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Bioremediation for Sustainable Environmental Cleanup

the C–F bonding, which reduced the band gap of g–C3N4 from 2.69 eV to 2.63 eV. Additionally, DFT

studies showed that adding F to the carbon in the bay pushes the VB and CB to higher energy values.

F-doped g-C3N4 displayed around 2.7 folds more activity than untreated g-C3N4 in photocatalytic

hydrogen evolution.

17.4.2.4 Metal Oxide Doping

One of the most promising semiconductors photocatalysts under investigation is TiO2, which also

has high stability, a cost-effective synthesis method and an appropriate conduction band location. In

1972, the pioneers (Fujishima and Honda 1972) investigated the photocatalytic efficiency of TiO2.

The researchers wanted to minimize the material’s bandgap by doping it with other elements and

composing it with other substances to absorb visible light energy to increase TiO2’s photocatalytic

efficiency. The g-C3N4 -TiO2 heterojunction may be generated using various synthetic techniques,

including solvothermal treatment, hydrothermal treatment, co-calcination and microwave

assistance (Acharya and Parida 2020). The hydrothermal and calcination methods are often used

to fabricate g-C3N4 - TiO2 heterojunction (Li et al. 2015). Kočí et al. (2017) successfully used

a hydrothermal method, followed by a calcination approach, to deposit TiO2 on the surface of

g-C3N4 (Rathi et al. 2018). The CuNi@g-C3N4 - TiO2 nanocatalyst exhibited a three and five times

greater photocatalytic activity RhB degradation than bare g-C3N4 and TiO2 nanorods. The produced

heterojunction exhibits greater photocatalytic effectiveness than g-C3N4 and TiO2 alone, according

to research by (Alcudia-Ramos et al. 2020).

ZnO nanostructures have attracted researchers due to their inexpensive fabrication cost, low

toxicity, good stability, high aspect ratio and appropriate bandgap energy. The g-C3N4-ZnO structure

has been created using various techniques, including hydrothermal, solvothermal, atomic layer

deposition and more (Mohammadi et al. 2020, Tan et al. 2019). It has been demonstrated that adding

ZnO to g-C3N4 may improve photocatalytic activity, including charge transfer and separation and

reduce the recombination of the photogenerated carriers (Paul et al. 2020, Ramachandra et al. 2020).

To improve the activity of the bulk g-C3N4, other types of metal oxides, including V2O5, NiO,

MoO3, Cu2O, Co3O4, CeO2, Bi2O3, Al2O3, etc., are also utilized (Jin et al. 2020, Shi et al. 2019,

Sumathi et al. 2019). By combining with other metals or doping with different substances, the

g-C3N4-based heterojunctions can be altered (Chaudhary and Ingole 2020). Cu is a standard

metal that is used to enhance photocatalytic activity. Other metal photocatalysts for enhanced

photocatalytic activity include Bi, Pd, Pt, Ni and Cd (Karimi et al. 2020, Zhao et al. 2021). In addition

to the composites based on metal oxide g-C3N4, some semiconductors are also used. Excellent

stability, economic synthesis, improved photogenerated electron reservoirs, photocatalysis and

electrocatalysis are all possible with carbon-based nanomaterials (Fan et al. 2019).

17.4.2.5 Nonmetal Oxide-Based g-C3N4 Nanocomposite

Regarding widespread practical applications, there are considerable obstacles due to the dearth of

metal-based photocatalysts in nature and their high price. In addition, these metal-doped semiconductor

photocatalysts self-degrade due to thermal instability. As a result, research into nonmetal-modified

g-C3N4 has grown. Nonmetals can acquire electrons and establish powerful covalent bonds in

the parent lattice structure due to their inherent characteristics, such as high electronegativity and

ionization energies. To increase g-C3N4’s photodegradation activity, phosphorus, sulfur, oxygen,

carbon, boron nitrogen and halogens have been used as nonmetal dopants.

Zhou et al. (2015) synthesized P-doped g-C3N4 via an economic copolymerization process.

P-doped g-C3N4 shows a rapid 100% RhB dye degradation activity. In a different work, CeO2 was

added via calcination after being heated with melamine and diammonium hydrogen phosphate to

couple it to P-doped g-C3N4. At an optimal concentration of 13.8% CeO2, the synthesized CeO2-P

doped g-C3N4 reduced the band gap of pure g-C3N4 from 2.71 eV to 2.32 eV. This behavior is

attributed to synergistic interactions between CeO2 and P-doped g-C3N4 and was further evaluated

to be 7.4 and 4.9 fold better than CeO2 and g-C3N4, respectively (Luo et al. 2015).