chemical sensor, various chemical receptors, the heart of the sensor, have been
employed like metal and metal oxide semiconductors, solid electrolytes, insulators,
catalytic materials, polymers, composites, etc. Among those, exploring the present
state-of-the-art nanomaterials used as receptor in chemical sensors to detect the
pollutants in the air is our primary goal. The semiconducting metal oxides have
been extensively used for this purpose, and some of those are commercialized as
well. Recently, the conjugated polymers have been tried to explore as better choice
for chemical receptor in sensor. However, the inorganic semiconductors as well as
conjugated polymers as receptor for chemical analytes are strongly associated with
inherent common serious problems like poor response, poor selectivity, incomplete
recovery, higher response and recovery time, low performances, etc. (Adhikari and
Kar 2010; Kar et al. 2015). Some of those problems could be easily addressed by
simply using the nano-dimensional inorganic semiconductor or conjugated polymers. Moreover, the use of nanohybrids would also open up a new dimension in the
field as nanohybrid combination of properties of different materials is possible with
keeping properties of nano-dimensional materials.
10.2 Nanomaterials as Receptor for Air Pollutants
The recent development has been directed toward the nanomaterials-based technology as it is well established that the properties of materials change as their size
approaches the nanoscale and as the percentage of atoms at the surface of the
material becomes significant. The nanomaterials are defined as the materials having
one of the dimensions is of the order of a nanometer (10
À9 miter) and more precisely
it should be less than 100 nm. Many important chemical and physical properties of
the materials are directly governed by surface area and surface properties, and
therefore in nanomaterials the dramatic changes of properties are observed due to
having a large surface area for a given volume, i.e., high aspect ratios. In general,
these materials classified by their geometries are broadly divided into four classes:
zero-dimensional, one-dimensional, two-dimensional, and three-dimensional
nanomaterials (Thostenson et al. 2005). The details on classification and their
examples are given elsewhere. Various chemical receptors in bulk form or in
nanoscale have been employed like metal and metal oxide semiconductors, solid
electrolytes, insulators, catalytic materials, polymers, composites, etc. However, the
sensing response is distinct and significantly improved in the nano-dimensional
materials. For example, the sensing response of hierarchical zinc oxide nanostructured was improved to 59% from 47% observed for micro rods toward 50–200 ppm
ethanol at operating temperature of 325
C (Das et al. 2016). Moreover, according to
our scope of discussion, only the nanomaterials or hybrid nanomaterials have been
considered here.
The nanomaterials are a generic name given to a vast number of materials, which
can have the wide properties and wide applications. These nanomaterials exist in
countless numbers because not all the nanomaterials should be used as a receptor for
10 Nanomaterials Based Sensors for Air Pollution Control
353
employed like metal and metal oxide semiconductors, solid electrolytes, insulators,
catalytic materials, polymers, composites, etc. Among those, exploring the present
state-of-the-art nanomaterials used as receptor in chemical sensors to detect the
pollutants in the air is our primary goal. The semiconducting metal oxides have
been extensively used for this purpose, and some of those are commercialized as
well. Recently, the conjugated polymers have been tried to explore as better choice
for chemical receptor in sensor. However, the inorganic semiconductors as well as
conjugated polymers as receptor for chemical analytes are strongly associated with
inherent common serious problems like poor response, poor selectivity, incomplete
recovery, higher response and recovery time, low performances, etc. (Adhikari and
Kar 2010; Kar et al. 2015). Some of those problems could be easily addressed by
simply using the nano-dimensional inorganic semiconductor or conjugated polymers. Moreover, the use of nanohybrids would also open up a new dimension in the
field as nanohybrid combination of properties of different materials is possible with
keeping properties of nano-dimensional materials.
10.2 Nanomaterials as Receptor for Air Pollutants
The recent development has been directed toward the nanomaterials-based technology as it is well established that the properties of materials change as their size
approaches the nanoscale and as the percentage of atoms at the surface of the
material becomes significant. The nanomaterials are defined as the materials having
one of the dimensions is of the order of a nanometer (10
À9 miter) and more precisely
it should be less than 100 nm. Many important chemical and physical properties of
the materials are directly governed by surface area and surface properties, and
therefore in nanomaterials the dramatic changes of properties are observed due to
having a large surface area for a given volume, i.e., high aspect ratios. In general,
these materials classified by their geometries are broadly divided into four classes:
zero-dimensional, one-dimensional, two-dimensional, and three-dimensional
nanomaterials (Thostenson et al. 2005). The details on classification and their
examples are given elsewhere. Various chemical receptors in bulk form or in
nanoscale have been employed like metal and metal oxide semiconductors, solid
electrolytes, insulators, catalytic materials, polymers, composites, etc. However, the
sensing response is distinct and significantly improved in the nano-dimensional
materials. For example, the sensing response of hierarchical zinc oxide nanostructured was improved to 59% from 47% observed for micro rods toward 50–200 ppm
ethanol at operating temperature of 325
C (Das et al. 2016). Moreover, according to
our scope of discussion, only the nanomaterials or hybrid nanomaterials have been
considered here.
The nanomaterials are a generic name given to a vast number of materials, which
can have the wide properties and wide applications. These nanomaterials exist in
countless numbers because not all the nanomaterials should be used as a receptor for
10 Nanomaterials Based Sensors for Air Pollution Control
353