Eco-friendly and facile fabrication of polyimide mesh with underwater superoleophobicity for oil/water separation via polydopamine/starch hybrid decoration

A Self-Cleaning TiO2 Bacterial Cellulose Super-Hydrophilic Underwater Super-Oleophobic Composite Membrane for Efficient Oil-Water Separation

Due to the increasingly serious problem of offshore oil spills, research related to oil-water separation has attracted more and more attention. Here, we prepared a super-hydrophilic/underwater super-oleophobic membrane (hereinafter referred to as BTA) using poly-dopamine (PDA) to adhesive TiO₂ nanoparticles on the surface of bacterial cellulose, coated with sodium alienate by vacuum-assisted filtration technique. This demonstrates its excellent underwater super-oleophobic property. Its contact angle is about 153°. Remarkably, BTA has 99% separation efficiency. More importantly, BTA still showed excellent anti-pollution property under ultraviolet light after 20 cycles. BTA has the advantages of low cost, environmentally friendliness and good anti-fouling performance. We believe it can play an important role in dealing with problems related to oily wastewater.

Multicomponent Composite Membrane with Three-Phase Interface Heterostructure as Photocatalyst for Organic Dye Removal

A multicomponent composite membrane (P-S-T/C) with three-phase interface heterostructure is ingeniously designed. A polydopamine (PDA)-modified conductive carbon fiber cloth (C_FC) is used as the substrate. Activated poly(vinylidene fluoride) (PVDF) with titanium dioxide (TiO₂) and a silicon dioxide (SiO₂) aerogel are electrospun as the top layer. The three-phase interface heterostructure was formed by TiO₂, conductive C_FC, and the SiO₂ aerogel. Its photocatalytic performance is validated by photodegradation of organic dyes in a low-oxygen (O₂) water environment. On combining with the capillary condensation of a bilayer structure, P-S-T/C exhibits excellent removal capability for anionic and cationic dyes. Moreover, P-S-T/C exhibits excellent stability and recyclability under simulated sunlight. The mechanism study indicates that the separated photogenerated carriers diffuse to the composite membrane surface rapidly on the three-phase interface of P-S-T/C. The abundant O₂ adsorbed on the porous SiO₂ aerogel surface acts as an electron (e^-)-trapping agent, which can also decrease the work function of the composite materials. Superoxide radicals (^•O₂ ^-) play a dominant role in the reaction of photodegradation supported by a free radical-trapping experiment. This work paves a way to design a membrane with photocatalytic performance by constructing the interface heterostructure.

Ionic liquid-modified polyimide membranes with in-situ-grown polydopamine for separation of oil–water emulsions

Leakage of oily industrial waste is not only a serious environmental and ecological hazard but also poses a significant health risk to people. Membrane separation, which is cost-effective and efficient, is one of the best solutions for reducing pollution discharge through oil–water separation. In this study, polydopamine (PDA) was incorporated into electrostatically spun ionic liquid-capped polyimide (IL-PI) membranes through an in situ growth method; the membranes exhibited the strong adsorption properties of PDA. The polyimide fibers were hydrophilically modified with an IL, which contains several hydrophilic groups, and PDA. Adjusting the polymerization time resulted in the formation of a composite membrane, which could effectively separate oil–water emulsions. Scanning electron microscopy analysis showed that with an increase in the PDA coating time, the PDA content in and on the surface of the composite membrane fibers significantly increased. In addition, the surface contact angle of the membrane decreased from 72.87° to 12.06° with the addition of the PDA coating, while the wettability was significantly improved. The PDA-modified fibrous membranes showed good separation of the emulsified oil–water mixtures. The maximum membrane flux and separation efficiency achieved was 280 L·m−2·h−1 and >99%, respectively. After 10 repeated cycles, the separation efficiency was maintained at >92%. This approach can be used for the design of future wastewater treatment solutions.

Polyimide based super-wettable membranes/materials for high performance oil/water mixture and emulsion separation: A review

This article reviews the application of highly heat and pressure resistant polyimide material for the development of membranes/materials that exhibit unique super-wettability, the characteristics pivotal for the efficient separation of oil-water mixture and emulsion. The polymerization of imide monomer in polyimide brings about the required porosity in the material, which in turn renders the crucial surface roughness, which is instrumental for establishing the desired super-wettability on the polyimide based membrane materials, in addition to the mechanical and thermal robustness. The membrane as the oil-water filtering medium can be either oil passing or water passing depends on the individual wettability of the membrane surface for oil and water, which in turn depend on the respective solid-liquid interfacial energy and the hierarchical surface roughness. Superhydrophobic/superoleophobic wetting characteristic of the surface repels water and allows oil to pass through the membrane medium, and the major disadvantage of this kind of oil/water separation is the rapid oil fouling of the membrane pores and the consequent less efficiency for oil water separation. On the other hand, the membrane surface engineered to have the Superhydrophilic/underwater superoleophobic wetting characteristics can be water passing, and the easy fouling of the membrane surface can be minimized. In the case of polyimide materials, there are lot of scopes to engineer the physical properties like surface energy and surface roughness of the membrane surface in order to obtain the required wettability. There have been many works focused on the application of different variants of polyimide materials for developing membrane for oil water separation. In this review, we present an itemized review of various works on polyimide materials based oil/water separation in terms of chemical, physical, structural and surface characteristics of the material.

Toward Efficient Oil Energy Recovery: Eco-Friendly Fabrication of a Biomimetic Durable Metal Mesh with a Moss-Like Silver Nanocluster Structure

With the purpose of oil energy recovery as well as achieving efficiency of oil/water separation, hydrophobic mesh materials have attracted extensive attention. However, fabrication of the current methods is not environmentally friendly, has high energy consumption, and creates serious pollution. Inspired by lotus leaves and rose petals, a biomimetic superhydrophobic surface was fabricated prepared on a stainless steel mesh by an in situ chemical reduction method with simple operation and mild conditions. The results of SEM, XRD, and XPS demonstrated that the mesh shows a stable and uniform moss-like rough structured surface. The SSM/Ag/ODA mesh, which was modified by moss-like Ag nanoclusters and low surface energy agents, has excellent superhydrophobicity with an excellent oil/water separation efficiency that reached up to 99.8%. The silver mirror phenomenon formed by the Ag nanoclusters further confirmed that silver ions were reduced and attached to the surface of the mesh. Moreover, the mesh can maintain superhydrophobicity under harsh conditions, such as a high concentration of a salty solution, organic solvents, alkaline, acidic solution, and even long-time UV irradiation, etc. More importantly, the modified mesh has excellent physical stability, in which the water contact angle on the mesh can be maintained above 150° after harsh mechanical wear. The hydrophobic mesh showed great potential to be applied for highly efficient oil/water separation and oil energy recovery even under complex and harsh conditions.