## 4 Demulsification Mechanism  
To further comprehend the demulsification process of the acidic oil-in-water emulsion actuated by Ti-Mt-APTES, the morphologies of the emulsions were observed with a metallographic microscope. Figure 9a shows the optical morphology of the acidic oil-in-water emulsion, indicating the oil droplets homogeneously dispersed in the water phase. As shown in Figure 9b, after demulsification, a small amount of diminutive oil droplets appeared in the newly formed water phase. As for the separated oil phase, there are bits of Ti-Mt-APTES floccules suspended in the oil phase, and a small quantity of large water droplets are also present (Figure 9c). Moreover, floccules of the Ti-Mt-APTES are also found at the oil/water interface, as collected large oil droplets (Figure 9d). These results demonstrate that Ti-Mt-APTES is an efficient demulsifier to separate oil from the acidic oil-in-water emulsion. FTIR spectra of Ti-Mt-APTES before and after demulsification are shown in Figure 10. In the case of demulsification, peaks at 2925 and 2852 cm\({}^{-1}\) strengthened, which correspond to antisymmetric  
Figure 8: Demulsification performance of Ti-Mt-APTES-0.1 under various stirring times. Figure 9: Micrographs of the oil–water mixture before and after demulsification: (**a**) the oil-in-water emulsion; (**b**) the newly separated water phase; (**c**) the newly separated oil phase; (**d**) Ti-Mt-APTES in oil-in-water emulsion. and symmetric stretching vibrations of -CH\({}_{2}\), most likely due to Ti-Mt-APTES catching oil droplets in the acidic oil-in-water emulsion. Furthermore, peaks related to H-O-H stretching and bending vibrations can be found at 3448 and 1640 cm\({}^{-1}\), and weaken after demulsification, indicating that the hydroxyl groups on the montmorillonite may be involved in demulsification, and the oil droplets may be adsorbed by intercalation of Ti-Mt-APTES. Therefore, when R\({}_{\text{A/M}}\) exceeds 0.10/1, the hydroxyl groups on the surface of montmorillonite are drastically reduced, which makes the demulsification performance lower. The high resolution XPS spectra of Ti-Mt-APTES before and after demulsification are given in Figure 11. The Ti 2p peaks of Ti-Mt-APTES are located at 458.5, 460.0, and 464.6 eV, respectively, and those after demulsification are located at 465.1, 460.0, and 459.0 eV, respectively, which can be attributed to the Ti\({}^{4+}\) oxidation sates or TiO\({}_{2}\) groups in montmorillonite [33]. The C 1s peaks are observed at 286.6 and 284.7 eV, and after demulsification, C 1s peaks were found at 286.0 and 284.64 eV, which were assigned to elemental carbon (C-C) and C-O [34]. However, those after demulsification are positioned at 286.0 and 284.6 eV. The N 1s peak is found at 401.6 eV and there was no change after demulsification, which indicates that APTES was successfully loaded onto clay [35]. The Ti-Mt-APTES spectra contain one O 1s peak located at 532.0 eV, that after demulsification was centered at 532.5 eV, and is allocated to single-bonded oxygen from the montmorillonite lattice [36]. From above, the peaks in the O 1s and C 1s regions show shifts to lower binding energy values, and the Ti 2p peak regions change. This phenomenon directly confirmed the interaction between oil droplets and Ti-Mt-APTES. Figure 10: FTIR spectra of Ti-Mt-APTES before and after demulsification. The zeta potentials of Na-Mt and Ti-Mt-APTES at various pH are presented in Figure 12. The zeta potential of Na-Mt remained negative under the measured pH range (pH = 2-8) and decreased with the increase of pH. However, Ti-Mt-APTES was positively charged, with a zeta potential value of 3.62 mV at pH 2.0, ascribed to the protonation of aminopropyl groups and titanium hydrate. By contrast, emulsified oil droplets are negatively charged in acidic emulsions [37]. Therefore, emulsified oil droplets can be efficiently seized on Ti-Mt-APTES by electrostatic interactions in acidic conditions.