Surface functionalization via synergistic grafting of surface-modified silica nanoparticles and layered double hydroxide nanosheets for fabrication of superhydrophilic but relatively oleophobic antifouling membranes

Advances of Layered Double Hydroxide-Based Materials for Tumor Imaging and Therapy

Layered double hydroxides (LDH) are a class of functional anionic clays that typically consist of orthorhombic arrays of metal hydroxides with anions sandwiched between the layers. Due to their unique properties, including high chemical stability, good biocompatibility, controlled drug loading, and enhanced drug bioavailability, LDHs have many potential applications in the medical field. Especially in the fields of bioimaging and tumor therapy. This paper reviews the research progress of LDHs and their nanocomposites in the field of tumor imaging and therapy. First, the structure and advantages of LDH are discussed. Then, several commonly used methods for the preparation of LDH are presented, including co-precipitation, hydrothermal and ion exchange methods. Subsequently, recent advances in layered hydroxides and their nanocomposites for cancer imaging and therapy are highlighted. Finally, based on current research, we summaries the prospects and challenges of layered hydroxides and nanocomposites for cancer diagnosis and therapy.

The antifouling mechanism and application of bio-inspired superwetting surfaces with effective antifouling performance

With the rapid development of industries, the issue of pollution on Earth has become increasingly severe. This has led to the deterioration of various surfaces, rendering them ineffective for their intended purposes. Examples of such surfaces include oil rigs, seawater intakes, and more. A variety of functional surface techniques have been created to address these issues, including superwetting surfaces, antifouling coatings, nano-polymer composite materials, etc. They primarily exploit the membrane's surface properties and hydration layer to improve the antifouling property. In recent years, biomimetic superwetting surfaces with non-toxic and environmental characteristics have garnered massive attention, greatly aiding in solving the problem of pollution. In this work, a detailed presentation of antifouling superwetting materials was made, including superhydrophobic surface, superhydrophilic surface, and superhydrophilic/underwater superoleophobic surface, along with the antifouling mechanisms. Then, the applications of the superwetting antifouling materials in antifouling domain were addressed in depth.

Superhydrophilic and oleophobic sponges prepared based on Mussel-Inspired chemistry for efficient oil-water separation

Superhydrophilic/oleophobic materials are considered to be the best materials for achieving oil-water separation, but their preparation is difficult and the existing methods are not universal. In this paper, a two-step modification strategy was used to prepare superhydrophilic/oleophobic sponges by adjusting the polar and nonpolar components of the materials using mussel-inspired chemistry. While remaining superhydrophilic, the modified sponge surface has a maximum contact angle of 135° with different oils in air. The modified sponge exhibited superoleophobicity in water, and the contact angle of oil could reach more than 150°. In addition, the modified sponges were also reusable, chemically stable, and mechanically durable. Its oil-water separation flux was up to 24900 Lm-2  h-1  bar-1 , and the separation efficiency was above 97 %. We believe that this method will provide an environmentally friendly and efficient way to prepare the superhydrophilic/oleophobic materials.

Antifouling Conductive Composite Membrane with Reversible Wettability for Wastewater Treatment

Membrane fouling severely hinders the sustainable development of membrane separation technology. Membrane wetting property is one of the most important factors dominating the development of membrane fouling. Theoretically, a hydrophilic membrane is expected to be more resistant to fouling during filtration, while a hydrophobic membrane with low surface energy is more advantageous during membrane cleaning. However, conventional membrane materials do not possess the capability to change their wettability on demand. In this study, a stainless steel mesh–sulfosuccinate-doped polypyrrole composite membrane (SSM/PPY(AOT)) was prepared. By applying a negative or positive potential, the surface wettability of the membrane can be switched between hydrophilic and relatively hydrophobic states. Systematic characterizations and a series of filtration experiments were carried out. In the reduction state, the sulfonic acid groups of AOT were more exposed to the membrane surface, rendering the surface more hydrophilic. The fouling filtration experiments verified that the membrane is more resistant to fouling in the hydrophilic state during filtration and easier to clean in the hydrophobic state during membrane cleaning. Furthermore, Ca²⁺ and Mg²⁺ could complex with foulants, aggravating membrane fouling. Overall, this study demonstrates the importance of wettability switching in membrane filtration and suggests promising applications of the SSM/PPY(AOT) membrane.

Layered double hydroxide-modified membranes for water treatment: Recent advances and prospects

Layered double hydroxides (LDHs) represent an exciting class of two-dimensional inorganic materials with unique physicochemical properties. They have been widely employed in water treatment due to their high surface areas, excellent ion exchange capacities, and highly tunable structures. They have also been employed in the fabrication and development of membranes for water treatment. 2D nanostructures as well as tailorable "structure forming units", surface functionalization with desired moieties, and interlayer galleries with adjustable heights and internal compositions make them attractive materials for membrane separations. This paper critically overviews the recent advancements in the synthesis and applications of LDH based membranes in water purification. The synthesis techniques and the effect of LDH incorporation into different membrane compositions have been described. LDH-based membranes showed excellent antifouling capability and improved water flux due to enhanced hydrophilicity. Such membranes have been successfully used for the treatment of inorganics, organics from environmental water samples. This review will be useful for understanding the current state of the LDH-based membranes for water purification and defining future research dimensions. In the end, we highlight some challenges and future prospects for the efficient application of LDH-based membranes in water decontamination.

Air superhydrophilic-superoleophobic SiO2-based coatings for recoverable oil/water separation mesh with high flux and mechanical stability

Due to the inherent differences in surface tension between water and oil, it is a challenge to fabricate air superhydrophilic-superoleophobic materials despite their promising potential in the field of oil/water separation. Herein, a facile approach is developed to fabricate air superhydrophilic-superoleophobic SiO₂ coating by combination of controllable modifying SiO₂ nanoparticle surface by both hydrophilic groups (i.e., -OH groups) and oleophobic groups (i.e., fluorinated groups) with constructing porous and hierarchical structures. Hydroxyl-modified SiO₂ nanoparticles (NPs) are synthesized using a base-catalysed procedure in the presence of ammonia or NaOH. Chitosan quaternary ammonium salt (HACC) is introduced to bind SiO₂ by forming a unique hydrogen bond between HACC and -OH, followed by adding pentadecafluorooctanoic acid (PFOA) to complex with HACC to form fluorinated groups. The SiO₂ coatings are fabricated on various substrates (e.g., glass, foam and Cu mesh) by spraying procedure and characterized using SEM, FTIR, XPS, etc. The contact angles of oils (e.g., pump oil, castor oil, corn oil, hexadecane and bean oil) and water on the coatings are over 150° and close to 0°, respectively. By optimization, the representative SiO₂-coated Cu mesh displayed high-efficiency of 99.2% in separating water from mixture of water/pump oil, and high penetration flux of 1.41 × 10⁴ L·m^-2 ·h^-1. Besides, the coating maintains its superhydrophilic-superoleophobic properties even after 110 cycles of sandpaper abrasion or after being immersed in water for 3 h. After 20 cycles of oil/water separation, the coating retains separation efficiency up to 97.93%. This study provides a new and universal protocol to fabricate unique superwetting surfaces with effective oil/water separation performance, long-term durability and outstanding reusability.

Hydrogen peroxide treated g-C3N4 as an effective hydrophilic nanosheet for modification of polyethersulfone membranes with enhanced permeability and antifouling characteristics

In this study, first, graphitic carbon nitride was treated with hydrogen peroxide (abbreviated as H₂O₂-g-C₃N₄), then was used as a new hydrophilic nanomaterial in the fabrication of polyethersulfone (PES) mixed matrix membrane (MMM) for improving flux, protein and dye separation efficiency and antifouling properties. The H₂O₂-g-C₃N₄ nanosheet was inserted into the doping solution to fabricate PES/H₂O₂-g-C₃N₄ nanocomposite membrane with the non-solvent induced phase inversion procedure. The results of the SEM and AFM images and also porosity and contact angle analysis were indicated that the modified membranes with H₂O₂-g-C₃N₄ had more porosity, smoother surface and more hydrophilic. Also, the influence of various weight percentage of H₂O₂-g-C₃N₄ was investigated systematically on the membrane performance. By blending of H₂O₂-g-C₃N₄ nanosheet in the membrane matrix, the permeability was raised from 4.1 (for bare membrane) to 30.1 L m^-2 h^-1 bar^-1. Additionally, the effect of the H₂O₂-g-C₃N₄ material on the antifouling features indicated that the flux recover ratio of the H₂O₂-g-C₃N₄ MMMs was improved and the resistance parameters were reduced. Also, the effect of the H₂O₂-g-C₃N₄ material on the antifouling features indicated that the flux recover ratio of the H₂O₂-g-C₃N₄ MMMs was improved and the resistance parameters were reduced. Finally, the dye rejection efficiency of the nanocomposite membranes for Orange II and Reactive Yellow 168 was improved. As a result, it could be mentioned that the mixing low amount of H₂O₂-g-C₃N₄ in the membrane structure could significantly improve the membrane flux and antifouling properties without reduction in membrane rejection efficiency.

Nanocomposite Membranes for Liquid and Gas Separations from the Perspective of Nanostructure Dimensions

One of the critical aspects in the design of nanocomposite membrane is the selection of a well-matched pair of nanomaterials and a polymer matrix that suits their intended application. By making use of the fascinating flexibility of nanoscale materials, the functionalities of the resultant nanocomposite membranes can be tailored. The unique features demonstrated by nanomaterials are closely related to their dimensions, hence a greater attention is deserved for this critical aspect. Recognizing the impressive research efforts devoted to fine-tuning the nanocomposite membranes for a broad range of applications including gas and liquid separation, this review intends to discuss the selection criteria of nanostructured materials from the perspective of their dimensions for the production of high-performing nanocomposite membranes. Based on their dimension classifications, an overview of the characteristics of nanomaterials used for the development of nanocomposite membranes is presented. The advantages and roles of these nanomaterials in advancing the performance of the resultant nanocomposite membranes for gas and liquid separation are reviewed. By highlighting the importance of dimensions of nanomaterials that account for their intriguing structural and physical properties, the potential of these nanomaterials in the development of nanocomposite membranes can be fully harnessed.