mechanism of photocatalysis, disadvantages of conventional methods of water
purification, and general classification of azo dyes. Significantly, immobilizing
bare metal oxide nanoparticles on the surface of certain carbonaceous support will
stabilized the nanoparticles and prevent leaching of nanoparticles into the water
bodies and also slow the electron–hole pair recombination. Also, the band edge
position of two combining semiconductors is an important aspect for the fabrication
of visible light-driven photocatalyst. The fabricated heterojunction may also utilized
the special phenomena of upconversion where, the light of longer wavelength emits
the light of shorter wavelength which is useful for wide band gap semiconductor to
be utilized as photocatalyst. Lastly, conclusion and future perspective which opens
up the area for further research to be carried out for constructing photocatalytic
system that can be widely applied for various pollutants were considered and
hypothesized.
Keywords Azo dye · Heterogeneous photocatalysis · Z-scheme photocatalyst ·
Carbonaceous nanocomposites · Photodegradation
4.1 Introduction
The continuous dispense of hazardous organic dye into water bodies from textile,
printing, food, and cosmetic industries poses an utmost threat to the environment
(Singh et al. 2017, 2018; Priya et al. 2016; Raizada et al. 2017, 2018, 2019a). The
effluents from the industries are major pollutant which damages the quality of water.
Although physisorption, coagulation and membrane filtration are the conventional
methods reported for azo dye degradation, none of them are efficient which can
remove the pollutant fully from the water (Singh et al. 2013a, b; Pare et al. 2008b).
Among various conventional techniques, chemical oxidation method utilizing
advanced oxidation method has earned considerable attention due to the conversion
of toxic pollutant into innoxious product (Kumar et al. 2019a, b; Gautam et al. 2017;
Singh et al. 2019b). Heterogeneous photocatalysis has emerged as green and
advanced oxidation method for the elimination of various pollutants from water
bodies (Blake 2001; Sudhaik et al. 2018a; Hasija et al. 2019a; Raizada et al. 2019c).
In heterogeneous photocatalysis, metal oxide semiconductor is suspended in
different phase in aqueous medium which is easy to separate from reaction medium
(Hasija et al. 2019b). An ample of photocatalyst have already been reported till date
and utilized in various fields; among them wastewater treatment is the exigently
required filed to be explored (Raizada et al. 2014a, b, 2016, 2019b; Sudhaik et al.
2018b). Water pollution is caused by many pollutants like pesticides, heavy metal
ions, microbial pollution, and pollution due to azo dyes. Among these, pollution due
to azo dyes is our major concern as azo dyes are nonbiodegradable due to complex
structure and major constituent of industrial wastewater which continuously
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P. Shandilya et al.
purification, and general classification of azo dyes. Significantly, immobilizing
bare metal oxide nanoparticles on the surface of certain carbonaceous support will
stabilized the nanoparticles and prevent leaching of nanoparticles into the water
bodies and also slow the electron–hole pair recombination. Also, the band edge
position of two combining semiconductors is an important aspect for the fabrication
of visible light-driven photocatalyst. The fabricated heterojunction may also utilized
the special phenomena of upconversion where, the light of longer wavelength emits
the light of shorter wavelength which is useful for wide band gap semiconductor to
be utilized as photocatalyst. Lastly, conclusion and future perspective which opens
up the area for further research to be carried out for constructing photocatalytic
system that can be widely applied for various pollutants were considered and
hypothesized.
Keywords Azo dye · Heterogeneous photocatalysis · Z-scheme photocatalyst ·
Carbonaceous nanocomposites · Photodegradation
4.1 Introduction
The continuous dispense of hazardous organic dye into water bodies from textile,
printing, food, and cosmetic industries poses an utmost threat to the environment
(Singh et al. 2017, 2018; Priya et al. 2016; Raizada et al. 2017, 2018, 2019a). The
effluents from the industries are major pollutant which damages the quality of water.
Although physisorption, coagulation and membrane filtration are the conventional
methods reported for azo dye degradation, none of them are efficient which can
remove the pollutant fully from the water (Singh et al. 2013a, b; Pare et al. 2008b).
Among various conventional techniques, chemical oxidation method utilizing
advanced oxidation method has earned considerable attention due to the conversion
of toxic pollutant into innoxious product (Kumar et al. 2019a, b; Gautam et al. 2017;
Singh et al. 2019b). Heterogeneous photocatalysis has emerged as green and
advanced oxidation method for the elimination of various pollutants from water
bodies (Blake 2001; Sudhaik et al. 2018a; Hasija et al. 2019a; Raizada et al. 2019c).
In heterogeneous photocatalysis, metal oxide semiconductor is suspended in
different phase in aqueous medium which is easy to separate from reaction medium
(Hasija et al. 2019b). An ample of photocatalyst have already been reported till date
and utilized in various fields; among them wastewater treatment is the exigently
required filed to be explored (Raizada et al. 2014a, b, 2016, 2019b; Sudhaik et al.
2018b). Water pollution is caused by many pollutants like pesticides, heavy metal
ions, microbial pollution, and pollution due to azo dyes. Among these, pollution due
to azo dyes is our major concern as azo dyes are nonbiodegradable due to complex
structure and major constituent of industrial wastewater which continuously
120
P. Shandilya et al.