Nanoarchitectured design of porous ZnO@copper membranes enabled by atomic-layer-deposition for oil/water separation

Superhydrophobic microporous membrane based on modified microfibrillated cellulose framework for efficient oil-water separation

The preparation of stable and efficient cellulose-based oil/water separation membranes is of great significance in solving the problem of industrial oily wastewater. Herein, rod-like hydroxyapatite (HAP) modified microfibrillated celluloses (MFCs) are used to form the fibrous framework to produce a microporous PDMS-MFC-HAP membrane. The membrane shows good superhydrophobicity with a water contact angle of 151.6°. It exhibits the oil-water separation performance for various water-in-oil emulsions. The separation flux of the membrane is up to 3665.3 L·m-2·h-1·bar-1 under 0.5 bar pressure with a separation efficiency of over 99.6 %. The PDMS-MFC-HAP membrane could maintain a high separation efficiency of 98.6 % after 20 cycles. This study provides a simple and effective method to fabricate cellulose-based superhydrophobic membranes, which have a greater potential to achieve oil-water separation for oily wastewater treatment with high efficiency.

Employing Atomic Force Microscopy (AFM) for Microscale Investigation of Interfaces and Interactions in Membrane Fouling Processes: New Perspectives and Prospects

Membrane fouling presents a significant challenge in the treatment of wastewater. Several detection methods have been used to interpret membrane fouling processes. Compared with other analysis and detection methods, atomic force microscopy (AFM) is widely used because of its advantages in liquid-phase in situ 3D imaging, ability to measure interactive forces, and mild testing conditions. Although AFM has been widely used in the study of membrane fouling, the current literature has not fully explored its potential. This review aims to uncover and provide a new perspective on the application of AFM technology in future studies on membrane fouling. Initially, a rigorous review was conducted on the morphology, roughness, and interaction forces of AFM in situ characterization of membranes and foulants. Then, the application of AFM in the process of changing membrane fouling factors was reviewed based on its in situ measurement capability, and it was found that changes in ionic conditions, pH, voltage, and even time can cause changes in membrane fouling morphology and forces. Existing membrane fouling models are then discussed, and the role of AFM in predicting and testing these models is presented. Finally, the potential of the improved AFM techniques to be applied in the field of membrane fouling has been underestimated. In this paper, we have fully elucidated the potentials of the improved AFM techniques to be applied in the process of membrane fouling, and we have presented the current challenges and the directions for the future development in an attempt to provide new insights into this field.

Environmental-friendly regenerated lignocellulose functionalized cotton fabric to prepare multi-functional degradable membrane for efficient oil-water separation and solar seawater desalination

Freshwater pollution and shortage have become an imminent problem. Therefore, it is necessary to develop a multi-functional membrane for the production of fresh water. In this work, the regenerated lignocellulose modified cotton fabric was developed as a novel, multi-functional and degradable membrane (LCPT@CF) for efficient oil-water separation and solar steam generation for the first time. The fabrication method has the merits of simple, environmentally friendly and cost effective. The regenerated lignocellulose was adhered on the surface of cotton fabric by tannic acid and polyvinyl alcohol complexes tightly, and the multilayered structures of the LCPT@CF can be formed, which endowed the membranes with underwater superoleophobic property and durability. The underwater superoleophobic property enabled LCPT@CF to purify various kinds of oil-in-water emulsions with a separation efficiency of more than 99.90%. Moreover, benefiting from the excellent photothermal conversion capacity of regenerated lignocellulose, the LCPT@CF achieved high evaporation rate of 1.39 kg m^-2 h^-1 and favorable evaporation efficiency of 84% under 1 sun illumination, and the LCPT@CF also presented excellent salt-resistance for evaporating seawater for 20 cycles, without salt accumulation. More importantly, the LCPT@CF could be naturally degradable by microorganisms in the natural condition within 3 months, which had outstanding environmental friendliness. These above results demonstrated that the green and efficient LCPT@CF could play great potential in oil-water separation and sewage purification.

Membrane Fabrication and Modification by Atomic Layer Deposition: Processes and Applications in Water Treatment and Gas Separation

Membrane-based separation processes are part of most water purification plants worldwide. Industrial separation applications, primarily water purification and gas separation, can be improved with novel membranes or modification to existing ones. Atomic layer deposition (ALD) is an emerging technique that is proposed to upgrade certain kinds of membranes independent of their chemistry and morphology. ALD deposits thin, defect-free, angstrom-scale, and uniform coating layers on a substrate's surface by reacting with gaseous precursors. The surface-modifying effects of ALD are described in the present review, followed by a description of various types of inorganic and organic barrier films and how these can be used in combination with ALD. The role of ALD in membrane fabrication and modification is categorized into different membrane-based groups according to the treated medium, i.e., water or gas. In all membrane types, the ALD-based direct deposition of inorganic materials, mainly metal oxides, on the membrane surface can improve antifouling, selectivity, permeability, and hydrophilicity. Therefore, the ALD technique can broaden the applications of membranes to the treatment of emerging contaminants in water and air. Finally, the advancement, limitations, and challenges of ALD-based membrane fabrication and modification are compared to provide a comprehensive guideline for developing next-generation membranes with improved filtration and separation performance.

Advances in Asymmetric Wettable Janus Materials for Oil–Water Separation

The frequent occurrence of crude oil spills and the indiscriminate discharge of oily wastewater have caused serious environmental pollution. The existing separation methods have some defects and are not suitable for complex oil–water emulsions. Therefore, the efficient separation of complex oil–water emulsions has been of great interest to researchers. Asymmetric wettable Janus materials, which can efficiently separate complex oil–water emulsions, have attracted widespread attention. This comprehensive review systematically summarizes the research progress of asymmetric wettable Janus materials for oil–water separation in the last decade, and introduces, in detail, the preparation methods of them. Specifically, the latest research results of two-dimensional Janus materials, three-dimensional Janus materials, smart responsive Janus materials, and environmentally friendly Janus materials for oil–water separation are elaborated. Finally, ongoing challenges and outlook for the future research of asymmetric wettable Janus materials are presented.

Electro-Enhanced Separation of Microsized Oil-in-Water Emulsions via Metallic Membranes: Performance and Mechanistic Insights

Conventional separation membranes suffer from evitable fouling and flux decrease for water treatment applications. Herein, a novel protocol of electro-enhanced membrane separation is proposed for the efficient treatment of microsized emulsions (∼1 μm) by rationally designing robust electroresponsive copper metallic membranes, which could mitigate oil fouling and coenhance permeance (from ∼1026 to ∼2516 L·m^-2·h^-1·bar^-1) and rejection (from ∼87 to ∼98%). High-flux Cu membranes exhibit superior ductility and electrical conductivity, enabling promising electroactivity. Separation performance and the fouling mechanism were studied under different electrical potentials and ionic strengths. Application of negative polarization into a large-pore (∼2.1 μm) Cu membrane is favorable to not only almost completely reject smaller-sized oil droplets (∼1 μm) but also achieve antifouling and anticorrosion functions. Moreover, surfactants around oil droplets might be redistributed due to electrostatic repulsion, which effectively enhances the steric hindrance effect between neighboring oil droplets, mitigating oil coalescence and consequently membrane fouling. Furthermore, due to the screening effect of surfactants, the presence of low-concentration salts increases the adsorption of surfactants at the oil-water interface, thus preventing oil coalescence via decreasing oil-water interfacial tension. However, under high ionic strengths, the fouling mechanism converts from cake filtration to a complete blocking model due to the reduced electrostatic repulsion between the Cu membrane and oil droplets. This work would provide mechanistic insights into electro-enhanced antifouling for not only oil emulsion separation but also more water treatment applications using rationally designed novel electroresponsive membranes.

Surface Engineering of Ceramic Nanomaterials for Separation of Oil/Water Mixtures

Oil/water mixtures are a potentially major source of environmental pollution if efficient separation technology is not employed during processing. A large volume of oil/water mixtures is produced via many manufacturing operations in food, petrochemical, mining, and metal industries and can be exposed to water sources on a regular basis. To date, several techniques are used in practice to deal with industrial oil/water mixtures and oil spills such as in situ burning of oil, bioremediation, and solidifiers, which change the physical shape of oil as a result of chemical interaction. Physical separation of oil/water mixtures is in industrial practice; however, the existing technologies to do so often require either dissipation of large amounts of energy (such as in cyclones and hydrocyclones) or large residence times or inventories of fluids (such as in decanters). Recently, materials with selective wettability have gained attention for application in separation of oil/water mixtures and surfactant stabilized emulsions. For example, a superhydrophobic material is selectively wettable toward oil while having a poor affinity for the aqueous phase; therefore, a superhydrophobic porous material can easily adsorb the oil while completely rejecting the water from an oil/water mixture, thus physically separating the two components. The ease of separation, low cost, and low-energy requirements are some of the other advantages offered by these materials over existing practices of oil/water separation. The present review aims to focus on the surface engineering aspects to achieve selectively wettability in materials and its their relationship with the separation of oil/water mixtures with particular focus on emulsions, on factors contributing to their stability, and on how wettability can be helpful in their separation. Finally, the challenges in application of superwettable materials will be highlighted, and potential solutions to improve the application of these materials will be put forward.

Quartz Sand Filter Media with Special Wettability for Continuous and Efficient Oil/Water Separation and Dye Adsorption

For continuous and efficient oil/water separation and adsorption of dyes, coconut shell powder was grafted onto the surface of quartz sand by dip-coating method to make coconut shell powder-covered quartz sand filter media (CSQS) with superhydrophilic and underwater superoleophobic properties and superoleophilic and underoil highly hydrophobic properties. The contact angles of the underwater oil and underoil water with CSQS were more than 151.2° and 134.2°, respectively. A continuous oil/water separation device was designed. The separation device filled with CSQS can separate oil/water mixture (whether heavy or light oil) into water and oil at the same time with a separation efficiency of above 99.92%. The filter layer can be recovered through reverse extrusion even after lyophobic liquid penetrated the filter layer; hence, the separation efficiency of the filter layer was still above 99.99% for diesel and water mixture. Simultaneously, CSQS can effectively adsorb methylene blue with the highest removal rate as 98.94%. CSQS can maintain stable wettability under harsh environment conditions. This paper provides a new idea on continuous and efficient oil/water separation and simultaneous dye adsorption.

Preparation of cellulose-coated cotton fabric and its application for the separation of emulsified oil in water

Cellulose is a natural material with dissolution-regeneration property and numerous hydrogen bonds in the molecule. By utilizing these properties, this paper reported the development of a multi-functional fabric consisting of cellulose and commercial cotton fabric. The morphology, mechanical and thermal properties along with the oil-water separation performance of the developed material were studied. The results showed that the cellulose dissolved in NaOH/urea solution was regenerated in a salt solution, and attached tightly onto the cotton fabric, forming a sandwich structure for the material. Such modification significantly enhanced the strength, thermal stability and hydrophilic performance of the fabrics. Interestingly, the prepared material exhibited a unique underwater oleophobic performance, and had the capability to separate highly emulsified oil-water mixtures. The relatively low cost for the material preparation, enhanced mechanical property and high separation performance distinguished the developed material a suitable candidate for the separation of emulsified oil from water in practical applications.