*2.2. Morphology Study*

The morphologies of bulk-CN, CNS, TiO2, and 0.5CNS/TiO2 composites were examined by SEM as shown in Figure 3. We can see that bulk-CN presents in the form of bulk morphology with a layered structure (Figure 3a) [48]. CNS revealed smaller particles like the nanosheet structure after thermal exfoliation with HNO3 − (Figure 3b). The BET surface area of bulk-CN and CNS were calculated to be 68.26 and 91.61 m2g−1, respectively. It is possible that the van der Waals forces and hydrogen bonds of g-C3N4 might be destroyed

with thermal treatment which results in the separation of g-C3N4 into small layers [49,50]. In addition, nitric acid might be intercalated into interlayers of bulk-CN which caused the expansion of their interlayer space and reduction of the layer thickness and hence increased its surface area [51,52]. The obtained TiO2 showed spherical-like morphology with a particle size around 10 nm. From Figure 3d, it can be seen that the CNS particles having thin-layered structures are well distributed on the surface of TiO2 particles, which is consistent with the presence of the peaks of g-C3N4 in XRD, XPS, and Raman spectra.

**Figure 3.** (**a**) SEM images of (**a**) bulk-CN, (**b**) CNS, (**c**) TiO2, and (**d**) 0.5CNS/TiO2.
