Efficient Fenton-Like Catalysis Boosting the Antifouling Performance of the Heterostructured Membranes Fabricated via Vapor-Induced Phase Separation and In Situ Mineralization

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.

Ultrahigh antifouling ultrafiltration membrane based on Ag NPs photoreduction modified PVP/BiOCl nanoflower for efficient membrane fouling removal

Polyethersulfone (PES) is widely used as an ultrafiltration (UF) membrane material in industrial production due to its excellent performance. However, its inherent hydrophobicity leads to severe membrane fouling issues during practical operation. In this study, focusing on the fouling issues of PES UF membrane, bismuth oxychloride (BiOCl) was chosen as the main nanomaterial. Ag NPs were introduced via photoreduction into BiOCl at the optimal ratio of polyvinylpyrrolidone (PVP) and BiOCl (wt%-0.3:100), resulting in the synthesis of Ag@BiOCl nanoparticles. These nanoparticles were then blended into the PES casting solution and fabricated into composite UF membranes using the reverse thermally induced phase separation (RTIPS) method. Analysis of UV-vis characterization results revealed that the introduction of Ag NPs widened the visible light absorption range of the composite material from 414.30 nm to 508.62 nm. PL spectroscopy results indicated that Ag NPs effectively inhibited the recombination of photogenerated electron-hole pairs, significantly enhancing the photocatalytic activity of Ag@BiOCl. Additionally, the introduction of Ag NPs induced the generation of oxygen vacancies (OVs) on the surface of the composite membrane. Under visible light, the contaminated composite membrane drove the OVs in the photocatalytic material to generate hot electrons (h+-e-). These h+-e- promoted the generation of more active oxygen species, thereby improving the efficiency of membrane fouling removal. The optimal membrane in the PES/Ag@BiOCl series, AGMC5-2 exhibited a pure water flux of 3960.43 L m-2 h-1, a humic acid (HA) rejection rate of 95.00%, and a flux recovery rate of 85.98%. The antibacterial rates against E. coli and S. aureus were 79.07% and 82.33%, respectively. In this study, the PES/Ag@BiOCl composite membrane demonstrated outstanding pure water flux, excellent pollutant rejection rates, significant self-cleaning, and antibacterial properties, effectively addressing membrane fouling issues caused by the inherent hydrophobicity of PES. The successful preparation of the PES/Ag@BiOCl composite membrane lays the foundation for the application of photocatalytic membranes in the field of water treatment.

Illuminating for purity: Photocatalytic and photothermal membranes for sustainable oil-water separation

The integration of photocatalytic and photothermal materials with oil-water separation membranes marks a significant advancement in sustainable separation technologies. These hybrid membranes exhibit exceptional functionalities, including resistance to oil fouling, self-cleaning, antibacterial properties, and reduced oil viscosity. Based on their reaction mechanisms, current photocatalytic and photothermal membranes are categorized into four types, i.e., photocatalytic membranes, photo-Fenton membranes, PMS-assisted photocatalytic membranes, and photothermal membranes. Under light irradiation, photocatalytically functionalized membranes generate reactive oxygen species (ROS) that degrade organic pollutants and inactivate bacteria on the membrane surfaces, enabling in-situ cleaning and regeneration. In addition to the above benefits, photothermal membranes achieve reduction of oil viscosity for higher membrane permeation and removal of light oil from membrane surfaces through light-induced heating. This review first explores the mechanisms underlying light-driven advanced oxidation processes (AOPs) and photothermal effects, followed by an in-depth discussion on the fabrication methods of these membranes. Additionally, the applications of photocatalytic and photothermal membranes in oil-water separation are examined, with an emphasis on how the photocatalytic and photothermal materials contribute to membrane functionality. Finally, this review presents the challenges currently faced by photocatalytic and photothermal membranes and outlines future research directions.

Facile Preparation of Sulfonated Polysulfone Composite Membranes with High Hydrophilicity and Visible-Light Driving Self-Cleaning Performance

The photo-Fenton reaction can efficiently degrade organic pollutants and thus is applied intensively for clearing out membrane fouling. However, the pollutant removal efficiency is greatly limited by the redox cycle rate of Fe2+/Fe3+ and the rapid recombination rate of the photogenerated electrons and holes. In order to overcome these drawbacks, a sulfonated polysulfone composite membrane was designed and prepared by incorporating titanium dioxide (TiO2) nanoparticles into a sulfonated polysulfone membrane and sequentially forming β-FeOOHs on the membrane surface. It was found that the synergy of TiO2 and β-FeOOH enhanced the hydrophilicity and improved the pure water flux of the composite membrane. As a result, the composite membrane exhibited superior separation performance for methylene blue and rhodamine B cationic dyes. The rejection rate was larger than 99.5%, and the pure water flux was larger than 125.7 L m-2 h-1, largely surpassing that of nanofiltration membranes. Meanwhile, the composite membrane exhibited an excellent self-cleaning performance, achieving a flux recovery rate over 99.7% after visible-light driving Fenton reaction treatment. The rejection rate still remained above 97.2% after 5 cycles of filtration and recovery, indicating the strong treatment ability of the membrane for dye wastewater.

In Situ Preparation of MnO2 on the Catechol/Silane-Coated Polypropylene Nonwoven Fabrics for Effective Removal of Cationic Dyes

Previous studies have confirmed that MnOx removes heavy metal ions and organic pollutants from water with dual effects of adsorption and oxidation coupling, significantly improving the ability to remove impurities. Nanometal oxides have a highly reactive surface but tend to agglomerate during preparation and are challenging to recycle after use. A common method is to combine nano-MnO2 with Fe3O4 to prepare magnetic materials for easy recycling. Our previous research has confirmed that catechol (CA) and (3-aminopropyl) triethoxysilane (KH550) can be co-deposited on the surface of polypropylene nonwovens to form a stable CK coating under alkaline conditions. In addition, the coating has many active groups, including hydroxyl groups, amino groups, etc. This study further investigates the secondary reactivity of CK coatings. The coordination of catechol groups and metal ions was used to anchor manganese ions to the coating. Meanwhile, the hydroxyl and amino groups were used to reduce manganese ions to Mn4+ in situ to prepare PP-(CK-MnO2). We found that the sample had an excellent decolorization effect on cationic dyes but was limited to anionic dyes. The decolorization mechanism of cationic dyes was further discussed. The results showed that the decolorization of cationic dyes had a dual effect of adsorption and oxidative degradation. Under acidic conditions, its oxidation properties were enhanced. It can be used as a highly effective decolorizing agent for cationic dyes, and the decolorization behavior is consistent with the first-order kinetics. As the pH increases, its oxidation properties gradually decrease. Although the electrostatic adsorption effect was enhanced, the overall decolorization performance was significantly reduced. Recycling experiments have proved that it can maintain >90% removal rate after five cycles. This study also demonstrated that the CK coating has dopamine-like properties, which can coordinate with metal ions to prepare metal-organic hybrid materials.

Co-doped Zr-UiO-66-NH2@carboxylated cellulose nanocrystals/PAN membrane for oil/water separation with photocatalysis-PMS synergistic self-cleaning and antibacterial activity

The development of superwetting membranes is a promising approach for separating emulsified oily wastewater. However, challenges such as low flux without external pressure and membrane fouling have hindered membrane performance. Herein, we fabricated a novel nanofibrous membrane by grafting Co-doped Zr-UiO-66-NH2 (UiO(Zr/Co)) nanoparticles onto carboxylated cellulose nanocrystals (CCNC)-polyacrylonitrile (PAN) mixed matrix electrospinning membrane via chemical bonds through EDC/NHS reaction. CCNC served a dual purpose by enhancing membrane hydrophilicity and providing connection points for UiO(Zr/Co). The as-prepared UiO(Zr/Co)@CCNC/PAN exhibited superhydrophilic/underwater superoleophobic and anti-fouling properties. The membrane demonstrated excellent demulsification and gravity-driven separation capabilities for various oil-in-water emulsions, with superior permeation flux (1588-2557 L m-2 h-1) and separation efficiency (above 99 %). Furthermore, UiO (Zr/Co)@CCNC/PAN could activate peroxomonosulfate (PMS) under visible light to remove both high viscous crude oil-fouling and bio-fouling, exhibiting impressive photocatalytic self-cleaning and antibacterial activity. The generation of reactive radicals (O2-, OH and SO4-) and non-radical (1O2) species in UiO(Zr/Co)@CCNC/PAN+PMS system through multiple pathways was confirmed. Additionally, the band structure of UiO(Zr/Co) and synergistic photocatalytic-PMS activation mechanism were investigated. This work provides new insights into the design and fabrication of MOF modified superwetting nanofibrous membrane with inherent bonding, high permeation flux, anti-fouling and self-cleaning properties.

Biomimetic Aramid Nanofiber/β-FeOOH Composite Coating for Polypropylene Separators in Lithium-Sulfur Batteries

Aramid nanofibers (ANFs), with attractive mechanical and thermal properties, have attracted much attention as key building units for the design of high-performance composite materials. Although great progress has been made, the potential of ANFs as fibrous protein mimetics for controlling the growth of inorganic materials has not been fully revealed, which is critical for avoiding phase separation associated with typical solution blending. In this work, we show that ANFs could template the oriented growth of β-FeOOH nanowhiskers, which enables the synthesis of ANFs/β-FeOOH hybrids as composite coatings for polypropylene (PP) separators in Li-S batteries. The modified PP separator exhibits enhanced mechanical properties, heightened thermal performance, optimized electrolyte wettability, and improved ion conductivity, leading to superior electrochemical properties, including high initial specific capacity, better rate capability, and long cycling stability, which are superior to those of the commercial PP separators. Importantly, the addition of β-FeOOH to ANFs could further contribute to the suppression of lithium polysulfide shuttling by chemical immobilization, inhibition of the growth of lithium dendrites because of the intrinsic high modulus and hardness, and promotion of reaction dynamics due to the catalytic effect. We believe that our work may provide a potent biomimetic pathway for the development of advanced battery separators based on ANFs.

Construction of Mineralization Nanostructures in Polymers for Mechanical Enhancement and Functionalization

Mineralization capable of growing inorganic nanostructures efficiently, orderly, and spontaneously shows great potential for application in the construction of high-performance organic-inorganic composites. As a thermodynamically spontaneous solid-phase crystallization reaction involving dual organic and inorganic components, mineralization allows for the self-assembly of sophisticated and exclusive nanostructures within a polymer matrix. It results in a diversity of functions such as enhanced strength, toughness, electrical conductivity, selective permeability, and biocompatibility. While there are previous reviews discussing the progress of mineralization reactions, many of them overlook the significant benefits of interfacial regulation and functionalization that come from the incorporation of mineralized structures into polymers. Focusing on different means of assembly of mineralized nanostructures in polymer, the work analyzes their design principles and implementation strategies. Then, their different advantages and disadvantages are analyzed by combining nanostructures with organic substrates as well as involving the basis of different functionalizations. It is anticipated to provide insights and guidance for the future development of mineralized polymer composites and their application designs.

Application of Photo-Fenton-Membrane Technology in Wastewater Treatment: A Review

Photo-Fenton coupled with membrane (photo-Fenton-membrane) technology offers great potential benefits in future wastewater treatment because it can not only degrade refractory organics, but also separate different pollutants from water; additionally, it often has a membrane-self-cleaning ability. In this review, three key factors of photo-Fenton-membrane technology, photo-Fenton catalysts, membrane materials and reactor configuration, are presented. Fe-based photo-Fenton catalysts include zero-valent iron, iron oxides, Fe-metal oxides composites and Fe-based metal-organic frameworks. Non-Fe-based photo-Fenton catalysts are related to other metallic compounds and carbon-based materials. Polymeric and ceramic membranes used in photo-Fenton-membrane technology are discussed. Additionally, two kinds of reactor configurations, immobilized reactor and suspension reactor, are introduced. Moreover, we summarize the applications of photo-Fenton-membrane technology in wastewater, such as separation and degradation of pollutants, removal of Cr(VI) and disinfection. In the last section, the future prospects of photo-Fenton-membrane technology are discussed.