Sequential Demulsification through the Hydrophobic-Hydrophilic-Hydrophobic Filtration Layer toward High-Performing Oil Recovery

Biomimetic materials for efficient emulsion separation: Based on the perspective of energy

Purifying emulsified oily wastewater is particularly crucial for solving environmental pollution and water scarcity. Membrane separation shows great potential for emulsified wastewater treatment. However, realizing continued effective emulsion separation remains a significant challenge. Fortunately, various kinds of creative schemes have been proposed to overcome the current dilemma. In this paper, biomimetic emulsion separation materials with unique wettability are introduced. Besides, This article summarizes the recently advanced emulsion separation strategies. First, we analyze the typical wettability theory and explore the trade-off between separation flux and efficiency. After that, based on emulsion types, the current common emulsion separation materials are summarized and analyzed. Notably, the integration of natural biological inspiration has made separation materials full of potential. Further, from the perspective of external energy input or no-external energy input, this article provides an overview of advanced emulsion separation materials and analyzes the potential separation mechanism. Encouragingly, efficient emulsion separation can be realized by membrane characteristics (microstructure, superwettability, electrostatic interaction) or the appropriate external stimulus (photo, electricity, magnetic). Finally, the challenges and trends are summarized. We hope that this article will provide inspiration for the advancement of novel generations of separation materials.

Functionalized inorganic hydrogel-based membrane for synergistic oil/water separation and catalytic degradation

Hydrogel-modified superwetting membranes typically exhibit remarkable resistance to oil fouling during oil/water separation but suffer from unfavorable stability due to the inevitable swelling and exfoliation. A functionalized inorganic hydrogel-based membrane (TIH@PVDF) with satisfactory durability was proposed for the first time to ingeniously integrate excellent anti-oil fouling and high flux recovery (FRR) for efficient oil/water separation. The TIH@PVDF membrane exhibited a high separation efficiency of over 99 % for oil-in-water emulsions (including liquid paraffin, isooctane, and hexadecane). Owing to the synergistic effect of hydration and catalytic ability from inorganic hydrogel, a FRR of 97.9 % was achieved by catalytic regeneration after seven cycles of oil/water separation, outperforming hydraulic cleaning (90.6 %). Most importantly, the TIH@PVDF membrane demonstrates outstanding capability in separating actual oil field-produced water, indicating its potential for practical application. Meanwhile, the existence of metallic elements in the inorganic hydrogel endowed the TIH@PVDF membrane with sufficient active sites to produce O2•- and 1O2 via peroxymonosulfate (PMS) activation towards organics decomposition. The TIH@PVDF membrane presented a satisfactory removal efficiency (99.1 %) of sulfamethoxazole during a single-pass catalytic separation process. This research may revolutionize the advancement of inorganic hydrogel-based catalytic membranes for oil/water separation and wastewater decontamination.

Facile Fabrication of Binary-Structured Fibrous Membranes with Antifouling and Flame-Retardant Properties for Durable Water/Oil Separation

Membrane fouling from dispersed droplets during water/oil separation undermines performance and limits long-term use. Additionally, there is an urgent need for flame-retardant fibrous membranes capable of purifying high-temperature polluted oils. Inspired by the binary structure of taro leaves, this study introduces a novel fibrous membrane with both antifouling and flame-retardant properties for water/oil treatment. Eco-friendly cellulose acetate (CA) and multifunctional thermoplastic polyurethane (TPU) were used to construct a microfiber-based substrate membrane via electrospinning. A TPU/ammonium polyphosphate (APP) nanofiber layer with a beads-on-string structure was then electrosprayed onto the substrate as a functional layer. This binary-structured composite membrane leverages the adhesive properties of TPU within both the base microfibers and the functional nanofibers, enhancing stability and structural integrity. The functional layer's re-entrant structure effectively prevents dispersed droplets from adhering under the continuous phase, enabling efficient separation performance in both oil-in-water and water-in-oil emulsions. The membrane demonstrated strong antifouling properties and excellent recyclability, maintaining stable flux and a consistently high separation efficiency (>99.6%) across multiple cycles. Additionally, its flame-retardant properties allowed the membrane to self-extinguish when removed from direct flame. This study presents a novel strategy for fabricating multifunctional separation membranes, with detailed analysis of the underlying mechanisms.

Bioinspired superwetting oil-water separation strategy: toward the era of openness

Bioinspired superwetting oil-water separation strategies have received significant attention for their potential in addressing global water scarcity and aquatic pollution challenges. Over the past two decades, the field has rapidly developed, reaching a pivotal phase of innovation in the oil-water separation process. However, many groundbreaking studies have not received extensive scientific recognition. In this review, we systematically examine the application of bioinspired superwetting materials for complex multiscale oil-water separation. We discuss the development of 2D membrane filtration and 3D sponge adsorption materials in confined spaces, summarizing the core separation mechanisms, key research findings, and the evolutionary logic of these materials. Additionally, we highlight emerging open-space separation strategies, emphasizing several novel dynamic separation devices of significant importance. We evaluate and compare the design concepts, separation principles, materials used, comprehensive performance, and existing challenges of these diverse strategies. Finally, we summarize these advantages, critical bottlenecks, and prospects of this field and propose potential solutions for real oil-water separation processes from a general perspective.

A Hydrogel-coated Wood Membrane with Intelligent Oil Pollution Detection for Emulsion Separation

Considering the potential threats posed by oily wastewater to the ecosystem, it is urgently in demand to develop efficient, eco-friendly, and intelligent oil/water separation materials to enhance the safety of the water environment. Herein, an intelligent hydrogel-coated wood (PPT/PPy@DW) membrane with self-healing, self-cleaning, and oil pollution detection performances is fabricated for the controllable separation of oil-in-water (O/W) emulsions and water-in-oil (W/O) emulsions. The PPT/PPy@DW is prepared by loading polypyrrole (PPy) particles on the delignified wood (DW) membranes, further modifying the hydrogel layer as an oil-repellent barrier. The layered porous structure and selective wettability endow PPT/PPy@DW with great separation performance for various O/W emulsions (≥98.69% for separation efficiency and ≈1000 L m-2 h-1 bar-1 for permeance). Notably, the oil pollution degree of PPT/PPy@DW can be monitored in real-time based on the changed voltage generated during O/W emulsion separation, and the oil-polluted PPT/PPy@DW can be self-cleaned by soaking in water to recover its separation performance. The high affinity of PPT/PPy@DW for water makes it effective in trapping water from the mixed surfactant-stabilized W/O emulsions. The prepared eco-friendly and low-cost multifunctional hydrogel wood membrane shows promising potential in on-demand oil/water separation and provides new ideas for the functional improvement of new biomass oil/water separation membrane materials.

Oriented Self-assembly of Flexible MOFs Nanocrystals into Anisotropic Superstructures with Homogeneous Hydrogels Behaviors

Building of metal-organic frameworks (MOFs) homogeneous hydrogels made by spontaneous crystallization remains a significant challenge. Inspired by anisotropically structured materials in nature, an oriented super-assembly strategy to construct micro-scale MOFs superstructure is reported, in which the strong intermolecular interactions between zirconium-oxygen (Zr─O) cluster and glutamic acid are utilized to drive the self-assembly of flexible nanoribbons into pumpkin-like microspheres. The confined effect between water-flexible building blocks and crosslinked hydrogen networks of superstructures achieved a mismatch transformation of MOFs powders into homogeneous hydrogels. Importantly, the elastic and rigid properties of hydrogels can be simply controlled by precise modulation of coordination and self-assembly for anisotropic superstructure. Experimental results and theoretical calculations demonstrates that MOFs anisotropic superstructure exhibits dynamic double networks with a superior water harvesting capacity (119.73 g g-1 ) accompanied with heavy metal removal (1331.67 mg g-1 ) and strong mechanical strength (Young's modulus of 0.3 GPa). The study highlights the unique possibility of tailoring MOFs superstructure with homogeneous hydrogel behavior for application in diverse fields.