## 3 Results and Discussion
### FeOx/g-C\({}_{3}\)N\({}_{4}\) Composite Characterisation
However, in comparison to (FeO\(\times\)/g-C\({}_{3}\)N\({}_{4}\))\(ex\), the (002) peak of g-C\({}_{3}\)N\({}_{4}\) is observed slightly shifted toward lower diffraction angle with considerably reduced intensity and also the (100) peak is apparently supressed. This suggests the intercalation of the layered structure of g-C\({}_{3}\)N\({}_{4}\) by the abundant urchin-like structures (size \(\sim\)10-20 nm) present on the surface of FeOx contributing to diminish the peak [57; 58]. According to the Bragg equation (\(\lambda\) = 2 disn\(\otimes\)), the expanded interlayer distance of the d-spacing due to the intercalation of iron urchins into g-C\({}_{3}\)N\({}_{4}\) layers may lead to the shift of the diffraction peak toward low angle. Moreover, the reduced intensity of the peak shows the possibility of  
Figure 3: Raman spectra of g-C\({}_{3}\)N\({}_{4}\) compared to composites (FeO\(\times\)/g-C\({}_{3}\)N\({}_{4}\))\(in\) and (FeO\(\times\)/g-C\({}_{3}\)N\({}_{4}\))\(ex\) (**a**) and FeOx supporting material (**b**). less dense lamellar structure of the g-C\({}_{3}\)N\({}_{4}\) in the composite due to the presence of small amounts of g-C\({}_{3}\)N\({}_{4}\) (in the form of thin petals) on the FeOx surface [59; 60]. These structural changes likely imply that in the in situ method of the formation of composite films, the g-C\({}_{3}\)N\({}_{4}\) interacts and reconfigures the surface of FeOx differently than ex situ method. The absorption spectra and Tauc plot of the FeOx/g-C\({}_{3}\)N\({}_{4}\) composites are presented in Figure 5. An absorption region can be observed from the visible range (<600 nm) while a constant increase up to the UV range of the spectrum is detected for both composite materials. Interestingly, the (FeOx/g-C\({}_{3}\)N\({}_{4}\))\(in\) composite film shows lower bandgap (\(\sim\)1.87 eV) than the (FeOx/g-C\({}_{3}\)N\({}_{4}\))\(ex\) composite (\(\sim\)1.95 eV). Also, the observed bandgaps (1.87 and 1.95 eV) are in agreement with the literature [61]. For both synthesis methods, due to the presence of FeOx as the supporting material, the absorbance is shifted towards the visible part of the spectrum in comparison to the bulk g-C\({}_{3}\)N\({}_{4}\) presented in Figure S7. Morphology and composition of the synthesized FeOx iron urchins and of the composites (FeOx/g-C\({}_{3}\)N\({}_{4}\))\(in\) and (FeOx/g-C\({}_{3}\)N\({}_{4}\))\(ex\) FeOx were investigated using SEM and EDXS techniques. Figure 6 presents the images of the surface of the FeOx urchin-like structure produced by PLD and annealed at 550 \({}^{\circ}\)C for 4 h in a tubular furnace used as the support material. EDXS results essentially confirm the presence of Fe and O on the microstructures (Figure S8). This agrees with previously published reports on this material [40; 42]. The mass of the FeOx films was 21 \(\pm\) 2 mg before the composite preparation steps. SEM images in Figure 7 show the morphology of the (FeOx/g-C\({}_{3}\)N\({}_{4}\))\(in\) composite. The formation of a petal-like microstructure (Figure 7a,b) is now observed as compared to the bare FeOx urchin. From Figure 7c, it is also observable that urchins present on the FeOx surface possibly intercalate the petal structure. A special formation of petal-like morphology growth is highlighted in (Figure 7d) as a single petal close-up (magnified image in the inset). Moreover, EDXS (Figure S9) confirms the presence of the C, N, Fe, and O elements in the composite film. The mass of the composite is about 10 mg more than the 21 \(\pm\) 2 mg of the initial FeOx. This corresponds to 5-10% conversion yield of melamine. Morphology of the synthesized composite (FeOx/g-C3N4)_ex_ are presented in Figure 8a-c. The visual inspection of the images demonstrates the absence of petal-like morphology and island separation (Figure 8d) between the FeOx particles and g-C3N4 deposited on the surface of the iron urchins. In this case, the mass increase was about 40 mg (about 60 mg total composite mass), due to the drying of 1 mL solution after the spin-coating process.