## 3 Results and Discussion
### MS of Coal Processed with VESFFs  
Figure 8 shows the Raman spectra of coal samples from two regions. The Raman spectra of the coal processed with VESFFs formulated with VESs of different ionic types as the main agent at 313.15 K had two peaks: a D peak (1335-1347 cm\({}^{-1}\)) and a G peak (1590-1600 cm\({}^{-1}\)). Due to the superposition of the G and D peaks, the Raman spectrum was analyzed using Peakfit software. For the determination of the approximate location and number of spectral peaks in the overlapping region, the Gauss + Lor Area and AutoFit Peaks I Second Derivative functions were selected. The first-order Raman spectrum band (1000-1800 cm\({}^{-1}\)) of the coal was analyzed to identify the presence of five distinct peaks. The peaks identified were D\({}_{1}\), D\({}_{2}\), D\({}_{3}\), D\({}_{4}\), and G. Of these, D\({}_{1}\) and G were the most prominent (Figure 9). The optimal first-order coal spectrum G band was identified at approximately 1590 cm\({}^{-1}\), which corresponds to the E\({}_{2g}\) symmetric stretching vibration mode in the aromatic layer of graphite crystals [44]. The D\({}_{1}\) band, which is associated with defects, typically occurs within the range of 1330-1370 cm\({}^{-1}\). This range corresponds to the A\({}_{1g}\) symmetry mode of the graphite lattice and is caused by defects within the aromatic layer or disordered structures, such as heteroatoms [27; 36; 45]. The D\({}_{2}\) band is approximately located at 1620 cm\({}^{-1}\), and its intensity diminishes as the tissue degree rises. The D\({}_{3}\) band is typically observed within the range of 1500-1550 cm\({}^{-1}\) and is postulated to originate from amorphous sp\({}^{2}\) carbon bonds, including those present in functional groups, organic molecules, and fragments in materials  
Figure 8: Raman spectrum of coal samples. Figure 7: Peak areas of -COOH and -C=O of test samples from two regions processed with VESFFs: (**a**) TS coal samples; (**b**) NC coal samples. exhibiting disordered structures. The D4 band was observed at approximately 1150 cm\({}^{-1}\) and is indicative of highly disordered materials, such as soot [44]. As illustrated in Table 3, the Raman spectrum D1 peak shift of the TS coal exhibited a range of 1322.7 to 1327.1 cm\({}^{-1}\), with a maximum difference of 4.4 cm\({}^{-1}\). The peak G shift exhibited a range of 1582.6 to 1596.7 cm\({}^{-1}\), with a maximum difference of 14.1 cm\({}^{-1}\). The maximum peak position difference (G-D1) was observed to be 274.0 cm\({}^{-1}\), while the minimum was 255.8 cm\({}^{-1}\). The Raman spectrum D1 peak shift of the NC coal varied in the range of 1323.6-1326.5 cm\({}^{-1}\), with a maximum difference of 2.9 cm\({}^{-1}\). The peak G shift varied in the range of 1572.9-1588.2 cm\({}^{-1}\), with a maximum difference of 15.3 cm\({}^{-1}\). The maximum peak position difference (G-D1) was 264.6 cm\({}^{-1}\) and the minimum was 246.4 cm\({}^{-1}\). The peak D1 shifts of the coal samples from two areas processed with VESFFs B, B2, C, and D showed few differences. The peak position difference (G-D1) of coal undergoing treatment with VESFFs B, B2, and C changed slightly (maximum 5.4 cm\({}^{-1}\)). The G peak of the VESFF D treatment on the TS coal shifted to a higher wavenumber domain, resulting in an increase in peak position difference (approximately 18.2 cm\({}^{-1}\)) in Figure 10a. This indicates a reduction in the bandwidth of the amorphous structure and an increase in the sp\({}^{2}\) content, which suggests that the carbon atoms were undergoing a transition towards a more ordered structure. The mean value of the dry ash-free volatile matter (\(V_{dd}\)) of the TS coal samples was 30.07%, while the mean value of the dry ash-free volatile matter (\(V_{dd}\)) of the NC coal samples was 10.6%. The TS coal samples were a type of highly volatile bituminous coal, having more side chains and functional groups on their surface molecules and larger defects in molecular structure than the NC coal samples.