Recent advances, synthetic and adaptive approaches of graphitic carbon nitride based nanocomposites towards sustainable applications: A review

Graphitic carbon nitride (g-C₃N₄) has emerged as a next-generation photocatalyst, attracting remarkable attention for energy and environmental applications owing to its unique structural and electronic properties. As the demand for efficient and cost-effective solar energy conversion materials grows, g-C₃N₄ stands out due to its tunable band gap (∼2.7 eV), excellent photochemical stability, and fascinating electronic band structure. Structurally, g-C₃N₄ is a layered, polymeric semiconductor composed of carbon and nitrogen atoms arranged in a tris-triazine framework, offering abundant opportunities for chemical modification and functionalization. Compared to graphene, g-C₃N₄ is an efficient visible-light-driven photocatalyst with a moderate band gap and excellent chemical and thermal stability, making it suitable for a wide range of reactions. This review focuses on various synthesis strategies for g-C₃N₄ nanomaterials, including quantum dots, nanosheets, and nanotubes, with controlled morphology and structure. However, pristine g-C₃N₄ suffers from limitations such as low surface area, poor light absorption, and rapid electron–hole recombination, which significantly restrict its photocatalytic efficiency in many applications. Therefore, this review summarizes several modification strategies for g-C₃N₄ including metal and non-metal doping, co-doping, heterojunction construction, coupling with metal-free carbon materials, and defect engineering. These approaches aim to enhance photocatalytic activity by extending light absorption, improving charge transfer and separation, increasing surface area, reducing band gap energy, and suppressing charge recombination. Moreover, this review provides a comprehensive overview of the state-of-the-art progress, emerging trends, and key challenges associated with novel g-C₃N₄ nanostructures. Their applications in diverse fields including photovoltaics, environmental remediation through photocatalytic degradation of hazardous pollutants, sustainable fuel generation via water splitting and CO₂ reduction, and sensing are discussed in detail. In addition, this critical review highlights the major limitations and unresolved issues of g–C₃N₄–based materials that must be addressed to enable large-scale, real-world implementation. Finally, future research directions are proposed, emphasizing innovative synthesis strategies, advanced structural engineering, and the integration of g-C₃N₄ with next-generation materials to unlock its full potential for energy and environmental applications.