onto photocatalyst surface, and (4) fate of charge carriers either on recombination
sites, surface reaction, or active sites.
The first demonstration early in 1972 by Fujishima and Honda commenced the
era of photocatalysis by photoelectrochemical (PEC) water splitting via aid of
titanium dioxide in the presence of ultraviolet light (Singh et al. 2014; Raizada
et al. 2014a, b). Since then, varieties of semiconductors as photocatalysts have been
reported, for instance ZnO, CaO, ZnWO 4 , WO 3 , ZrO 2 , BiTiO 3 , SrTiO 3 , Fe 2 O 3 ,
Ag 2 CO 3 , BiOBr, BiOCl, CaFe 2 O 4 , MnFe 2 O 4 , ZnFe 2 O 4 , BiFe 2 O 4 , TaON, etc.
(Raizada et al. 2014a, b, 2017a, b, 2019a, b, c; Priya et al. 2016a, b; Pan et al.
2012; Hua et al. 2019; Shandilya 2018a, b, 2019). The most ruggedly employed
photocatalysts, TiO 2 and zinc oxide, are widely used owing to their flexible,
biocompatible, and non-toxic nature (Raizada et al. 2019a, b, c). However, their
photocatalytic performance is hindered by large band gap of 3.2 eV which is
accompanied by decreased electron and hole pair separation, lowered migration
ability, and poor solar light energy utilization potential (Lai et al. 2016). Metal
oxides are pursued significantly for complete mineralization and photodegradation
of pollutants from simulated water. They have been considered as a green, economical source due to its substantial properties of enhanced interfacial tension, with
superior mechanical, optical, magnetic, and thermal characteristics. Its key features
such high density and less size result in more reactive centers for attachment of
pollutant groups and bacterial disinfection (Zhang et al. 2009; Pathania et al. 2014;
Singh et al. 2017; Gautam et al. 2016a, b, c).
Very recently in 2006, “gold rush” attention has been accomplished by metal-free
carbon, nitrogen-based n-type polymeric semiconductors, and graphitic carbon
nitride (g-C 3 N 4 ) (Zhou et al. 2018). The most communal carbon nitride allotrope
is two-dimensional g-C 3 N 4 consisting of triazine-based delocalized π-conjugated
graphitic planes formed by covalently linked sp
2 hybridized nitrogen and carbon
(Kroke et al. 2002). The inherent characteristic of g-C 3 N 4 involving tunable band
structure with optical midway band gap of 2.7 eV and positions of conduction band
and valence band potentials located at À1.09 and + 1.56 eV at pH 7, respectively,
with visible light absorption of 450–460 nm (Wirnhier et al. 2013; Liebig et al.
1844). The peculiar properties of g-C 3 N 4 include thermal stability up to 600
C and
high chemical resistance to acids, alkalis, or organic solvents Zhu et al. (2014).
Additionally, its porous texture and larger guest-accessible surface area provide
more active sites and suppressed recombination of photoexcited charge carriers.
The band structure, morphology, electronic properties, optical absorption, facile
fabrication, and its cost-effective, Earth-abundant, non-toxic nature provide insightful outlooks in the arena of solar energy conservation (Kessler et al. 2017; Zhao et al.
2015; Zhang et al. 2010). With such unique attributes, g-C 3 N 4 is successfully
contributing in various realms of environmental applications, including air purification, water splitting to produce oxygen and hydrogen, carbon dioxide reduction to
hydrocarbon fuels, bacterial disinfection, and photodegradation of contaminants
(Zuluaga et al. 2015; Bojdys et al. 2008; Zhang et al. 2018). The fabrication of
visible light-driven photocatalyst is immensely opted by researchers to exploit
inexhaustible abundant solar energy resource in photocatalysis process. For effective
56
P. Raizada et al.
sites, surface reaction, or active sites.
The first demonstration early in 1972 by Fujishima and Honda commenced the
era of photocatalysis by photoelectrochemical (PEC) water splitting via aid of
titanium dioxide in the presence of ultraviolet light (Singh et al. 2014; Raizada
et al. 2014a, b). Since then, varieties of semiconductors as photocatalysts have been
reported, for instance ZnO, CaO, ZnWO 4 , WO 3 , ZrO 2 , BiTiO 3 , SrTiO 3 , Fe 2 O 3 ,
Ag 2 CO 3 , BiOBr, BiOCl, CaFe 2 O 4 , MnFe 2 O 4 , ZnFe 2 O 4 , BiFe 2 O 4 , TaON, etc.
(Raizada et al. 2014a, b, 2017a, b, 2019a, b, c; Priya et al. 2016a, b; Pan et al.
2012; Hua et al. 2019; Shandilya 2018a, b, 2019). The most ruggedly employed
photocatalysts, TiO 2 and zinc oxide, are widely used owing to their flexible,
biocompatible, and non-toxic nature (Raizada et al. 2019a, b, c). However, their
photocatalytic performance is hindered by large band gap of 3.2 eV which is
accompanied by decreased electron and hole pair separation, lowered migration
ability, and poor solar light energy utilization potential (Lai et al. 2016). Metal
oxides are pursued significantly for complete mineralization and photodegradation
of pollutants from simulated water. They have been considered as a green, economical source due to its substantial properties of enhanced interfacial tension, with
superior mechanical, optical, magnetic, and thermal characteristics. Its key features
such high density and less size result in more reactive centers for attachment of
pollutant groups and bacterial disinfection (Zhang et al. 2009; Pathania et al. 2014;
Singh et al. 2017; Gautam et al. 2016a, b, c).
Very recently in 2006, “gold rush” attention has been accomplished by metal-free
carbon, nitrogen-based n-type polymeric semiconductors, and graphitic carbon
nitride (g-C 3 N 4 ) (Zhou et al. 2018). The most communal carbon nitride allotrope
is two-dimensional g-C 3 N 4 consisting of triazine-based delocalized π-conjugated
graphitic planes formed by covalently linked sp
2 hybridized nitrogen and carbon
(Kroke et al. 2002). The inherent characteristic of g-C 3 N 4 involving tunable band
structure with optical midway band gap of 2.7 eV and positions of conduction band
and valence band potentials located at À1.09 and + 1.56 eV at pH 7, respectively,
with visible light absorption of 450–460 nm (Wirnhier et al. 2013; Liebig et al.
1844). The peculiar properties of g-C 3 N 4 include thermal stability up to 600
C and
high chemical resistance to acids, alkalis, or organic solvents Zhu et al. (2014).
Additionally, its porous texture and larger guest-accessible surface area provide
more active sites and suppressed recombination of photoexcited charge carriers.
The band structure, morphology, electronic properties, optical absorption, facile
fabrication, and its cost-effective, Earth-abundant, non-toxic nature provide insightful outlooks in the arena of solar energy conservation (Kessler et al. 2017; Zhao et al.
2015; Zhang et al. 2010). With such unique attributes, g-C 3 N 4 is successfully
contributing in various realms of environmental applications, including air purification, water splitting to produce oxygen and hydrogen, carbon dioxide reduction to
hydrocarbon fuels, bacterial disinfection, and photodegradation of contaminants
(Zuluaga et al. 2015; Bojdys et al. 2008; Zhang et al. 2018). The fabrication of
visible light-driven photocatalyst is immensely opted by researchers to exploit
inexhaustible abundant solar energy resource in photocatalysis process. For effective
56
P. Raizada et al.