## 3 Results and Discussion
### Oxygenated Functional Groups on Coal Surfaces Processed with VESFFs  
Figure 4 illustrates the FTIR spectra of coal samples from two regions following treatment with FFs. Although the peak intensities were different, it can be seen that the coal  
Figure 3: Adsorption mode of VESs on coal surfaces: (**a**) mixing of cationic–zwitterionic VESs; (**b**) mixing of anionic–zwitterionic VESs. Figure 2: Zeta potential of coal in VESFFs and deionized water. subjected to treatment with FFs had similar adsorption peaks. This finding is indicative of the fact that despite the disparate nature of the FFs utilized for the treatment of the coal samples, the types of surface functional groups present within the treated coal samples remain consistent, albeit with varying degrees of abundance. Because the coal samples examined by FTIR spectroscopy were not demineralized prior to the FF treatment, the absorption peaks at 1000-1100 cm\({}^{-1}\) in the FTIR spectrum are attributed to the stretching and vibration of -Si-O- groups. The spectral band 1800-2300 cm\({}^{-1}\) is the absorption peak of diamond, which is an interference peak and is not discussed. Figure 5 illustrates the peak separation and fitting of the FTIR spectral curves of coal samples sourced from two distinct regions processed with VESFF B. The study focuses on analyzing the vibrations of -COOH and -C=O on the coal surface, as well as the vibrations of -Si-O- in clay minerals, such as the kaolinite present in coal. As illustrated in Figure 6, the surfaces of the coal from two regions processed with VESFFs exhibited a higher content of -Si-O- in comparison to the coal processed with deionized water. This suggests that the action of the VESFFs resulted in the loss of soluble minerals, such as pyrite, that were present in the coal matrix, thereby increasing the exposure of -Si-O-. The impact of the VESFF C was the most significant. As illustrated in Figure 7, the carboxyl groups of the coal from two different locations exhibited an increase following treatment with FFs B, B\({}_{2}\), C, and D, with the most pronounced effect observed for VESFF D. In conclusion, the coal that underwent treatment with VESFFs B, B\({}_{2}\), C, and D displayed a markedly elevated degree of exposure of HLGs. The C and D FFs, which were formulated with cationic VESs plus zwitterionic VESs and anionic VESs plus zwitterionic VESs as the main agents, exhibited the most pronounced effect. The B, B\({}_{2}\), and C VESFF formulations contained NaSal. The chemical composition of NaSal includes carboxyl and hydroxyl groups, and its solution has greater acid hydrolysis activity than alkaline hydrolysis activity. Therefore, VESFFs B, B\({}_{2}\), and C are weakly acidic and can dissolve minerals, such as calcite and pyrite, in coal, resulting in more exposure of -Si-O- functional groups. According to previous studies [23], VESFF C has a lower removal ability for kaolinite and montmorillonite than VESFF B\({}_{2}\), and a lower removal and dissolution ability for illite than VESFFs D and B. Thus, the coal subjected to treatment with VESFF C retained the greatest amount of clay minerals, such as kaolinite. Consequently, the coal processed with VESFF C exhibited a greater number of Si-O functional groups, which resulted in excellent wettability of the FFs on the coal surface. VESFF C is more likely to invade pores with smaller pore sizes and thus has a more pronounced effect on micropores and transition pores. Figure 4: FTIR spectra of test samples from two regions processed with VESFFs. The anion VES in VESFF D has oxidizing properties on the coal surface, which can break aromatic hydrocarbons and bridge bonds in the basic structural units of coal, oxidizing the aromatic hydrocarbons (-CH) and cycloalkanes on the coal surface into carbonyl groups (C=O) and hydroxyl groups (-OH), further generating stable carboxyl groups (-COOH) and anhydride groups (43).