2.5 Strategies to improve g-C3N4 photocatalytic performance

In order to overcome the individual drawback of pure g-C3N4, many attempts have been made to improve the photocatalytic capability including surface modification of the photocatalyst structure. Generally, the surface modification aims to improve the photocatalyst specific surface area, charge separation and optical. There are currently five modification techniques which have been investigated including the introduction of heteroatoms (i.e. metals and non-metals) within g-C3N4 framework, noble metal deposition, hybridizing g-C3N4 with carbon nanomaterials and coupling g-C3N4 with a photocatalyst. The principle, advantages and disadvantages of each technique are summarized in Table 1.

On the other hand, the development of the heterostructure photocatalyst via the introduction of additional compounds into the g-C3N4 network is one of the most promising strategies to enhance the overall catalytic performance of g-C3N4 photocatalyst [22]. In general, the g-C3N4-based heterostructure can be developed by coupling the g-C3N4 with other types of photocatalyst as co-catalyst. The formation of the heterostructure with suitable band position would suppress the recombination rate of the photogenerated electron–hole pairs, which lead to higher


#### Table 1.

Surface modification of g-C3N4 technique to improve its photocatalytic performance.

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

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 comparison to the unmodified photocatalyst.

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 mediator.

