Alginate-based nanofibrous membrane with robust photo-Fenton self-cleaning property for efficient crude oil/water emulsion separation

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.

Alginate-based materials as adsorbent for sustainable water treatment

With the encroaching issue of water pollution, the use of involved chemicals to remove pollutants from water is not only a risk of chemical contamination, a potential hazard to the environment and human health but also requires significant investment in managing and improving the chemicals. Therefore, alginate as one of the nanomaterial-adorned polysaccharides-based entity that usually extract from brown algae has been used as novel and more efficient catalysts in the removal of a variety of aqueous pollutants from wastewater, including ionic metals and organic/inorganic pollutants by using the adsorption techniques. Adsorption is a technique used in water treatment where non-polar or particles less soluble in water are stuck to the surface of the adsorbent and therefore purifying it. An example of pollutant typically removed via this method is an organic dye. Alginate-based composites due to their ability to bind to metals like Cd, Au, Cu, Fe, Ni, Pb, and Zn, are a common low-cost and highly effective adsorbents used to remove heavy metals, industrial paints, pesticides, and antibiotics. This review focusses on augmenting the recent status, challenges, and further prospects in alginate-based materials for their potential role exclusively in wastewater treatment, including their modification as adsorbents and their adsorption behaviors. Various applications of alginate-based adsorbent are showcased and tabulated their role in treatment of diverse range of pollutants. It can be concluded that the role of alginate in wastewater treatment is indispensable in the future with its biodegradability, low cost, stability, and high-water permeability properties. However, some challenges need to be identified and overcome to ensure the application of alginate in wastewater treatment can be widely used throughout the world, especially in Malaysia, a country with an abundance of water.

New Antifouling Dual Iron-Based Photo-Fenton Catalytic Membrane Dedicated to Long-Term Treatment of Oils and Dyes

Combining the photo-Fenton catalytic reaction with membrane separation technology can effectively treat oils and dyes in water. However, single iron-based catalysts suffer from limited photogenerated carrier utilization and slow Fe3+/Fe2+ redox reactions, leading to membrane contamination. In this study, iron oxyhydroxide and Prussian blue were grown on a PVDF membrane, optimizing electron transfer to improve the catalytic efficiency (the methylene blue degradation efficiency was nearly 50% in 10 min and the reaction rate constant was 0.094 min-1). The membrane flux for multicomponent oily wastewater reached 965.3 L·m-2 h-1, with an over 99.9% dye removal rate. The flux of actual printing and dyeing wastewater after continuous filtration for 60 min reached 373.6 L·m-2 h-1. Moreover, the catalytic and filtration mechanisms were explained in detail. The strategy provided in this study has certain practical application value in printing and dyeing wastewater treatment.

Ultra-Antifouling Liquid-Like Surfaces for Sustainable Viscous Water-in-Oil Emulsions Separation and Oil Recovery

The demand for efficient separation techniques in industries dealing with high viscosity emulsions has surged due to their widespread applications in various scenarios, including emulsion-based drug delivery systems, the removal of emulsified impurities in formulations and oil spill remediation. However, membrane fouling is a major challenge for conventional separation methods, leading to decreased efficiency and increased maintenance costs. Herein, a novel approach is reported by constructing liquid-like surfaces with double anti-fouling structure, incorporating soft nanomicelles within a rigid, chemically cross-linked network for both anti-membrane-fouling and effective viscous water-in-oil emulsion separation. The coating significantly outperforms perfluorinated and commercial polytetrafluoroethylene (PVDF) membranes, effectively preventing the adhesion of viscous oils like crude oil and pump oil, and alleviating severe membrane fouling. For high-viscosity emulsions (97.3 cP and 52.8 cP), it maintains over 99% separation efficiency after 3 h continuous use. Even after 15 h immersion in strong acids, alkalis, salts, or organic solvents, its separation efficiency remains above 95%. In addition, thanks to the anti-membrane-fouling ability, this work achieved 6 h continuous emulsion separation performance for the first time, demonstrating unparalleled long-term stability. Overall, this study offers valuable insights into the development of innovative coatings for efficient and eco-friendly separation of high-viscosity emulsions.

Cellulose-based underwater superoleophobic coatings with robust anti-viscous oil-fouling property for complex oily wastewater remediation

Underwater superoleophobic coatings, known for their anti-oil-fouling properties, have garnered significant interest in the context of oily wastewater remediation. However, these coatings encounter challenges in preventing viscous oil contamination and structural damage, and easily become ineffective when treating crude oil/water pollutants. Additionally, the non-renewable and non-biodegradable components pose a huge risk to environmental safety and sustainable development. Herein, a cellulose-based coating that combines robust underwater superoleophobicity with anti-viscous oil-fouling characteristic is designed via the extraction of micro/nanoscale heteromorphic cellulose crystals (EHCC) and subsequent crosslinking with carboxymethyl chitosan (CCS). Leveraging the hierarchical micro/nanostructures constructed by EHCC and intensified hydration capability facilitated by multiple hydrogen bonding interactions, the EHCC-CCS coating demonstrates excellent superhydrophilicity/underwater superoleophobicity and ultralow-viscous oil-adhesion property. Moreover, the EHCC-CCS coating exhibits robust chemical resistance and mechanical tolerance. Importantly, it adapts effectively to various flat and porous substrates, offering outstanding anti-oil-fouling and self-cleaning performances. Notably, the EHCC-CCS-coated textile is applied in separating immiscible oil/water mixtures with varying oil viscosities, and the EHCC-CCS-coated PVDF membrane achieves to purify surfactant-stabilized crude oil/water emulsion. The findings provide a straightforward and cost-effective approach for large-scale production of fully biobased coatings with durable underwater superoleophobicity and excellent anti-viscous oil-fouling capability for complex oily wastewater remediation.

A critical review of sodium alginate-based composites in water treatment

The global freshwater crisis is a pressing issue, especially in areas with little rainfall and inner continental regions. The growing attention to water scarcity has induced increased interest in research on advanced water treatment technologies. As an abundant bioactive material in nature, sodium alginate (SA) has been widely used in water management due to its outstanding water absorption and holding ability, reversible swelling property, and pollutant adsorption performance. Building on this, progress made in using various modified forms of SA to access clean water is addressed in this review. Covering studies concern the adsorption and separation of pollutants in wastewater by SA-based absorbents and freshwater harvesting by SA-based collectors. This review explores SA-based composites' composition-structure-construction designs and emphasizes the impact of materials like inorganic materials, functional polymers, and porous matrices and how they can be exploited for water treatment. It also highlights the mechanisms of contaminants adsorption and freshwater desorption of SA-based composites. Finally, the shortcomings and future orientation of SA-based composites are proposed, including performance optimization, structural modification, application expansion, and mechanism in-depth investigation. This review aims to offer a theoretical basis and technical guidance for the use of natural materials to respond to the shortage of freshwater resources.

An eco-friendly construction of superwetting alginate-based aerogels with self-cleaning performance for multifunctional water treatment

The increasingly complex oily wastewater has become a severe environmental issue worldwide, calling for the eco-friendly methods toward multifunctionality, high efficiency and sustainability. This work presents a superwetting alginate-based aerogels prepared by a feasible mineralization without the assistance of intermediates. In this strategy, in-situ grown β-FeOOH nanoparticles on whole porous alginate aerogels, not only provides the hierarchical topography and more -OH groups, enhancing underwater oleophobicity (152 ± 4.4°) and fouling resistance of porous aerogels, but also endows with the outstanding photo-Fenton self-cleaning ability for pollutant degradation. As a result, the outstanding separation selectivity for oil and water (>99.5 %), and superior reusability is achieved without the significant diminution of permeation ability (897-1136 L·m-2·h-1). Furthermore, with the advantage of excellent photocatalytic performance under sunlight, the oily wastewater containing soluble organic pollutants can be remediated by simultaneous separation and photocatalysis decomposition under a gravity-driven filtration solely, revealing a promising potential for complex oily wastewater treatment with the rationally usage of sunlight.

Constructing a composite microfiltration carbon membrane by TiO2 and Fe2O3 for efficient separation of oil-water emulsions

Membrane-based separation technology has attracted enormous attention for oil/water emulsion treatment. Here, composite microfiltration carbon membranes (MCMs) were prepared from the precursor of phenolic resin doping with TiO2 and Fe2O3 via the processes of stereotype and pyrolysis. The functional groups, thermal stability, porous structure, microstructure, morphology, and hydrophilicity of the membrane samples were analyzed by Fourier-transform infrared spectroscopy, thermogravimetric analysis, bubble pressure method, X-ray diffraction, scanning electron microscope, and water contact angle, respectively. The effect of dopant amount on the separation performance of MCMs was investigated. The results show that a mixed matrix system is constructed by TiO2 and Fe2O3 in MCMs, which is beneficial for further optimizing the pore size, porosity, and hydrophilicity of MCMs for oily wastewater treatment by varying the dopant amount. The maximum oil rejections are achieved at 98.9% and 99.6% for MCMs with a dopant content of TiO2 and Fe2O3 at 25%, respectively. In brief, this study offers an attractive strategy for improving the separation performance of MCMs for oily wastewater.

A solar-driven degradation-evaporation strategy for membrane self-cleaning in the efficient separation of viscous crude oil/water emulsions

Membrane separation techniques are promising methods for effectively treating hazardous emulsified oily wastewater, but membrane fouling remains a serious challenge because the high viscosity and complex composition of crude oil make it easy to adhere to membranes and difficult to be removed by conventional physical or chemical cleaning means. Herein, a two-stage solar-driven (photo-Fenton degradation/evaporation) strategy was proposed to realize the self-cleaning of membranes fouled by viscous crude oil (>60,000 mPa s), wherein the photo-Fenton process helped to degrade the heavy components into light components, and all light components removed during the solar-driven evaporation process. A 1D/2D heterostructure membrane with photo-Fenton activity and anti-crude-oil-fouling performance was prepared via a facile self-assembly vacuum-assist method. The addition of rod-like g-C₃N₄ (RCN) increased the interlayer distance of α-FeOOH/porous g-C₃N₄ (FPCN) nanosheets, resulting in a high permeation flux. The FPCN-RCN membrane exhibited both high permeation flux of 779 ± 19 L m^-2h^-1bar^-1 and a separation efficiency of 99.4% for highly viscous crude oil-in-water emulsion. Importantly, the viscous crude oil fouled on the membrane was completely removed by the photo-Fenton degradation/solar-driven evaporation strategy, and the flux recovery rate of the membrane was ∼100%. Therefore, the FPCN-RCN membrane combined with the novel self-cleaning strategy exhibits great potential for practical emulsified oily wastewater treatment.

Robust and multifunctional natural polyphenolic composites for water remediation

The scarcity of clean water has become a global environmental problem which constrains the development of public health, economy, and sustainability. In recent years, natural polyphenols have drawn increasing interests as promising platforms towards diverse water remediation composites and devices, owing to their abundant and renewable resource in nature, highly active surface chemistry, and multifunctionality. This review aims to summarize the most recent advances and highlights of natural polyphenol-based composite materials (e.g., nanofibers, membranes, particles, and hydrogels) for water remediation, by focusing on their structural and functional features, as well as their diversified applications including membrane filtration, solar distillation, adsorption, advanced oxidation processes, and disinfection. Finally, the future challenges in this field are also prospected. It is anticipated that this review will provide new opportunities towards the future development of natural polyphenols and other kinds of naturally occurring molecules in water purification applications.

Tannic acid-based functional coating: surface engineering of membranes for oil-in-water emulsion separation

Recent progress in the tannic acid-based functional coating for surface engineering of membranes toward oil-in-water emulsion separation is summarized.