Fig. 8 Ion chromatogram (IC) of SDS solution after interaction with MIL-100(Fe)
Above IC and LC-MS results confirmed that the SDS was degraded by MIL-100(Fe). However, this reaction with SDS did not influence the crystal structure of MIL-100(Fe) obviously, because XRD pattern of the used MIL-100(Fe) was the same as that of the fresh MIL-100(Fe) (Fig. S14 ).
Finally, the influence of electrostatic interaction on the demulsification was studied by the zeta potentials and demulsification efficiencies for different model emulsions. The negative charge increased continuously because of hydroxylation 41when the pH was increased from 4.0 to 10.0 (Fig. 9a ). The zeta potentials of MIL-100(Fe) and model emulsion at the condition of demulsification were 19.8 mV and -67.2 mV, which suggested that there was electrostatic attraction between MIL-100(Fe) and model emulsion stabilized by SDS. And the electrostatic attraction weakened along with an increased of pH, which would decrease the adsorption capacity droved by the electrostatic attraction for emulsion on MIL-100(Fe). Therefore, the DE would decrease when the pH increased. But the results of demulsification performance shown that the DE of MIL-100(Fe) maintained around 90% with the range of pH (4~10) (Fig. 3b ). Additionally, the DE for the model emulsion stabilized by Tween 80, a kind of nonionic surfactant, was up to 91% using MIL-100(Fe) at the same conditions (Fig. 9b ). It could conclude that the contribution of adsorption droved by the electrostatic attraction on demulsification was minor. However, the electrostatic repulsion hampered contact with MIL-100(Fe) and emulsion, causing a low demulsification efficiency for the model emulsion stabilized by cetyl ammonium bromide (CTAB, a kind of cationic surfactant) (Fig. 9b ).