CHAPTER 9: Metal-free Functionalised Carbons in Photocatalysis

Since Fujishima and Honda showed that the TiO₂ electrode is capable of splitting water under UV irradiation in the 1970s, the heterogeneous photocatalytic process became a hot topic for decades, as it shows potential in driving many important reactions (i.e., H₂ production, CO₂ reduction, organic synthesis) by solar irradiation. Although the majority of photocatalyst materials that have been studied are based on inorganic semiconductors (especially metal oxides, sulfides, and nitrides), the demand for developing highly efficient photocatalysts using earth-abundant elements is gradually increasing. Carbon-based photocatalyst materials have attracted great attention as they constitute light elements (i.e., H, N, O, S, P) and require no metal elements. Besides, the physiochemical properties (i.e., light absorption, electronic structure, stability, and surface acidity) of carbon-based materials can be further functionalised by introducing different functional groups, making them a powerful platform for material engineering. In this chapter, we will go through carbon-based photocatalyst materials from a linear structured polymer, polymer network, covalent organic framework, to the popular polymeric carbon nitrides and derivatives. The design strategy, synthesis methodology, and optimisation will be discussed in detail. Last but not least, the application of carbon-based materials in other photocatalytic reactions beyond H₂ production will also be discussed.