two co-existing semiconductors materials (Ag 2 O/Bi 2 WO 6 , CdS/TiO 2 )
(Bessekhouad et al. 2004; Cao et al. 2011; Chen et al. 2012; Khan et al. 2012; Li
et al. 2012; Liu et al. 2012; Nasr et al. 1997; Shi et al. 2012; Wang et al. 2012; Yu
et al. 2012). To be effective, both type of catalysts is associated with two difference
semiconducting materials to create the heterojunction which provides unprecedented
capability of light absorption and charge separation. Both type-I and type-II proven
to be effective and it has been mere choice of type while choosing the environmental
materials. In this section, we have given general overview of technology, degradation mechanism and factor influencing catalytic activity.
7.1.2.1 The Contaminants of Domestic Water
The industrial waste containing many type of contaminants including biological,
chemical and physical materials. Within the scope of the present work, chemical
contaminants in water remediation is analyzed. Chemical contaminants can be
organic and inorganic type chemicals with micro or macro size. As by the definition,
water remediation method should completely mineralize the organic impurities
without any side-product toxins. The purification process is essentially convert the
toxic chemicals in to the less toxic ones. Organic contaminants are synthetic
compounds namely 1. Dyes: dyes are colorful materials often released by textile
industry e.g. rhodamine B, congo red, methylene blue and methylene blue. The dyes
are homogenous impurities and major cause of the water pollution, 2. Aliphatic
compounds: They are often come from side product in mass production of chemicals
e.g. carbon tetrachloride, chloroform, bromoform and glycolic acid. Aromatic compounds are inevitable in industry often found in the plastic and emulsion industries
as solvent and reactant. The major aromatic compounds are 2,4-dichlorophenol,
toluene, 4-nitrophenol, chlorobenzene and benzoic acid. The aromatic compounds
are miscible or partially miscible with water. But aromatic compounds have very
good affinity towards the catalytic surfaces due to anchoring group and hence the
heterogenous catalyst is effective. Other very common form water pollutants are
pesticides parathion, dicarzol, diuron, alachlor, trichlorfon and turbophos. Since
most of the second world countries are depend on agriculture, the mass scale
pollution is raised from the pesticides. There is other type of contaminants which
can contribute less towards water pollution such as drugs (e.g paracetamol,
proguanil, chloromycetin and explosives (tear gas chloropicrin). As per the catalytic
theory, the contaminants adsorbed on the active surface of the catalyst. The contaminants form elastic bond with the surface of the catalyst through the anchoring groups
(e.g –OH group of the phenol anchor with the catalyst through co-ordinate bond).
The contaminants may photodegrade at the surface of the photocatalyst where
critical bonds are broken and the catalyst become less toxic.
200
J. Nimita Jebaranjitham et al.
(Bessekhouad et al. 2004; Cao et al. 2011; Chen et al. 2012; Khan et al. 2012; Li
et al. 2012; Liu et al. 2012; Nasr et al. 1997; Shi et al. 2012; Wang et al. 2012; Yu
et al. 2012). To be effective, both type of catalysts is associated with two difference
semiconducting materials to create the heterojunction which provides unprecedented
capability of light absorption and charge separation. Both type-I and type-II proven
to be effective and it has been mere choice of type while choosing the environmental
materials. In this section, we have given general overview of technology, degradation mechanism and factor influencing catalytic activity.
7.1.2.1 The Contaminants of Domestic Water
The industrial waste containing many type of contaminants including biological,
chemical and physical materials. Within the scope of the present work, chemical
contaminants in water remediation is analyzed. Chemical contaminants can be
organic and inorganic type chemicals with micro or macro size. As by the definition,
water remediation method should completely mineralize the organic impurities
without any side-product toxins. The purification process is essentially convert the
toxic chemicals in to the less toxic ones. Organic contaminants are synthetic
compounds namely 1. Dyes: dyes are colorful materials often released by textile
industry e.g. rhodamine B, congo red, methylene blue and methylene blue. The dyes
are homogenous impurities and major cause of the water pollution, 2. Aliphatic
compounds: They are often come from side product in mass production of chemicals
e.g. carbon tetrachloride, chloroform, bromoform and glycolic acid. Aromatic compounds are inevitable in industry often found in the plastic and emulsion industries
as solvent and reactant. The major aromatic compounds are 2,4-dichlorophenol,
toluene, 4-nitrophenol, chlorobenzene and benzoic acid. The aromatic compounds
are miscible or partially miscible with water. But aromatic compounds have very
good affinity towards the catalytic surfaces due to anchoring group and hence the
heterogenous catalyst is effective. Other very common form water pollutants are
pesticides parathion, dicarzol, diuron, alachlor, trichlorfon and turbophos. Since
most of the second world countries are depend on agriculture, the mass scale
pollution is raised from the pesticides. There is other type of contaminants which
can contribute less towards water pollution such as drugs (e.g paracetamol,
proguanil, chloromycetin and explosives (tear gas chloropicrin). As per the catalytic
theory, the contaminants adsorbed on the active surface of the catalyst. The contaminants form elastic bond with the surface of the catalyst through the anchoring groups
(e.g –OH group of the phenol anchor with the catalyst through co-ordinate bond).
The contaminants may photodegrade at the surface of the photocatalyst where
critical bonds are broken and the catalyst become less toxic.
200
J. Nimita Jebaranjitham et al.