Multifunctional filtration membrane with anti-viscous-oils-fouling capacity and selective dyes adsorption ability for complex wastewater remediation

Superhydrophilic PVDF membrane fabricated on modified TiO2/CS-SDAEM nanoparticles deposited on GA/CNTs hydrophilic layer to achieve self-cleaning photodegradation and low contamination rate for dyestuff separation

In this work CS-SDAEM polymer brushes with long-chain structure were synthesized, and TiO2/CS-SDAEM nanoparticles were prepared by modifying them on the TiO2 surface. The prepared modified membrane can effectively degrade dyes through photocatalysis and can reduce the contamination rate of the membrane during use. The separation membrane achieves efficient removal of contamination by self-cleaning. The results of the membrane surface analysis test show that the formation of coordination bonds between o-benzenetriol of GA and TiO2, and the chemical reaction between CS and GA, which promote the stability between coating components. The results of filtering tests show that with the excellent anti-fouling performance of long-chain polymer brush, the photodegradability of TiO2 and a large number of hydrophilic groups contained in GA and CS, PVDF- TiO2/CS-SDAEM membranes overcome the above shortcomings and achieve super-hydrophilicity, anti-fouling and self-cleaning. In addition, DFT model simulations of photocatalytic processes show that there is a charge transfer between CS and TiO2, which increases the width of the high light absorption band and improves the efficiency of photodegradation. Modified membranes achieve efficient self-cleaning processes and low flux decline rates, which hold great promise for use in real wastewater application scenarios.

Construction of CS-SDAEM long-chain polysaccharide derivative on TA@CNTs coated PVDF membrane with effective oil-water emulsion purification and low contamination rate

Currently, the most effective way to improve the anti-fouling performance of water treatment separation membrane is to enhance the hydrophilicity of the membrane surface, but it can still cause contamination, leading to the occurrence of flux reduction. The construction of a strong hydration layer to resist wastewater contamination is still a challenging task. In this study, a defect-free hydration layer barrier was achieved by grafting chitosan polysaccharide derivatives (CS-SDAEM) on the membrane, which achieved in effective fouling prevention and low flux decline rate. A layer of tannic acid-coated carbon nanotubes (TA@CNTs) has been uniformly deposited on the commercial PVDF membrane so that the surface was rich in -COOH groups, providing sufficient reaction sites. These reactive groups facilitate the grafting of amphiphilic polymers onto the membrane. This modification strategy achieved in enhancing the antifouling performance. The modified membrane achieved low contamination rate with DR of 16.9 % for wastewater filtration, and the flux recovery rate was above 95 % with PWF of 1100 (L·m-2·h-1). The membrane had excellent anti-fouling performance, which provided a new route for the future development of water treatment membrane.

Smart and Multifunctional Materials Based on Electroactive Poly(vinylidene fluoride): Recent Advances and Opportunities in Sensors, Actuators, Energy, Environmental, and Biomedical Applications

From scientific and technological points of view, poly(vinylidene fluoride), PVDF, is one of the most exciting polymers due to its overall physicochemical characteristics. This polymer can crystalize into five crystalline phases and can be processed in the form of films, fibers, membranes, and specific microstructures, being the physical properties controllable over a wide range through appropriate chemical modifications. Moreover, PVDF-based materials are characterized by excellent chemical, mechanical, thermal, and radiation resistance, and for their outstanding electroactive properties, including high dielectric, piezoelectric, pyroelectric, and ferroelectric response, being the best among polymer systems and thus noteworthy for an increasing number of technologies. This review summarizes and critically discusses the latest advances in PVDF and its copolymers, composites, and blends, including their main characteristics and processability, together with their tailorability and implementation in areas including sensors, actuators, energy harvesting and storage devices, environmental membranes, microfluidic, tissue engineering, and antimicrobial applications. The main conclusions, challenges and future trends concerning materials and application areas are also presented.

Zwitterionic Biomaterials

The term "zwitterionic polymers" refers to polymers that bear a pair of oppositely charged groups in their repeating units. When these oppositely charged groups are equally distributed at the molecular level, the molecules exhibit an overall neutral charge with a strong hydration effect via ionic solvation. The strong hydration effect constitutes the foundation of a series of exceptional properties of zwitterionic materials, including resistance to protein adsorption, lubrication at interfaces, promotion of protein stabilities, antifreezing in solutions, etc. As a result, zwitterionic materials have drawn great attention in biomedical and engineering applications in recent years. In this review, we give a comprehensive and panoramic overview of zwitterionic materials, covering the fundamentals of hydration and nonfouling behaviors, different types of zwitterionic surfaces and polymers, and their biomedical applications.

Protonated cross-linkable nanocomposite coatings with outstanding underwater superoleophobic and anti-viscous oil-fouling properties for crude oil/water separation

Superhydrophilic/underwater superoleophobic coatings that effectively prevent viscous oil contamination have been of considerable interest for the great potential in oil spill remediation and oilfield wastewater treatment. In the present work, a protonated cross-linkable nanocomposite coating with robust underwater superoleophobicity and intensified hydration capability is proposed through the synthesis of active polymeric nanocomplex (PNC), cross-linking reaction between PNC and hydrophilic chitosan (CS), and final protonation to further improve water affinity. Benefiting from the hierarchical structure and strong hydration capability induced by electrostatic interactions and hydrogen bondings, the nanocomposite coating coated textile exhibits excellent superhydrophilicity (within 0.28 s with water contact angle reaching 0°), underwater superoleophobicity (underwater crude oil contact angle at 160°), and ultralow oil adhesion even to highly viscous silicone oil. Moreover, the nanocomposite coating presents a robust chemical resistance, mechanical tolerance, and storage stability. Simultaneously, the nanocomposite coating adapts well to various porous substrates (e.g., stainless steel mesh and Ni sponge) with great anti-oil-fouling and self-cleaning performances. Importantly, the coating coated textile is successfully applied in crude oil/water separation with excellent efficiency and repeatability. The findings conceivably stand out as a new methodology to fabricate superhydrophilic/underwater superoleophobic materials with outstanding anti-viscous oil-fouling property for practically treating oily wastewater.

Adsorption of dyes methyl violet and malachite green from aqueous solution on multi-step modified rice husk powder in single and binary systems: Characterization, adsorption behavior and physical interpretations

A novel modified rice husk (MRH) has been prepared for removing cationic dyes in both single system and binary system. SEM-EDS, FT-IR, XRD and XPS were used to characterize the physical and chemical properties of MRH. It showed that the maximum adsorption capacity of MRH for methyl violet (MV) and malachite green (MG) in single system was 154.49 and 996.97 mg g^-1, while in binary system was 530.94 and 408.58 mg g^-1, respectively. The experimental results showed that the pseudo-second-order kinetic model was better to describe the kinetic behavior of MV and MG adsorption. By using double layer adsorption model, we found that the n_D for MV adsorption were 2.52, 2.65 and 3.34 at 298, 308 and 318 K, respectively, and the n_D for MG adsorption were 4.59, 4.85 and 4.30, respectively. These results illustrated that multiple dye molecules were adsorbed on one adsorption site in non-parallel direction, indicating that the adsorption of dyes is multi-molecular mechanism. Furthermore, synergistic and antagonistic adsorption might be existed simultaneously in binary system. In summary, MRH has been shown well adsorption properties and reusability and our finding might provide a new idea for developing low-cost, efficient and reusable adsorbent to remove dyes from wastewater.

Construction of durable superhydrophilic activated carbon fibers based material for highly-efficient oil/water separation and aqueous contaminants degradation

Developing filtering materials with high permeation flux and contaminant removal rate is of great importance for oily wastewater remediation. Herein, a robust three-dimensional (3D) activated carbon fibers (ACFs) based composite with uniformly grown layered double hydroxide (LDH) on the surface was successfully constructed through a feasible hydrothermal strategy. The LDH with a high surface energy and vertically aligned structure could provide superhydrophilicity to ACFs. Systematic investigation confirmed that the 3D material could overcome the size mismatch between the ACFs macropores and tiny emulsified droplets through the combination of size-sieving filtration on the surface and oil droplet coalescence in the fiber network. This process efficiently separated the intractable surfactant-stabilized oil-in-water emulsions with high permeation flux (up to 4.16 × 10⁶ L m^-2 h^-1 bar^-1). Notably, the LDH also had well-dispersed catalytic active sites, which could initiate advanced oxidation processes (AOPs) to efficiently eliminate various types of water-soluble organic pollutants (e.g., pharmaceuticals, phenolic compounds and organic dyes). The resulting modified ACFs exhibited exceptional removal rates for both oil and organic pollutants in the complex sewage during the continuous filtration process. These versatile abilities integrated with the facile preparation method reported herein provide outstanding prospects for the large-scale treatment of oily wastewater.

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

A photocatalytic membrane with significant degradation and antifouling performance has become an important part in wastewater treatment. However, the low catalyst loading on the polymer membrane limits its performance improvement. Herein, we fabricated poly(vinylidene fluoride) (PVDF) and poly(acrylic acid) (PAA) blend membranes with a rough surface via a vapor-induced phase separation (VIPS) process. Then Fe³⁺ was cross-linked with the carboxyl groups on the membrane surface and further in situ mineralized into β-FeOOH nanorods. The resultant membranes exhibit not only hydrophilicity and underwater superoleophobicity but also favorable separation efficiency and high water flux in oil-in-water emulsions separation. Under visible light irradiation, the membrane can degrade methylene blue (MB) to 95.2% in 180 min. More importantly, the membrane has a significant photocatalytic self-cleaning ability for crude oil with a flux recovery ratio (FRR) as high as 94.1%. This work brings a new strategy to fabricate the rough and porous surface for high loading of the hydrophilic photo-Fenton catalyst, improving the oil/water emulsion separation and antifouling performance of the membranes.