substrates, MWCNTs were also synthesised using a sputtered Fe
catalyst layer with acetylene as the carbon source which enabled control over the
positioning of the growth. In each case, the growth parameters were varied until
aligned growth was achieved. Doping of MWCNTs was also carried out as this may
enhance and enable some control over the electrical properties of the CNTs; nitrogen
was also added as a dopant by including 1,4-diazine as a precursor, and the effects
on morphology of the MWCNTs produced were studied.
The chemistry of the surface is also known to affect the sensing properties of CNTs.
A batch of MWCNTs produced via the injected catalyst method were purifed by
acid reflux, base washing and high temperature vacuum annealing, then modified
with platinum or palladium metal nanoparticles via a reduction of the metal salts
under hydrogen. MWCNTs were also coated with the polymer polyethyleneimine
and with copperphthalocyanine.
Prototype sensor devices were fabricated by electrophoretic deposition of these modified MWCNTs, and gas testing was carried out with the gases NO2, NH3, CO, H2
and C3H6. The mechanisms of sensing were investigated by repeating the tests at
different temperatures, which revealed which sensing mechanisms were dominant
and responses were compared between the differently modified MWCNTs. Sensor
response was also investigated with a series of vapours to probe the dispersive and
polar interactions on the MWCNT walls.
relevant for sensing applications in both the gas and liquid phase. This
study presents an evaluation of cheap readily available CVD grown MWCNTs for
use as fire gas sensors. Current fire detectors exploit heat and smoke detectors and
it is hoped that the inclusion of gas detectors will increase the speed and reliability
of detection.
In order to prepare a variety of different MWCNTs a range of CVD synthesis were
employed including an injected catalyst method where MWCNTs grew in dense
mats from quartz substrates, MWCNTs were also synthesised using a sputtered Fe
catalyst layer with acetylene as the carbon source which enabled control over the
positioning of the growth. In each case, the growth parameters were varied until
aligned growth was achieved. Doping of MWCNTs was also carried out as this may
enhance and enable some control over the electrical properties of the CNTs; nitrogen
was also added as a dopant by including 1,4-diazine as a precursor, and the effects
on morphology of the MWCNTs produced were studied.
The chemistry of the surface is also known to affect the sensing properties of CNTs.
A batch of MWCNTs produced via the injected catalyst method were purifed by
acid reflux, base washing and high temperature vacuum annealing, then modified
with platinum or palladium metal nanoparticles via a reduction of the metal salts
under hydrogen. MWCNTs were also coated with the polymer polyethyleneimine
and with copperphthalocyanine.
Prototype sensor devices were fabricated by electrophoretic deposition of these modified MWCNTs, and gas testing was carried out with the gases NO2, NH3, CO, H2
and C3H6. The mechanisms of sensing were investigated by repeating the tests at
different temperatures, which revealed which sensing mechanisms were dominant
and responses were compared between the differently modified MWCNTs. Sensor
response was also investigated with a series of vapours to probe the dispersive and
polar interactions on the MWCNT walls.
Date Issued
2008-10
Date Awarded
2009-05
Copyright Statement
Attribution NoDerivatives 4.0 International Licence (CC BY-ND)
Advisor
Shaffer, Milo
Creator
Pearce, Ruth Elizabeth
Publisher Department
Chemistry
Publisher Institution
Imperial College London
Qualification Level
Doctoral
Qualification Name
Doctor of Philosophy (PhD)