## 3 Design Consideration for g-C\({}_{3}\)N\({}_{4}\)/CQDs-Based Nanocomposites
### g-C\({}_{3}\)N\({}_{4}\)/CQDs-Based Nanocomposites for Pollutant Degradation  
The fast-growing urbanization and agricultural industries have led to inevitable discharge of the large quantity of hazardous, toxic, and interminably pollutants into the natural environment. Hence, with the goal of conserving the environment and apprehending the sustainable advances of human life, the photodegradation of pollutants is a research focus worldwide. In this regard, g-C\({}_{3}\)N\({}_{4}\)/CQDs-based nanocomposites, as novel heterogeneous photocatalysts, have recently attained great research attention due to their potential application in the eradication of a wide-range of contaminants [58; 59]. For instance, [PERSON] and co-workers studied the photocatalytic performance of CQDs-decorated g-C\({}_{3}\)N\({}_{4}\), synthesized by a novel method using CQDs and dicyandiamide as chemicals, employed for rhodamine B (RhB) elimination in the presence of the UV light region [60]. This study demonstrated the photoactivity of g-C\({}_{3}\)N\({}_{4}\)/CQDs nanocomposite (0.013 mol\({}^{-1}\)min\({}^{-1}\)) to be three times greater than bare g-C\({}_{3}\)N\({}_{4}\) (0.0044 mol\({}^{-1}\)min\({}^{-1}\)). In another piece of research, [PERSON] and his peer group combined g-C\({}_{3}\)N\({}_{4}\) with distinct mole fractions of CQDs to evaluate the photocatalytic activity for photodegradation of phenol under visible-light irradiation [61]. Figure 3: Schematic representation of the role of CQDs in the g-C\({}_{3}\)N\({}_{4}\)/CQDs-based nanocomposite, (**a**) CQDs hampers electron-hole pair recombination, (**b**) CQDs enables photoexcitation of electrons even with 550 nm incident light, CQDs serve as electron mediator in (**c**) type-II, and (**d**) Z-schemes. Adapted from Ref. [23]. The nanocomposite was prepared through feasible impregnation thermal technique and composite containing 0.5 wt% of CQDs, displaying a 3.7 times higher rate constant with best photodegradation ability than bare g-C\({}_{3}\)N\({}_{4}\) (Figure 4a). The proposed mechanism of the g-C\({}_{3}\)N\({}_{4}\)/CQDs nanocomposites under visible-light illumination were delineated in (Figure 4b). The up-conversion photoluminescence (UCPL) properties of CQDs enabled the conversion of longer wavelengths into smaller wavelengths (\(\lambda\) = 460 nm), resulting in photo-excitation of charge pairs by g-C\({}_{3}\)N\({}_{4}\). Subsequently, the matched band configuration imitates electrons migration from CB of g-C\({}_{3}\)N\({}_{4}\) to CQDs, giving maximum charge carrier separation. Importantly, the photostability of the g-C\({}_{3}\)N\({}_{4}\)/CQDs nanocomposite was also significantly bettered wherein the photocatalytic performance of the photocatalyst endured up to five successive consecutive cycles under light illuminations (Figure 4c). Additionally, a g-C\({}_{3}\)N\({}_{4}\)/CQDs nanocomposite was fabricated through a simple hydrothermal approach and displayed outstanding degradation activity of 71.53% towards 2,4-dichlorophenol, 1.5-fold greater than bare g-C\({}_{3}\)N\({}_{4}\)[62]. Henceforth, from the above discussion it can be concluded that the best efficacy of the photocatalyst was attributed to CQDs, which acted as electron sinks and hamper the recombination of charge pairs with enhanced separation rate. In addition, UV-visible diffuse reflectance spectrum (UV-vis DRS) analysis detected CQDs as photosensizers for g-C\({}_{3}\)N\({}_{4}\), enabling wider-range light harvesting of solar light. This broad-spectrum absorption generates more electrons for the enhancement of photocatalytic performance. Very recently, a defect-enriched g-C\({}_{3}\)N\({}_{4}\)/N-doped CQDs nanocomposite was synthesized via impregnation approach using urea and citric acid as starting materials by [PERSON] and co-workers [63]. The synthesized binary nanocomposite exhibited excellent light-harvesting capability, narrow band-gap, and feasible electron transport capability, resulting in improved photocatalytic activity towards RhB degradation.