that the stability of the sensor was increased with increasing silicon dioxide content
(Su and Tsai 2004). As reported by the authors, the humidity sensing performance of
chemically reduced graphene oxide–poly(diallyldimethylammonium chloride)
nanocomposite film was superior over the other reported graphene-based humidity
sensor (Zhang et al. 2014a, b). Zinc oxide nanorods and nanowires were reported to
have high sensitivity, good long-term stability, and fast response time to a moisture
pulse of 97% relative humidity (Zhang et al. 2005). Similarly, high-density singlecrystalline zinc oxide nanowires on patterned gallium–silicon dioxide–silicon template electrodes were reported for the sensing of humidity by measuring current–
voltage characteristics of the fabricated device at 80
C (Chang et al. 2010). The
humidity sensing response including linearity, hysteresis, response–recovery time,
and stability of the titania-loaded mesoporous silica nanocomposite sensor was
reported for humid range of 11–98% room humidity at 25
C (Tomer and Duhan
2015).
10.5.7 Ammonia
The ammonia contamination in the air caused mainly by high agricultural activity;
natural waste product of livestock; industrial manufacturing of basic chemicals,
metals, textiles, and paper products; automotive emissions; etc. adversely affects
human as well as environmental health. High levels of ammonia vapor contamination can result the effects like eye irritation and respiratory tracts of animals, negative
impact on wildlife, livestock, and decrease in agricultural productivity (Timmer et al.
2005; Eerden et al. 1998). The threshold limit value has been set at 25 ppm over 10 h
a day for exposure of ammonia vapors.
The irreversible response was reported for ammonia sensor using bare SWNT
(Quang et al. 2006). The operating temperature of tungsten trioxide sensors for
ammonia was decreased down to 150
C by using tungsten trioxide films impregnated with CNT (Bittencourt et al. 2006). The operating temperature was further
decreased down to room temperature for ammonia sensing with detection limit to
10 ppm by using SWNT–tin dioxide nanocomposite (Hoa et al. 2007). The ammonia
sensor was developed using nanocomposite of functionalized SWNT with the polymers like poly(m-aminobenzene sulfonic acid) (Bekyarova et al. 2004) or poly
(methyl methacrylate) (Li et al. 2007). The ammonia sensor was developed using
p–n heterojunction of polyaniline coated on electrospun titanium dioxide fiber,
which was 1000 times more sensitive than the best polyaniline sensor for gas
(Gong et al. 2010). The polyaniline nanowires deposited on gold electrodes showed
a rapid and reversible resistance change upon exposure to ammonia gas even at low
concentrations of 0.5 ppm. The oriented single-wire geometry was explained as the
reason for instant response and complete recovery by easy adsorption/desorption of
gas (Liu et al. 2004). In another study, the effect of polymerization temperature on
the gas response of polyaniline–titanium dioxide nanocomposite thin film deposited
on a silicon substrate with gold interdigital electrodes was investigated for ammonia
10 Nanomaterials Based Sensors for Air Pollution Control
387
(Su and Tsai 2004). As reported by the authors, the humidity sensing performance of
chemically reduced graphene oxide–poly(diallyldimethylammonium chloride)
nanocomposite film was superior over the other reported graphene-based humidity
sensor (Zhang et al. 2014a, b). Zinc oxide nanorods and nanowires were reported to
have high sensitivity, good long-term stability, and fast response time to a moisture
pulse of 97% relative humidity (Zhang et al. 2005). Similarly, high-density singlecrystalline zinc oxide nanowires on patterned gallium–silicon dioxide–silicon template electrodes were reported for the sensing of humidity by measuring current–
voltage characteristics of the fabricated device at 80
C (Chang et al. 2010). The
humidity sensing response including linearity, hysteresis, response–recovery time,
and stability of the titania-loaded mesoporous silica nanocomposite sensor was
reported for humid range of 11–98% room humidity at 25
C (Tomer and Duhan
2015).
10.5.7 Ammonia
The ammonia contamination in the air caused mainly by high agricultural activity;
natural waste product of livestock; industrial manufacturing of basic chemicals,
metals, textiles, and paper products; automotive emissions; etc. adversely affects
human as well as environmental health. High levels of ammonia vapor contamination can result the effects like eye irritation and respiratory tracts of animals, negative
impact on wildlife, livestock, and decrease in agricultural productivity (Timmer et al.
2005; Eerden et al. 1998). The threshold limit value has been set at 25 ppm over 10 h
a day for exposure of ammonia vapors.
The irreversible response was reported for ammonia sensor using bare SWNT
(Quang et al. 2006). The operating temperature of tungsten trioxide sensors for
ammonia was decreased down to 150
C by using tungsten trioxide films impregnated with CNT (Bittencourt et al. 2006). The operating temperature was further
decreased down to room temperature for ammonia sensing with detection limit to
10 ppm by using SWNT–tin dioxide nanocomposite (Hoa et al. 2007). The ammonia
sensor was developed using nanocomposite of functionalized SWNT with the polymers like poly(m-aminobenzene sulfonic acid) (Bekyarova et al. 2004) or poly
(methyl methacrylate) (Li et al. 2007). The ammonia sensor was developed using
p–n heterojunction of polyaniline coated on electrospun titanium dioxide fiber,
which was 1000 times more sensitive than the best polyaniline sensor for gas
(Gong et al. 2010). The polyaniline nanowires deposited on gold electrodes showed
a rapid and reversible resistance change upon exposure to ammonia gas even at low
concentrations of 0.5 ppm. The oriented single-wire geometry was explained as the
reason for instant response and complete recovery by easy adsorption/desorption of
gas (Liu et al. 2004). In another study, the effect of polymerization temperature on
the gas response of polyaniline–titanium dioxide nanocomposite thin film deposited
on a silicon substrate with gold interdigital electrodes was investigated for ammonia
10 Nanomaterials Based Sensors for Air Pollution Control
387