mostly suited for the degradation of water/wastewater containing low concentrations
of pollutants (Schneider et al. 2014). For water/wastewater purification, the oxidizing radicals can degrade the pollutants by reduction and oxidation reactions
(Friedmann et al. 2010). The inherent electronic band structure of semiconductors
is mostly characterized by its valence band (VB), conduction band (CB), band-gap
energy, and Fermi level (Sze 2008). The VB is formed by the interactions of the
highest occupied molecular orbital, while the CB is formed by the interactions of the
lowest unoccupied molecular orbital. The band gap is the energy difference between
the conduction band minimum (CBM) and the valence band maximum (VBM). The
band structure is very important as it determines the redox ability and visible lightdriven activity of semiconductor-based photocatalyst materials.
1.2.1 Basic Principles and Mechanism for Photocatalytic
Pollutant Removal
A typical photocatalytic system comprises of two components: a catalytically active
site and light-harvesting center to aid the pollutant degradation process (Gao et al.
2017). To enhance the activity of both components, their interactions that depend on
the charge kinetics upon photoexcitation and behaviors in a photocatalytic system are
of significant interest. The light-harvesting center in a heterogeneous photocatalytic
system is mostly a semiconductor. The series of reductive and oxidative reactions that
occur during the photocatalytic process has been widely proposed.
Under properly simulated light irradiation with photon energy greater than or
equal to the semiconductor band-gap energy, electrons (e
À ) and holes (h
+
) are
generated as shown in Eq. (1.1) and Fig. 1.1.
Fig. 1.1 Photodegradation mechanism of organic pollutants in water resources
4
F. Opoku et al.
of pollutants (Schneider et al. 2014). For water/wastewater purification, the oxidizing radicals can degrade the pollutants by reduction and oxidation reactions
(Friedmann et al. 2010). The inherent electronic band structure of semiconductors
is mostly characterized by its valence band (VB), conduction band (CB), band-gap
energy, and Fermi level (Sze 2008). The VB is formed by the interactions of the
highest occupied molecular orbital, while the CB is formed by the interactions of the
lowest unoccupied molecular orbital. The band gap is the energy difference between
the conduction band minimum (CBM) and the valence band maximum (VBM). The
band structure is very important as it determines the redox ability and visible lightdriven activity of semiconductor-based photocatalyst materials.
1.2.1 Basic Principles and Mechanism for Photocatalytic
Pollutant Removal
A typical photocatalytic system comprises of two components: a catalytically active
site and light-harvesting center to aid the pollutant degradation process (Gao et al.
2017). To enhance the activity of both components, their interactions that depend on
the charge kinetics upon photoexcitation and behaviors in a photocatalytic system are
of significant interest. The light-harvesting center in a heterogeneous photocatalytic
system is mostly a semiconductor. The series of reductive and oxidative reactions that
occur during the photocatalytic process has been widely proposed.
Under properly simulated light irradiation with photon energy greater than or
equal to the semiconductor band-gap energy, electrons (e
À ) and holes (h
+
) are
generated as shown in Eq. (1.1) and Fig. 1.1.
Fig. 1.1 Photodegradation mechanism of organic pollutants in water resources
4
F. Opoku et al.