Synthesis, structure, and selected photocatalytic applications of graphitic carbon nitride: a review

The exhaustion of non-renewable resources and the detrimental consequences to the environment by their excessive use have created a dire need of an alternative energy source. In this context, the discovery of graphitic carbon nitride (g-C3N4) as a semiconductor photocatalyst to utilize solar energy for environmental remediation has gathered great attention in the past decade. With a suitable band gap of 2.7 eV that allows it to operate in the visible-light range, high physiochemical stability, appealing electronic band structure, appropriate optical absorption, and "earth-abundant" nature allowing economic feasibility, g-C3N4 comes as an excellent metal-free photocatalyst for solving the energy crisis and offers a wide range of applications. However, pure g-C3N4 exhibits a restricted photocatalytic efficiency mainly because of low surface area and low mobility of photogenerated charge carriers which can be significantly improved by applying various approaches such as forming composite with another semiconductor, incorporating a cocatalyst, and various other alterations. Hence, in this mini-review, a comprehensive study on g-C3N4 as a potent visible-light photocatalyst is presented with special emphasis on its structure, synthesis, and various modifications which helps in enhancement of its photocatalytic efficiency. Advancements in photoredox applications including water splitting for hydrogen production, CO2 photoreduction, degradation of pollutants, bacterial disinfection, and other newly emerging applications such as electrochemical energy storage, organic synthesis, and N-2 fixation have been discussed in detail. Finally, the mini-review ends with an insight into the current challenges faced to develop better g-C3N4-based systems and the scope for further fruitful research in this area.