Hexagonal-borocarbonitride (h-BCN) based heterostructure photocatalyst for energy and environmental applications: A review

Formulation of heterojunction with remarkable high efficiency by utilizing solar light is promising to synchronously overcome energy and environmental crises. In this concern, hexagonal-borocarbonitride (h-BCN) based Z-schemes have proved potential candidates due to their spatially separated oxidation and reduction sites, robust light-harvesting ability, high charge pair migration and separation, and strong redox ability. H-BCN has emerged as a hotspot in the research field as a metal-free photocatalyst with a tunable bandgap range of 0-5.5 eV. The BCN photocatalyst displayed synergistic benefits of both graphene and boron nitride. Herein, the review demonstrates the current state-of-the-art in the Z-scheme photocatalytic application with a special emphasis on the predominant features of their photoactivity. Initially, fundamental aspects and various synthesis techniques are discussed, including thermal polymerization, template-assisted, and template-free methods. Afterward, the reaction mechanism of direct Z-scheme photocatalysts and indirect Z-scheme (all-solid-state) are highlighted. Moreover, the emerging Step-scheme (S-scheme) systems are briefly deliberated to understand the charge transfer pathway mechanism with an induced internal electric field. This review critically aims to comprehensively summarize the photo-redox applications of various h-BCN-based heterojunction photocatalysts including CO2 photoreduction, H2 evolution, and pollutants degradation. Finally, some challenges and future direction of h-BCN-based Z-scheme photocatalyst in environmental remediation are also proposed.