Environmental Applications of Interfacial Materials with Special Wettability.

Environmental pollution has been one of the people’s most significant concerns for decades. In today’s industrialized and modernized society, the problem of environmental pollution has become more and more serious, directly affecting the sustainable development of each country. The unique surface properties of materials and interfaces produced by biomimetic approaches can be leveraged to create practical solutions to challenging environmental issues. Among them, superhydrophobic materials get a lot of attention because of their exceptional capacities in various environmental applications such as oil-water separation, membrane-based water purification and desalination, biofouling prevention, high-performance vapor condensation, and atmospheric water capture. This chapter reviews and discusses the fundamental principles of superhydrophobicity, recent works in preparing superhydrophobic surfaces, their potential environmental applications, and the challenges confronted in their new applications.

Abstract

Clean water resources are essential to our human society. Oil leakage has caused water contamination, which leads to serious shortage of clean water, environmental deterioration, and even increasing number of deaths. It is of great urgency to solve the oil-polluted water problems worldwide. Efficient oil/water separation, especially emulsified oil/water mixture separation, is widely used to mitigate water pollution issues. Recently, advanced materials with special wettability have been employed for oily wastewater remediation. Moreover, by endowing them with various intelligent functions, smart materials can effectively separate complex oil/water mixtures including extremely stable emulsions. In this review, oil/water separation mechanisms and various fabrication methods of special wettability separation materials are summarized. We highlight the special wettable materials with intelligent functions, including photocatalytic, self-healing, and switchable oil/water separation materials, which can achieve self-cleaning, self-healing, and efficient oily wastewater treatment. In each section, the acting mechanisms, fabricating technologies, representative studies, and separation efficiency are briefly introduced. Lastly, the challenges and outlook for oil/water separation based on the special wettability materials are discussed.

Abstract

A review of membrane wettability for the treatment of saline water deploying membrane distillation

It is well known that properties of materials are largely determined by their structures. Here we introduce the special double-structural materials, which are composed of micrometre and nanometre building blocks and commonly exist in nature. This review mainly focuses on recent developments of double-structural and functional materials with special wettability. We highlight excellent properties possessed by micro- and nanostructures which initially originated from the organisms with special functions in the biological world. The excellent properties shown by such structures are discussed in three parts: special wettability, mechanical properties, and optical properties, primarily including superhydrophobicity, superhydrophilicity, superoleophobicity, low and high adhesion, low friction, structural color, antireflection and so on. We will also briefly address the research prospects and directions of micro- and nano-structures. Further study on the relationship between structures and properties will be conducive to better transfer micro- and nanostructures to the engineering materials so as to obtain desired performances and a wide range of applications.

Oil leakage and the discharge of oil/water mixtures by domestic and industrial consumers have caused not only severe environmental pollution and a threat to all species in the ecosystem but also a huge waste of precious resources. Therefore, the separation of oil/water mixtures, especially stable emulsion, has become an urgent global issue. Recently, materials containing a special wettability feature for oil and water have drawn immense attention because of their potential applications for oil/water separation application. In this paper, we systematically summarize the fundamental theories, separation mechanism, design strategies, and recent developments in materials with special wettability for separating stratified and emulsified oil/water mixtures. The related wetting theories that unveil the physical underlying mechanism of the oil/water separation mechanism are proposed, and the practical design criteria for oil/water separation materials are provided. Guided by the fundamental design criteria, various porous materials with special wettability characteristics, including those which are superhydrophilic/underwater superoleophobic, superhydrophobic/superoleophilic, and superhydrophilic/in-air superoleophobic, are systemically analyzed. These superwetting materials are widely employed to separate oil/water mixtures: from stratified oil/water to emulsified ones. In addition, the materials that implement the demulsification of emulsified oil/water mixtures via the ingenious design of the multiscale surface morphology and construction of special wettability are also discussed. In each section, we introduce the design ideas, base materials, preparation methods, and representative works in detail. Finally, the conclusions and challenges for the oil/water separation research field are discussed in depth.

Green hydrophobic and superhydrophobic coatings and surfaces for water related applications: A review.

Metals are important and irreplaceable engineered materials in our society. Nature is a school for scientists and engineers, which has long served as a source of inspiration for humans. Inspired by nature, a variety of metallic surfaces with special wettability have been fabricated in recent years through the combination of surface micro- and nanostructures and chemical composition. These metallic surfaces with special wettability exhibit important applications in anti-corrosion, microfluidic systems, oil-water separation, liquid transportation, and other fields. Recent achievements in the fabrication and application of metallic surfaces with special wettability are presented in this review. The research prospects and directions of this field are also briefly addressed. We hope this review will be beneficial to expand the practical applications of metals and offer some inspirations to the researchers in the fields of engineering, biomedicine, and materials science.

Effective separation of highly viscous crude oil/water mixtures remains a worldwide challenge. Employing special wettable materials with adsorptive properties as an emerging separation strategy has attracted extensive attention in the treatment of crude oil spillage. Such a separation technique combines excellent wettability materials and their adsorption performance to achieve energy efficient removal or recovery of high viscosity crude oil. Particularly, special wettable adsorption materials with thermal properties provide novel ideas and directions for the construction of rapid, green, economic and all-weather crude oil/water adsorption separation materials. Negatively, the high viscosity of crude oil makes most special wettable adsorption separation materials and surfaces extremely susceptible to adhesion and contamination in practical applications, leading to rapid functional failure. Moreover, such an adsorption separation strategy towards high-viscosity crude oil/water mixture separation has rarely been summarized. Consequently, there are still some potential challenges in separation selectivity and adsorption capacity of special wettable adsorption separation materials which urgently need to be summarized to guide the future development. In this review, the special wettability theories and construction principles of adsorption separation materials are first introduced. Then, the composition and classification of crude oil/water mixtures, particularly focusing on enhancing the separation selectivity and adsorption capacity of adsorption separation materials, are comprehensively and systematically discussed via regulating surface wettability, designing pore structures and reducing crude oil viscosity. Meanwhile, the separation mechanisms, construction ideas, fabrication strategies, separation performances, practical applications, and the advantages and disadvantages of special wettable adsorption separation materials are also analyzed. Finally, the challenges and future prospects for adsorption separation of high-viscosity crude oil/water mixtures are expounded.

Porous materials have become a burgeoning research interest in materials science because of their intrinsic porous characteristics, versatile chemical compositions, and abundant functionalities. Re...

Metal mesh-based special wettability materials for oil-water separation: A review of the recent development

Both the wettability and pore size of filtration materials are of great importance in oil/water separation. However, conventional strategies have mainly focused on the fabrication of filtration materials with special wettability, regardless of the pore size. Herein, we demonstrated the design and construction of special wettable nanofibrous mats with tunable pore sizes as filtration materials for selective and efficient separation of oil from oil/water mixtures. The nanofibrous mats with different pore sizes were prepared by the electrospinning approach using a stainless steel wire mesh as the collector, and the results indicated that the pore size of the nanofibrous mats gradually increased with the decrease in the mesh number. The results of the wettability behavior demonstrated that all of the nanofibrous mats showed highly hydrophobic and superoleophilic properties. Owing to the special wettability and the porous structure, the nanofibrous mats were sequentially applied for oil/water separation, and they showed excellent ability to separate both layered oil/water mixture and water-in-oil emulsion; moreover, it was also found that the oil flux could be highly improved by controlling the pore size of the nanofibrous mat and that the oil flux of the nanofibrous mat with the largest pore size was about 10 times higher than that of the conventional nonwoven mat that had the smallest pore size. The nanofibrous mats developed with controllable pore sizes can therefore be practically used as highly efficient filtration materials in the management of oily water.

A review on super-wettable porous membranes and materials based on bio-polymeric chitosan for oil-water separation

The PM (particulate matter)-induced haze problem has caused serious environmental and health concerns. It is still a huge challenge to control PM pollution because of the complex structure, diverse sources and intricate evolution mechanism of the particles. In recent years, there has been increasing efforts to develop advanced strategies for PM treatment. Herein, we wish to provide a systematic summary of recent progress in air filtration. The review covers the definition of PM, the characterization of PM, the mechanism of PM capture, advanced purification materials, and special multifunctional performances. As for characterizing PM particles, removal efficiency, pressure drop, flow rate, quality factor and optical transparency are the basic parameters. For the advanced filters with excellent filtration performance, some special properties such as thermal stability, antibacterial property, flame retardancy, recyclability and special wettability are in great need under certain extreme conditions. Finally, some future prospects for filtration materials, like material choice and structural design, are also discussed.