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.     

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.     

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.     

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.     

Transparent Mesoporous Nanocomposite Films for Self‐Cleaning Applications

A versatile approach is studied for the elaboration of TiO₂ based photocatalytic coatings for self‐cleaning applications on transparent substrates. The basic principle of the synthesis relies on the use of preformed TiO₂ colloidal particles that are further dispersed within a transparent silica binder with a mesoporous structure. Film porosity in the nanometer range is controlled by achieving the sol–gel silica condensation around self‐organized micellar assemblies of a templating copolymer surfactant. The latter also acts as a stabilizer for the TiO₂ particles, thus preserving their high dispersion within the film so that excellent optical properties are maintained even for high TiO₂ loading (up to 50 %). Studies of photodegradation kinetics show that such mesoporous films are at least 15 times more active than films synthesized with a usual microporous silica binder. Moreover, the measured quantum‐yield efficiency (1.1 %) is found to be among the highest reported up to now. Improved photoactivity of the films is discussed as resulting from the closer proximity between the organic molecules and the surface of the TiO₂ crystallites as well as the improved diffusion rate of water and oxygen through the interconnected pore network.     

Double Stimuli‐Responsive Isoporous Membranes via Post‐Modification of pH‐Sensitive Self‐Assembled Diblock Copolymer Membranes

Double stimuli‐responsive membranes are prepared by modification of pH‐sensitive integral asymmetric polystyrene‐b‐poly(4‐vinylpyridine) (PS‐b‐P4VP) diblock copolymer membranes with temperature‐responsive poly(N‐isopropylacrylamide) (pNIPAM) by a surface linking reaction. PS‐b‐P4VP membranes are first functionalized with a mild mussel‐inspired polydopamine coating and then reacted via Michael addition with an amine‐terminated pNIPAM‐NH₂ under slightly basic conditions. The membranes are thoroughly characterized by nuclear magnetic resonance (¹H‐NMR), Fourier transform infrared spectroscopy and X‐ray‐induced photoelectron spectroscopy. Additionally dynamic contact angle measurements are performed comparing the sinking rate of water droplets at different temperatures. The pH‐ and thermo‐double sensitivities of the modified membranes are proven by determining the water flux under different temperature and pH conditions.     

Electric Field Controlled Self‐Assembly of Hierarchically Ordered Membranes

Self‐assembly in the presence of external forces is an adaptive, directed organization of molecular components under nonequilibrium conditions. While forces may be generated as a result of spontaneous interactions among components of a system, intervention with external forces can significantly alter the final outcome of self‐assembly. Superimposing these intrinsic and extrinsic forces provides greater degrees of freedom to control the structure and function of self‐assembling materials. In this work we investigate the role of electric fields during the dynamic self‐assembly of a negatively charged polyelectrolyte and a positively charged peptide amphiphile in water leading to the formation of an ordered membrane. In the absence of electric fields, contact between the two solutions of oppositely charged molecules triggers the growth of closed membranes with vertically oriented fibrils that encapsulate the polyelectrolyte solution. This process of self‐assembly is intrinsically driven by excess osmotic pressure of counterions and the electric field is found to modify the kinetics of membrane formation as well as membrane morphology and properties. Depending on the strength and orientation of the field we observe a significant increase or decrease of up to nearly 100% in membrane thickness, or the controlled rotation of nanofiber growth direction by 90 degrees which leads to a significant increase in mechanical stiffness. These results suggest the possibility of using electric fields to control structure in self‐assembly processes that involve the diffusion of oppositely charged molecules.     

Tough and Self‐Recoverable Thin Hydrogel Membranes for Biological Applications

Tough and self‐recoverable hydrogel membranes with micrometer‐scale thickness are promising for biomedical applications, which, however, rarely be realized due to the intrinsic brittleness of hydrogels. In this work, for the first time, by combing noncovalent DN strategy and spin‐coating method, we successfully fabricated thin (thickness: 5–100 µm), yet tough (work of extension at fracture: 10⁵–10⁷ J m^?3) and 100% self‐recoverable hydrogel membranes with high water content (62–97 wt%) in large size (≈100 cm²). Amphiphilic triblock copolymers, which form physical gels by self‐assembly, were used for the first network. Linear polymers that physically associate with the hydrophilic midblocks of the first network, were chosen for the second network. The inter‐network associations serve as reversible sacrificial bonds that impart toughness and self‐recovery properties on the hydrogel membranes. The excellent mechanical properties of these obtained tough and thin gel membranes are comparable, or even superior to many biological membranes. The in vitro and in vivo tests show that these hydrogel membranes are biocompatible, and postoperative nonadhesive to neighboring organs. The excellent mechanical and biocompatible properties make these thin hydrogel membranes potentially suitable for use as biological or postoperative antiadhesive membranes.     

Ultra‐Thin Self‐Assembled Protein‐Polymer Membranes: A New Pore Forming Strategy

Self‐assembled membranes offer a promising alternative for conventional membrane fabrication, especially in the field of ultrafiltration. Here, a new pore‐making strategy is introduced involving stimuli responsive protein‐polymer conjugates self‐assembled across a large surface area using drying‐mediated interfacial self‐assembly. The membrane is flexible and assembled on porous supports. The protein used is the cage protein ferritin and resides within the polymer matrix. Upon denaturation of ferritin, a pore is formed which intrinsically is determined by the size of the protein and how it resides in the matrix. Due to the self‐assembly at interfaces, the membrane constitutes of only one layer resulting in a membrane thickness of 7 nm on average in the dry state. The membrane is stable up to at least 50 mbar transmembrane pressure, operating at a flux of about 21 000–25 000 L m^?2 h^?1 bar^?1 and displayed a preferred size selectivity of particles below 20 nm. This approach diversifies membrane technology generating a platform for “smart” self‐assembled membranes.     

Bioinspired Multifunctional Foam with Self‐Cleaning and Oil/Water Separation

Oil/water separation is a worldwide challenge. Learning from nature provides a promising approach for the construction of functional materials with oil/water separation. In this contribution, inspired by superhydrophobic self‐cleaning lotus leaves and porous biomaterials, a facile method is proposed to fabricate polyurethane foam with simultaneous superhydrophobicity and superoleophilicity. Due to its low density, light weight, and superhydrophobicity, the as‐prepared foam can float easily on water. Furthermore, the foam demonstrates super‐repellency towards corrosive liquids, self‐cleaning, and oil/water separation properties, possessing multifunction integration. We expect that this low‐cost process can be readily and widely adopted for the design of multifunctional foams for large‐area oil‐spill cleanup.     

A Versatile Approach towards Multifunctional Robust Microcapsules with Tunable,Restorable, and Solvent‐Proof Superhydrophobicity for Self‐Healing and Self‐Cleaning Coatings

Numerous microencapsulation techniques have been developed to encase various chemicals, for which specific processing parameters are required to address the widely differing features of the encapsulated materials. Microencapsulation of reactive agents is a powerful technique that has been extensively applied to self‐healing materials. However, the poor solvent compatibility and insufficient thermal stability of microcapsules continue to pose challenges for long‐term storage, processing, and service in practical applications. Here, an easily modifiable and highly versatile method is reported for preparing various chemicals filled poly(urea‐formaldehyde) microcapsules that exhibit superior tightness against solvents and heat and that possess widely tunable, repetitiously self‐restorable, and solvent‐proof superhydrophobicity. In addition, the low‐cost fabrication of biomimetic multifunctional smart coatings is demonstrated for self‐healing anticorrosion and self‐cleaning antifouling applications by directly dispersing the superhydrophobic microcapsules into and onto a polymer matrix. The methodology presented in this study should inspire the development of multifunctional intelligent materials for applications in related fields.     

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.     

Nepenthes Pitcher Inspired Anti‐Wetting Silicone Nanofilaments Coatings: Preparation,Unique Anti‐Wetting and Self‐Cleaning Behaviors

Nepenthes pitcher inspired anti‐wetting coatings, fluoro‐SNs/Krytox, are successfully fabricated by the combination of fluoro‐silicone nanofilaments (fluoro‐SNs) and Krytox liquids, perfluoropolyethers. Fluoro‐SNs with different microstructure are grown onto glass slides using trichloromethylsilane by simply repeating the coating step, and then modified with 1H,1H,2H,2H‐perfluorodecyltrichlorosilane. Subsequently, the Krytox liquid is spread on the fluoro‐SNs coatings via capillary effect. The fluoro‐SNs/Krytox coatings feature ultra‐low sliding angle for various liquids, excellent stability, and transparency. The sliding speed of liquid drops on the fluoro‐SNs/Krytox coating is obviously slower than on the lotus inspired superhydrophobic and superoleophobic coatings, and is controlled by composition of the coating (e.g., morphology of the fluoro‐SNs, type of Krytox and its thickness) and properties of the liquid drops (e.g., density and surface tension). In addition, the self‐cleaning property of the fluoro‐SNs/Krytox coating is closely related to properties of liquid drops and dirt.     

Mussel‐Inspired Polydopamine‐Treated Reinforced Composite Membranes with Self‐Supported CeOx Radical Scavengers for Highly Stable PEM Fuel Cells

The physical and chemical degradations of a state‐of‐the‐art proton exchange membrane (PEM) composed of a perfluorinated sulfonic acid (PFSA) ionomer and polytetrafluoroethylene (PTFE) reinforcement are induced through the repeated expansion/shrinkage of the ionomer and free radical attacks. Such degradations essentially originate from the loose structure of the materials and the low interactive binding force among the PEM constituents. In this study, the need for simplified design principles of adhesives led to the use of mussel‐inspired polydopamine (PD) as an interfacial modifier for the fabrication of highly durable PEM. Indeed, a self‐polymerized dopamine layer acts as an interfacial glue, and enables efficient impregnation of a hydrophilic PFSA ionomer into porous hydrophobic PTFE with high packing density, resulting in strong adhesion between the PTFE and the PFSA polymers in the membrane. In addition, the redox property of the PD end groups spontaneously reduces the partial Ce salts in the ionomer solution and anchors them to the PD@PTFE substrate as defective cerium oxide (CeO_x) nanoparticles, reducing the dissolution and subsequent migration under cell operations. Finally, a CePD@PTFE membrane shows outstanding durability in fuel cells under an accelerated humidity cycling test with a reduction in the degree of physical and chemical failures.     

Self‐Supporting,Double Stimuli‐Responsive Porous Membranes From Polystyrene‐block‐poly(N,N‐dimethylaminoethyl methacrylate) Diblock Copolymers

Asymmetric membranes are prepared via the non‐solvent‐induced phase separation (NIPS) process from a polystyrene‐block‐poly(N,N‐dimethylaminoethyl methacrylate) (PS‐b‐PDMAEMA) block copolymer. The polymer is prepared via sequential living anionic polymerization. Membrane surface and volume structures are characterized by scanning electron microscopy. Due to their asymmetric character, resulting in a thin separation layer with pores below 100 nm on top and a macroporous volume structure, the membranes are self‐supporting. Furthermore, they exhibit a defect‐free surface over several 100 µm². Polystyrene serves as the membrane matrix, whereas the pH‐ and temperature‐sensitive minority block, PDMAEMA, renders the material double stimuli‐responsive. Therefore, in terms of water flux, the membranes are able to react on two independently applicable stimuli, pH and temperature. Compared to the conditions where the lowest water flux is obtained, low temperature and pH, activation of both triggers results in a seven‐fold permeability increase. The pore size distribution and the separation properties of the obtained membranes were tested through the pH‐dependent filtration of silica particles with sizes of 12–100 nm.