## 3 Design Consideration for g-C\({}_{3}\)N\({}_{4}\)/CQDs-Based Nanocomposites
### g-C\({}_{3}\)N\({}_{4}\)/CQDs-Based Nanocomposites for Different Antibiotic Degradation  
At the present time, the existence of antibiotics in environmental conditions has received great attention as evolving contaminants, as a result of inappropriate use and effluents discharge from the industrial waste. This causes a serious threat to human and environmental health, primarily attributed to bioaccumulation and hydrophilicity, as well as firm biological stability and activity of antibiotics [67]. Thus, in recent times, an abundance of research data has focused mainly on antibiotic removal from water. For instance, [PERSON] and his peer group reported a g-C\({}_{3}\)N\({}_{4}\)/CQDs composite prepared using thermal polymerization approach towards diclofenac degradation under the visible light of 400 nm [68]. The obtained composite displayed 15-fold enhanced photoactivity in the degradation procedure, in comparison to bare g-C\({}_{3}\)N\({}_{4}\) as CQDs deposition not only altered the structure and morphology of the g-C\({}_{3}\)N\({}_{4}\) but also improved the optical absorption range. In order to identify the role of reactive oxidative species in photodegradation of diclofenac, distinct scavengers have been added to the system. With the addition of ammonium oxalate no response was observed in diclofenac degradation, which indicated h\({}^{+}\) played no role in degradation process (Figure 6a). On the other hand, when p-benzoquinone and tert-butyl alcohol was added a decreased (first-order) K\({}_{1}\) values for diclofenac degradation were detected from 0.14 to 2.7 \(\times\) 10\({}^{-3}\) min\({}^{-1}\) and 9.0 \(\times\) 10\({}^{-2}\) min\({}^{-1}\), respectively. This signified that both \({}^{\bullet}\)O\({}_{2}\)\({}^{-}\) and \({}^{\bullet}\)OH radicals facilitated the degradation procedure and \({}^{\bullet}\)O\({}_{2}\)\({}^{-}\) was a dominant species (Figure 6b). In another piece of work, [PERSON] and co-workers reported the novel CQDs decorated g-C\({}_{3}\)N\({}_{4}\) nanosheet-based nanocomposite, synthesized via facile thermally oxidative etching method for the removal of sulfataazine [34]. The increase in band gap for the CQDs/g-C\({}_{3}\)N\({}_{4}\) nanosheet corresponding to the exfoliation temperature was evaluated using fluorescence spectrum, which displayed blue shift emission, attributed from quantum confinement effect of the changed electronic CQDs levels (Figure 6c). Additionally, the transient photocurrent density of the as-synthesized photocatalyst under visible-light irradiation was delineated in (Figure 6d). The CQDs/g-C\({}_{3}\)N\({}_{4}\) nanosheet (calined at 500 \({}^{\circ}\)C) achieved maximum photocurrent density revealing more effective separation efficiency of the charge pairs than a simple CQDs/g-C\({}_{3}\)N\({}_{4}\) nanocomposite. In a similar study by [PERSON] et al., the same nanocomposite was fabricated using thermal polymerization approach with in situ growth of g-C\({}_{3}\)N\({}_{4}\)[69]. The energy dispersive X-ray spectroscopy depicted the N and C atoms in 3 wt% CQDs-g-C\({}_{3}\)N\({}_{4}\) and an abundance of C was observed, ascribed to in-plane multiple C ring, indicating 3 wt% CQDs-g-C\({}_{3}\)N\({}_{4}\) were in-plane composite (Figure 6e). Additionally, density functional theory intentions of electronic structure found the in-depth understanding of the relationship between as-prepared photocatalyst and their photoactivity. For a pure g-C\({}_{3}\)N\({}_{4}\) semiconductor, CB and VB were basically composed of 2p orbitals of C and N, respectively. On the contrary, CQDs/g-C\({}_{3}\)N\({}_{4}\) possessed smaller band energy with few new energy levels above 0.75 eV, with CB and VB  
Figure 5: (**a**) Fourier transform infrared spectrum, (**b**) time-resolved photoluminescence analysis, and (**c**) electron impedance spectroscopy of Zn\({}_{2}\)V\({}_{2}\)O\({}_{7}\)/CQDs/g-C\({}_{3}\)N\({}_{4}\) hybrid and Zn\({}_{2}\)V\({}_{2}\)O\({}_{7}\). Reproduced with permission from Ref.