# An Experimental Study of Glycerol Carbonate Synthesis over g-C\({}_{3}\)N\({}_{4}\) Catalysts
## 3 Results and Discussions
### Catalyst Characterization
For the Mg 1s spectrum, the peak at 1303 eV is evidence of the presence of Mg(II) ions. In the Mg 2p spectrum, the peak at 49.7 eV corresponds to elemental magnesium (Mg\({}^{0}\)) [40; 52]. After two cycles of use under optimal reaction conditions, no significant changes were observed in the spectral peaks except for the disappearance of the peak at 166 eV, which corresponds to S2p, suggesting a potential loss of sulfur atoms during the reaction. These findings confirm the stability of the catalyst, which was further supported by microscopic analysis. \begin{table}
\begin{tabular}{c c c c c} \hline \multirow{2}{*}{**Catalysts**} & **BET Surface Area** & **Pore Volume** & **Average Pore Width** & **Average Crystallite Size** \\  & **(m\({}^{2}\)/g)** & **(cm\({}^{3}\)/g)** & **(nm)** & **(nm)** \\ \hline CN & 10.85 & 0.062 & 5.20 & 10.94 \\ PSCN & 10.10 & 0.085 & 29.396 & 17.57 \\ MgPSCN & 9.19 & 0.063 & 16.09 & 10.71 \\ LiPSCN & 17.32 & 0.128 & 29.396 & 6.86 \\ \hline \end{tabular}
\end{table} 
Table 1: Textural properties and crystallite sizes. Figure 1: The X-ray diffraction (XRD) patterns of catalysts. Figure 3 presents SEM images of the porous samples, highlighting distinct morphological characteristics. The morphology of bare g-C\({}_{3}\)N\({}_{4}\) (CN) (Figure 3A) exhibits an irregular granular and layered structure with numerous pores, as also shown in the previous literature [28; 57]. This porous structure is attributed to the liberation of ammonia (NH\({}_{3}\)) and carbon dioxide (CO\({}_{2}\)) gases during the thermal decomposition of melamine [44]. In contrast, CN doped with phosphorus and sulfur (PSCN) (Figure 3B) demonstrates a thinner, plate-like structure with a higher surface porosity compared to undoped g-C\({}_{3}\)N\({}_{4}\). A significant difference is observed in the layer distribution and pore size, with the pores in PSCN increasing in dimension as confirmed by textural analysis. Figure 3: Scanning electron microscopy images of CN (**A**), PSCN (**B**), MgPSCN (**C**), and LiPSCN (**D**) catalysts. Figure 2: Survey scan of XPS of MgPSCN before and after use. Doping with magnesium, phosphorus, and sulfur (MgPSCN) (Figure 3C) results in the formation of numerous grains with varying nano-scale dimensions, displaying smaller diameters than those in PSCN. Additionally, notable distortions in the layered morphology are evident. In contrast, lithium-doped g-C\({}_{3}\)N\({}_{4}\) (LiPSCN) (Figure 3D) shows a less uniform and smaller layered structure compared to PSCN, although the LiPSCN sample remains more uniform, larger in size, and more compactly bonded than MgPSCN [40]. The elemental mapping results of the samples showed well-defined distributions for C, N, P, S, Mg, and Li, as indicated in Figure 4. The elemental analysis indicates the presence of C and N in CN samples, with a C/N ratio of 0.48%. Upon doping with phosphorus (P) and sulfur (S), an increase in the carbon-to-nitrogen ratio to 0.80% was observed in the PSCN sample. Similarly, for the MgPSCN and LiPSCN catalysts, the carbon-to-nitrogen ratios increased compared to the CN catalyst, with values of 0.663% and 0.551%, respectively, when doped with magnesium (Mg), phosphorus (P), and sulfur (S). This suggests that deamination has taken place due to the co-doping of Mg and Li in the pure g-C\({}_{3}\)N\({}_{4}\) matrix [40]. The above discussion further supports the successful co-doping of pure g- C\({}_{3}\)N\({}_{4}\) with P, S, Mg, and Li. To analyze the specific surface area and pore structure of the samples, nitrogen adsorption-desorption measurements were conducted. As illustrated in Figure 5, all samples display type-IV isotherms, which are characteristic of mesoporous materials according  
Figure 4: EDX spectra of CN (**A**), PSCN (**B**), MgPSCN (**C**), and LiPSCN (**D**) catalysts. to the IUPAC classification, indicating the presence of well-defined mesopores [57; 58].