2015). Moreover, the agglomeration of nanostructured particles and the low specific
surface area not only increases the diffusion barriers of the reagents but also
decreases the surface oxidation and reduction kinetics, which reduces the
photocatalytic performance. Thus, several factors, such as surface reaction kinetics,
charge carrier kinetics, diffusion, and adsorption, are kinetically significant in
designing highly efficient photocatalyst materials.
1.3 Factors Controlling Photocatalytic Pollutant Removal
A major concern with the heterogeneous photocatalytic process for organic synthesis
by oxidation is the highly oxidizing environment and non-selectivity, with products
being lost due to complete mineralization. Although semiconductor photocatalysts
have potential applications, they still have unwanted disadvantages, such as the wide
band gap that limits wider use of solar energy, large interfacial area that induces slow
charge carrier migration, nanoscale features, and single phase that causes fast recombination of photogenerated charge carriers. Their effectiveness to the photocatalytic
reaction is influenced by factors (Friedmann et al. 2016), such as the excitation of
charge carriers from the bulk to the surface, as well as the separation/recombination of
charge carriers that occurs in the bulk or at the surface. Besides the band structures and
diffusion kinetics, other factors, such as surface properties, crystallinity, morphological architecture, and material choice, must be considered when designing stable and
efficient visible light-driven photocatalytic materials (Mori and Yamashita 2010).
Thus, choosing the right semiconductor is quite significant, because it determines
the visible light photocatalytic performance (Yan et al. 2014). Moreover, the right
morphological architecture between the redox reaction center and the photogenerated
charge carriers junction can effectively enhance the separation and migration of charge
carrier (Yan et al. 2014). The high degree of crystallinity with crystal defects will
minimize the recombination rate at the interface, thereby enhancing the efficiency of
the photoinduced charge carriers to partake in the redox reaction (Gu et al. 2014). The
surface area, which relies on the geometrical shape and porosity of the photocatalysts,
influences the photocatalytic performance (Zhu et al. 2010). The adsorption capacity
of the semiconductor photocatalysts toward pollutant degradation increases if there are
more atoms present on the surface. The absence of well-designed porous
interconnected network assembly at larger length scales may unfavorably affect the
overall photocatalytic performance.
1.4 Characterization of Nanomaterials
To show the behavior of charge carriers in the photocatalytic material, it is vital to
analyze the charge kinetic via several characterization techniques with emphasis on
spectroscopic techniques. Currently, several characterization techniques have been
1 Nanotechnology for Water and Wastewater Treatment Using Graphene. . .
7
surface area not only increases the diffusion barriers of the reagents but also
decreases the surface oxidation and reduction kinetics, which reduces the
photocatalytic performance. Thus, several factors, such as surface reaction kinetics,
charge carrier kinetics, diffusion, and adsorption, are kinetically significant in
designing highly efficient photocatalyst materials.
1.3 Factors Controlling Photocatalytic Pollutant Removal
A major concern with the heterogeneous photocatalytic process for organic synthesis
by oxidation is the highly oxidizing environment and non-selectivity, with products
being lost due to complete mineralization. Although semiconductor photocatalysts
have potential applications, they still have unwanted disadvantages, such as the wide
band gap that limits wider use of solar energy, large interfacial area that induces slow
charge carrier migration, nanoscale features, and single phase that causes fast recombination of photogenerated charge carriers. Their effectiveness to the photocatalytic
reaction is influenced by factors (Friedmann et al. 2016), such as the excitation of
charge carriers from the bulk to the surface, as well as the separation/recombination of
charge carriers that occurs in the bulk or at the surface. Besides the band structures and
diffusion kinetics, other factors, such as surface properties, crystallinity, morphological architecture, and material choice, must be considered when designing stable and
efficient visible light-driven photocatalytic materials (Mori and Yamashita 2010).
Thus, choosing the right semiconductor is quite significant, because it determines
the visible light photocatalytic performance (Yan et al. 2014). Moreover, the right
morphological architecture between the redox reaction center and the photogenerated
charge carriers junction can effectively enhance the separation and migration of charge
carrier (Yan et al. 2014). The high degree of crystallinity with crystal defects will
minimize the recombination rate at the interface, thereby enhancing the efficiency of
the photoinduced charge carriers to partake in the redox reaction (Gu et al. 2014). The
surface area, which relies on the geometrical shape and porosity of the photocatalysts,
influences the photocatalytic performance (Zhu et al. 2010). The adsorption capacity
of the semiconductor photocatalysts toward pollutant degradation increases if there are
more atoms present on the surface. The absence of well-designed porous
interconnected network assembly at larger length scales may unfavorably affect the
overall photocatalytic performance.
1.4 Characterization of Nanomaterials
To show the behavior of charge carriers in the photocatalytic material, it is vital to
analyze the charge kinetic via several characterization techniques with emphasis on
spectroscopic techniques. Currently, several characterization techniques have been
1 Nanotechnology for Water and Wastewater Treatment Using Graphene. . .
7