migrate to reaction sites on the surface, leading to decrease in the recombination
probability.
For formation of hydroxyl radicals and superoxide ions via redox reactions,
the oxidative reaction between holes and water molecules or other organic compounds leads to generation of HO
• and H
+ (which can further form H 2 O 2 ), while
the reductive reaction between electron and O 2 molecules leads to generation of
superoxide ions (O 2
•) (which can further form HO 2
•
, H 2 O 2 , and HO
• ) (Sirelkhatim
et al. 2015). However, this step is the surface chemical reactions, where the
photogenerated electrons and holes can recombine with each other if the active
sites for redox reactions do not exist on the surface, which depends on the surface
character and surface area.
For the last step (photodecomposition of organic compounds via reaction with
active species on the catalyst surface), radicals, ions, or molecules (HO
•
, O 2
•- , OH
À ,
and H 2 O 2 ) obtained from the reactions are key reactive oxygen species (ROS) in the
initiation of other photocatalytic reactions which can react with the target organic
compounds to degrade or otherwise convert them into harmless by-products or
value-added chemicals or fuels (Payormhorm et al. 2017a; Payormhorm et al.
2017b). Recently, several catalysts have been progressed to produce good quality
of photocatalysts like photoconversion processes such as solar to electricity, light to
hydrogen, and light to mechanical works.
1.3 Organic Pollutants in Water
There are various types of pollutants in wastewater (e.g., organic pollutants, inorganic pollutants, pathogens, and radioactive pollutants). Organic pollutants are a
main part of environmental pollution, which may cause an adverse effect on aquatic
organisms even at low levels of exposure (Mao et al. 2017; Ahmad et al. 2018; Yu
et al. 2019). Organic pollutants are found in various wastewater sources, e.g.,
domestic, industrial, and agricultural sectors.
Many kinds of organic pollutants, such as pharmaceuticals and personal care
products (PPCPs), textile, food, beverage, persistent organic pollutants (POPs),
insecticide, pesticide, oil, fertilizers, and chemical, are included in wastewater.
1.3.1 Sources of Organic Pollutants in Wastewater
Organic pollutants are found in three main wastewater sources which are domestic,
industrial, and agricultural sectors. The examples of organic pollutants in wastewater
from these three sectors are shown in Table 1.3.
12
P. Kemacheevakul and S. Chuangchote
probability.
For formation of hydroxyl radicals and superoxide ions via redox reactions,
the oxidative reaction between holes and water molecules or other organic compounds leads to generation of HO
• and H
+ (which can further form H 2 O 2 ), while
the reductive reaction between electron and O 2 molecules leads to generation of
superoxide ions (O 2
•) (which can further form HO 2
•
, H 2 O 2 , and HO
• ) (Sirelkhatim
et al. 2015). However, this step is the surface chemical reactions, where the
photogenerated electrons and holes can recombine with each other if the active
sites for redox reactions do not exist on the surface, which depends on the surface
character and surface area.
For the last step (photodecomposition of organic compounds via reaction with
active species on the catalyst surface), radicals, ions, or molecules (HO
•
, O 2
•- , OH
À ,
and H 2 O 2 ) obtained from the reactions are key reactive oxygen species (ROS) in the
initiation of other photocatalytic reactions which can react with the target organic
compounds to degrade or otherwise convert them into harmless by-products or
value-added chemicals or fuels (Payormhorm et al. 2017a; Payormhorm et al.
2017b). Recently, several catalysts have been progressed to produce good quality
of photocatalysts like photoconversion processes such as solar to electricity, light to
hydrogen, and light to mechanical works.
1.3 Organic Pollutants in Water
There are various types of pollutants in wastewater (e.g., organic pollutants, inorganic pollutants, pathogens, and radioactive pollutants). Organic pollutants are a
main part of environmental pollution, which may cause an adverse effect on aquatic
organisms even at low levels of exposure (Mao et al. 2017; Ahmad et al. 2018; Yu
et al. 2019). Organic pollutants are found in various wastewater sources, e.g.,
domestic, industrial, and agricultural sectors.
Many kinds of organic pollutants, such as pharmaceuticals and personal care
products (PPCPs), textile, food, beverage, persistent organic pollutants (POPs),
insecticide, pesticide, oil, fertilizers, and chemical, are included in wastewater.
1.3.1 Sources of Organic Pollutants in Wastewater
Organic pollutants are found in three main wastewater sources which are domestic,
industrial, and agricultural sectors. The examples of organic pollutants in wastewater
from these three sectors are shown in Table 1.3.
12
P. Kemacheevakul and S. Chuangchote