physical characteristics (Zhu et al. 2009). Another important material, which is SnS 2 ,
is oxidatively more stable as compared with CdS, and Li et al. have demonstrated
that SnS 2 exhibits much improved photocatalytic performance than CdS under
visible light (Li et al. 2012).
Most of the abovementioned metal-based semiconductor photocatalysts are either
functional in limited light window or non-economic, which confines their long-term
and commercial applications. A metal-free and economic photocatalyst, i.e., graphitic carbon nitride (g-C 3 N 4 ), overcomes the above limitations associated with
metal-based photocatalysts (Shi et al. 2018). In recent times, the use of graphitic
carbon nitride,g-C 3 N 4 has been extended to reduce CO 2 . Photocatalytic degradation
of organic pollutants, such as dyes and heavy metal ions, has revealed that graphitic
carbon nitride is an emerging photocatalyst for environmental remediation. As
mentioned above, inorganic nanoparticles have been extensively investigated as
sorbents or catalysts for the treatment of wastewater. Individual inorganic
nanoparticles still cannot fulfill all the unambiguous requirements needed for environmental remediation. These limitations can be overcome by functionalization of
such inorganic nanoparticles with functional organic polymers by forming core–
shell nanocomposite materials. Furthermore, such modifications can also prevent the
aggregation of nanoparticles and enhance the adsorption properties by stabilizing
their uniform dispersion (Shin and Jang 2007). The most significant benefit of
inorganic nanoparticles is their high capacity of adsorption owing to their large
surface area. However, selective adsorption of some pollutants cannot be achieved
using these pure nanomaterials in practical applications. This issue not only
decreases the efficiency of adsorption but also influences the recyclability of materials. Scientists have investigated that these issues can be handled via surface
modification of nanomaterials with functional groups such as protonic acids or
bases through van der Waals or electrostatic interactions. For example, the aminofunctionalized nanomaterials demonstrate outstanding capacity for the removal of
toxic metallic species from polluted water due to labile protonation in acidic
environment. Likewise, nanomaterials modified with carboxylate moieties were
extensively used to capture cationic pollutant via complexation (Fresnais et al.
2013). Another approach to achieve selective adsorption is to functionalize inorganic
nanoparticles with molecular imprinted polymers. Molecular imprinted polymers
have been employed for molecular recognition purpose in several fields, such as
solid-phase extraction, membrane separation, chromatograph separation, drug delivery, sensors, and catalysis (Vallano and Remcho 2000). Surface-imprinted inorganic
nanomaterials not only function as excellent selective adsorbent but also overcome
few disadvantages, such as the comparatively less unit volume identification sites of
the matrix-embedded polymer. Molecular imprinted polymer-modified silica and
carbon-based materials have been used for the removal of toxic metallic species and
synthetic dyes from wastewater (Liu et al. 2014). The nanocomposites of other
unique properties having inorganic nanoparticles prove to be more practical. For
instance, magnetic nanoparticles and molecular imprinted polymer composite can be
magnetically separated after use. There are several advanced techniques used to
control their structure and enlarge their specific surface area, consequently
672
B. Akram et al.
is oxidatively more stable as compared with CdS, and Li et al. have demonstrated
that SnS 2 exhibits much improved photocatalytic performance than CdS under
visible light (Li et al. 2012).
Most of the abovementioned metal-based semiconductor photocatalysts are either
functional in limited light window or non-economic, which confines their long-term
and commercial applications. A metal-free and economic photocatalyst, i.e., graphitic carbon nitride (g-C 3 N 4 ), overcomes the above limitations associated with
metal-based photocatalysts (Shi et al. 2018). In recent times, the use of graphitic
carbon nitride,g-C 3 N 4 has been extended to reduce CO 2 . Photocatalytic degradation
of organic pollutants, such as dyes and heavy metal ions, has revealed that graphitic
carbon nitride is an emerging photocatalyst for environmental remediation. As
mentioned above, inorganic nanoparticles have been extensively investigated as
sorbents or catalysts for the treatment of wastewater. Individual inorganic
nanoparticles still cannot fulfill all the unambiguous requirements needed for environmental remediation. These limitations can be overcome by functionalization of
such inorganic nanoparticles with functional organic polymers by forming core–
shell nanocomposite materials. Furthermore, such modifications can also prevent the
aggregation of nanoparticles and enhance the adsorption properties by stabilizing
their uniform dispersion (Shin and Jang 2007). The most significant benefit of
inorganic nanoparticles is their high capacity of adsorption owing to their large
surface area. However, selective adsorption of some pollutants cannot be achieved
using these pure nanomaterials in practical applications. This issue not only
decreases the efficiency of adsorption but also influences the recyclability of materials. Scientists have investigated that these issues can be handled via surface
modification of nanomaterials with functional groups such as protonic acids or
bases through van der Waals or electrostatic interactions. For example, the aminofunctionalized nanomaterials demonstrate outstanding capacity for the removal of
toxic metallic species from polluted water due to labile protonation in acidic
environment. Likewise, nanomaterials modified with carboxylate moieties were
extensively used to capture cationic pollutant via complexation (Fresnais et al.
2013). Another approach to achieve selective adsorption is to functionalize inorganic
nanoparticles with molecular imprinted polymers. Molecular imprinted polymers
have been employed for molecular recognition purpose in several fields, such as
solid-phase extraction, membrane separation, chromatograph separation, drug delivery, sensors, and catalysis (Vallano and Remcho 2000). Surface-imprinted inorganic
nanomaterials not only function as excellent selective adsorbent but also overcome
few disadvantages, such as the comparatively less unit volume identification sites of
the matrix-embedded polymer. Molecular imprinted polymer-modified silica and
carbon-based materials have been used for the removal of toxic metallic species and
synthetic dyes from wastewater (Liu et al. 2014). The nanocomposites of other
unique properties having inorganic nanoparticles prove to be more practical. For
instance, magnetic nanoparticles and molecular imprinted polymer composite can be
magnetically separated after use. There are several advanced techniques used to
control their structure and enlarge their specific surface area, consequently
672
B. Akram et al.