(Okano and Totsuka 1986). Moreover, the primary pollutant like oxides of nitrogen
may cause secondary pollution like ground-level smog and/or acid rain. The threshold limit value has been set at 3 ppm over 10 h a day for nitrogen dioxide exposure.
The pristine CNT networks without any chemical functionalization might be used
as gas sensor with improved performances. For example, bare SWNT drop-cast onto
interdigitated electrodes (Li et al. 2003) or CNT film deposited on platinum–substrate (Santucci et al. 2003) was reported for the detection of nitrogen dioxide with
low detection limit. The single crystalline particles were only slightly aggregated and
directly used for thick film sensor deposition. The tin dioxide nanoparticle synthesized by flame spray pyrolysis followed by drop coating film responded well to both
reducing gases like propanal and oxidizing gases like nitrogen dioxide (Sahm et al.
2004). The zinc oxide nanorod was highly responsive to nitrogen dioxide gas with
short response and recovery time having a detection limit of 10 ppb at 250
C
(Oh et al. 2009). The high sensitivities to low nitrogen dioxide levels together with
fast response times were observed for both tin dioxide and indium oxide materials
over that of the tungsten trioxide (Starke et al. 2002). The tin dioxide nanowires were
reported to show higher sensitivity for nitrogen dioxide gas compared to tin dioxide
powder-based thin films, tin dioxide coating on carbon nanotubes, or single/multiple
tin dioxide nanobelts (Choi et al. 2008). The sensitivity of the tube-like zinc oxide
toward nitrogen dioxide gas was much higher with shorter response time than that of
the flower-like zinc oxide gas sensor (Chen et al. 2011). The details of sensing
characteristics as well as sensing parameters were optimized for the three nitrogen
oxides: nitrogen dioxide, nitric oxide, and nitrous oxide by using zinc oxide, indium
oxide, and tungsten trioxide nanowire receptor (Rout et al. 2006a). All-graphene
sensor consisting the material in both sensor electrodes and active sensing area was
exhibited selective and reversible responses to nitrogen dioxide at room temperature
under high humidity conditions as well as bending strain (Kim et al. 2015). The
graphene oxide-based resistive sensor reported low-concentration nitrogen dioxide
and ammonia gases in air flow at room temperature (Lu et al. 2009). The ozonetreated graphene sensor was demonstrated to show better sensing performances such
as percentage response, detection limit, and response time for extremely low ppb
nitrogen dioxide gas concentrations over that of the pristine graphene (Chung et al.
2012). The standard sensing plot as well as correlation between percentage response
and concentrations is shown in Fig. 10.19. The nanocomposite films of tungsten
films impregnated with CNT showed sensitivity to 500 ppb nitrogen dioxide under
ambient conditions (Bittencourt et al. 2006). The poly(ethylene imine)-coated
SNWT nanocomposite was introduced as good nitrogen dioxide sensor with the
lowest detection limit of 100 ppt (Qi et al. 2003). The SWCNT decorated with metal
nanoparticles such as platinum, palladium, gold, silver, etc. has shown unique and
improved sensing characteristics for nitric oxide gas in the atmosphere over the bare
SWNT networks (Kauffman and Star 2007). The drop-cast CNT–tin dioxide
nanocomposite onto a cylindrical ceramic tube at internal heating temperature of
300
C reported cross sensitivity to nitric acid gas concentrations between 2 and
50 ppm (Liang et al. 2004). The highest response to nitrogen dioxide was observed
by zinc oxide–tin dioxide nanocomposite with 1:1 zinc and tin molar ratio via
10 Nanomaterials Based Sensors for Air Pollution Control
375
may cause secondary pollution like ground-level smog and/or acid rain. The threshold limit value has been set at 3 ppm over 10 h a day for nitrogen dioxide exposure.
The pristine CNT networks without any chemical functionalization might be used
as gas sensor with improved performances. For example, bare SWNT drop-cast onto
interdigitated electrodes (Li et al. 2003) or CNT film deposited on platinum–substrate (Santucci et al. 2003) was reported for the detection of nitrogen dioxide with
low detection limit. The single crystalline particles were only slightly aggregated and
directly used for thick film sensor deposition. The tin dioxide nanoparticle synthesized by flame spray pyrolysis followed by drop coating film responded well to both
reducing gases like propanal and oxidizing gases like nitrogen dioxide (Sahm et al.
2004). The zinc oxide nanorod was highly responsive to nitrogen dioxide gas with
short response and recovery time having a detection limit of 10 ppb at 250
C
(Oh et al. 2009). The high sensitivities to low nitrogen dioxide levels together with
fast response times were observed for both tin dioxide and indium oxide materials
over that of the tungsten trioxide (Starke et al. 2002). The tin dioxide nanowires were
reported to show higher sensitivity for nitrogen dioxide gas compared to tin dioxide
powder-based thin films, tin dioxide coating on carbon nanotubes, or single/multiple
tin dioxide nanobelts (Choi et al. 2008). The sensitivity of the tube-like zinc oxide
toward nitrogen dioxide gas was much higher with shorter response time than that of
the flower-like zinc oxide gas sensor (Chen et al. 2011). The details of sensing
characteristics as well as sensing parameters were optimized for the three nitrogen
oxides: nitrogen dioxide, nitric oxide, and nitrous oxide by using zinc oxide, indium
oxide, and tungsten trioxide nanowire receptor (Rout et al. 2006a). All-graphene
sensor consisting the material in both sensor electrodes and active sensing area was
exhibited selective and reversible responses to nitrogen dioxide at room temperature
under high humidity conditions as well as bending strain (Kim et al. 2015). The
graphene oxide-based resistive sensor reported low-concentration nitrogen dioxide
and ammonia gases in air flow at room temperature (Lu et al. 2009). The ozonetreated graphene sensor was demonstrated to show better sensing performances such
as percentage response, detection limit, and response time for extremely low ppb
nitrogen dioxide gas concentrations over that of the pristine graphene (Chung et al.
2012). The standard sensing plot as well as correlation between percentage response
and concentrations is shown in Fig. 10.19. The nanocomposite films of tungsten
films impregnated with CNT showed sensitivity to 500 ppb nitrogen dioxide under
ambient conditions (Bittencourt et al. 2006). The poly(ethylene imine)-coated
SNWT nanocomposite was introduced as good nitrogen dioxide sensor with the
lowest detection limit of 100 ppt (Qi et al. 2003). The SWCNT decorated with metal
nanoparticles such as platinum, palladium, gold, silver, etc. has shown unique and
improved sensing characteristics for nitric oxide gas in the atmosphere over the bare
SWNT networks (Kauffman and Star 2007). The drop-cast CNT–tin dioxide
nanocomposite onto a cylindrical ceramic tube at internal heating temperature of
300
C reported cross sensitivity to nitric acid gas concentrations between 2 and
50 ppm (Liang et al. 2004). The highest response to nitrogen dioxide was observed
by zinc oxide–tin dioxide nanocomposite with 1:1 zinc and tin molar ratio via
10 Nanomaterials Based Sensors for Air Pollution Control
375