2D Heterostructure Membranes with Sunlight‐Driven Self‐Cleaning Ability for Highly Efficient Oil–Water Separation

Introducing solar energy into membrane filtration to decrease energy and chemicals consumption represents a promising direction in membrane fields. In this study, a kind of 0D/2D heterojunction is fabricated by depositing biomineralized titanium dioxide (TiO₂) nanoparticles with delaminated graphitic carbon nitride (g‐C₃N₄) nanosheets, and subsequently a kind of 2D heterostructure membrane is fabricated via intercalating g‐C₃N₄@TiO₂ heterojunctions into adjacent graphene oxide (GO) nanosheets by a vacuum‐assisted self‐assembly process. Due to the enlarged interlayer spacing of GO nanosheets, the initial permeation flux of GO/g‐C₃N₄@TiO₂ membrane reaches to 4536 Lm^?2 h^?1 bar^?1, which is more than 40‐fold of GO membranes (101 Lm^?2 h^?1 bar^?1) when utilized for oil/water separation. To solve the sharp permeation flux decline, arising from the adsorption of oil droplets, the a sunlight‐driven self‐cleaning process is followed, maintaining a flux recovery ratio of more than 95% after ten cycles of filtration experiment. The high permeation flux and excellent sunlight‐driven flux recovery of these heterostructure membranes manifest their attractive potential application in water purification.     

Developments and Challenges in Self‐Healing Antifouling Materials

Self‐healing antifouling materials have gained rapidly increasing interest over the past decade and have been studied and used in a rapidly increasing range of applications. Recent developments and challenges in self‐healing antifouling materials are summarized in four sections: first, the different mechanisms for both antifouling and self‐healing are briefly discussed. Second, three main categories of self‐healing antifouling materials based on surface replenishing and dynamic covalent and noncovalent interactions are discussed, with a focus on the preparation, characterization, and central characteristics of different self‐healing antifouling materials. Third, different types of potential applications of self‐healing antifouling materials are summarized, such as injectable hydrogels and oil/water separations. Finally, a summary of future development of the field is provided, and a number of critical limitations that are still outstanding are highlighted.     

Self‐Recovering Triboelectric Nanogenerator as Active Multifunctional Sensors

A novel self‐recovering triboelectric nanogenerator (STENG) driven by airflow is designed as active multifunctional sensors. A spring is assembled into the STENG and enables the nanogenerator to have self‐recovering characteristic. The maximum output voltage and current of the STENG is about 251 V and 56 μA, respectively, corresponding to an output power of 3.1 mW. The STENG can act as an active multifunctional sensors that includes a humidity sensor, airflow rate sensor, and motion sensor. The STENG‐based humidity sensor has a wide detection range of 20%–100%, rapid response time of 18 ms, and recovery time of 80 ms. Besides, the STENG could be utilized in the application of security monitoring. This work expands practical applications of triboelectric nanogenerators as active sensors with advantages of simple fabrication and low cost.     

Tough Elastomers with Superior Self‐Recoverability Induced by Bioinspired Multiphase Design

Incorporating reversible sacrificial bonds in network polymers not only toughens these materials but also endows them with self‐recoverability. However, self‐recoverability is only realized for dispersed energy less than 10 MJ m^?3. It remains a challenge to achieve simultaneous high stretchability, toughness, and recoverability. Here, inspired by the structure of mussel byssus cuticles, a new design strategy is proposed and demonstrated to improve both the toughness and self‐recoverability of elastomers by introducing a microphase‐separated structure with different physical crosslink densities. This structure can be achieved using a carefully designed comonomer sequence distribution of hydrogen bonding units in an ABA‐type triblock copolymer. The A blocks form hard domains with dense crosslinking that prevents macroscopic deformation, while the B blocks form a softer matrix with sparse and dynamic crosslinks that serve as sacrificial bonds. This elastomer exhibits high toughness (≈62 MJ m^?3), self‐healing, and most notably, excellent self‐recovery (recovery against 650% elongation and 17 MPa tensile stress with a dissipated energy >27 MJ m^?3 at room temperature). This combination of toughness, self‐healing, and self‐recovery expands the range of applications of these advanced dynamic materials.     

Polyester Materials with Superwetting Silicone Nanofilaments for Oil/Water Separation and Selective Oil Absorption

Superhydrophobic and superoleophilic polyester materials are successfully prepared by one‐step growth of silicone nanofilaments onto the textile via chemical vapor deposition of trichloromethylsilane. The successful growth of silicone nanofilaments is confirmed with scanning electron microscopy, energy‐dispersive X‐ray analysis, and investigation of the wetting behavior of water on the textile. Even microfibers deeply imbedded inside a woven material could be coated very well with the nanofilaments. The coated textile is water repellant and could only be wetted by liquids of low surface tension. The applications of the coated textile as a membrane for oil/water separation and as a bag for selective oil absorption from water are studied in detail. Owing to the superwetting properties and flexibility of the coated textile, excellent reusability, oil/water separation efficiency, and selective oil absorption capacity are observed, which make it very promising material, e.g., for practical oil absorption.     

Bioinspired Multifunctional Hybrid Hydrogel Promotes Wound Healing

Inspired by the coordinated multiple healing mechanism of the organism, a four‐armed benzaldehyde‐terminated polyethylene glycol and dodecyl‐modified chitosan hybrid hydrogel with vascular endothelial growth factor (VEGF) encapsulation are presented for efficient and versatile wound healing. The hybrid hydrogel is formed through the reversible Schiff base and possesses self‐healing capability. As the dodecyl tails can insert themselves into and be anchored onto the lipid bilayer of the cell membrane, the hybrid hydrogel has outstanding tissue adhesion, blood cell coagulation and hemostasis, anti‐infection, and cell recruitment functions. Moreover, by loading in and controllably releasing VEGF from the hybrid hydrogel, the processes of cell proliferation and tissue remodeling in the wound bed can be significantly improved. Based on an in vivo study of the multifunctional hybrid hydrogel, it is demonstrated that acute tissue injuries such as vessel bleeding and liver bleeding can be repaired immediately because of the outstanding adhesion and hemostasis features of the hydrogel. Moreover, the chronic wound‐healing process of an infectious full‐thickness skin defect model can also be significantly enhanced by promoting angiogenesis, collagen deposition, macrophage polarization, and granulation tissue formation. Thus, this multifunctional hybrid hydrogel is potentially valuable for clinical applications.     

An Amphiphobic Hydraulic Triboelectric Nanogenerator for a Self‐Cleaning and Self‐Charging Power System

Raindrop falling, which is one kind of water motions, contains large amount of mechanical energy. However, harvesting energy from the falling raindrop to drive electronics continuously is not commonly investigated. Therefore, a self‐cleaning/charging power system (SPS) is reported, which can be exploited to convert and store energy from falling raindrop directly for providing a stable and durable output. The SPS consists of a hydraulic triboelectric nanogenerator (H‐TENG) and several embedded fiber supercapacitors. The surface of H‐TENG is amphiphobic, enabling the SPS self‐cleaning. The fiber supercapacitor which uses α‐Fe₂O₃/reduced graphene oxide composite possesses remarkable specific capacitance, excellent electrical stability, and high flexibility. These properties of the fiber supercapacitor make it suitable for a wearable power system. A power raincoat based on the SPS is demonstrated as application. After showering by water flow, which simulates falling raindrops, for 100 s, the power raincoat achieves an open‐circuit voltage of 4 V and lights a light‐emitting diode for more than 300 s. With features of low cost, easy installation, and good flexibility, the SPS harvesting energy from the falling raindrop renders as a promising sustainable power source for wearable and portable electronics.     

Visible‐Light‐Activated Photocatalytic Films toward Self‐Cleaning Membranes

Membranes are among the most promising means of delivering increased supplies of fit‐for‐purpose water, but membrane fouling remains a critical issue restricting their widespread application. Coupling photocatalysis with membrane separation has been proposed as a potentially effective approach to reduce membrane fouling. However, commonly used materials in photocatalysis limit use of low‐cost sources such as sunlight due to their large bandgaps. There are few examples of in situ photocatalytic self‐cleaning of membranes, with removal from the filtration system and ex situ illumination being more common. In this work, a visible‐light‐activated photocatalytic film prepared by nitrogen doping into the lattice of TiO₂ is deposited on commercial ceramic membranes via atomic layer deposition. The synergy between membrane separation and redox reactions between organic pollutants and reactive oxygen species produced by the visible‐light‐activated layer offers a possibility for stable and sustainable membrane operation under in situ solar irradiation.     

Dual‐Action Flexible Antimicrobial Material: Switchable Self‐Cleaning,Antifouling, and Smart Drug Release

A switchable material with a smart antimicrobial dual‐action functionality, which is based on a highly stretchable silicon polymer gradiently doped with polyyrrole, is proposed. The material exhibits superhydrophobic and self‐cleaning properties, high aerophilicity as well as the possibility of smart, electrically triggerable release of an incorporated drug. During the immersion of the material in water, an air gap is formed on its surface which prevents a formation of biofouling, attachment of microorganisms, and burst release of the incorporated drug. An application of external electric field switches the surface properties from the superhydrophobic to highly hydrophilic state that enables a wetting of the material surface and electrically triggered release of a loaded drug. After the electric field switching off and sample drying, the material surface returns to its intrinsic superhydrophobic state with the original self‐cleaning properties so that the material surface can be simply cleaned, removing the bacteria. High flexibility and stretchability are additional favorable properties of the proposed smart antimicrobial material, making it a suitable candidate for a range of medical and related applications.     

Multifunctional Organic–Inorganic Hybrid Aerogel for Self‐Cleaning,Heat‐Insulating,and Highly Efficient Microwave Absorbing Material

Multifunctionalization is the future development direction for microwave absorbing materials, but has not yet been explored. The effective integration of multiple functions into one material remains a huge challenge. Herein, an aerogel‐type microwave absorber assembled with multidimensional organic and inorganic components is synthesized. Polyacrylonitrile fibers and polybenzoxazine membranes work as the skeleton and crosslinker, respectively, forming a 3D framework, in which carbon nanotubes are interconnected into an electrically conductive network, and Fe₃O₄ nanoparticles are uniformly dispersed throughout the aerogel. Remarkably, the microwave absorption performances of the aerogel achieve ultralight, ultrathin (1.5 mm), and strong absorption (reflection loss of ?59.85 dB) features. In particular, its specific reflection loss values considerably outperform the current magnetic–dielectric hybrids with similar components. Moreover, the aerogel possesses strong hydrophobicity and good thermal insulation, endowing it attractive functions of self‐cleaning, infrared stealth, and heat insulation that is even comparable to commercial products. The excellent multifunction benefits from the cellular structure of aerogel, the assembly of multidimensional nanomaterials, and the synergistic effect of organic–inorganic components. This study paves the way for designing next‐generation microwave absorbing materials with great potential for multifunctional applications.     

From Fragility to Flexibility: Construction of Hydrogel Bridges toward a Flexible Multifunctional Free‐Standing CaCO3 Film

Free‐standing CaCO₃ materials are an important member in biological systems because of their existence in many natural organisms such as nacre, shell, and crustacean cuticle. However, toughness of those artificial mineral films is sacrificed once their inorganic content is up to 90%, thus free‐standing characteristics have seldom been achieved for CaCO₃ films, let alone their real applications. Herein a fast and simple method for constructing hydrogel “bridges” for CaCO₃ microparticles is presented, developing highly flexible free‐standing CaCO₃ films with only 5% organic content. Such integrated films have underwater superoleophobicity and self‐cleaning function, which guarantee their repeated application in oil/water separation. Furthermore, heavy metal ions can be efficiently removed by simple filtration with the films. Because of the self‐similar structure, the films are able to resist mechanical abrasion without losing the anti‐wetting property and separation efficiency. The free‐standing CaCO₃ films are put forward for the first time to practical application, demonstrating the strategy can bring a brilliant prospect to artificial biomineral materials.     

Directed Emission from Self‐Assembled Microhelices

Bottom‐up assembly can organize simple building blocks into complex architectures for light manipulation. The optical properties of self‐assembled polycrystalline barium carbonate/silica double helices are studied using fluorescent Fourier and Mueller matrix microscopy. Helices doped with fluorescein direct light emission along the long axis of the structure. Furthermore, light transmission measured normal and parallel to the long axis exhibits twist sense‐specific circular retardance and waveguiding, respectively, although the measurements suffer from depolarization. The helices thus integrate highly directional emission with enantiomorph‐specific polarization. This optical response emerges from the arrangement of nanoscopic mineral crystallites in the microscopic helix, and demonstrates how bottom‐up assembly can achieve ordering across multiple length scales to form complex functional materials.     

Bioinspired Reversibly Cross‐linked Hydrogels Comprising Polypeptide Micelles Exhibit Enhanced Mechanical Properties

Noncovalently cross‐linked networks are attractive hydrogel platforms because of their facile fabrication, dynamic behavior, and biocompatibility. The majority of noncovalently cross‐linked hydrogels, however, exhibits poor mechanical properties, which significantly limit their utility in load bearing applications. To address this limitation, hydrogels are presented composed of micelles created from genetically engineered, amphiphilic, elastin‐like polypeptides that contain a relatively large hydrophobic block and a hydrophilic terminus that can be cross‐linked through metal ion coordination. To create the hydrogels, heat is firstly used to trigger the self‐assembly of the polypeptides into monodisperse micelles that display transition metal coordination motifs on their coronae, and subsequently cross‐link the micelles by adding zinc ions. These hydrogels exhibit hierarchical structure, are stable over a large temperature range, and exhibit tunable stiffness, self‐healing, and fatigue resistance. Gels with polypeptide concentration of 10%, w/v, and higher show storage moduli of ≈1 MPa from frequency sweep tests and exhibit self‐healing within minutes. These reversibly cross‐linked, hierarchical hydrogels with enhanced mechanical properties have potential utility in a variety of biomedical applications.     

Photocatalytic Nanofiltration Membranes with Self‐Cleaning Property for Wastewater Treatment

Membrane fouling is one of the most severe problems restricting membrane separation technology for wastewater treatment. This work reports a photocatalytic nanofiltration membrane (NFM) with self‐cleaning property fabricated using a facile biomimetic mineralization process. In this strategy, a polydopamine (PDA)/polyethyleneimine (PEI) intermediate layer is fabricated on an ultrafiltration membrane via a co‐deposition method followed by mineralization of a photocatalytic layer consisting of β‐FeOOH nanorods. The PDA–PEI layer acts both as a nanofiltration selective layer and an intermediate layer for anchoring the β‐FeOOH nanorods via strong coordination complexes between Fe³⁺ and catechol groups. In visible light, the β‐FeOOH layer exhibits efficient photocatalytic activity for degrading dyes through the photo‐Fenton reaction in the presence of hydrogen peroxide, endowing the NFM concurrently with effective nanofiltration performance and self‐cleaning capability. Moreover, the mineralized NFMs exhibit satisfactory stability under simultaneous filtration and photocatalysis processing, showing great potential in advanced wastewater treatment.     

Bioinspired,Stimuli‐Responsive,Multifunctional Superhydrophobic Surface with Directional Wetting,Adhesion, and Transport of Water

A novel smart stimuli responsive surface can be fabricated by the subsequent self‐assembly of the graphene monolayer and the TiO₂ nanofilm on various substrates, that is, fabrics, Si wafers, and polymer thin films. Multiscale application property can be achieved from the interfacial interaction between the hierarchical graphene/TiO₂ surface structure and the underlying substrate. The smart surface possesses superhydrophobic property as a result of its hierarchical micro‐ to nanoscale structural roughness. Upon manipulating the UV induced hydrophilic conversion of TiO₂ on graphene/TiO₂ surface, smart surface features, such as tunable adhesiveness, wettability, and directional water transport, can be easily obtained. The existence of graphene indeed enhances the electron–hole pair separation efficiency of the photo‐active TiO₂, as the time required for the TiO₂ superhydrophilic conversion is largely reduced. Multifunctional characteristics, such as gas sensing, droplet manipulation, and self‐cleaning, are achieved on the smart surface as a result of its robust superhydrophobicity, tunable wettability, and high photo‐catalytic activity. It is also revealed that the superhydrophilic conversion of TiO₂ is possibly caused by the atomic rearrangement of TiO₂ under UV radiation, as a structural transformation from {101} to {001} is observed after the UV treatment.     

Construction of Self‐Healing Internal Electric Field for Sustainably Enhanced Photocatalysis

The construction of internal electric field is generally considered an effective strategy to enhance photocatalytic performance due to its significant role in charge separation. However, static internal electric field is prone to be saturated either by inner or outer shield effect, and thus its effect on the improvement of photocatalysis can easily vanish. Here, the self‐healing internal electric field is proposed and successfully endowed to a designed helical structural composite microfiber polyvinylidene fluoride/g‐C₃N₄ (PVDF/g‐C₃N₄) based on the bioinspired simple harmonic vibration. Importantly, the saturation and recovery of internal electric field are characterized by transient photovoltage and photoluminescence. The results indicate that the internal electric field could be saturated within about 10 min and refreshed with the assistance of rebuilt piezoelectric potential. The lifetime of photogenerated carriers is about 10^?4 s and the number of effective carriers is greatly increased in the presence of self‐healing internal electric field. The results provide direct experimental evidence on the role of self‐healing internal electric field in charge transfer behavior. This work represents a new design strategy of photocatalysts, and it may open up new horizons for solving energy shortage and environmental issues.