surface of the catalyst due to the excess of the protons. Similarly, low pH values have
high concentration of OH
À ions and induce the negative charge on the surface of the
catalyst. If the contaminants are charged, or Lewis base or acid, the charge on the
surface can attached or detach contaminants effectively due to electrostatic interaction. Hence the performance of the catalyst can be tuned to the maximum level by
adjusting the pH of the solution. The charge on the surface also prevent the
aggregation of the surface of the catalysts due to same charge on the surface and
hence electrostatic repulsion. The temperature is a conventional key parameter
enhance the performance of the catalyst. By increasing the temperature, the collision
between the photocatalyst and contaminant adsorbents increases which reflected in
catalyst-contaminant binding efficiency. Hence performance of the catalyst is linearly related with the temperature of the reaction. The other parameters also influence
the performance of catalyst such as shape of catalyst, nano size of photocatalyst,
morphology of the catalyst and band alignment of photocatalyst. Relating performance with those parameters are beyond the scope of the present work. In summary,
by controlling above mentioned parameters, effectiveness and efficiency of the
catalyst can be improved to desired level.
7.1.3 State of Art Materials for Water Remediation
The photocatalytic based water remediation is an exciting area and considerable
efforts put forward and numerous state of art materials were developed (Dong et al.
2015; Malato et al. 2009). The materials which can co-coordinatively bond with
more number of contaminants were found to be effective catalysis such as TiO 2 and
ZnO. Among that TiO 2 , (Fujishima and Honda 1972) is very first compound utilized
for the photocatalytic degradation and it currently fine-tuned to highest performance
(Dapeng and Jiuhui 2009; Sin et al. 2012). Along with photochemical performance,
TiO 2 gained it position by very good stability towards photons and less corrosive to
most of the chemical contaminants. Hence, TiO 2 is ideal model system for
photocatalytic water degradation and by following TiO 2 many associated catalysts
was developed. Most of the cations are the transition metals and such as Ti, Fe, Ni,
Zn, Cd, Cu, Ag and more (Ajmera et al. 2002; Bessekhouad et al. 2004;
Bessekhouad et al. 2005; Bi and Xu 2013; Choi and Hoffmann 1996; Kondo and
Jardim 1991; Liu et al. 2013; Srinivas et al. 2015; Thuy et al. 2014; Tongying et al.
2012; Wenhua et al. 2000). Since the transition metals are having partially filled
d-orbitals, high charge forming ability and have good coordinating tendency make
them good candidates for the photocatalysis process. The high charge of the
co-ordination metals (Ti
4+ , Mn
5+ ) helps the ligand molecules (adsorbents) by electrostatic attraction. The bigger size of the transition metals also provides the possibility of high coordination number and hence one metal on photocatalytic surface
can adsorb up to six molecules. High charge and high co-ordination number of
transition metals synergistically promote adsorption of the contaminants. The
anionic species in photocatalyst is mostly chalcogenide elements namely sulfide,
7 Earth Abundant Materials for Environmental Remediation and Commercialization
203
high concentration of OH
À ions and induce the negative charge on the surface of the
catalyst. If the contaminants are charged, or Lewis base or acid, the charge on the
surface can attached or detach contaminants effectively due to electrostatic interaction. Hence the performance of the catalyst can be tuned to the maximum level by
adjusting the pH of the solution. The charge on the surface also prevent the
aggregation of the surface of the catalysts due to same charge on the surface and
hence electrostatic repulsion. The temperature is a conventional key parameter
enhance the performance of the catalyst. By increasing the temperature, the collision
between the photocatalyst and contaminant adsorbents increases which reflected in
catalyst-contaminant binding efficiency. Hence performance of the catalyst is linearly related with the temperature of the reaction. The other parameters also influence
the performance of catalyst such as shape of catalyst, nano size of photocatalyst,
morphology of the catalyst and band alignment of photocatalyst. Relating performance with those parameters are beyond the scope of the present work. In summary,
by controlling above mentioned parameters, effectiveness and efficiency of the
catalyst can be improved to desired level.
7.1.3 State of Art Materials for Water Remediation
The photocatalytic based water remediation is an exciting area and considerable
efforts put forward and numerous state of art materials were developed (Dong et al.
2015; Malato et al. 2009). The materials which can co-coordinatively bond with
more number of contaminants were found to be effective catalysis such as TiO 2 and
ZnO. Among that TiO 2 , (Fujishima and Honda 1972) is very first compound utilized
for the photocatalytic degradation and it currently fine-tuned to highest performance
(Dapeng and Jiuhui 2009; Sin et al. 2012). Along with photochemical performance,
TiO 2 gained it position by very good stability towards photons and less corrosive to
most of the chemical contaminants. Hence, TiO 2 is ideal model system for
photocatalytic water degradation and by following TiO 2 many associated catalysts
was developed. Most of the cations are the transition metals and such as Ti, Fe, Ni,
Zn, Cd, Cu, Ag and more (Ajmera et al. 2002; Bessekhouad et al. 2004;
Bessekhouad et al. 2005; Bi and Xu 2013; Choi and Hoffmann 1996; Kondo and
Jardim 1991; Liu et al. 2013; Srinivas et al. 2015; Thuy et al. 2014; Tongying et al.
2012; Wenhua et al. 2000). Since the transition metals are having partially filled
d-orbitals, high charge forming ability and have good coordinating tendency make
them good candidates for the photocatalysis process. The high charge of the
co-ordination metals (Ti
4+ , Mn
5+ ) helps the ligand molecules (adsorbents) by electrostatic attraction. The bigger size of the transition metals also provides the possibility of high coordination number and hence one metal on photocatalytic surface
can adsorb up to six molecules. High charge and high co-ordination number of
transition metals synergistically promote adsorption of the contaminants. The
anionic species in photocatalyst is mostly chalcogenide elements namely sulfide,
7 Earth Abundant Materials for Environmental Remediation and Commercialization
203