Multi-bioinspired and Multistructural Integrated Patterned Nanofibrous Surface for Spontaneous and Efficient Fog Collection

Bioinspired Slippery Surfaces for Liquid Manipulation from Tiny Droplet to Bulk Fluid

Slippery surfaces, which originate in nature with special wettability, have attracted considerable attention in both fundamental research and practical applications in a variety of fields due to their unique characteristics of superlow liquid friction and adhesion. Although research on bioinspired slippery surfaces is still in its infancy, it is a rapidly growing and enormously promising field. Herein, a systematic review of recent progress in bioinspired slippery surfaces, beginning with a brief introduction of several typical creatures with slippery property in nature, is presented. Subsequently,this review gives a detailed discussion on the basic concepts of the wetting, friction, and drag from micro- and macro-aspects and focuses on the underlying slippery mechanism. Next, the state-of-the-art developments in three categories of slippery surfaces of air-trapped, liquid-infused, and liquid-like slippery surfaces, including materials, design principles, and preparation methods, are summarized and the emerging applications are highlighted. Finally, the current challenges and future prospects of various slippery surfaces are addressed.

Synergistic Effect of Neighboring Superhydrophilic Patterns on Superhydrophobic Surfaces for Enhanced Fog Collection

In this work, a superhydrophobic surface loaded with elliptical superhydrophilic patterns in a V-shaped arrangement has been fabricated with the help of shape memory membranes with uniform vertically penetrative channels (i.e., SMEUVs, as a mask). The special geometry (elliptical) and arrangement (V-shaped) of superhydrophilic patterns play important roles in the enhancement of fog collection. The former not only facilitates droplet detachment from superhydrophilic regions but also dominates its directional transport. The latter promotes the coalescence of tiny droplets based on directional flow pathway toward collection area, minimizing the risk of re-evaporation of them and providing fresh sites for subsequent nucleation and growth of droplets. The combination of them contributes to the synergistic effect of neighboring superhydrophilic patterns on the superhydrophobic surface. As a result, the optimal specimen (V-shaped arrangement of elliptical superhydrophilic patterns) in this work exhibits much higher fog collection efficiency (∼4 times) relative to the reference (superhydrophobic or superhydrophilic surface). Our results are significant for the design and fabrication of fog collection systems.

Multibioinspired Hybrid Superwetting Surface for Efficient Fog Collection and Power Generation

Obtaining water and renewable energy from the atmosphere provides a potential solution to the growing energy shortage. Leveraging the synergistic inspiration from desert beetles, cactus spines, and rice leaves, here, a multibioinspired hybrid wetting rod (HWR) is prepared through simple solution immersion and laser etching, which endows an efficient water collection from the atmosphere. Importantly, benefiting from the bionic asymmetric pattern design and the three-dimensional structure, the HWR possesses an omnidirectional fog collection with a rate of up to 23 g cm-2 h-1. We further show that the HWR could be combined with a droplet-based electricity generator to convert kinetic energy from falling droplets into electrical energy with a maximum output voltage of 200 V and a current of 2.47 μA to light up 28 LEDs. Collectively, this research provides a strategy for synchronous fog collection and power generation, which is promising for environmentally friendly energy production.

Nature-inspired adhesive systems

Many organisms in nature thrive in intricate habitats through their unique bio-adhesive surfaces, facilitating tasks such as capturing prey and reproduction. It's important to note that the remarkable adhesion properties found in these natural biological surfaces primarily arise from their distinct micro- and nanostructures and/or chemical compositions. To create artificial surfaces with superior adhesion capabilities, researchers delve deeper into the underlying mechanisms of these captivating adhesion phenomena to draw inspiration. This article provides a systematic overview of various biological surfaces with different adhesion mechanisms, focusing on surface micro- and nanostructures and/or chemistry, offering design principles for their artificial counterparts. Here, the basic interactions and adhesion models of natural biological surfaces are introduced first. This will be followed by an exploration of research advancements in natural and artificial adhesive surfaces including both dry adhesive surfaces and wet/underwater adhesive surfaces, along with relevant adhesion characterization techniques. Special attention is paid to stimulus-responsive smart artificial adhesive surfaces with tunable adhesive properties. The goal is to spotlight recent advancements, identify common themes, and explore fundamental distinctions to pinpoint the present challenges and prospects in this field.

Magnetically Driven Cactus Spinelike Superhydrophobic Fe3O4 Vertical Array for High-Performance Fog Harvesting

Cactus spinelike materials have attracted much attention due to high fog harvesting efficiency, but great challenges in structure fabrication and structural controllability still remain. In this study, we proposed a magnetically driven spray-coating method to fabricate a cactus spinelike superhydrophobic Fe3O4 vertical array on nonwoven cotton fabric. This method is simple and controllable; a mixture containing magnetic Fe3O4 particles and organosilicon resin was atomized into tiny droplets and arranged along the magnetic field lines. Different from the traditional method to prepare a cactus spinelike structure via liquid flow under magnet, which is usually accompanied with a big structure size and an unobvious structure feature due to the high viscosity of magnetic liquid. However, if the magnetic liquid is transformed into tiny magnetic droplets by a spraying method, it is promising to prepare micrometer-scale conical structures, and the reduction degree of bionic structures is high. When the fabricated structure is used for fog harvesting, it shows an extremely high efficiency of approximately 6.33 g cm-2 h-1, which is superior to most state-of-the-art fog harvesting materials. Considering the advantages of simplicity, structure controllability, and high fog harvesting rate, the reported strategy provides an avenue to build up high-performance fog harvesting materials.

Multi-biomimetic Double Interlaced Wetting Janus Surface for Efficient Fog Collection

Various methods to solve water scarcity have attracted increasing attention. However, most existing water harvesting schemes have a high demand for preparation methods and costs. Here, a multi-biomimetic double interlaced wetting Janus surface (DIWJS) was prepared by laser for effective fog collection. The as-prepared surfaces are composed of superhydrophilic points/hydrophobic substrates on the A-side and superhydrophilic stripes/hydrophobic substrates on the B-side. The interlaced wettability and superhydrophilic points on the A side are conducive to capture and permeation of droplets. The superhydrophilic stripes and interlaced wettability on the B-side are conducive to transportation and shedding of droplets. Therefore, the overall fog collection process is accelerated. The proposal of smart farm model validates broad application prospects of DIWJS. This work provides an advanced and multi-biomimetic surface and provides important insights for green, low-cost, and versatile strategies to solve water scarcity issues.

Magnetically driven Janus conical vertical array for all-weather freshwater collection

The engineering of multifunctional structures with special surface wettability is highly desirable for all-weather freshwater production, but relevant research is scarce. In this study, a Janus conical vertical array was designed and fabricated via a magnetically driven spray-coating method for the first time. Benefiting from the special structure and wettability enhancement of the array in terms of solar absorption, fog capture and merging, droplet movement and evaporation area, all-weather freshwater production consisting of high-quality daytime solar vapor generation (water evaporation rate approximately 2.43 kg m-2 h-1, 1 kW m-2) and nighttime fog collection (water collection rate approximately 3.536 g cm-2 h-1) can be realized concurrently. When the designed array is employed for outdoor environments (114°35'E, 30°38'N, average daily temperature 34.9 °C, average daily humidity 64.0%), reliable and efficient daily pure water yields of 19.13 kg m-2-26.09 kg m-2 are obtainable. We believe that the proposed strategy for fabricating a Janus conical vertical array is novel in the integration of solar vapor generation and fog collection, which has great significance for all-weather freshwater production.

Active Surface Area-Dependent Water Harvesting of Desert Beetle-Inspired Hybrid Wetting Surfaces

The increasing frequency of water scarcity is an acute worldwide problem. Nature-inspired water harvesting from fog is an important method to obtain freshwater in arid areas. Existing literature reports varied and diversified results in water harvesting capacity by employing a biphilic surface with control over hydrophilic and hydrophobic patterns. In this study, we first demonstrate a facile and scalable method to fabricate a biphilic surface using a simple electroless etching and desilanization technique. Considering the nucleation, growth, and transport of condensate, biphilic surfaces with controlled active surface area of hydrophilic spots were given special attention. We studied the water collection performance of pattern shape with its associated active surface area and further evaluated the critical surface area beyond which the water collection efficiency decreases. A high water collection capacity of 2050 mg cm-2 h-1 was achieved, and the hydrophilic active area-engineered surface retained its efficiency even after 50 test cycles. We further demonstrate high collection efficiency with a square pattern compared to a triangular path-like-patterned surface. The observations and surface engineering strategies reported in this study can provide insights into efficient and sustainable water harvesting devices.

Thermodynamically Induced Interfacial Condensation for Efficient Fog Harvesting

Fog harvesting is a sustainable approach to dealing with the global freshwater crisis. A range of strategies in microstructure design and wettability remodeling for fog management are clearly explained. However, the influence of thermodynamic endothermic and exothermic processes on fog harvesting is rarely explored. Here, a thermodynamically induced interfacial condensation-enhanced fog-harvesting fabric (AWF-6) is developed that also incorporates asymmetric geometry and surface chemistry. By coupling the high thermal conductivity interface supported by boron nitride nanosheets (BNNS), the Laplace pressure difference generated by nanoneedles, and the wettability gradient constructed by stearic acid (STA), the fabric achieves a water collection rate (WCR) of 1538.4 mg h cm-2 , which is the maximum value in state-of-the-art cotton-based fog harvesting devices (FHDs). Furthermore, the potential application of AWF-6 in agricultural irrigation is demonstrated. This study shows a thermodynamic proposal for building next-generation fibrous FHDs.

Overview of the design of bionic fine hierarchical structures for fog collection

Nature always uses its special wisdom to construct elegant and suitable schemes. Consequently, organisms in the flora and fauna are endowed with fine hierarchical structures (HS) to adapt to the harsh environment due to many years of evolution. Water is one of the most important resources; however, easy access to it is one the biggest challenges faced by human beings. In this case, fog collection (FC) is considered an efficient method to collect water, where bionic HS can be the bridge to efficiently facilitate the process of the FC. In this review, firstly, we discuss the basic principles of FC. Secondly, the role of HS in FC is analyzed in terms of the microstructure of typical examples of plants and animals. Simultaneously, the water-harvesting function of HS in a relatively new organism, fungal filament, is also presented. Thirdly, the HS design in each representative work is analyzed from a biomimetic perspective (single to multiple biomimetic approaches). The role of HS in FC, and then the FC performance of each work are analyzed in order of spatial dimension from a bionic perspective. Finally, the challenges at this stage and the outlook for the future are presented.

Research progress of bionic fog collection surfaces based on special structures from natural organisms

With the increasing shortage of water resources, people are seeking more innovative ways to collect fog to meet the growing need for production and the demand for livelihood. It has been proven that fog collection is efficient for collecting water in dry but foggy areas. As a hot research topic in recent years, bionic surfaces with fog collection functions have attracted widespread attention in practical applications and basic research. By studying natural organisms and bionic surfaces, more avenues are provided for the development of fog collection devices. Firstly, starting from biological prototypes, this article explored the structural characteristics and fog collection mechanisms of natural organisms such as spider silk, desert beetles, cactus, Nepenthes and other animals and plants (Sarracenia, shorebird and wheat awn), revealing the fog collection mechanism of the natural organisms based on microstructures. Secondly, based on the theory of interfacial tension, we would delve into the fog collection function's theoretical basis and wetting model, expounding the fog collection mechanism from a theoretical perspective. Thirdly, a detailed introduction was given to prepare bionic surfaces and recently explore fog collection devices. For bionic surfaces of a single biological prototype, the fog collection efficiency is about 2000-4000 mg cm-2 h-1. For bionic surfaces of multiple biological prototypes, the fog collection efficiency reaches 7000 mg cm-2 h-1. Finally, a critical analysis was conducted on the current challenges and future developments, aiming to promote the next generation of fog collection devices from a scientific perspective from research to practical applications.

Engineering the Structural Uniformity of Gel Polymer Electrolytes via Pattern-Guided Alignment for Durable, Safe Solid-State Lithium Metal Batteries

Ultrathin and super-toughness gel polymer electrolytes (GPEs) are the key enabling technology for durable, safe, and high-energy density solid-state lithium metal batteries (SSLMBs) but extremely challenging. However, GPEs with limited uniformity and continuity exhibit an uneven Li+ flux distribution, leading to nonuniform deposition. Herein, a fiber patterning strategy for developing and engineering ultrathin (16 µm) fibrous GPEs with high ionic conductivity (≈0.4 mS cm-1 ) and superior mechanical toughness (≈613%) for durable and safe SSLMBs is proposed. The special patterned structure provides fast Li+ transport channels and tailoring solvation structure of traditional LiPF6 -based carbonate electrolyte, enabling rapid ionic transfer kinetics and uniform Li+ flux, and boosting stability against Li anodes, thus realizing ultralong Li plating/stripping in the symmetrical cell over 3000 h at 1.0 mA cm-2 , 1.0 mAh cm-2 . Moreover, the SSLMBs with high LiFePO4 loading of 10.58 mg cm-2 deliver ultralong stable cycling life over 1570 cycles at 1.0 C with 92.5% capacity retention and excellent rate capacity of 129.8 mAh g-1 at 5.0 C with a cut-off voltage of 4.2 V (100% depth-of-discharge). Patterned GPEs systems are powerful strategies for producing durable and safe SSLMBs.

Origami-like 3D Fog Water Harvestor with Hybrid Wettability for Efficient Fog Harvesting

Collecting water in fog has also become a breakthrough to solve the hidden danger of water shortage in some arid areas. The three-dimensional (3D) structure fog collection material can increase the surface area in direct contact with the fog flow and reduce the quick flow of fog, which can effectively improve the fog collection efficiency. Imitating the three-dimensional structure of corrugated paper, the 3D fog collecting material with hybrid wettability was prepared by chemical and physical means. We discuss the influence of different wettability combinations on the fog collection efficiency of 3D structures and study the influence of spraying times and illumination times on the surface wettability during the construction of wettability. We also study the influence of the concavity and tip as well as the bending angle on the fog collection in the 3D structure and obtain the most reasonable concavity and convex ratio and bending angle. The superhydrophilic and superhydrophobic 3D structure fog harvesting material prepared by us performs well in the fog harvesting process, and the fog harvesting efficiency reaches 1.442 g cm-2 h-1. The fog collection efficiency is 418% of the original zinc sheet. At the same time, compared with the superhydrophilic and superhydrophobic hybrid two-dimensional (2D) plane, the increase is 168%, and compared with the superhydrophobic 3D structure, the increase is 150%.

Multi-bioinspired hierarchical integrated hydrogel for passive fog harvesting and solar-driven seawater desalination

In recent years, with the outbreak and epidemic of the novel coronavirus in the world, how to obtain clean water from the limited resources has become an urgent issue of concern to all mankind. Atmospheric water harvesting technology and solar-driven interfacial evaporation technology have shown great potential in seeking clean and sustainable water resources. Here, inspired by a variety of organisms in nature, a multi-functional hydrogel matrix composed of polyvinyl alcohol (PVA), sodium alginate (SA) cross-linked by borax as well as doped with zeolitic imidazolate framework material 67 (ZIF-67) and graphene owning macro/micro/nano hierarchical structure has successfully fabricated for producing clean water. The hydrogel not only can reach the average water harvesting ratio up to 22.44 g g-1 under the condition of fog flow after 5 h, but also be capable of desorbing the harvested water with water release efficiency of 1.67 kg m-2 h-1 under 1 sun. In addition to excellent performance in passive fog harvesting, the evaporation rate over 1.89 kg m-2 h-1 is attained under 1 sun on natural seawater during long-term. This hydrogel indicates its potential in producing clean water resources in multiple scenarios in different dry or wet states, and which holds great promise for flexible electronic materials and sustainable sewage or wastewater treatment applications.

Design of a self-cleanable multilevel anticounterfeiting interface through covalent chemical modulation

Counterfeit products have posed a significant threat to consumers safety and the global economy. To address this issue, extensive studies have been exploring the use of coatings with unclonable, microscale features for authentication purposes. However, the ease of readout, and the stability of these features against water, deposited dust, and wear, which are required for practical use, remain challenging. Here we report a novel class of chemically functionalizable coatings with a combination of a physically unclonable porous topography and distinct physiochemical properties (e.g., fluorescence, water wettability, and water adhesion) obtained through orthogonal chemical modifications (i.e., 1,4-conjugate addition reaction and Schiff-base reaction at ambient conditions). Unprecedentedly, a self-cleanable and physically unclonable coating is introduced to develop a multilevel anticounterfeiting interface. We demonstrate that the authentication of the fluorescent porous topography can be verified using deep learning. More importantly, the spatially selective chemical modifications can be read with the naked eye via underwater exposure and UV light illumination. Overall, the results reported in this work provide a facile basis for designing functional surfaces capable of independent and multilevel decryption of authenticity.

Interlayered Interface of a Thin Film Composite Janus Membrane for Sieving Volatile Substances in Membrane Distillation

Hypersaline wastewater treatment using membrane distillation (MD) has gained significant attention due to its ability to completely reject nonvolatile substances. However, a critical limitation of current MD membranes is their inability to intercept volatile substances owing to their large membrane pores. Additionally, the strong interaction between volatile substances and MD membranes underwater tends to cause membrane wetting. To overcome these challenges, we developed a dual-layer thin film composite (TFC) Janus membrane through electrospinning and sequential interfacial polymerization of a polyamide (PA) layer and cross-linking a polyvinyl alcohol/polyacrylic acid (PP) layer. The resulting Janus membrane exhibited high flux (>27 L m^-2 h^-1), salt rejection of ∼100%, phenol rejection of ∼90%, and excellent resistance to wetting and fouling. The interlayered interface between the PA and PP layer allowed the sieve of volatile substances by limiting their dissolution-diffusion, with the increasing hydrogen bond network formation preventing their transport. In contrast, small water molecules with powerful dynamics were permeable through the TFC membrane. Both experimental and molecular dynamics simulation results elucidated the sieving mechanism. Our findings demonstrate that this type of TFC Janus membrane can serve as a novel strategy to design next-generation MD membranes against volatile and non-volatile contaminants, which can have significant implications in the treatment of complex hypersaline wastewater.

Smart Energy-Absorbing Aerogel-Based Honeycombs with Selectively Nanoconfined Shear-Stiffening Gel

Aerogels, shaped as fibers, films, as well as monoliths, have demonstrated a plethora of applications in both academia and industry due to charming properties including ultralow density, large specific surface area, high porosity, etc., however studies on more complicated aerogel forms (e.g., honeycombs) with more powerful applications have not been fully explored. Herein, the Kevlar aerogel honeycomb is firstly constructed through a dry ice-assisted 3D printing method, where the Kevlar nanofiber ink is printed directly in dry ice freezing atmosphere, followed by supercritical fluid drying. The subsequent 3D Kevlar/shear-stiffening gel (SSG) honeycomb (3D-KSH) can be obtained by selective nanoconfining of SSG into nanopores of the aerogel skeleton wall (with the loading amount of 93 wt%) rather than into open honeycomb channels, solving the leakage, creep deformation, and shape design infeasibility of the SSG. Combining the advantages of Kevlar, honeycomb and SSG, the fabricated 3D-KSH shows obvious smart responsive behavior to external stimulus. Additionally, the 3D-KSH has high strain rate sensitivity (sensitivity factor of 4.16 × 10^-4 ) and excellent impact protection performance (energy absorption value up to 176 J g^-1 at the strain rate of 6300 s^-1 ), which will significantly broaden application prospect in some intelligent protection fields.

Efficient Fabrication of Micro/Nanostructured Polyethylene/Carbon Nanotubes Foam with Robust Superhydrophobicity, Excellent Photothermality, and Sufficient Adaptability for All-Weather Freshwater Harvesting

The integration of fog collection and solar-driven evaporation has great significance in addressing the challenge of the global freshwater crisis. Herein, a micro/nanostructured polyethylene/carbon nanotubes foam with interconnected open-cell structure (MN-PCG) is fabricated using an industrialized micro extrusion compression molding technology. The 3D surface micro/nanostructure provides sufficient nucleation points for tiny water droplets to harvest moisture from humid air and a fog harvesting efficiency of 1451 mg cm^-2 h^-1 is achieved at night. The homogeneously dispersed carbon nanotubes and the graphite oxide@carbon nanotubes coating endow the MN-PCG foam with excellent photothermal properties. Benefitting from the excellent photothermal property and sufficient steam escape channels, the MN-PCG foam attains a superior evaporation rate of 2.42 kg m^-2 h^-1 under 1 Sun illumination. Consequently, a daily yield of ≈35 kg m^-2 is realized by the integration of fog collection and solar-driven evaporation. Moreover, the robust superhydrophobicity, acid/alkali tolerance, thermal resistance, and passive/active de-icing properties provide a guarantee for the long-term work of the MN-PCG foam during practical outdoor applications. The large-scale fabrication method for an all-weather freshwater harvester offers an excellent solution to address the global water scarcity.

Overflow Control for Sustainable Development by Superwetting Surface with Biomimetic Structure

Liquid flowing around a solid edge, i.e., overflow, is a commonly observed flow behavior. Recent research into surface wetting properties and microstructure-controlled overflow behavior has attracted much attention. Achieving controllable macroscale liquid dynamics by manipulating the micro-nanoscale liquid overflow has stimulated diverse scientific interest and fostered widespread use in practical applications. In this review, we outline the evolution of overflow and present a critical survey of the mechanism of surface wetting properties and microstructure-controlled liquid overflow in multilength scales ranging from centimeter to micro and even nanoscale. We summarize the latest progress in utilizing the mechanisms to manipulate liquid overflow and achieve macroscale liquid dynamics and in emerging applications to manipulate overflow for sustainable development in various fields, along with challenges and perspectives.

Survival in desert: Extreme water adaptations and bioinspired structural designs

Deserts are the driest places in the world, desert creatures have evolved special adaptations to survive in this extreme water shortage environment. The collection and transport of condensed water have been of particular interest regarding the potential transfer of the underlying mechanisms to technical applications. In this review, the mechanisms of water capture and transport were first summarized. Secondly, an introduction of four typical desert creatures including cactus, desert beetles, lizards, and snakes which have special adaptations to manage water was elaborated. Thirdly, the recent progress of biomimetic water-collecting structures including cactus, desert beetles, and lizards inspired designs and the influence of overflow on water collection was demonstrated. Finally, the conclusions were drawn, and future issues were pointed out. The present study will further promote research on bioinspired water management strategies.

Hierarchical Natural Pollen Cell-Derived Composite Sorbents for Efficient Atmospheric Water Harvesting

Freshwater scarcity is a critical challenge threatening human survival especially due to poverty and arid and off-grid regions. Sorption-based atmospheric water harvesting (AWH) has emerged as a promising strategy for clean water production. However, most of the high-capacity sorbents are limited by the poor sorption/desorption kinetics and uncontrollable liquid leakage problem. Inspired by the plant transpiration process, we develop an environmentally friendly LiCl@pollen cell-polypyrrole (LiCl@PC-PPy) composite sorbent by confining the LiCl hygroscopic agent in the cages of the PC-PPy. The composite sorbent exhibits much improved sorption/desorption kinetics owing to the hydrophilicity of the hierarchical porous structure of the pollen cells, which provides abundant water sorption active sites and diffusion pathways and forms a concave meniscus on cell skeletons to maximize the thermal utilization efficiency. Moreover, the big cavities of the PC-PPy cages can serve as a water reservoir to reduce liquid leakage. As a result, the sorbent can capture atmospheric water to 85% of its own weight under 60% relative humidity (RH) within 2 h and rapidly release the water within 1 h under weak light irradiation of 0.8 sun. As a proof-of-concept demonstration, the fabricated AWH device can absorb 1.55 gwater/gsorbent at night and collect 1.53 gwater/gsorbent of water in 1-day outdoor operation, and the collected water can meet the drinking water standards defined by the World Health Organization (WHO) and Environmental Protection Agency (EPA).

Design of a Venation-like Patterned Surface with Hybrid Wettability for Highly Efficient Fog Harvesting

Inspired by Namib Desert beetle and leaf venation, a wettability-integrated system consisting of wettability-hybrid coatings and venation-like patterns was designed and successfully fabricated via a simple, low-cost, and eco-friendly route. The as-prepared surface can construct a 3D topography with a water layer and efficiently drain through the venation-like patterns. The combination of multiple mechanisms enhances the fog harvesting ability significantly. Meanwhile, the synergistic mechanisms of fog harvesting enhancement by a wettability-integrated surface were further studied and discussed.

Recent advances in biomimetic surfaces inspired by creatures for fog harvesting

In this review, the recent advances in artificial surfaces for fog harvesting are introduced with emphasis on the surfaces and their mechanisms used to enhance water capture and transportation, providing prospects for coping with water shortages.