# Photocatalytic Properties of Immobilised Graphitic Carbon Nitride on the Alumina Substrate
## 3 Results and Discussion  
### Catalyst Characterisation  
Alumina substrate densification is well covered in the literature, and a process for the production of various alumina objects and crucibles has been commercialised within our institution, yielding a fully densified corundum (\(\alpha\)-Al\({}_{2}\)O\({}_{3}\)) phase. Synthesis of g-C\({}_{3}\)N \begin{table}
\begin{tabular}{c c} \hline Organic pollutant & Methylene blue \\ IUPAC name & 3.7-bis(dimethylamino)-phenothiazzin-5-ium chloride \\ Chemical formula & C\({}_{16}\)H\({}_{18}\)ClN\({}_{3}\)S \\ Molar mass/g\(\cdot\)mol\({}^{-1}\) & 319.85 \\ Chemical structure & \\ \end{tabular}
\end{table} 
Table 2: Physico-chemical properties of the understudied organic pollutant MB dye. is subtler especially if we consider small changes, which could influence the electronic structure and with-it photocatalytic activity. The crystal structure was studied first by XRD, and the corresponding pattern of g-C\({}_{3}\)N\({}_{4}\) is presented in Figure 3A. The diffractogram shows two characteristic diffraction peaks at 13.3\({}^{\circ}\) (100) and 27.5\({}^{\circ}\) (002), which correspond to the in-plane spacing of repeated tri-s-triazine rings and the interlayer stacking reflection, respectively [26]. The spectrum is broad due to the small crystal size and reflects the sheet-like (2D) morphology of the material. This is evident because the (002) peak corresponding to interlayer stacking dominates the spectrum. Equivalently, because these planes represent the majority of the total and are parallel with the XRD sample holder, they provide more signals in a standard X-ray powder diffraction configuration setup. A slight elevation of the whole spectra could point out to a presence of less crystalline phase; however, if the 2D sheet is very thin, similar features would also be found. The decomposition of g-C\({}_{3}\)N\({}_{4}\) powder measured by TGA analysis nicely follows expected temperature dependence (Figure 3B). There are no bumps that would indicate the presence of impurities [27]. According to evolved gas analysis (not shown), a small decrease in mass at 100 \({}^{\circ}\)C correspond to water loss, while in the degradation region also CO\({}_{2}\) and N\({}_{2}\) were detected. The degradation is completed at around 700 \({}^{\circ}\)C. Optical properties of the prepared g-C\({}_{3}\)N\({}_{4}\) were characterised by UV-visible diffuse reflection spectrum (UV-vis DRS) in Figure 4A. This semiconductor catalyst is supposed to be effective in simulated solar irradiation because g-C\({}_{3}\)N\({}_{4}\) absorbs light from the UV to the visible region, with slight variations with respect to the doping or shape of the crystals [28]. Utilizing Kubelka-Munk transformation (Figure 4B), the Eg value of 2.62 eV was estimated, which is similar to other reports and corresponds to an absorption edge starting in blue at 473 nm and extending to the UV region. The fingerprint vibrational spectrum, which corresponds to specific chemical bonding in molecules was measured with FTIR, as shown in Figure 5. Normal modes of bond vibrations for g-C\({}_{3}\)N\({}_{4}\) can be easily identified. Most characteristics are those in the range between 1100-1700 cm\({}^{-1}\). The strong peaks observed at approximately 1228, 1311, 1393, and 1456 cm\({}^{-1}\) correspond to the aromatic C-N stretching vibrations, whereas the heterocycles C=N stretching vibrations are found at 1539 and 1627 cm\({}^{-1}\)[29; 30]. The typical peak of 805 cm\({}^{-1}\) represents the tri-s-triazine structure. The broad peaks located at 3000-3300 cm\({}^{-1}\) are assigned to the stretching of N-H and C-H bonds. Figure 3: (**A**) X-ray diffractogram and (**B**) TGA analysis of _g_-C\({}_{3}\)N\({}_{4}\). In contrast to other methods, the FTIR spectrum also revealed changes in the \(g\)-C\({}_{3}\)N\({}_{4}\) sample after catalytic treatment. The sample which was repeatedly exposed to the reaction (as revealed later) exhibited few differences. Most apparent is the loss of sharpness of individual peaks.