Oil/water separation is a field of high significance as it has direct practical implications for resolving the problem of industrial oily wastewater and other oil/water pollution. Therefore, the development of functional materials for efficient treatment of oil-polluted water is imperative. In this feature article, we have reviewed the recent progress of oil/water separation technologies based on filtration and absorption methods using various materials that possess surface superwetting properties. In each section, we present in detail representative work and describe the concepts, employed materials, fabrication methods, and the effects of their wetting/dewetting behaviors on oil/water separation. Finally, the challenges and future research directions of this promising research field are briefly discussed.

Oil/water separation techniques: a review of recent progresses and future directions

Design and fabrication of superwetting fiber-based membranes for oil/water separation applications

Oil–water separation is critical for the water treatment of oily wastewater or oil-spill accidents. The oil contamination in water not only induces severe water pollution but also threatens human beings’ health and all living species in the ecological system. To address this challenge, different nanoscale fabrication methods have been applied for endowing biomimetic porous materials, which provide a promising solution for oily-water remediation. In this review, we present the state-of-the-art developments in the rational design of materials interface with special wettability for the intelligent separation of immiscible/emulsified oil–water mixtures. A mechanistic understanding of oil–water separation is firstly described, followed by a summary of separation solutions for traditional oil–water mixtures and special oil–water emulsions enabled by self-amplified wettability due to nanostructures. Guided by the basic theory, the rational design of interfaces of various porous materials at nanoscale with special wettability towards superhydrophobicity–superoleophilicity, superhydrophilicity–superoleophobicity, and superhydrophilicity–underwater superoleophobicity is discussed in detail. Although the above nanoscale fabrication strategies are able to address most of the current challenges, intelligent superwetting materials developed to meet special oil–water separation demands and to further promote the separation efficiency are also reviewed for various special application demands. Finally, challenges and future perspectives in the development of more efficient oil–water separation materials and devices by nanoscale control are provided. It is expected that the biomimetic porous materials with nanoscale interface engineering will overcome the current challenges of oil–water emulsion separation, realizing their practical applications in the near future with continuous efforts in this field.

Rational design of materials interface at nanoscale towards intelligent oil–water separation

Specially Wettable Membranes for Oil–Water Separation

Polymeric materials with switchable superwettability for controllable oil/water separation: A comprehensive review

The development of stimuli-responsive materials with the ability of controllable oil/water separation is crucial for practical applications. Here, a novel pH responsive nonfluorine-containing copolymer was designed. The copolymer together with silica can be dip-coated on different materials including cotton fabric, filter paper, and polyurethane foam. The coated materials exhibit switchable superhydrophilicity and superhydrophobicity and can be applied in continuous separation of oil/water/oil three phase mixtures, different surfactant stabilized emulsion (oil-in-water, water-in-oil, and oil-in-acidic water) as well as oil uptake and release via in situ and ex situ pH change. We expect that the coatings highlight the practical applications because of the cost-effective preparation process and fluorine-free strategy.

In Situ and Ex Situ pH-Responsive Coatings with Switchable Wettability for Controllable Oil/Water Separation.

Membranes with special functionalities, such as self-cleaning, especially those for oil/water separation, have attracted much attention due to their wide applications. However, they are difficult to recycle and reuse after being damaged. Herein, we put forward a new N-substituted polyurethane membrane concept with self-healing ability to address this challenge. The membrane obtained by electrospinning has a self-cleaning surface with an excellent self-healing ability. Importantly, by tuning the membrane composition, the membrane exhibits different wettability for effective separation of oil/water mixtures and water-in-oil emulsions, whilst still displaying a self-healing ability and durability against damage. To the best of our knowledge, this is the first report to demonstrate a self-healing membrane for oil/water separation, which provides the fundamental research for the development of advanced oil/water separation materials.

Electrospun N-Substituted Polyurethane Membranes with Self-Healing Ability for Self-Cleaning and Oil/Water Separation.

With the development of society, oil pollution has become more and more serious, it is becoming a global issue to separate oil and water mixture. Currently, a variety of functional materials have been successfully prepared for oil/water separation. Among them, polyurethane is an attractive candidate due to its low cost, wear-resistance and excellent mechanical properties. This report summarizes the design strategy of polyurethane-based materials and their applications in oil/water separation. The progress made so far will guide further development of polyurethane-based materials for oil/water separation.

https://www.worldscientific.com/doi/pdf/10.1142/S1793292017300018

Recent Progress of Polyurethane-Based Materials for Oil/Water Separation

Compressible, amphiphilic graphene-based aerogel using a molecular glue to link graphene sheets and coated-polymer layers

The invention discloses a method for preparing a fluorine-contained N-position-substituted polyurethane super-hydrophobic and super-oleophobic thin film through the electrospinning technology, and relates to the technical field of high polymer materials and preparation methods of high polymer materials. The method includes the steps of firstly, synthesizing prepolymer; secondly, conducting the chain-extension reaction; thirdly, generating polyanion; fourthly, preparing fluorine-contained N-position-substituted polyurethane; fifthly, preparing the polymer electrospinning thin film. On the basis of traditional polyurethane, the hydrogen in the N position is substituted with a fluorine-contained monomer, the N-position-substituted polyurethane is synthesized, the N-position-substituted polyurethane super-hydrophobic and super-oleophobic thin film is prepared through the electrospinning method, the water contact angle of the thin film can reach as high as 160 degrees, and the oil contact angle can reach as high as 154 degrees. The multi-carbon fluorine-contained group of the related fluorine-contained polyurethane is directly connected with nitrogen atoms, and the thin film made of the substance has the ultra-high waterproof and oil-proof performance and the self-cleaning capacity.

Method for preparing fluorine-contained N-position-substituted polyurethane super-hydrophobic and super-oleophobic thin film through electrospinning technology

Zhao Dang

Papers

In Situ and Ex Situ pH-Responsive Coatings with Switchable Wettability for Controllable Oil/Water Separation.

Electrospun N-Substituted Polyurethane Membranes with Self-Healing Ability for Self-Cleaning and Oil/Water Separation.

Recent Progress of Polyurethane-Based Materials for Oil/Water Separation

Compressible, amphiphilic graphene-based aerogel using a molecular glue to link graphene sheets and coated-polymer layers

Method for preparing fluorine-contained N-position-substituted polyurethane super-hydrophobic and super-oleophobic thin film through electrospinning technology