2018), degradation of methomyl pesticide boron-doped diamond electrode (Costa
et al. 2017), and degradation of the insecticide propoxur by boron-doped diamond/
air-diffusion cell (Guelfi et al. 2017) have been reported.
Treatments of Organic Dyes
Cu-doped and Zn-doped TiO 2 nanoparticles synthesized by sol–gel method were
applied for methyl orange degradation (Khairy and Zakaria 2014). The small
crystallite size and doping were found to cause an increase in the adsorption edge
wavelength with decrease in band gap energy. Cu-doped TiO 2 showed the optimum
photocatalytic activity for methyl orange degradation.
Magnesium- and iron-doped ZnO nanoparticles were fabricated to use for degradation of methyl orange and/or methylene blue under UV irradiation (Paula et al.
2019; Saleh and Djaja 2014). It was found that the various parameters, i.e., pH,
dopant concentrations, and photocatalytic dosage, affected the photocatalytic activity, especially dopant concentration is the most important factor.
NaTaO 3 photocatalysts were synthesized with doping of Sr cations through
crystallization in molten NaCl flux, resulting in an increase in the population of
excited electrons. However, the reaction rate of the obtained photocatalysts showed
less enhancement compared with the increase in electron population, which ascribed
to a limited fraction of electrons overriding the energy gradient and returning back to
the surface (An et al. 2018).
Doping of graphitic carbon nitride (g-C 3 N 4 ) by various types of metals (Na, K,
transition metals, and rare earth metals) and nonmetal materials (phosphorus, sulfur,
oxygen, nitrogen, carbon, boron, and halogen) for photocatalytic remediation of
organic dyes in water was reviewed (Hasija et al. 2019). It was shown that the
photocatalytic activity for degradation of organic pollutants (rhodamine B and
methylene blue) of the doped materials was successfully enhanced up to 50%
compared with the bare ones, because of changes of band gaps of the materials.
Co-doing of two metal dopants or a metal ion with a nonmetal dopant for
synergistic photocatalytic effects, i.e., the working together of two things to produce
an effect greater than the sum of their individual effects, of the dopants is an
alternative way to modify metal oxide photocatalysts (Sanitnon et al. 2019). For
an example, ferroelectric Fe
3+ Cr
3+ codoped BaTiO 3 nanopowders for the
photocatalytic oxidation of azo dyes were fabricated (Amaechi et al. 2019). The
photocatalytic activity of the powders was found to be maintained after three cycle
uses, and the powders could be reused without generating any secondary residue.
1.5.2 Composite of Semiconductors
Composite (also called coupling) of two or more semiconductors is considered as an
effective method for modification of photocatalysts, because the separation of photo34
P. Kemacheevakul and S. Chuangchote
et al. 2017), and degradation of the insecticide propoxur by boron-doped diamond/
air-diffusion cell (Guelfi et al. 2017) have been reported.
Treatments of Organic Dyes
Cu-doped and Zn-doped TiO 2 nanoparticles synthesized by sol–gel method were
applied for methyl orange degradation (Khairy and Zakaria 2014). The small
crystallite size and doping were found to cause an increase in the adsorption edge
wavelength with decrease in band gap energy. Cu-doped TiO 2 showed the optimum
photocatalytic activity for methyl orange degradation.
Magnesium- and iron-doped ZnO nanoparticles were fabricated to use for degradation of methyl orange and/or methylene blue under UV irradiation (Paula et al.
2019; Saleh and Djaja 2014). It was found that the various parameters, i.e., pH,
dopant concentrations, and photocatalytic dosage, affected the photocatalytic activity, especially dopant concentration is the most important factor.
NaTaO 3 photocatalysts were synthesized with doping of Sr cations through
crystallization in molten NaCl flux, resulting in an increase in the population of
excited electrons. However, the reaction rate of the obtained photocatalysts showed
less enhancement compared with the increase in electron population, which ascribed
to a limited fraction of electrons overriding the energy gradient and returning back to
the surface (An et al. 2018).
Doping of graphitic carbon nitride (g-C 3 N 4 ) by various types of metals (Na, K,
transition metals, and rare earth metals) and nonmetal materials (phosphorus, sulfur,
oxygen, nitrogen, carbon, boron, and halogen) for photocatalytic remediation of
organic dyes in water was reviewed (Hasija et al. 2019). It was shown that the
photocatalytic activity for degradation of organic pollutants (rhodamine B and
methylene blue) of the doped materials was successfully enhanced up to 50%
compared with the bare ones, because of changes of band gaps of the materials.
Co-doing of two metal dopants or a metal ion with a nonmetal dopant for
synergistic photocatalytic effects, i.e., the working together of two things to produce
an effect greater than the sum of their individual effects, of the dopants is an
alternative way to modify metal oxide photocatalysts (Sanitnon et al. 2019). For
an example, ferroelectric Fe
3+ Cr
3+ codoped BaTiO 3 nanopowders for the
photocatalytic oxidation of azo dyes were fabricated (Amaechi et al. 2019). The
photocatalytic activity of the powders was found to be maintained after three cycle
uses, and the powders could be reused without generating any secondary residue.
1.5.2 Composite of Semiconductors
Composite (also called coupling) of two or more semiconductors is considered as an
effective method for modification of photocatalysts, because the separation of photo34
P. Kemacheevakul and S. Chuangchote