# An Experimental Study of Glycerol Carbonate Synthesis over g-C\({}_{3}\)N\({}_{4}\) Catalysts
## 3 Results and Discussions  
### Catalyst Characterization  
The structure and phase identification of the samples, including bare g-C\({}_{3}\)N\({}_{4}\) (CN), g-C\({}_{3}\)N\({}_{4}\) doped with P and S (PSCN), g-C\({}_{3}\)N\({}_{4}\) doped with P, S, and Mg (MgPSCN), and g-C\({}_{3}\)N\({}_{4}\) doped with P, S, and Li (LiPSCN), were determined by using X-ray diffraction analysis. The XRD patterns for these materials are given in Figure 1. Two prominent peaks with high intensity were observed at 20 \(\approx\) 12.24\({}^{\circ}\) and 27.32\({}^{\circ}\), which correspond to the diffraction planes of bare g-C\({}_{3}\)N\({}_{4}\). These diffraction values agree with the data in the literature [47; 48; 49; 50]. The pronounced peak at 20 \(\approx\) 27.24\({}^{\circ}\) corresponds to the (002) diffraction plane, attributed to the interlayer stacking of conjugated aromatic structures, with an interlayer distance of 0.324 nm. The lower-intensity peak at 20 \(\approx\) 12.24\({}^{\circ}\) corresponds to the (100) diffraction plane, indicating the in-plane structural arrangement of tri-s-triazine units with an interlayer distance of 0.680 nm [26; 28; 32]. For the samples doped with P and S, the intensity of the (002) diffraction peak decreased, indicating a reduction in crystallinity compared to bare g-C\({}_{3}\)N\({}_{4}\) likely due to the disruption of crystal growth by the addition of P and S. The intensity of the (100) peak also diminished, suggesting that the incorporation of these dopants distorted the formation of nitride pores and altered the interlayer distance, indicating strong interactions between the dopants and the host g-C\({}_{3}\)N\({}_{4}\) matrix [28; 51]. The g-C\({}_{3}\)N\({}_{4}\) samples doped with Li and Mg exhibited similar diffraction peaks to those of bare g-C\({}_{3}\)N\({}_{4}\), indicating that the overall structure of g-C\({}_{3}\)N\({}_{4}\) remained largely unchanged by Li and Mg doping [52]. Additionally, no separate diffraction peaks corresponding to Li or Mg were detected in the MgPSCN and LiPSCN samples, confirming that Li and Mg were successfully doped into the g-C\({}_{3}\)N\({}_{4}\) framework [40]. After the addition of Li and Mg the peak intensities for both the (002) and (100) diffraction planes decreased, suggesting that the presence of these dopants further reduced the crystallinity of the material [40]. Moreover, the distortion of nitride pores and the alteration of the interlayer distance further indicate strong interactions between the dopants and the host g-C\({}_{3}\)N\({}_{4}\)[52; 53]. The average crystallite size (D) of the catalysts was determined using the Debye-Scherrer Equation (1), which is as follows [54]:  
\[\mathrm{D=}\frac{\mathrm{k\cdot\lambda}}{\beta\cdot\cos\theta} \tag{1}\]  
where \(\lambda\) is the wavelength of the X-rays used (Cu K\(\alpha\) = 0.15406 nm), \(\beta\) is the full width at half maximum (FWHM) of the diffraction peak, \(\theta\) is the Bragg diffraction angle, and k is the shape factor, typically assumed to be 0.98. The average crystallite sizes of CN, PSCN, MgPSCN, and LiPSCN, calculated using this equation, were found to be 10.94, 17.57, 10.71, and 6.86 nm, respectively (Table 1). The full X-ray photoelectron spectroscopy (XPS) survey of the MgPSCN catalyst before use, as illustrated in Figure 2, is evidence of the presence of C, N, O, P, S, and Mg elements in MgPSCN. The observed peaks at 285 eV, 395 eV, 529 eV, 136 eV, 166 eV, 49.7 eV, and 1303 eV correspond to C1s, N1s, O1s, P2p, S2p, Mg2p, and Mg1s, respectively [52; 55]. The peak at 285 eV is attributed to the sp\({}^{2}\) hybridization of C=C bonds, while the peak at approximately 136.0 eV corresponds to P-N/P-O bonds. Additionally, peaks in the sulfur spectrum at 166 eV and 228 eV were observed, corresponding to S2p and S1s, indicating the incorporation of sulfur atoms (S-doped) in nitrogen sites within the structure [56]. The peak at 395 eV suggests the presence of tri-coordinated nitrogen in N-(C)\({}_{3}\) groups.