Graphitic carbon nitrides (g-$C_3$N₄), which possess distinctive graphite-like structure, and their composites have found relevance in several applications. This is attributed to their favorable band gap, metal-free nature, high thermal and photo-stability. Other properties including good mechanical properties, chemical inertness, non-toxicity, good biocompatibility and excellent electroluminescent properties have also accentuated their increased applications in different areas. Entirely new properties are obtained when they combine with other nanomaterials to form nanocomposites, and all these properties are now being explored for various benefits. This review highlights the historical background of g-$C_3$N₄, the recent progress in the application of the materials in its pristine form, the composite with different inorganic compounds and nanomaterials. Particular attention is given to their applications in nitrogen fixation, as reference material for differentiating oxygen site, in energy storage device, sensing, chemical synthesis, water splitting, photocatalytic heavy metal ions reduction, environmental remediation from pollutants and medicine. The properties were highlighted and different applications were discussed, with the aim of exploring other new areas of applications of g-$C_3$N₄. The different routes that have been utilized for the synthesis of g-$C_3$N₄, the various nanostructures obtained and the analytical techniques that are required for their characterization were discussed. Finally, in the interest of the recent development and focus on photo enhanced process, diverse ways of enhancing the photocatalytic activities of g-$C_3$N${}_4$ and its composites were investigated.

石墨碳氮化物（g-$C_3$N ₄）具有独特的类石墨结构，其复合材料在多种应用中具有相关性。这归因于它们的有利带隙，无金属性质，高热稳定性和光稳定性。其他性能，包括良好的机械性能，化学惰性，无毒性，良好的生物相容性和出色的电致发光性能，也突显了它们在不同领域中的日益广泛的应用。当它们与其他纳米材料结合形成纳米复合材料时，便获得了全新的性能，而现在正在探索所有这些性能以获得各种益处。这篇评论重点介绍了g-$C_3$N ₄，其原始形式的材料，具有不同无机化合物和纳米材料的复合材料的应用的最新进展。特别注意它们在固氮，作为区分氧位的参考材料，储能装置，传感，化学合成，水分解，光催化重金属离子还原，污染物和药物的环境修复中的应用。着重介绍了这些属性，并讨论了不同的应用，以期探索g-g应用的其他新领域$C_3$N ₄。已用于合成g-$C_3$N ₄，讨论了获得的各种纳米结构以及表征其所需的分析技术。最后，为了最新的发展并专注于光增强过程，采用多种方式增强g-的光催化活性。$C_3$ñ${}_4$ 并对其复合材料进行了研究。