Zhongxin Xue

Special wettable materials for oil/water separation

Oil/water separation is an important field, not only for scientific research but also for practical applications aiming to resolve industrial oily wastewater and oil-spill pollution, as well as environmental protection. Recently, research into the role of special wettability for oil/water separation has attracted much attention. In this review we summarize the design, fabrication, applications and recent developments of special wettable materials for oil/water separation. Based on the different types of separation, we organize this review into three parts: “oil-removing” type materials with superhydrophobicity and superoleophilicity (that selectively filter or absorb oil from oil/water mixtures), “water-removing” type materials with superhydrophilicity and superoleophobicity (that selectively separate water from oil/water mixtures), and smart controllable separation materials. In each section, we present in detail the representative work, introduce the design idea, outline their fabrication methods, and discuss the role of special wettability on the separation. Finally, the challenges and outlook for the future of this subject are discussed.

Mussel-inspired chemistry and Michael addition reaction for efficient oil/water separation.

An oil/water separation mesh with high separation efficiency and intrusion pressure of water has been successfully developed by combining mussel-inspired chemistry and Michael addition reaction. The substrate of the stainless steel mesh was first coated with the adhesive polydopamine (PDA) film by simple immersion in an aqueous solution of dopamine at pH of 8.5. Then n-dodecyl mercaptan (NDM) was conjugated with PDA film through Michael addition reaction at ambient temperature. The as-prepared mesh showed highly hydrophobicity with the water contact angle of 144° and superoleophilicity with the oil contact angle of 0°. It can be used to separate a series of oil/water mixtures like gasoline, diesel, etc. The separation efficiency remains high after 30 times use (99.95% for hexane/water mixture). More importantly, the relatively high intrusion pressure (2.2 kPa) gives the opportunity to separation of large amount of oil and water mixtures. This study provides a new prospect to simply introduce multiple molecules on the adhesive PDA-based mesh to achieve various functional oil/water separation materials.

Dual-scaled porous nitrocellulose membranes with underwater superoleophobicity for highly efficient oil/water separation.

Large-area dual-scaled porous nitrocellulose (p-NC) membranes are fabricated by a facile, inexpensive and scalable perforating approach. These p-NC membranes show stable superhydrophilicity in air and underwater superoleophobicity. The p-NC membranes with intrinsic nanopores and array of microscale perforated pores could selectively and efficiently separate water from various oil/water mixtures with high efficiency (>99%) rapidly.

Clam's shell inspired high-energy inorganic coatings with underwater low adhesive superoleophobicity.

Unique underwater low adhesive superoleophobicity is discovered on the pallium-covered region of a short clams shell. This property originates from the shells inorganic composition of CaCO(3) and surface micro/nano-hierarchical structures. The oil-repellent shell provides an innovative strategy to develop novel underwater superoleophobic coatings using inorganic oxides such as copper oxide. This kind of coating is anticipated to be applied on engineering metals to protect aquatic equipment from oil contamination.

Straightforward oxidation of a copper substrate produces an underwater superoleophobic mesh for oil/water separation.

A superhydrophilic and underwater superoleophobic Cu(OH)2-covered mesh with micro- and nanoscale hierarchical composite structures is successfully fabricated through a one-step chemical oxidation of a smooth-copper mesh. Such mesh, without any further modification, can selectively separate water from oil/water mixtures with high separation efficiency, and possess excellent stability even after 60 uses. This method provides a simple, low-cost, and scalable strategy for the purification of oily wastewater.

Superoleophilic and superhydrophobic biodegradable material with porous structures for oil absorption and oil–water separation

In this work, novel biodegradable poly(lactic acid) oil absorption and filtration materials with superhydrophobic and superoleophilic properties were successfully fabricated. The as-prepared materials can separate oil from oil–water mixtures with high selectivity, high separation efficiency, stable performance, and easy recyclability, and are ideal candidates for applications in the cleanup of oil pollutants and the separation of oil and water. The used materials can be easily disposed because of their biodegradable essence and thus overcome the hard disposal and environmental contaminant limitations of traditional oil–water separation materials. This work provides a new design idea to prepare oil–water separation materials with consideration of both excellent separation ability and environmental friendliness, which shows attractive potential applications in industrial oily wastewater and oil spill cleanup.

Fabrication of a silica gel coated quartz fiber mesh for oil–water separation under strong acidic and concentrated salt conditions

A superhydrophilic and underwater superoleophobic mesh is prepared by compounding a quartz fiber with silica gel, and is further enhanced by adding 1,2-bis(triethoxysilyl)ethane and a high molecular weight polyacrylamide. Driven by gravity solely, the as-prepared mesh can separate oil–water mixtures with high efficiency in strong acidic and high salt conditions.

Bio-inspired anisotropic micro/nano-surface from a natural stamp: grasshopper wings

Bio-inspired micro/nano-surfaces with novel anisotropic functionalities were obtained by utilizing the outward wings of grasshopper as a natural stamp. The two-step replica exhibited anisotropic high hydrophobicity and light reflection.