Oleophilic to oleophobic wettability switching of isoporous through-hole membranes by surface structure control for low-voltage electrowetting-based oil-water separation

Biomimetic materials in oil/water separation: Focusing on switchable wettabilities and applications

Clean water resources are crucial for human society, as the leakage and discharge of oily wastewater not only harm the economy but also disrupt our living environment. Therefore, there is an urgent need for efficient oil-water separation technology. Surfaces with switchable superwetting behavior have garnered significant attention due to their importance in both fundamental research and practical applications. This review introduces the fundamental principles of wettability in the oil-water separation process, the basic theory of switchable wettability, and the mechanisms involved in oil-water separation. Subsequently, the review discusses the research progress, challenges, and issues associated with three conventional types of special wettability materials: superhydrophobic/superoleophilic materials, superhydrophilic/superoleophobic materials, and superhydrophilic/underwater superoleophobic materials. Most importantly, it provides a detailed exploration of recent advancements in switchable wettability smart materials, which combine elements of traditional special wettability materials. These include stimulus-responsive smart materials, pre-wetting-induced materials, and Janus materials. The discussion covers key response factors, detailed examples of representative works, design concepts, and fabrication strategies. Finally, the review offers a comprehensive summary of switchable superwetting smart materials, encompassing their advantages and disadvantages, persistent challenges, and future prospects.

A 3D smart wood membrane with high flux and efficiency for separation of stabilized oil/water emulsions

Oily sewage discharged from indiscriminate industrial and frequent oil spills have become a serious global problem. There is an urgent need to separate stable oil/water emulsions by efficient and environmentally friendly methods. Membrane separation technology has the advantages of low energy consumption and low cost, thus is an effective solution to the problems of oily wastewater. However, the manufacture of multifunctional membranes with high efficiency, high flux and self-cleaning using renewable materials remains a challenge. Herein, three-dimensional (3D) smart membranes with switchable superhydrophobic-hydrophilic surfaces were prepared by grafting photo-responsive poly-spiropyran (PSP) on wood-based substrates via surface atom transfer radical polymerization. This novel membrane can efficiently separate stabilized water-in-oil and oil-in-water emulsions due to reversible hydrophilic-hydrophobic transition by switching UV and visible light irradiation. Remarkably, after immobilization, the PSP grafted on the wood substrate exhibited a faster photo response effect than the free spiropyran (SP). More importantly, the prepared 3D smart membranes showed exceptional high flux (4392 L•m^-2•h^-1) and efficiency (above 99.99 %), good cycle stability (99.99 % after 12 times) and durability (available for at least 60 days) for the separation of surfactant-stabilized water-in-oil emulsions. This work opens a new avenue for the design of functional biomass-derived membranes for efficient and sustainable oily wastewater treatment with high flux, easy scale-up, and green regeneration.

Global research trends in petrochemical wastewater treatment from 2000 to 2021

Petrochemical wastewater (PWW) is a huge industrial contaminant that generates a wide range of resistive and poisonous organic pollutants that harm animals and plants in natural water bodies when discharged untreated or partially treated. Therefore, it is vital to develop technologies that are simple, efficient, and profitable for the treatment of oily wastewater. Although much study has been undertaken on the treatment of PWW, there has not been any recent work on bibliometric analysis of global research trends on this issue. A bibliometric analysis will help current and future researchers figure out where the gaps are and how to fill them. The present study's focus is to examine the characteristics and trends of research on oily wastewater treatment with an emphasis on the treatment of PWW. This research was performed on five important aspects, including characterization of research publications, countries' performances and collaborations, an analysis of the best papers with the most citations, keyword analysis (including frequency distribution of the keyword analysis, the transformation of the keyword combination across time, and exploration of changes in rank over time), and journal analysis, according to the 2457 papers in the Science Citation Index Expanded using the Web of Science (WoS) database from 2000 to 2021. For further analysis, the contingency matrix, bump diagram, and inter-temporal network stream were employed.

Crosslinked biomimetic coating modified stainless-steel-mesh enables completely self-cleaning separation of crude oil/water mixtures

The development of high-flux, durable and completely self-cleaning membranes is highly desired for separation of massive oil/water mixtures. Herein, differently crosslinked poly(2-methacryloyloxylethyl phosphorylcholine) (PMPC) brush grafted stainless steel mesh (SSM) membranes (SSM/PMPCs) were fabricated by integrating of mussel inspired universal adhesion and crosslinking chemistry with surface-initiated activators regenerated by electron transfer atom transfer radical polymerization (SI-ARGET-ATRP). The durability and self-cleaning performance of the prepared SSM membranes were evaluated by separating sticky crude oil/water mixtures in a continuous recycling dead-end filtration device. The water filtration flux driven by gravity reached 60,000 L⋅m^-2⋅h^-1 with a separation efficiency of over 99.98%. Furthermore, zero-flux-decline was observed during a 5 h continuous filtration when assisted by mechanical stirring. More significantly, such a completely self-cleaning separation of the well crosslinked SSM/PMPC2 membrane under optimized flux and stirring conditions had been operated cumulatively for 190 h in 30 days without any additional cleaning. These significant advances are more promising for practical applications in crude oil-contaminated water treatments and massive oil/water mixture separation.

Polymeric Membranes for Oil-Water Separation: A Review

This review is devoted to the application of bulk synthetic polymers such as polysulfone (PSf), polyethersulfone (PES), polyacrylonitrile (PAN), and polyvinylidene fluoride (PVDF) for the separation of oil-water emulsions. Due to the high hydrophobicity of the presented polymers and their tendency to be contaminated with water-oil emulsions, methods for the hydrophilization of membranes based on them were analyzed: the mixing of polymers, the introduction of inorganic additives, and surface modification. In addition, membranes based on natural hydrophilic materials (cellulose and its derivatives) are given as a comparison.