Design of Robust Thermal and Anion Dual-Responsive Membranes with Switchable Response Temperature

Recent advances in membrane technologies applied in oil-water separation

Effective treatment of oily wastewater, which is toxic and harmful and causes serious environmental pollution and health risks, has become an important research field. Membrane separation technology has emerged as a key area of investigation in oil-water separation research due to its high separation efficiency, low costs, and user-friendly operation. This review aims to report on the advances in the research of various types of separation membranes around emulsion permeance, separation efficiency, antifouling efficiency, and stimulus responsiveness. Meanwhile, the challenges encountered in oil-water separation membranes are examined, and potential research avenues are identified.

Advanced stimuli-responsive membranes for smart separation

Membranes have been extensively studied and applied in various fields owing to their high energy efficiency and small environmental impact. Further conferring membranes with stimuli responsiveness can allow them to dynamically tune their pore structure and/or surface properties for efficient separation performance. This review summarizes and discusses important developments and achievements in stimuli-responsive membranes. The most commonly utilized stimuli, including light, pH, temperature, ions, and electric and magnetic fields, are discussed in detail. Special attention is given to stimuli-responsive control of membrane pore structure (pore size and porosity/connectivity) and surface properties (wettability, surface topology, and surface charge), from the perspective of determining the appropriate membrane properties and microstructures. This review also focuses on strategies to prepare stimuli-responsive membranes, including blending, casting, polymerization, self-assembly, and electrospinning. Smart applications for separations are also reviewed as well as a discussion of remaining challenges and future prospects in this exciting field. This review offers critical insights for the membrane and broader materials science communities regarding the on-demand and dynamic control of membrane structures and properties. We hope that this review will inspire the design of novel stimuli-responsive membranes to promote sustainable development and make progress toward commercialization.

Recent advances in bio-inspired ionic liquid-based interfacial materials from preparation to application

Natural creatures always display unique and charming functions, such as the adhesion of mussels and the lubrication of Nepenthes, to maintain their life activities. Bio-inspired interfacial materials infused with liquid, especially for ionic liquids (ILs), have been designed and prepared to meet the emerging and rising needs of human beings. In this review, we first summarize the recent development of bio-inspired IL-based interfacial materials (BILIMs), ranging from the synthesis strategy to the design principle. Then, we discuss the advanced applications of BILIMs from anti-adhesive aspects (e.g., anti-biofouling, anti-liquid fouling, and anti-solid fouling) to adhesive aspects (e.g., biological sensor, adhesive tape, and wound dressing). Finally, the current limitations and future prospects of BILIMs are provided to feed the actual needs.

Cross-Linked Networks of 1,6-Hexanedithiol with Gold Nanoparticles to Improve Permeation Flux of Polyethersulfone Membrane

It is a great challenge to design and prepare polymeric membranes with excellent permeability and good rejection. In this study, a modifier of gold nanoparticles for crosslinking and self-assembly by 1,6-hexanedithiol is fabricated and used to modify the polyethersulfone membrane as an additive, which forms a uniform porous membrane by liquid-liquid phase conversion technology. The morphology of the membrane is investigated by scanning electron microscopy (SEM), the change of the hydrophilicity of the membrane surface after modification is measured by the contact angle goniometer, and the performance of the fabricated membrane is measured by evaluating the pure water flux and the rejection ratio of bovine serum albumin. The results indicate that the permeability of the modified membrane has a significant improvement. When the mass fraction of the modifying agent is 5 wt%, the water flux of the modified membrane reaches up to 131.6 L m^-2 h^-1, and has a good rejection ratio to bovine serum albumin. In short, this work plays an important role in improving the flux of the membrane and maintaining good separation performance.

Planning of smart gating membranes for water treatment

The use of membranes in desalination and water treatment has been intensively studied in recent years. The conventional membranes however have various problems such as uncontrollable pore size and membrane properties, which prevents membranes from quickly responding to alteration of operating and environmental conditions. As a result the membranes are fouled, and their separation performance is lowered. The preparation of smart gating membranes inspired by cell membranes is a new method to face these challenges. Introducing stimuli-responsive functional materials into traditional porous membranes and use of hydrogels and microgels can change surface properties and membrane pore sizes under different conditions. This review shows potential of smart gating membranes in water treatment. Various types of stimuli-response such as those of thermo-, pH-, ion-, molecule-, UV light-, magnetic-, redox- and electro-responsive gating membranes along with various gel types such as those of polyelectrolyte, PNIPAM-based, self-healing hydrogels and microgel based-smart gating membranes are discussed. Design strategies, separation mechanisms and challenges in fabrication of smart gating membranes in water treatment are also presented. It is demonstrated that experimental and modeling and simulation results have to be utilized effectively to produce smart gating membranes.

Design of poly ionic liquids modified cotton fabric with ion species-triggered bidirectional oil-water separation performance

A novel ion species-responsive oil-water separation material was designed: poly ionic liquid (PIL) was carried on the graphene oxide (GO) by free radical polymerization, then the PIL modified GO sheets (GO-PIL) were coated on cotton fabric (CF). The wettability of the obtained GO-PIL coated CF (GO-PIL@CF) could be switched between hydrophilic and hydrophobic state with the exchange of different types of counteranions. Water contact angle of the GO-PIL@CF could be switched between 0 to about 145°; and correspondingly the underwater oil contact angle would change between about 148 to 0°. Because of the switchable wettability, the GO-PIL@CF could selectively separate water or oil from the oil-water mixtures. Meanwhile, due to the loose fibrous structure, the GO-PIL@CF showed relatively high permeate fluxes; in the hydrophilic state the water flux was about 36000 L/m²h, while in the hydrophobic state the fluxes for the low-density oils (n-hexane and toluene) were about 59,000 and 65000 L/m²h, respectively. Consequently, the separation processes could be completed simply by gravity. In addition, because of the soft and flexible mechanical property, the GO-PIL@CF could serve as wrappage of traditional absorbents and be applied directly as absorbent to remove water or oil selectively from their mixtures.

Building a smart surface with converse temperature-dependent wettability based on poly(acrylamide-co-acrylonitrile)

A smart surface with converse temperature-dependent (CTD) wettability was fabricated from an upper critical solution temperature-type (UCST-type) poly(acrylamide-co-acrylonitrile) (P(AAm-co-AN)) copolymer. The obtained surface exhibits a remarkable and reversible hydrophobic-hydrophilic transition depending on temperature with a high response rate. The static water contact angle of the surface decreases from 103° ± 2° to 60° ± 1° as the temperature increases from 30 °C to 80 °C. Further, the wettability of the UCST-type surface shows a positive linear relationship between wettability and temperature. This study for the first time provides an UCST-type smart surface with wettability that decreases by over 35° as the temperature increases by only 20 °C.