Three-dimensional (3D)-printed membranes via stereolithography (SLA) are promising in oil−water separation, which is the key in the purification of industrial oily wastewater. To achieve gravity-driven oil−water separation, the membrane material needs to be simultaneously hydrophilic/oleophobic. However, most of the state-of-the-art materials for SLA do not meet the requirement. While wateradsorbing hydrogel is simultaneously hydrophilic/oleophobic and there have been reports on 3D printing of hydrogels in biomedical applications, the hydrogel is too soft for membrane application. Here, we report a simple approach to tackle the issue: a hydrogel coating on SLA-based plastic membranes. The coating is fabricated, using [2-(methacryloyloxy) ethyl] dimethyl-(3-sulfopropyl) ammonium hydroxide as the zwitterionic monomer and acrylamide as the comonomer, via in situ polymerization on SLA-based plastic membranes. The contact angle tests and Fourier transform infrared spectrum show that such a membrane readily adsorbs water and becomes simultaneously hydrophilic/oleophobic. The oil−water separation tests indicate that the water-adsorbed membrane is highly efficient in gravitydriven oil−water separation in 31 repeating cycles. Our results indicate the great potential of 3D-printed membranes in oil−water separation.

Supported liquid membranes (SLMs) are promising in separating miscible liquid–liquid mixtures, which has been a key challenge in wastewater treatment and other applications. However, SLMs suffer from poor durability due to the loss of the liquid phase. In current work, ionic liquids (ILs) with high stability have been impregnated into polyvinylidene fluoride membranes to separate miscible benzene–heptane mixtures. The two imidazolium-based ILs, that is, 1-butyl-3-methylimidazolium hexafluorophosphate ([BMIM]­[PF6]) and 1-butyl-3-methylimidazolium tris­(pentafluoroethyl) trifluorophosphate ([BMIM]­[FAP]), were tested in supported ionic liquid membranes (SILMs) for the benzene–heptane separation. Both ILs show successful separation within 48 h as indicated by nuclear magnetic resonance results. Compared to the SILM with [BMIM]­[FAP], the SILM with [BMIM]­[PF6] has lower throughput and higher selectivity. The higher selectivity can be attributed to the higher hydrophilicity of [BMIM]­[PF6], which results in strong repulsion against heptane. The lower throughput can be attributed to the higher hydrophilicity as well since it lowers the solubility of benzene in [BMIM]­[PF6]. The stability of IL in SILMs has also been investigated via multiple separation cycles. The scanning electron microscopy, weight change of SILMs, and separation results indicate that the separation efficiency of the [BMIM]­[PF6] SILM does not degrade for up to 144 h. The SILM has been further optimized with curvature design (i.e., curved SILM) to increase the interfacial area and thus increase the separation throughput, where the curved SILM separation device was 3D-printed. The findings here have important implications on design and application of SILMs in separating miscible liquid–liquid mixtures.

3D printed membrane device, supported ionic liquid membrane, hydrogel-coated hydrophilic/oleophobic membrane, multi-component multi-phase separation.