2. General overview on g-C3N4 photocatalyst

the report by the WHO/UNICEF Joint Monitoring Programme, the current statistics reveal that there are approximately 2.1 billion people who are lack access to clean drinking water. Another report by UNESCO (2017) claims that approximately 80% of the wastewater flow is discharged into the ecosystem without any treatment thus contaminating a large portion of the water bodies. In this sense, the excessive release of anthropogenic pollutants originated from industrial use such as the phenolic compound, heavy metals and dyes had resulted in a deterioration in water quality and pose harmful effect on the living organism, which further emphasizes

Engineering photocatalytic material had emerged as a promising technology to bridge the gap between global energy challenge and environmental remediation. Since the pioneering discovery of photocatalytic water splitting by Fujishima and Honda in 1972, photocatalytic material has attracted interdisciplinary attention due to its diverse potential in various discipline such as solar energy conversion, photocatalytic water splitting for hydrogen production and carbon dioxide reduction, organic pollutants degradation and synthesis of organic compounds [7–9]. For the wastewater treatment field, photocatalytic degradation of pollutants is favorable over the conventional method due to its several advantages. This technique does not require non-renewable energy consumption as it exploits the sustainable

solar energy [10–12]. Applicable both for gaseous and aqueous treatment, photocatalysis technology reportedly can degrade a wide range of pollutants and toxic compounds without causing any secondary pollutants. Moreover, the

photocatalyst can be easily synthesized through various methods from an abundant readily available precursor. The whole process is not only simple to conduct, low in cost and require a relatively short process time, making the method sustainable for

At presents, there are a various ongoing effort for the development of the sustainable photocatalytic system, with the focused centered on the development of noble metal-free photocatalyst as TiO2, g-C3N4, BiVO4, ZnO, and carbonaceous materials [12–17]. Among these photocatalysts, graphitic carbon nitride (g-C3N4) has elicited significant interest as the next generation of the photocatalyst in engineering photocatalytic field for environmental pollutants degradation due to its excellent physiochemical properties [18–21]. The g-C3N4 is novel, metal-free photocatalyst with good light absorption properties owing to its medium band-gap energy of 2.7 eV [19, 22, 23]. The polymeric nature of this conjugated materials allows for facile modification of the photocatalyst to improve its optical properties besides permit multiple excitations from absorption of a single photon, both of which are favorable for efficient pollutants degradation. However, the practical application of g-C3N4 is still hindered by some of its individual properties such as low visible light utilization, the high recombination rate of photogenerated electron–hole pairs and slow electron transfer which lead to lower photocatalytic performance [22]. Hence, various strategies have been adopted such as energy band engineering, copolymerization with nitrogen precursor and development of heterostructure system in order to overcome the individual drawbacks of pristine

In recognition of the great potential of g-C3N4 as a promising visible light driven photocatalyst, this chapter is aiming to provide an overview on the most recent related studies on the development of g-C3N4 photocatalyst in the environmental pollution remediation. The history and basic principle of photocatalyst system are well explained in order to promote better understanding on the g-C3N4. Afterward, the fundamental properties of g-C3N4 and the synthesizing techniques are briefly summarized. Next, the current strategies to enhance the

the need to tackle the water pollution issue [4–6].

Nanocatalysts

wastewater purification in a large scale application.

g-C3N4 [24–26].

28

The history of engineering photocatalytic material could be traced back to 1972, where photoelectrochemical splitting of water in the presence of TiO2 and ultraviolet light by Fujishima and Honda had served as the starting point for photocatalytic reaction [27]. Since then, numerous semiconductor-based photocatalysts have been investigated in an attempt to produce a robust photocatalyst for an efficient novel photocatalytic system. Among them, TiO2, BiVO4, Fe2O3 and ZnO had been identified as a potential promising photocatalytic material [28–30]. Although Titanium oxide (TiO2) had dominated the photocatalytic arena, this photocatalyst suffers from its negative characteristics which hinder the practical exploitation of this material for large scale application [8, 9]. Hence, other potential materials have been tested and explored in the search for robust photocatalyst for large scale application. Among them, g-C3N4 had emerged as one of the promising material and become the new research hotspot for various scientific application owing to its excellent features.

#### 2.1 Introduction to g-C3N4 photocatalyst

Graphitic carbon nitride is one of the oldest artificial polymer reported back in 1834. Structurally analogous to graphene, this conjugated polymer is a novel, metalfree with a medium band gap of 2.7 eV [31]. Generally, there are several allotropes of C3N4 such as α-C3N4, β-C3N4, pseudocubic C3N4, cubic C3N4, g-h triazine and g-C3N4. However, g-C3N4 is considered the most stable form of C3N4 under ambient conditions. Figure 1 illustrates the basic tectonic units to establish the allotropes of the g-C3N4 photocatalyst. It was reported that the tri-s-triazine-based g-C3N4 photocatalyst was the most stable phases of C3N4 at ambient conditions. This postulation was further verified by Kroke et al. [32] with their first-principles density functional theory (DFT) calculations. Meanwhile, only the pseudocubic and g-h triazine phases have direct band gaps while the other phases have indirect band gap energies [32].

#### Figure 1.

The basic tectonic units for g-C3N4 photocatalyst (a) triazine and (b) tri-s-triazine (heptazine) structures. (Adapted with permission from Ref. [22]).

formed at ca. 520°C through the further condensation of the unit. Nevertheless, the overheating of the sample over 700°C resulted in the disappearance of g-C3N4 to "residue-free" through the production of nitrogen and cyano fragments. With respect to the experimental approaches, the reaction mechanism of the combined polyaddition and polycondensation process was further verified by the ab initio calculations using a plane wave basis set with a 550 eV energy cutoff [34]. Based on the calculations, Figure 3 illustrates the cohesive energy of the molecules increased following the polyaddition pathway, confirming that melamine was produced upon

Recent Development of Graphitic Carbon Nitride-Based Photocatalyst for Environmental…

Meanwhile, the most commonly used precursor in thermal condensation method includes those with nitrogen-rich and oxygen-free compounds, which contain the required C-N structure. The compounds with pre-bonded C-N core structure such as melamine, cyanamide, dicyanamide, urea and thiourea are among the commonly used precursors for the synthesis of g-C3N4. In addition to that, triazine and heptazine derivatives also had been tested as a precursor. For example, Mo et al. [34] prepared the g-C3N4 photocatalyst via manipulating the calcination temperature on the morphological structure of melamine. It was found that the g-C3N4 photocatalyst can only be formed when the calcination temperature above 500°C, evidently from the XRD analysis. Furthermore, it was found that the absorption band edge was red shifted along with the change of color from light yellow to dark orange, indicating the enhanced visible light absorption was obtained for samples with increasing calcination temperatures. On the other hand, Dong et al. [36] prepared the g-C3N4 using urea via a facile template-free. Their group studies the effects of pyrolysis time on the microstructure and activity of g-C3N4 photocatalyst. They suggested that the surface areas of the photocatalyst can be significantly increased by just

prolonging the pyrolysis time to 240 minutes at under 550°C. They claimed that the surface area of g-C3N4 photocatalyst prepared via this method is higher than g-C3N4 photocatalyst prepared via templating method. Similarly, Chen et al. [37] prepared g-C3N4 photocatalyst by pyrolyzing urea in a muffle furnace at 550°C for 2 hours with a heating rate of 5°C/min. Meanwhile, Yang et al. [38] prepared ultrathin g-C3N4 photocatalyst nanosheets via thermal exfoliation of bulk urea-derived g-C3N4 under an argon atmosphere. In addition, Figure 4 summarizes the synthesis process of g-C3N4 photocatalyst by thermal polymer-

Calculated energy diagram for the development of C3N4 using cyanamide as the precursor. Cyanamide was condensed to melamine. Further condensation proceeded by a triazine route (dash-dot line) or tri-s-triazine

heating the cyanamide [22].

DOI: http://dx.doi.org/10.5772/intechopen.81639

ization of different precursors.

(dashed line). (Adapted with permission from Ref. [33]).

Figure 3.

31

Figure 2. Historical development of g-C3N4 photocatalyst in photocatalysis field.

Carbon nitride, C3N4 is not new at all, and it is considered one of the oldest reported artificial polymers in the scientific literature [26]. Figure 2 shows the historical development of g-C3N4 in photocatalysis arena. This g-C3N4 was first reported by Berzelius and Liebig in the year 1834 and named as melon [33]. Although it was first discovered back in 1834, the material is not exploited until 2009 when Wang et al. first reported the utilization of this material in photocatalysis field [26]. Since then, a lot of researchers started to unravel the promising potential of the g-C3N4 photocatalyst in a wide range of different photocatalytic applications. Nevertheless, owing to the limited experimental data, there is a prevailing discussion about the actual existence of a graphitic material with idealized composition C3N4 and possible structure models for g-C3N4 photocatalyst. Gratifyingly, due to the similar structure with graphite, triazine (C3N4) had been put forward as the elementary block of g-C3N4. Moreover, tri-striazine rings also shown promises to be energetically favored with respect to the triazine-based modification as the tri-s-triazine rings are cross-linked by trigonal nitrogen atoms [34]. Ideally, the condensed g-C3N4 consists of only carbon and nitrogen atoms with a C/N molar ratio of 0.75. Nonetheless, there is no perfectly condensed g-C3N4 was reported and they are as-grown polymer materials that are not single crystals. Hence, the g-C3N4 photocatalyst can be seen as a family of layered graphitic carbon nitride compounds with a C/N ratio close to 0.75.

#### 2.2 Synthesis method for the development of g-C3N4 photocatalyst

Since the potential of carbon nitride in the photocatalysis arena had been known, various synthesis method and technique had been instigated such as chemical vapor deposition, sonochemical, solvothermal, and thermal annealing of nitrogen-rich precursor [24, 32, 33]. Following the variation in synthesis technique, the various compound can be used as the precursor such as melamine, cyanamide, dicyanamide, urea, and thiourea. However, thermal condensation of nitrogen-rich precursor has emerged as the most attractive methods due to its simplicity and use of cheap, earth-abundant precursors.

In the first reported work by Wang et al. [35], cyanamide was used as the starting precursor of g-C3N4. It was found that the cyanamide molecules were condensed to dicyanamide and melamine at temperatures of ca. 203 and 234°C. Next, the ammonia was removed via condensation process, resulting in the formation of melamine-based products at the temperature around 335°C. When the temperature was heated up to ca. 390°C, the tri-s-triazine units was formed via rearrangements of melamine. Finally, the polymeric g-C3N4 photocatalyst was

Recent Development of Graphitic Carbon Nitride-Based Photocatalyst for Environmental… DOI: http://dx.doi.org/10.5772/intechopen.81639

formed at ca. 520°C through the further condensation of the unit. Nevertheless, the overheating of the sample over 700°C resulted in the disappearance of g-C3N4 to "residue-free" through the production of nitrogen and cyano fragments. With respect to the experimental approaches, the reaction mechanism of the combined polyaddition and polycondensation process was further verified by the ab initio calculations using a plane wave basis set with a 550 eV energy cutoff [34]. Based on the calculations, Figure 3 illustrates the cohesive energy of the molecules increased following the polyaddition pathway, confirming that melamine was produced upon heating the cyanamide [22].

Meanwhile, the most commonly used precursor in thermal condensation method includes those with nitrogen-rich and oxygen-free compounds, which contain the required C-N structure. The compounds with pre-bonded C-N core structure such as melamine, cyanamide, dicyanamide, urea and thiourea are among the commonly used precursors for the synthesis of g-C3N4. In addition to that, triazine and heptazine derivatives also had been tested as a precursor. For example, Mo et al. [34] prepared the g-C3N4 photocatalyst via manipulating the calcination temperature on the morphological structure of melamine. It was found that the g-C3N4 photocatalyst can only be formed when the calcination temperature above 500°C, evidently from the XRD analysis. Furthermore, it was found that the absorption band edge was red shifted along with the change of color from light yellow to dark orange, indicating the enhanced visible light absorption was obtained for samples with increasing calcination temperatures.

On the other hand, Dong et al. [36] prepared the g-C3N4 using urea via a facile template-free. Their group studies the effects of pyrolysis time on the microstructure and activity of g-C3N4 photocatalyst. They suggested that the surface areas of the photocatalyst can be significantly increased by just prolonging the pyrolysis time to 240 minutes at under 550°C. They claimed that the surface area of g-C3N4 photocatalyst prepared via this method is higher than g-C3N4 photocatalyst prepared via templating method. Similarly, Chen et al. [37] prepared g-C3N4 photocatalyst by pyrolyzing urea in a muffle furnace at 550°C for 2 hours with a heating rate of 5°C/min. Meanwhile, Yang et al. [38] prepared ultrathin g-C3N4 photocatalyst nanosheets via thermal exfoliation of bulk urea-derived g-C3N4 under an argon atmosphere. In addition, Figure 4 summarizes the synthesis process of g-C3N4 photocatalyst by thermal polymerization of different precursors.

#### Figure 3.

Calculated energy diagram for the development of C3N4 using cyanamide as the precursor. Cyanamide was condensed to melamine. Further condensation proceeded by a triazine route (dash-dot line) or tri-s-triazine (dashed line). (Adapted with permission from Ref. [33]).

Carbon nitride, C3N4 is not new at all, and it is considered one of the oldest reported artificial polymers in the scientific literature [26]. Figure 2 shows the historical development of g-C3N4 in photocatalysis arena. This g-C3N4 was first reported by Berzelius and Liebig in the year 1834 and named as melon [33]. Although it was first discovered back in 1834, the material is not exploited until

2009 when Wang et al. first reported the utilization of this material in

Historical development of g-C3N4 photocatalyst in photocatalysis field.

2.2 Synthesis method for the development of g-C3N4 photocatalyst

compound can be used as the precursor such as melamine, cyanamide,

of cheap, earth-abundant precursors.

30

Figure 2.

Nanocatalysts

Since the potential of carbon nitride in the photocatalysis arena had been known, various synthesis method and technique had been instigated such as chemical vapor deposition, sonochemical, solvothermal, and thermal annealing of nitrogen-rich precursor [24, 32, 33]. Following the variation in synthesis technique, the various

dicyanamide, urea, and thiourea. However, thermal condensation of nitrogen-rich precursor has emerged as the most attractive methods due to its simplicity and use

In the first reported work by Wang et al. [35], cyanamide was used as the starting precursor of g-C3N4. It was found that the cyanamide molecules were condensed to dicyanamide and melamine at temperatures of ca. 203 and 234°C. Next, the ammonia was removed via condensation process, resulting in the formation of melamine-based products at the temperature around 335°C. When the temperature was heated up to ca. 390°C, the tri-s-triazine units was formed via rearrangements of melamine. Finally, the polymeric g-C3N4 photocatalyst was

photocatalysis field [26]. Since then, a lot of researchers started to unravel the promising potential of the g-C3N4 photocatalyst in a wide range of different photocatalytic applications. Nevertheless, owing to the limited experimental data, there is a prevailing discussion about the actual existence of a graphitic material with idealized composition C3N4 and possible structure models for g-C3N4 photocatalyst. Gratifyingly, due to the similar structure with graphite, triazine (C3N4) had been put forward as the elementary block of g-C3N4. Moreover, tri-striazine rings also shown promises to be energetically favored with respect to the triazine-based modification as the tri-s-triazine rings are cross-linked by trigonal nitrogen atoms [34]. Ideally, the condensed g-C3N4 consists of only carbon and nitrogen atoms with a C/N molar ratio of 0.75. Nonetheless, there is no perfectly condensed g-C3N4 was reported and they are as-grown polymer materials that are not single crystals. Hence, the g-C3N4 photocatalyst can be seen as a family of layered graphitic carbon nitride compounds with a C/N ratio close to 0.75.

#### Figure 4.

Schematic illustration of the synthesis process of g-C3N4 photocatalyst via thermal polymerization of different precursors. The black, blue, white, red and yellow balls denote C, N, H, O and S atoms, respectively. (Adapted with permission from Ref. [22]).

#### 2.3 Fundamental properties of g-C3N4 photocatalyst

Graphitic carbon nitride possesses an excellent physical, chemical and mechanical properties, giving a reason on why researchers are eager into the science of nanotechnology of g-C3N4. This compound possesses excellent visible light absorption than most of the metal oxide photocatalyst owing to its mild band gap energy. Given its π-conjugated properties, g-C3N4 can act as an electron sink, leading to suppression of recombination of photo excited charge carriers. Moreover, the polymeric nature of this material allows for multiple excitations from absorption of a single photon, leading to an efficient generation of the reactive species responsible for pollutant degradation. In addition, g-C3N4 possesses high resistance to thermal and chemical environment, as well as too acidic and basic media, making it as a stable material.

key towards photoreaction process. In this system, photon energy is required to activate the photocatalyst in which make this photocatalyst system to be one of the frontier renewable energy technology in which it can utilize the solar energy. The g-C3N4 photocatalyst has a small band gap energy around 2.6–2.7 eV which falls within the visible-light region [25]. It is estimated that

Electronic structure of the polymeric g-C3N4 photocatalyst. (Reproduced with permission from Ref. [39]).

Recent Development of Graphitic Carbon Nitride-Based Photocatalyst for Environmental…

DOI: http://dx.doi.org/10.5772/intechopen.81639

Initially, the g-C3N4 photocatalyst will absorb photon energy with an energy equivalent or greater than its band gap energy, causing an electron (е¯) in the valence band (VB) to be excited and migrate to the conduction band (CB).

Then, the electron will be excited and leave photogenerated holes (h<sup>+</sup>

valence band. The photogenerated holes and photoexcited electrons will migrate to the surface of the photocatalyst and trapped there. The photogenerated holes then react with adsorbed water to produce strong oxidizing ˙OH radicals whereas the photoexcited electrons react with adsorbed oxygen to generate ˙O2¯

e�CBð Þþ g � C3N4 O2 ! •O2

The formation of these radicals will further react with recalcitrant pollutant and

VBð Þ g � C3N4 (1)

� (2)

VBð Þþ g � C3N4 OH� ! •OH (3)

) in the

the valence band (VB) and the conduction band (CB) of the g-C3N4

g � C3N4 þ hV ! e�CBð Þþ g � C3N4 h<sup>þ</sup>

photocatalyst are 1.56 and 1.09 eV, respectively [40].

h<sup>þ</sup>

subsequently degraded the recalcitrant pollutant.

radicals [41].

33

Figure 5.

Furthermore, Wang et al. [39] performed a density functional theory (DFT) calculations in order to gain insight into the electronic structure of g-C3N4 photocatalyst (as shown in Figure 5). They reported that the valence band and conduction band are mainly composed of the nitrogen pz orbitals and carbon pz orbitals, respectively. The light illumination excited the electrons and holes for the oxidation and reduction process to occur independently in the nitrogen atoms and carbon atoms. Congruously, the g-C3N4 photocatalyst has a specific microstructure, with surface termination as defects and nitrogen atoms for electron localization or anchoring inorganic/organic functional motifs as the active sites [32].

However, the practical application of g-C3N4 is still hindered by some of its undesirable properties which lead to lower photocatalytic performance. The individual structure of g-C3N4 has low specific surface area and quantum efficiency, which limit the sorption capacity of the photocatalyst [26]. This photocatalyst also suffers from high recombination rate of the photogenerated electron–hole pairs.

#### 2.4 Photocatalytic principles and mechanism over g-C3N4 photocatalyst

Photocatalyst can be described as a combination of catalysis and photochemistry in which absorption of photon energy from light via catalyst is the Recent Development of Graphitic Carbon Nitride-Based Photocatalyst for Environmental… DOI: http://dx.doi.org/10.5772/intechopen.81639

Figure 5. Electronic structure of the polymeric g-C3N4 photocatalyst. (Reproduced with permission from Ref. [39]).

key towards photoreaction process. In this system, photon energy is required to activate the photocatalyst in which make this photocatalyst system to be one of the frontier renewable energy technology in which it can utilize the solar energy. The g-C3N4 photocatalyst has a small band gap energy around 2.6–2.7 eV which falls within the visible-light region [25]. It is estimated that the valence band (VB) and the conduction band (CB) of the g-C3N4 photocatalyst are 1.56 and 1.09 eV, respectively [40].

Initially, the g-C3N4 photocatalyst will absorb photon energy with an energy equivalent or greater than its band gap energy, causing an electron (е¯) in the valence band (VB) to be excited and migrate to the conduction band (CB).

$$\mathbf{g} - \mathbf{C\_3N\_4} + \mathbf{hV} \rightarrow \mathbf{e^-}\_{\text{CB}}(\mathbf{g} - \mathbf{C\_3N\_4}) + \mathbf{h}^+ \mathbf{v\_{VB}}(\mathbf{g} - \mathbf{C\_3N\_4}) \tag{1}$$

Then, the electron will be excited and leave photogenerated holes (h<sup>+</sup> ) in the valence band. The photogenerated holes and photoexcited electrons will migrate to the surface of the photocatalyst and trapped there. The photogenerated holes then react with adsorbed water to produce strong oxidizing ˙OH radicals whereas the photoexcited electrons react with adsorbed oxygen to generate ˙O2¯ radicals [41].

$$\bullet \text{e}^- \text{c}\_\text{CB} (\text{g} - \text{C}\_3 \text{N}\_4) + \text{O}\_2 \rightarrow \bullet \text{O}\_2^- \tag{2}$$

$$\bullet \text{ h}^+ \text{v}\_\text{VB} (\text{g} - \text{C}\_\text{\text{\textdegree}} \text{N}\_4) + \bullet \text{OH}^- \rightarrow \bullet \text{OH} \tag{3}$$

The formation of these radicals will further react with recalcitrant pollutant and subsequently degraded the recalcitrant pollutant.

2.3 Fundamental properties of g-C3N4 photocatalyst

Figure 4.

Nanocatalysts

32

with permission from Ref. [22]).

Graphitic carbon nitride possesses an excellent physical, chemical and mechanical properties, giving a reason on why researchers are eager into the science of nanotechnology of g-C3N4. This compound possesses excellent visible light absorption than most of the metal oxide photocatalyst owing to its mild band gap energy. Given its π-conjugated properties, g-C3N4 can act as an electron sink, leading to suppression of recombination of photo excited charge carriers. Moreover, the polymeric nature of this material allows for multiple excitations from absorption of a single photon, leading to an efficient generation of the reactive species responsible for pollutant degradation. In addition, g-C3N4 possesses high resistance to thermal and chemical environment, as well as too acidic and basic media, making it as a stable material. Furthermore, Wang et al. [39] performed a density functional theory (DFT)

Schematic illustration of the synthesis process of g-C3N4 photocatalyst via thermal polymerization of different precursors. The black, blue, white, red and yellow balls denote C, N, H, O and S atoms, respectively. (Adapted

calculations in order to gain insight into the electronic structure of g-C3N4 photocatalyst (as shown in Figure 5). They reported that the valence band and conduction band are mainly composed of the nitrogen pz orbitals and carbon pz orbitals, respectively. The light illumination excited the electrons and holes for the oxidation and reduction process to occur independently in the nitrogen atoms and carbon atoms. Congruously, the g-C3N4 photocatalyst has a specific microstructure, with surface termination as defects and nitrogen atoms for electron localization or

anchoring inorganic/organic functional motifs as the active sites [32].

However, the practical application of g-C3N4 is still hindered by some of its undesirable properties which lead to lower photocatalytic performance. The individual structure of g-C3N4 has low specific surface area and quantum efficiency, which limit the sorption capacity of the photocatalyst [26]. This photocatalyst also suffers from high recombination rate of the photogenerated electron–hole pairs.

2.4 Photocatalytic principles and mechanism over g-C3N4 photocatalyst

Photocatalyst can be described as a combination of catalysis and photochemistry in which absorption of photon energy from light via catalyst is the •O2 � þ recalcitrant pollutants ! degradation of pollutant (4)

photocatalytic performance efficiency. For example, Wang et al. [19] reported the enhanced photocatalytic performance of g-C3N4/{010} facets BiVO4 photocatalyst fabricated via ultrasonic dispersion method. The aforementioned heterostructure photocatalyst was capable of removing 88.3% of RhB pollutant within 30 minutes under visible light irradiation. Meanwhile, Huo et al. [20] successfully formed the BiVO4/Polydopamine/g-C3N4 heterostructure photocatalyst via facile ultrasonic dispersion and self-assembly at the room temperature. They observed a remarkable photocatalytic degradation of glyphosate under visible light irradiation in compari-

Recent Development of Graphitic Carbon Nitride-Based Photocatalyst for Environmental…

Furthermore, the photocatalytic activity of pure photocatalyst can be enhanced by the addition of carbon materials as an electron bridge mediator. The addition of carbon nanomaterial provides a structure with a larger specific surface area over which the active component can be well-dispersed, thus increasing the active sites. During the photocatalytic degradation of organic pollutants, carbon materials can be used as an adsorbent to improve the adsorption capacity of semiconductors. Besides, carbon materials can be doped as a photosensitizer for band gap

narrowing, which is favorable for expanding the visible light absorption region of semiconductors. The incorporation of electron bridge mediator within the network of the heterostructure system will facilitate the migration of the electron transfer within the photocatalyst, leading to the enhanced charge separation efficiency and photocatalytic activity. In this sense, GO/RGO and CNTs are among the carbon nanomaterial that has been explored to acts as an electron bridge

3. Recent progress on the development of g-C3N4 photocatalyst for

Pollutants concentration

Glyphosate 0.1 mM 125 W

MB 6 mg/L 150 W

Source of light

sunlight irradiation

mercury lamp

light

halogen lamp

10 mg/L Visible

Degradation efficiency

99.5% of phenol removal achieved after 60 min of irradiation

> 100% degradation after 150 minutes

g-C3N4/BiVO4 photocatalyst was about 8 and 7 times higher than that of pure BiVO4 and g-C3N4

Ternary hybrid exhibits 5 times higher photocatalytic activity compared to bare g-C3N4

Ref.

[42]

[20]

[43]

[44]

Type of pollutants

ZnO/g-C3N4 Impregnation Phenol 5 mg/L Simulated

NR Methylene

blue

son to the unmodified photocatalyst.

DOI: http://dx.doi.org/10.5772/intechopen.81639

environmental remediation

Method

Ultrasonic dispersion and self-assembly

Facile hydrothermal method

Photocatalyst Synthesized

mediator.

BiVO4/ PDA/g-C3N4

g-C3N4/ BiVO4

g-C3N4/TiO2/ CNT

35

•OH þ recalcitrant pollutants ! degradation of pollutant (5)
