Intrinsic Defects in Polymeric Carbon Nitride for Photocatalysis Applications

Abstract

Introducing intrinsic defects in polymeric carbon nitride (PCN) without the addition of exotic atoms have been verified as an available strategy to boost the photocatalytic performance. This minireview focuses on the fundamental classifications and positive roles of intrinsic defects in PCN for photocatalysis applications. The intrinsic defects in PCN are classified into several types, such as nitrogen vacancy, carbon vacancy and derivative functional groups such as cyano, amino and cyanamide groups. The critical roles of these defects on the electronic configuration, charge transfer and surface properties of PCN are also carefully classified and elaborated. Furthermore, the photocatalysis applications of the defective PCN including photocatalytic water splitting, N 2 fixation, H 2 O 2 production, CO 2 reduction and NO removal are summarized. In the end, the challenges and opportunities of defect chemistry in PCN for photocatalysis field are presented.

Overall Regulation of Exciton Dynamics by Defect Engineering in Polymeric Photocatalysts for Hydrogen Evolution

“…Some strategies have been applied to regulate the exciton dynamics; for instance, nanostructuring such as forming nanocrystals or quantum dots enhances the multiple exciton generation because of the quantum confinement effect, , and surface plasmon resonance promotes the exciton generation by near-field enhancement and the exciton dissociation via exciton-plasmon coupling . Among them, engineering defects (four main categories according to the dimensions, e.g., the point, line, planar, and volume) has been considered as an effective, comprehensive, and facile way to enhance the performance of photocatalysts, − such as increasing light absorption by narrowing the band gap, improving charge transfer and separation via temporarily trapping photogenerated electrons and holes, or maneuvering surface reactions through adsorption and activation of reactant molecules. , In addition, the effect of defects on regulating the exciton dynamics is also explored. , On the positive side, a proper amount of defects in photocatalysts can promote exciton dissociation. ,− For example, the formation of ordered–disordered chains in the heptazine-based melon (HM) [which is also called polymeric carbon nitride (CN)], which has suitable band structures with the built-in electric field at the abundant ordered–disordered interfaces, can accelerate the exciton dissociation into free electrons and holes and thus effectively enhance the PC performance . Another study shows that the incorporation of oxygen vacancies in the low-dimensional bismuth oxybromide (BiOBr) can promote exciton dissociation because the oxygen vacancies significantly distort the surrounding localization of band-edge states, leading to the instability of excitons .…”

Modulation of Surface Oxygen Defects on ZnO/ZnS Catalysts to Promote Photocatalytic H2 Production

“…[3] For a long time, material scientists used to preclude structural defects in various materials to avoid any mechanical failure. However, the advanced techniques developed in recent decades have discovered the great potential of defect structures with functional materials in nanoscale, which endows the defect engineering more promising in diverse important applications, such as photocatalysis, [4,5] electrocatalysis, [6] and electrochemical energy storage. [7] Specifically, the rationally controlled defects with unique electronic structures and charge redistribution can offer new opportunities to tune the photocatalytic properties in water splitting for hydrogen (H 2 ) production.…”

Activity Enhancement of Defective Carbon Nitride for Photocatalytic Ammonia Generation by Modification with Pyrite

“…22,23,24,25,26 Owing to the polymeric structure of C3N4, the number of possible defects is vast and versatile. 27,28,21,20,18 A frequently exploited strategy for activity enhancement in C3N4 is the introduction of nitrogen vacancies, which are of the same size as the nitrogen atoms in molecular N2, and can thus act as efficient adsorption and activation centres. 27 Another important class of defects are cyano or cyanamide groups, that act as electron-withdrawing groups, assisting in charge separation and suppressing recombination.…”