Recent advancements in graphitic carbon nitride based direct Z- and S-scheme heterostructures for photocatalytic H2O2 production

Escalating global energy demands and the pressing need for sustainable and environmentally friendly energy sources have intensified research in the field of renewable energy, particularly solar energy. Hydrogen peroxide (H2O2), as a green and sustainable oxidant, is important for environmental remediation, chemical synthesis, and as a next-generation energy fuel. Solar energy harnessed in photocatalysis enables light-driven H2O2 production, offering an eco-friendly synthesis method. High-performance photocatalysts are essential for achieving viable solar H2O2 synthesis. Photocatalysis, particularly using g-C3N4, a visible-light-responsive metal-free semiconductor, presents a promising avenue for future large-scale H2O2 production. This is due to its unique properties, such as its oxygen-reduction-friendly conduction band, tuneable molecular structure, stability, cost-effectiveness, Earth abundance, facile synthesis, non-toxicity, numerous active sites, surface imperfections and high selectivity for H2O2 generation, making it a vital material in the renewable energy sector. However, challenges like rapid exciton recombination, limited light absorption capacity, suboptimal electrical conductivity, low specific surface area, and slow water oxidation kinetics need to be addressed to enhance its catalytic efficiency. Hence, the development of direct Z- or more relevant S-scheme heterostructures of g-C3N4 could promote the charge carrier separation efficiency, optimize the redox potential and improve the photocatalytic activity significantly. This review focuses on g-C3N4 as a photocatalyst, emphasizing its properties and the potential of direct Z- and S-scheme heterojunctions in photocatalytic H2O2 production. It introduces the background and surge in research on these heterojunctions, covers design principles, charge transfer mechanisms, advanced characterization methods, driving force enhancement strategies, Fermi level adjustment tactics, and principles of H2O2 production, including formation pathways, kinetics, detection, and performance evaluation. It offers insights into g-C3N4-based heterostructures' potential for application in H2O2 production and concludes with future prospects and challenges, focusing on strategies to enhance yields and suggesting new research directions.