Enhancing Demulsification Performance for Oil-Water Separation through Encapsulating Ionic Liquids in the Pore of MIL-100(Fe)

Emulsion poses a greater challenge for the remediation of oily wastewater, which can be effectively resolved by the metal-organic framework of MIL-100(Fe). The formula Fe3O(H2O)(2) (OH) (BTC)(2) pronounces that MIL-100(Fe) suffers from an intrinsic defect of less charged atoms, which limits its demulsification performance for oil-water separation. Herein, cations of the ionic liquid (1-allyl-3-methylimidazolium, Amim(+)) were encapsulated in the micropore of MIL-100(Fe) in situ to increase the positive charge density of MIL-100(Fe). Zeta potential demonstrated that the encapsulation of Arnim' increased the positive charge amount of MIL-100(Fe). N-2 probe isothermal adsorption/desorption and spectral measurements (X-ray photoelectron spectroscopy, ultraviolet-visible diffuse reflection spectroscopy, and attenuated total-reflectance infrared spectroscopy) revealed the host-guest interactions of pi center dot center dot center dot Fe complexation and pi center dot center dot center dot cation electrostatic attraction between Amim(+) and MIL-100(Fe) for the composite materials. Amim(+)/Fe3+ encapsulation greatly enhanced the demulsification performance of MIL-100(Fe) for oil-in-water (O/W) emulsion stabilized by sodium dodecyl sulfate. Amim(+)- encapsulated MIL-100(Fe) with an Amim(+)/Fe3+ molar ratio of 1:1 [Amim@MIL-100(Fe)-3:3] showed a demulsification efficiency (DE) of 94% within 30 s, compared with MIL-100(Fe) within 30 min. The maximum DE of Amim@MIL-100(Fe)-3:3 was found to be more than 98% within 5 min. The DE lost by MIL-100(Fe) at the third run decreased from 36 to 17% after encapsulating Amim(+). The analysis of surface charge and interfacial tension implied a demulsification mechanism of capturing-fusion, which could be promoted by the greater electrostatic attraction. Finally, the role of Amim(+) on the outstanding demulsification performance by Amim(+)-tencapsulated MIL-100(Fe) could be explained by the enhanced nonbonded interaction of electrostatic attraction and van der Waals based on the molecular dynamics simulation.

Automated summary

The encapsulation of ionic liquid cations (Amim(+)) in MIL-100(Fe) micropores enhanced the positive charge density of the framework, significantly improving the demulsification performance for oil-in-water emulsions. The efficiency of Amim@MIL-100(Fe)-3:3 reached 94% within 30 seconds, showcasing a substantial enhancement compared to MIL-100(Fe) within 30 minutes. This performance improvement was attributed to the increased electrostatic attraction facilitated by the presence of Amim(+).