was designed to decolorization of a synthetic (methylene blue-contained) wastewater
and an actual (reactive purple-contained) dye wastewater. A pump was used to
circulate the water on the 15
tiled TiO 2 -coated substrates, i.e., glass, ceramic tile,
and stainless steel sheets (Sirirerkratana et al. 2019). Two reactors – a batch
reactor and a continuous reactor – were designed for degradation of acid violet
7 dye (AV7) using ZnO/polypyrrole powder photocatalysts. In the batch reactor, the
powder photocatalysts were fixed on a rectangular glass plate, and the fixed glass
was immersed in the dye solution. In a continuous annular reactor, the powders were
supported on the inner wall of an external quartz ring that covered a UV lamp quartz
tube (González-Casamachin et al. 2019).
1.7 Conclusions
Photocatalysis is a process which a chemical reaction is accelerated in the presence
of a catalyst on exposure to light. Photocatalysis could be classified to be two types,
i.e., homogeneous and heterogeneous photocatalysis, on the basis of appearances of
the physical state of reactants. Ozonation (UV/O 3 ), photo-Fenton processes (Fe
2+
and Fe
2+ /H 2 O 2 ), UV/H 2 O 2 , and UV/H 2 O 2 /O 3 are examples of homogeneous
photocatalysis, while photocatalysts in heterogeneous photocatalysis are typically
semiconductor materials (i.e., metal oxides) which can be used in powder and
suspension forms or coated forms on other substrates. Both homogeneous and
heterogeneous photocatalytic processes have been utilized as alternative technologies for remediation of organic pollutants in water, including (i) pharmaceuticals and
personal care products (synthetic compounds with specific properties for human or
animal healthcare and medical purposes); (ii) persistent organic pollutants (organochlorine pesticides and industrial chemicals with long half-lives and persistence in
the environment); and (iii) organic dyes (synthetic organic substances for colorants).
Homogeneous photocatalysis has many advantages, e.g., high oxidation properties.
It is, however, not popular in various photocatalytic applications, because it is
difficult to separate the photocatalysts from the solution, the photocatalysts have
low potential to reuse, purification of products is necessary, and almost homogeneous photocatalysts absorb narrowly light within the solar spectrum. It has been
proven that heterogeneous photocatalysis is one of the most potential methods for
the treatment of organic pollutants in water. Anyhow, relatively large band gap
energy causes some limitations of metal oxide-based heterogeneous photocatalysts.
Modifications of the electronic band can be achieved by doping and composites of
semiconductors. Another modification technique in heterogeneous photocatalysts is
the utilization of electrical potential in photocatalysis. The coated semiconductor
photocatalysts are used as photoelectrodes in photo-electrocatalytic applications. In
addition, the photocatalytic reactor configuration for wastewater treatment by heterogeneous photocatalysis can be classified as two main groups, including fixed bed
reactor and slurry-type reactor. Apart from the conventional photocatalytic reactors,
the combination of photocatalysis with another treatment process has also been
1 Photocatalytic Remediation of Organic Pollutants in Water
39
and an actual (reactive purple-contained) dye wastewater. A pump was used to
circulate the water on the 15
tiled TiO 2 -coated substrates, i.e., glass, ceramic tile,
and stainless steel sheets (Sirirerkratana et al. 2019). Two reactors – a batch
reactor and a continuous reactor – were designed for degradation of acid violet
7 dye (AV7) using ZnO/polypyrrole powder photocatalysts. In the batch reactor, the
powder photocatalysts were fixed on a rectangular glass plate, and the fixed glass
was immersed in the dye solution. In a continuous annular reactor, the powders were
supported on the inner wall of an external quartz ring that covered a UV lamp quartz
tube (González-Casamachin et al. 2019).
1.7 Conclusions
Photocatalysis is a process which a chemical reaction is accelerated in the presence
of a catalyst on exposure to light. Photocatalysis could be classified to be two types,
i.e., homogeneous and heterogeneous photocatalysis, on the basis of appearances of
the physical state of reactants. Ozonation (UV/O 3 ), photo-Fenton processes (Fe
2+
and Fe
2+ /H 2 O 2 ), UV/H 2 O 2 , and UV/H 2 O 2 /O 3 are examples of homogeneous
photocatalysis, while photocatalysts in heterogeneous photocatalysis are typically
semiconductor materials (i.e., metal oxides) which can be used in powder and
suspension forms or coated forms on other substrates. Both homogeneous and
heterogeneous photocatalytic processes have been utilized as alternative technologies for remediation of organic pollutants in water, including (i) pharmaceuticals and
personal care products (synthetic compounds with specific properties for human or
animal healthcare and medical purposes); (ii) persistent organic pollutants (organochlorine pesticides and industrial chemicals with long half-lives and persistence in
the environment); and (iii) organic dyes (synthetic organic substances for colorants).
Homogeneous photocatalysis has many advantages, e.g., high oxidation properties.
It is, however, not popular in various photocatalytic applications, because it is
difficult to separate the photocatalysts from the solution, the photocatalysts have
low potential to reuse, purification of products is necessary, and almost homogeneous photocatalysts absorb narrowly light within the solar spectrum. It has been
proven that heterogeneous photocatalysis is one of the most potential methods for
the treatment of organic pollutants in water. Anyhow, relatively large band gap
energy causes some limitations of metal oxide-based heterogeneous photocatalysts.
Modifications of the electronic band can be achieved by doping and composites of
semiconductors. Another modification technique in heterogeneous photocatalysts is
the utilization of electrical potential in photocatalysis. The coated semiconductor
photocatalysts are used as photoelectrodes in photo-electrocatalytic applications. In
addition, the photocatalytic reactor configuration for wastewater treatment by heterogeneous photocatalysis can be classified as two main groups, including fixed bed
reactor and slurry-type reactor. Apart from the conventional photocatalytic reactors,
the combination of photocatalysis with another treatment process has also been
1 Photocatalytic Remediation of Organic Pollutants in Water
39