3.4 Interaction for demulsification
As mentioned above, the hydrophilic domain of MIL-100(Fe) was the key point of demulsification. However, the interaction between the hydrophilic domain of the MIL-100(Fe) and emulsion was not understood well. In order to uncover the interaction, the fresh and used MIL-100(Fe) were measured by ATR-IR and XPS. Compared with the fresh MIL-100(Fe), the symmetric vibration absorption band of carboxylate (ν as(COO)-) for the used MIL-100(Fe) changed unsymmetrically and was blue shift (Fig. 7a ). While the vibration absorption band of FeO6 octahedron for the used MIL-100(Fe) at 619 cm-1 was red shift32 (Fig. 7b ). What’s more, the new absorption band of alkyl chain (-CH2-) at 2855 cm-1 and 2927 cm-1(Fig. 7c ) suggested the organic species were remained in the MIL-100(Fe) after demulsification. The residual alkyl chain could decrease the surface energy of used MIL-100(Fe), causing a hydrophobic surface. The XPS results of the used MIL-100(Fe) presented in Fig. 7d displayed that a signal of Fe2+ appeared at 709.1 eV, and the relative content for the unsaturated Fe3+to the saturated Fe3+ changed from 45% to 95%28. The change for the Fe3+implied the reaction between the node of MIL-100(Fe) and the model emulsion might exist. However, what most interesting was that there was no signal of S in the XPS for the used MIL-100(Fe) (Fig. S7 ).