Ligand-functionalized UiO-66 as demulsifiers for SDS-stabilized oil-in-water emulsions: mechanism and performance

Systematic comparison of ligand functionalization effects on surface properties and demulsification using UiO-66. • Hydrophobic (UiO-66-4F) and electrostatic (UiO-66-NH 2 ) mechanisms both achieve ∼80% demulsification efficiency. • The hydrophobic mechanism is more versatile across different surfactants and oil phases than the electrostatic one. • Surface wettability and charge are key factors governing demulsification performance. • The findings provide insights into tailoring MOF surface chemistry for demulsifier development. The role of surface functional groups in metal–organic frameworks (MOFs)-based demulsification remains poorly understood. Herein, four isostructural UiO-66 derivatives (–H, –NH 2 , –NO 2 , –F) were systematically evaluated as discrete demulsifiers for SDS‑stabilized oil‑in‑water emulsions. The study combined batch demulsification tests with measurements of SDS and toluene adsorption, dynamic interfacial tension, surface wettability, and zeta potential. The hydrophobic fluorinated sample (UiO-66-4F) achieved approximately 80% demulsification efficiency, attributed to strong hydrophobic interactions. The hydrophilic yet positively charged amino‑functionalized sample (UiO-66-NH 2 ) also achieved about 80% efficiency, but via electrostatic attraction to the negatively charged oil‑water interface. Unmodified UiO-66 and the nitro derivative (UiO-66-NO 2 ) exhibited lower efficiencies (<65%). Further tests showed that UiO-66-NH 2 was effective only for anionic surfactants, whereas UiO-66-4F was less affected by surfactant charge. Both MOFs showed higher efficiency for aromatic oils than for aliphatic oils. These results identify two distinct design paradigms – hydrophobic capture and electrostatic neutralization – for MOF‑based particle demulsifiers. Tailoring surface hydrophobicity or charge provides effective demulsification depending on the target emulsion chemistry. This work advances the understanding of structure–property relationships in MOF demulsifiers and offers practical guidelines for developing separation materials. Download: Download high-res image (215KB) Download: Download full-size image