Thus, the present chapter addresses different aspects of semiconductor
photocatalysis for microbial destruction. In this regard, the photocatalytic mechanism behind microbial destruction, their various experimental models, the influencing factors determining the efficiency of disinfection and an overview of most
widely explored semiconductors are discussed.
2.2 Semiconductor Photocatalysis
Semiconductor based photocatalysis have attracted considerable attention from
different researchers as the process can be employed in different fields such as
bioremediation, disinfection, energy conversion and energy storage.
The basic mechanism behind photocatalysis is discussed as follows. When a
Semiconductor is irradiated with light having energy higher than the band gap of the
material, electrons (e
À
) and holes (h
+
) are generated in the conduction band and
valence band, respectively. These photogenerated charge carriers can migrate to the
surface of the semiconductor and participate in the redox reactions. The
photogenerated holes possess high oxidizing power and thus can lead to the formation of reactive oxygen species (ROS) such as OH
. , O 2
., HO 2
. , where OH
. is
primarily known to be the most responsible species for the disinfection of bacteria
and related pathogens (Laxma Reddy et al. 2017). The schematic representation of a
Semiconductor based photocatalytic process explaining the mechanism of charge
carrier generation is shown in Fig. 2.1. The reactions involved in Semiconductor
based photocatalysis are represented in Eqs. 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, and 2.8
given below (Gong et al. 2019):
TiO 2 þ hν → e
2 CB
ð Þþh
þ VB
ð Þ
ð2:1Þ
h
þ VB
ð ÞþH 2 O ad
ð Þ→ TiO 2 þ OH: ad
ð Þ þ H
ð2:2Þ
h
þ VB
ð ÞþOH ad
ð Þ→ TiO 2 þ OH:
ð2:3Þ
Fig. 2.1 Basic mechanism
of semiconductor based
photocatalytic disinfection
process. A is the electron
acceptor and D is the
electron donor in the
electrolyte. CB Conduction
band, VB valence band
2 Photo-Assisted Antimicrobial Activity of Transition Metal Oxides
31
photocatalysis for microbial destruction. In this regard, the photocatalytic mechanism behind microbial destruction, their various experimental models, the influencing factors determining the efficiency of disinfection and an overview of most
widely explored semiconductors are discussed.
2.2 Semiconductor Photocatalysis
Semiconductor based photocatalysis have attracted considerable attention from
different researchers as the process can be employed in different fields such as
bioremediation, disinfection, energy conversion and energy storage.
The basic mechanism behind photocatalysis is discussed as follows. When a
Semiconductor is irradiated with light having energy higher than the band gap of the
material, electrons (e
À
) and holes (h
+
) are generated in the conduction band and
valence band, respectively. These photogenerated charge carriers can migrate to the
surface of the semiconductor and participate in the redox reactions. The
photogenerated holes possess high oxidizing power and thus can lead to the formation of reactive oxygen species (ROS) such as OH
. , O 2
., HO 2
. , where OH
. is
primarily known to be the most responsible species for the disinfection of bacteria
and related pathogens (Laxma Reddy et al. 2017). The schematic representation of a
Semiconductor based photocatalytic process explaining the mechanism of charge
carrier generation is shown in Fig. 2.1. The reactions involved in Semiconductor
based photocatalysis are represented in Eqs. 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, and 2.8
given below (Gong et al. 2019):
TiO 2 þ hν → e
2 CB
ð Þþh
þ VB
ð Þ
ð2:1Þ
h
þ VB
ð ÞþH 2 O ad
ð Þ→ TiO 2 þ OH: ad
ð Þ þ H
ð2:2Þ
h
þ VB
ð ÞþOH ad
ð Þ→ TiO 2 þ OH:
ð2:3Þ
Fig. 2.1 Basic mechanism
of semiconductor based
photocatalytic disinfection
process. A is the electron
acceptor and D is the
electron donor in the
electrolyte. CB Conduction
band, VB valence band
2 Photo-Assisted Antimicrobial Activity of Transition Metal Oxides
31