Polydopamine and Its Derivative Materials: Synthesis and Promising Applications in Energy, Environmental, and Biomedical Fields

Oil spills and industrial organic pollutants have induced severe water pollution and threatened every species in the ecological system. To deal with oily water, special wettability stimulated materials have been developed over the past decade to separate oil-and-water mixtures. Basically, synergy between the surface chemical composition and surface topography are commonly known as the key factors to realize the opposite wettability to oils and water and dominate the selective wetting or absorption of oils/water. In this review, we mainly focus on the development of materials with either super-lyophobicity or super-lyophilicity properties in oil/water separation applications where they can be classified into four kinds as follows (in terms of the surface wettability of water and oils): (i) superhydrophobic and superoleophilic materials, (ii) superhydrophilic and under water superoleophobic materials, (iii) superhydrophilic and superoleophobic materials, and (iv) smart oil/water separation materials with switchable wettability. These materials have already been applied to the separation of oil-and-water mixtures: from simple oil/water layered mixtures to oil/water emulsions (including oil-in-water emulsions and water-in-oil emulsions), and from non-intelligent materials to intelligent materials. Moreover, they also exhibit high absorption capacity or separation efficiency and selectivity, simple and fast separation/absorption ability, excellent recyclability, economical efficiency and outstanding durability under harsh conditions. Then, related theories are proposed to understand the physical mechanisms that occur during the oil/water separation process. Finally, some challenges and promising breakthroughs in this field are also discussed. It is expected that special wettability stimulated oil/water separation materials can achieve industrial scale production and be put into use for oil spills and industrial oily wastewater treatment in the near future.

Biomimetic super-lyophobic and super-lyophilic materials applied for oil/water separation: a new strategy beyond nature

Polydopamine is one of the simplest and most versatile approaches to functionalizing material surfaces, having been inspired by the adhesive nature of catechols and amines in mussel adhesive proteins. Since its first report in 2007, a decade of studies on polydopamine molecular structure, deposition conditions, and physicochemical properties have ensued. During this time, potential uses of polydopamine coatings have expanded in many unforeseen directions, seemingly only limited by the creativity of researchers seeking simple solutions to manipulating surface chemistry. In this review, we describe the current state of the art in polydopamine coating methods, describe efforts underway to uncover and tailor the complex structure and chemical properties of polydopamine, and identify emerging trends and needs in polydopamine research, including the use of dopamine analogs, nitrogen-free polyphenolic precursors, and improvement of coating mechanical properties.

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Polydopamine Surface Chemistry: A Decade of Discovery.

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.

Special wettable materials for oil/water separation

Membrane technology enhancement in oil–water separation. A review

We report a simple and inexpensive method for fabricating double-layer TiO2-based mesh. The upper layer is a TiO2 coated mesh film with micro- and nano-structures, while the lower is the same TiO2 mesh film but modified with ODP (octadecyl phosphonic acid) to impart its superhydrophobic and superoleophilic properties. Such a mesh can be successfully used for the separation of insoluble oil from water due to its special wettability, as well as the degradation of soluble pollutants in water under UV light because of the photocatalytic abilities of TiO2, making it a promising candidate for water purification.

Integrated oil separation and water purification by a double-layer TiO2-based mesh

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 mole...

Mussel-Inspired Chemistry and Michael Addition Reaction for Efficient 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.

Superoleophilic and superhydrophobic biodegradable material with porous structures for oil absorption and 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.

Kan Li

Papers

Integrated oil separation and water purification by a double-layer TiO2-based mesh

Mussel-Inspired Chemistry and Michael Addition Reaction for Efficient Oil/Water Separation

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

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