## 2 g-C\({}_{3}\)N\({}_{4}\) as a Potential Photocatalyst  
Recently, a robust and visible-light-driven semiconductor, graphitic carbon nitride (g-C\({}_{3}\)N\({}_{4}\)) with a characteristic two-dimensional structure has attained great attention from researchers in field of photocatalysis due to its unique properties [40; 41; 42]. These properties comprise of earth-abundance, high physicochemical stability, appealing electronic band structure, and facile synthesis methods using low-cost precursors, i.e., melamine, cyanamide, thiourea, etc., [43]. [PERSON] et al., in 2009 reported g-C\({}_{3}\)N\({}_{4}\) as a metal-free conjugated semiconductor photocatalyst when employed for photocatalytic water splitting under visible-light illumination [44]. In addition, g-C\({}_{3}\)N\({}_{4}\) not only accompanied suitable band energy of 2.7 eV with 1.07 V CB position but also possesses high chemical and thermal stability because of its tri-s-triazine structure and high degree of polymerization. However, its practical applications are strictly hampered due to its inherent drawbacks, such as lower visible-light range, smaller specific surface area, lower quantum yield, and high rate of recombination due to weak van der Waals interactions between adjacent carbon nitride layers [45; 46]. Therefore, researchers have focused more on altering g-C\({}_{3}\)N\({}_{4}\) with fine surface and electronic characteristics via morphology control and band assembly engineering. In order to improve the photocatalytic efficiency of the pristine g-C\({}_{3}\)N\({}_{4}\), various modifications have been employed, including doping, heterostructure formation, and incorporation of carbonaceous nanomaterials, such as reduced graphene oxide (rGO), carbon dots (CDs), and carbon nanospheres [47; 48]. In addition, quantum dots have attained a key research focus due to their exclusive size-dependent characteristics and definite optical and electronic properties. An incipient zero-dimensional (0D) carbon quantum dots (CQDs) nanomaterial exhibits an average size of less than 10 nm. Coupling with CQDs rather than other semiconductor quantum dots is a feasible procedure to enhance the photocatalytic activity of g-C\({}_{3}\)N\({}_{4}\), owing to physiochemical durability, photochemical stability, water solubility, non-toxicity, ultra-small dimension, and photoinduced electron transport properties [49; 50; 51]. Additionally, their excellent up-conversion photoluminescence (PL) characteristic as a result of multiple-photon excitation, indicated maximum visible-light absorption [52]. It has been noticed that they possess excellent electron reservoir/transport features and distinct emission traps due to quantum confinement effect with \(\pi\) conjugate structure. The usage of metal-free CQDs as remarkable co-catalyst generates a key basis for interface engineering of g-C\({}_{3}\)N\({}_{4}\) photocatalyst. Therefore, the g-C\({}_{3}\)N\({}_{4}\)/CQDs based nanocomposites have some diverse merits over the bare g-C\({}_{3}\)N\({}_{4}\), such as broader visible-light absorption, ultra-high specific surface area, and enhanced electron-hole pair migration and separation efficiency [53]. This review provides the summary of the latest research progression in the coupling of g-C\({}_{3}\)N\({}_{4}\) with CQDs and other semiconductors for the preparation of new nanocomposites. The growth of number publications as a function of the year for CQDs/g-C\({}_{3}\)N\({}_{4}\)-based photocatalysts for wastewater treatment evaluated using the keyword 'CQDs/g-C\({}_{3}\)N\({}_{4}\) + wastewater' for the last ten years, as shown in Figure 2. Firstly, we introduced the design consideration of the g-C\({}_{3}\)N\({}_{4}\)/CQDs-based nanocomposite. Next, we will provide a detailed discussion on the recent developments of these nanocomposites in the field of photocatalysis, particularly for the treatment of organic contaminants in water.