## 4 Conclusions  
Four VESFFs were formulated using VESs with different hydrocarbon chain lengths and different ionic types as the main reagents. The effects of deionized water and four VESFFs on the zeta potential, functional groups with oxygen content, and MS of soft coal and hard coal surfaces were compared. The research results are helpful to reveal the mechanism of VESFFs on the micropores of coal, and can provide theoretical guidance for the optimization of VESFF formulations. The following conclusions were reached.  
1. VESFFs B, B\({}_{2}\), C, and D increased the electrical properties of the surface of the coal, and the electrostatic force between the pore wall and coal particles became greater than the Van der Waals force, leading to a repulsive effect beneficial for removing particles from the coal surface.
2. The coal samples subjected to treatment with VESFF C had more -Si-O- functional groups. VESFF C was more likely to penetrate into nanopores and thereby had a more pronounced effect on micropores and transition pores. The anionic VESs in VESFF D have oxidizing properties that destroy aromatic hydrocarbons and bridge bonds in the basic structural units on the surface of coal, generating stable carboxyl (-COOH) and anhydride groups.
3. The aromatic lamellae extension (\(L_{a}\)) in the aromatic crystal nuclei of the TS coal processed with VESFF D increased, resulting in an increase in micropore volume. VESFFs C and D were beneficial for increasing the aromatic layer extension (\(L_{a}\)) in the aromatic crystal nuclei of NC coal, resulting in an increase in micropore volume.
4. The treatment with VESFFs resulted in the aromatic ring spacing (\(d_{002}\)) of the TS coal becoming smaller than that of the deionized-water-treated coal, decreasing in the following order: D \(>\) C \(>\) B\({}_{2}\) \(>\) B. This indicates that VESFFs B, B\({}_{2}\), C, and D all increased the micropore volume of the TS coal. The interlayer spacing (\(d_{002}\)) of the aromatic rings in the macromolecules of the NC coal subjected to treatment with VESFFs B\({}_{2}\) and C increased. This suggests that VESs with longer hydrocarbon chain lengths are not conducive to increasing micropores in NC coal.  
M.Y.: Methodology, Validation, Writing--original draft, Writing--review and editing, Resources, Funding acquisition; S.G.: Investigation, Data curation, Methodology; Y.C.: Data curation, Writing--review and editing, Validation, Funding acquisition. All authors have read and agreed to the published version of the manuscript.  
This work was supported by National Natural Science Foundation of China (NSFC) [No. 52204230]; The Natural Science Foundation of Shanxi Province [No. 202203021212212]; The China Postdoctoral Science Foundation [2023M731834]; Scientific and Technological Innovation Programs of Higher Education Institutions in Shanxi (STIP) [2021L056]; and the Natural Science Foundation of Chongqing [CSTB2023 NSCQ-MSX0854].  
Figure 12: FWHM of D peak and G peak of coal samples processed with FFs.  
**Institutional Review Board Statement:** Not applicable.  
**Informed Consent Statement:** Not applicable.  
**Data Availability Statement:** Data are available on demand.  
**Conflicts of Interest:** [PERSON] was employed by the company Pingdingshan Tianan Coal Mining Co., Ltd. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.