g-C3N4 based mixed metal/semiconductor heterojunction nanocomposites towards photocatalytic water splitting for hydrogen production: A review

Now a days, the developemnt of eco-friendly, economical, and efficient photocatalysts for escalating global energy crisis and environmental degradation underscore the urgent need for sustainable hydrogen production via water splitting. For this, traditional photocatalysts are constrained by their limited light absorption, rapid electron-hole recombination, and stability concerns. The non-metal semiconductor polymeric photocatalyst known as g-C3N4 possesses an acceptable energy band gap (2.7 eV), excellent structure, low toxicity, chemical stability, high thermal resistance, cost-effectiveness, easy synthesis, and the ability to absorb light. However, despite all these excellent properties, g-C3N4 has some alarming drawbacks that limit its performance for photocatalytic H2 generation via photocatalytic water splitting, these drawbacks include massive recombination of charge carriers, limited visible light absorption, and low surface area. A lot of attempts and/or efforts has been made to address these drawbacks for better performance of g-C3N4–based composites. However, despite all these attempts, there is still little review papers that discuss more on the recent synthesis method and strategies to enhance the performance of g-C3N4–based photocatalyst for hydrogen production. In this review, we explore the photocatalytic water splitting for hydrogen production using g-C3N4 based mixed metal-semiconductor heterojunction nanocomposites under light irradiation. The study also goes further to discuss more on the structure and properties of g-C3N4, recent synthesis methods, coupled with metal, semiconductors to form heterojunctions, and elemental doping, as well as photocatalytic performance of H2 generation of g-C3N4 based heterojunction nanocomposites. Moreover, we outlook the challenges and future directions of g-C3N4-based photocatalysts, which also provides a reference for the design of other g-C3N4 based catalysts.