## 3 Design Consideration for g-C\({}_{3}\)N\({}_{4}\)/CQDs-Based Nanocomposites
### g-C\({}_{3}\)N\({}_{4}\)/CQDs-Based Nanocomposites for Pollutant Degradation
Moreover, this binary hybrid displayed the complete RhB elimination rate of 100% along with a H\({}_{2}\) generation rate of 3.68 umol h\({}^{-1}\) g\({}^{-1}\). The g-C\({}_{3}\)N\({}_{4}\)/N-doped CQDs nanocomposite possessed the outstanding electron delocalization feature, which was confirmed using electron paramagnetic resonance (EPR) results (Figure 4d). The spin intensity of the photocatalyst was mainly accelerated with the optimum doping of the N-doped CQDs, revealing the delocalization of single electron and giving enhanced migration and separation efficacy of the electron-hole pairs of the composite. The presence of N-doped CQDs on the surface of defect-rich g-C\({}_{3}\)N\({}_{4}\) with lattice spacing (100) was observed in a transmission electron microscopy (TEM) image to form hybrid photocatalyst (Figure 4e). Similarly, the S-doped CQDs/g-C\({}_{3}\)N\({}_{4}\) hybrid was studied for methyl orange degradation with higher sulfur content under visible-light illumination, yielding increased photoactivity [64]. From N\({}_{2}\)-adsorption-desorption results, we determined the surface area of the photocatalyst and found type-IV adsorption isotherm due to a weak Van der Waals interaction and porous nature (Figure 4f). The excellent surface area was exhibited by the 1:1 S-doped CQDs-10 wt%/g-C\({}_{3}\)N\({}_{4}\) sample, i.e., 111.72 m\({}^{2}\)/g, which was 4-fold enhanced to pristine g-C\({}_{3}\)N\({}_{4}\) (27.58 m\({}^{2}\)/g). The complete photodegradation efficiency of MO dye was achieved under a UV-visible light range of \(\lambda\) > 350 nm within 40 min, while under visible-light irradiation, it reached about 94.3% within 80 min. In other work, a jamun-like designed g-C\({}_{3}\)N\({}_{4}\)/CQDs/Zn\({}_{2}\)V\({}_{2}\)O\({}_{7}\) hybrid composite has been reported for the photodegradation of RhB dye [65]. The Fourier transform infrared (FTIR) spectrum of bare Zn\({}_{2}\)V\({}_{2}\)O\({}_{7}\) and g-C\({}_{3}\)N\({}_{4}\)/CQDs/Zn\({}_{2}\)V\({}_{2}\)O\({}_{7}\) were delineated in (Figure 5a). All featured peaks of bare g-C\({}_{3}\)N\({}_{4}\) (range of 1235-1650 cm\({}^{-1}\)) and Zn\({}_{2}\)V\({}_{2}\)O\({}_{7}\) (646, 781, and 831 cm\({}^{-1}\)) matched well with the observed peaks in the g-C\({}_{3}\)N\({}_{4}\)/CQDs/Zn\({}_{2}\)V\({}_{2}\)O\({}_{7}\) hybrid, confirming the formation of nanocomposite. However, no peak was observed for the CQDs in the composite, indicating no destruction in the crystallinity and framework of both Zn\({}_{2}\)V\({}_{2}\)O\({}_{7}\) and g-C\({}_{3}\)N\({}_{4}\) photocatalyst with CQDs deposition during preparation procedure. Additionally, photoluminescence (PL) spectra of as-synthesized g-C\({}_{3}\)N\({}_{4}\)/CQDs/Zn\({}_{2}\)V\({}_{2}\)O\({}_{7}\) hybrid possessed lower recombination rate of charge pairs due to weak emission peak than bare Zn\({}_{2}\)V\({}_{2}\)O\({}_{7}\) and g-C\({}_{3}\)N\({}_{4}\) photocatalyst as a result of the synergistic effect between the Zn\({}_{2}\)V\({}_{2}\)O\({}_{7}\), g-C\({}_{3}\)N\({}_{4}\), and CQDs (Figure 5b). Furthermore, electron impedance spectroscopy (EIS) analysis measured the internal charge transport resistance (R\({}_{\rm ct}\)) on the interfacial contact of bare Zn\({}_{2}\)V\({}_{2}\)O\({}_{7}\) and g-C\({}_{3}\)N\({}_{4}\)/CQDs/Zn\({}_{2}\)V\({}_{2}\)O\({}_{7}\) electrodes and detected smaller R\({}_{\rm ct}\) for the g-C\({}_{3}\)N\({}_{4}\)/CQDs/Zn\({}_{2}\)V\({}_{2}\)O\({}_{7}\) photocatalyst (Figure 5c). This hybrid photocatalyst exhibited the best conducting nature, which basically enhanced the photodegradation efficiency of RhB (97% in 30 min). In addition, [PERSON] et al., loaded CQDs on the surface of the g-C\({}_{3}\)N\({}_{4}\) and further combined with BiVO\({}_{4}\) forming a g-C\({}_{3}\)N\({}_{4}\)/CQDs/BiVO\({}_{4}\) Z-scheme heterostructure through sonication technique under LED light [66].