1. Introduction

The exponential growth of the industries over the past decade had exerted substantial pressure on sustainability, mainly on the pillars of the environment. While the gap towards an improved well-being brings many intended benefits. The environmental sustainability challenge is also growing at a large scale and complexity, resulting in severe environmental impacts including water pollutions. Within this context, the rise of industrialization alongside with the rapid growth of the global population has been intimately linked with a higher generation of wastewater [1–3]. The statistical glance from United Nations World Water Assessment Programme (2003) has reported that around 2 million tons of industrial sewage and agricultural waste have been discharged into the water bodies every day. Based on

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

overall performance of g-C3N4 photocatalyst are explained. Subsequently, the current perspective and future directions of the g-C3N4 photocatalyst are included

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

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

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

The basic tectonic units for g-C3N4 photocatalyst (a) triazine and (b) tri-s-triazine (heptazine) structures.

2. General overview on g-C3N4 photocatalyst

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

in this chapter.

excellent features.

gap energies [32].

Figure 1.

29

(Adapted with permission from Ref. [22]).

2.1 Introduction to g-C3N4 photocatalyst

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 wastewater purification in a large scale application.

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 g-C3N4 [24–26].

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

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

overall performance of g-C3N4 photocatalyst are explained. Subsequently, the current perspective and future directions of the g-C3N4 photocatalyst are included in this chapter.
