A bioinspired structured graphene surface with tunable wetting and high wearable properties for efficient fog collection

A review of the methods of harvesting atmospheric moisture

Moisture is an inherent constituent of air present across the world. The relative humidity varies with the change in temperature and climate specific to a region. In some regions of the world, there may be a relatively inadequate number of grains of moisture in the air in comparison with other regions. These factors widen the scope for the deployment of decentralized technology to capture water. The effectiveness in capturing moisture gains significance in these regions. Among the numerous forms of moisture, fog and dew are studied in depth. Over time, flora and fauna in different ecosystems have adapted to capture moisture as well as repel excesses of it according to their requirements. Therefore, bio-inspired studies and tailored engineering strategies have been incorporated in this review. Since efficient technologies are required at moisture-scarce locations, active moisture harvesting has also been studied. The use of innovative materials along with different energy sources to capture water is elaborated. The effects of climate change and environmental contamination on harvested moisture are therefore assessed. Community participation and economical use of harvested fog or dew influence the sustainability of moisture-capture projects. Therefore, this article also provides an insight into the services of decentralized water-harvesting projects run by diverse organizations and researchers across the globe.

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.

Comparing Water Transport Properties of Janus Membranes Fabricated from Copper Mesh and Foam Using a Femtosecond Laser

One of the important aspects of manipulating and controlling liquid transport is the design of membrane surfaces. Janus membranes with opposite wettability characteristics can be manufactured for efficient directional water transfer. In this work, two types of materials were used to fabricate membranes with an asymmetric wettability behavior: copper foam and copper mesh. One side of the membranes was treated by scanning with a femtosecond laser beam, as a result of which it was converted to a superhydrophilic state, while the untreated side remained hydrophobic. Both membranes demonstrated excellent properties of a water diode through which water droplets could easily pass from the hydrophobic side to the hydrophilic side, but not vice versa. This behavior was achieved by finding the optimal laser scanning speed. This type of Janus membrane has found applications in collecting water droplets from fog; therefore, the samples obtained were also tested in terms of harvesting micro-droplets. The Janus mesh-based structure has demonstrated a higher water collection efficiency (3.9 g/cm² h) compared to the foam-based membrane (2.5 g/cm² h). Since the fog-water conversion efficiency decreased over time (to 0.5 g/cm² h in 2 weeks) due to the absorbance of organic pollutants, a coating of titanium oxide was applied to the laser-treated side of the Janus membranes. As a result, the effective function of the systems became distinctly long-lasting and was well maintained for at least 60 days. Moreover, the fabricated systems were protected from further degradation by simply placing them under sunlight for several hours. Our results prove to be useful in developing asymmetric hydrophobic-superhydrophilic membranes, which have potential applications in high-precision drop control and in harvesting water from arid environments.

Self-Healing Superwetting Surfaces, Their Fabrications, and Properties

The research on superwetting surfaces with a self-healing function against various damages has progressed rapidly in the recent decade. They are expected to be an effective approach to increasing the durability and application robustness of superwetting materials. Various methods and material systems have been developed to prepare self-healing superwetting surfaces, some of which mimic natural superwetting surfaces. However, they still face challenges, such as being workable only for specific damages, external stimulation to trigger the healing process, and poor self-healing ability in the water, marine, or biological systems. There is a lack of fundamental understanding as well. This article comprehensively reviews self-healing superwetting surfaces, including their fabrication strategies, essential rules for materials design, and self-healing properties. Self-healing triggered by different external stimuli is summarized. The potential applications of self-healing superwetting surfaces are highlighted. This article consists of four main sections: (1) the functional surfaces with various superwetting properties, (2) natural self-healing superwetting surfaces (i.e., plants, insects, and creatures) and their healing mechanism, (3) recent research development in various self-healing superwetting surfaces, their preparation, wetting properties in the air or liquid media, and healing mechanism, and (4) the prospects including existing challenges, our views and potential solutions to the challenges, and future research directions.

Unclogged Janus Mesh for Fog Harvesting

Janus membranes with asymmetric surface wettability have been extensively utilized in various fields, including fog harvesting, because of their novel liquid transport properties. However, Janus membranes have an inherent disadvantage in terms of aerodynamic efficiency in harvesting fog because of the clogged water bridges caused by the small pore size. In the present work, we applied Janus wettability to mesh geometry with systematically varying hole sizes. For a clogged mesh with a small hole size, capillary water transport to the mesh back via the wettability gradient in the direction of fog flow helps harvest more fog by enhancing water drainage, similarly to the Janus membrane. The advantage of the capillary water transport extends to a clog-free mesh with larger hole sizes but more preferably to a Janus mesh with a superhydrophilic back, which presents the highest level of fog-harvesting yield because of the fast shedding frequency and short onset time. In contrast, a Janus mesh with a superhydrophobic front, which also has a wettability gradient along the fog flow, produces a lower fog-harvesting performance, particularly at slow fog speeds, because of the dropwise deposition of large water drops that locally disturb fog flow around a protruding water surface. On the other hand, the other type of Janus mesh with a superhydrophilic front is observed to minimize this disadvantage in the local fog flow by virtue of the filmwise deposition. It is also found that some Janus treatments can help protect mesh holes from clogging up by either forming a thin water meniscus or resisting water transport through the mesh holes.

Optical Modification of 2D Materials: Methods and Applications

2D materials are under extensive research due to their remarkable properties suitable for various optoelectronic, photonic, and biological applications, yet their conventional fabrication methods are typically harsh and cost-ineffective. Optical modification is demonstrated as an effective and scalable method for accurate and local in situ engineering and patterning of 2D materials in ambient conditions. This review focuses on the state of the art of optical modification of 2D materials and their applications. Perspectives for future developments in this field are also discussed, including novel laser tools, new optical modification strategies, and their emerging applications in quantum technologies and biotechnologies.

Photoredox Catalysis for the Fabrication of Water-Repellent Surfaces with Application for Oil/Water Separation

Silanization processes with perfluoroalkyl silanes have been demonstrated to be effective in developing advanced materials with many functional properties, including hydrophobicity, water repellency, and self-cleaning properties. However, practical industrial applications of perfluoroalkyl silanes are limited by their extremely high cost. On the basis of our recent work on photoredox catalysis for amidation with perfluoroalkyl iodides, its application for surface chemical modification on filter paper, as an illustrative example, has been developed and evaluated. Before photocatalytic amidation, the surface is functionalized with amine functional groups by silanization with 3-(trimethoxysilyl)propylamine. All chemically modified surfaces have been fully characterized by attenuated total reflection infrared (ATR-IR), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy with energy-dispersive spectroscopy (SEM-EDS), and three-dimensional (3D) profiling to confirm the successful silanization and photocatalytic amidation. After surface modification of the filter papers with perfluoroalkanamide, they show high water repellency and hydrophobicity with contact angles over 120°. These filter papers possess high wetting selectivity, which can be used to effectively separate the organic and aqueous biphasic mixtures. The perfluoroalkanamide-modified filter papers can be used for separating organic/aqueous biphasic mixtures over many cycles without lowering the separating efficiency, indicating their reusability and excellent durability.

Tailoring Materials with Specific Wettability in Biomedical Engineering

As a fundamental feature of solid surfaces, wettability is playing an increasingly important role in our daily life. Benefitting from the inspiration of biological paradigms and the development in manufacturing technology, numerous wettability materials with elaborately designed surface topology and chemical compositions have been fabricated. Based on these advances, wettability materials have found broad technological implications in various fields ranging from academy, industry, agriculture to biomedical engineering. Among them, the practical applications of wettability materials in biomedical-related fields are receiving remarkable researches during the past decades because of the increasing attention to healthcare. In this review, the research progress of materials with specific wettability is discussed. After briefly introducing the underlying mechanisms, the fabrication strategies of artificial materials with specific wettability are described. The emphasis is put on the application progress of wettability biomaterials in biomedical engineering. The prospects for the future trend of wettability materials are also presented.

Bio-inspired graphene-based nano-systems for biomedical applications

The increasing demands of environmentally sustainable, affordable, and scalable materials have inspired researchers to explore greener nanosystems of unique properties which can enhance the performance of existing systems. Such nanosystems, extracted from nature, are state-of-art high-performance nanostructures due to intrinsic hierarchical micro/nanoscale architecture and generous interfacial interactions in natural resources. Among several, bio-inspired nanosystems graphene nanosystems have emerged as an essential nano-platform wherein a highly electroactive, scalable, functional, flexible, and adaptable to a living being is a key factor. Preliminary investigation project bio-inspired graphene nanosystems as a multi-functional nano-platform suitable for electronic devices, energy storage, sensors, and medical sciences application. However, a broad understanding of bio-inspired graphene nanosystems and their projection towards applied application is not well-explored yet. Considering this as a motivation, this mini-review highlights the following; the emergence of bio-inspired graphene nanosystems, over time development to make them more efficient, state-of-art technology, and potential applications, mainly biomedical including biosensors, drug delivery, imaging, and biomedical systems. The outcomes of this review will certainly serve as a guideline to motivate scholars to design and develop novel bio-inspired graphene nanosystems to develop greener, affordable, and scalable next-generation biomedical systems.

Aerodynamics-assisted, efficient and scalable kirigami fog collectors

To address the global water shortage crisis, one of the promising solutions is to collect freshwater from the environmental resources such as fog. However, the efficiency of conventional fog collectors remains low due to the viscous drag of fog-laden wind deflected around the collecting surface. Here, we show that the three-dimensional and centimetric kirigami structures can control the wind flow, forming quasi-stable counter-rotating vortices. The vortices regulate the trajectories of incoming fog clusters and eject extensive droplets to the substrate. As the characteristic structural length is increased to the size of vortices, we greatly reduce the dependence of fog collection on the structural delicacy. Together with gravity-directed gathering by the folds, the kirigami fog collector yields a collection efficiency of 16.1% at a low wind speed of 0.8 m/s and is robust against surface characteristics. The collection efficiency is maintained even on a 1 m² collector in an outdoor setting.

Water shortage not only occurs in arid regions, but also in humid area with little precipitation, despite abundant fog. Authors develop robust and scalable 3D centimetric kirigami structures to control wind flow and regulate the trajectories of incoming fog, yielding high fog collection efficiency.

Flexible, superhydrophobic and multifunctional carbon nanofiber hybrid membranes for high performance light driven actuators

Recently, a series of super-hydrophobic materials have been prepared and efforts have been made to further expand their applications, especially in electronics and smart actuators. However, it remains challenging to develop light weight, flexible and super-hydrophobic materials integrating multifunctionalities such as superior photothermal conversion, corrosion resistance, and controllable actuation. Herein, a superhydrophobic and multi-responsive carbon nanofiber (CNF) hybrid membrane with an outstanding photo-thermal effect is fabricated by electrospinning the mixture of polyacrylonitrile and nickel acetylacetonate, followed by two step heat treatment and subsequent fluorination. The superhydrophobic CNF hybrid membrane with outstanding anti-corrosion and self-cleaning performance can float on the water surface spontaneously, thus effectively reducing the motion resistance. The light driven actuation with controllable movement can be achieved by adjusting the laser irradiated location, in which the localized absorption of light is transformed into thermal energy, and hence an imbalanced surface tension is created. The multifunctional hybrid membrane also opens up an arena of applications such as freestanding flexible electronics, drug delivery, and environmental protection.

Experimental and DFT studies of gadolinium decorated graphene oxide materials for their redox properties and as a corrosion inhibition barrier layer on Mg AZ13 alloy in a 3.5% NaCl environment

Magnesium alloys are broadly used worldwide in various applications; however, the serious disadvantage of these alloys are subject to corrosion and in aggressive/corrosive environments. A coating containing gadolinium-based composite materials can increase the alloy protection by strong electron transfer between the host alloy and the lanthanide-containing protective layer. This investigation aims to develop a Gd nanorod functionalised graphene oxide material as a corrosion inhibition barrier on the Mg alloy surface. The obtained functional materials were characterised by various spectroscopy techniques. The corrosion inhibition and composite material stability were studied by the electrochemical methods. The electrochemical stability was shown to increase with the applied current. The hydrogen evolution constantly increased and the corrosion inhibition significantly improved. Also, the computational studies of the material were performed, and their results support the experimental findings. Overall, the resultant composite material's corrosion resistance and cyclic stability are improved, and it could be used as a sodium-ion battery cathode material due to its high reversibility.

A Coral Reef-like Structure Fabricated on Cellulose Paper for Simultaneous Oil-Water Separation and Electromagnetic Shielding Protection

The functional design of paper-based material surfaces with renewable functions and environmentally friendly properties is prevalent nowadays. Herein, a superhydrophobic surface with a coral reef-like structure was prepared on filter paper by electroless copper plating, rapid silver nitrate etching, and facile 1-hexadecanethiol impregnation. After low-surface-energy thiol treatment, this unique coral reef-like structure surface showed excellent superhydrophobicity with a water contact angle of 163.8° and superoleophobicity with an oil contact angle of 0°, which could be used for oil-water separation and had a separation efficiency above 89.17% after 12 consecutive oil-water separations. Because the copper layer and silver nanostructure are both excellent conductive materials, the modified paper exhibited excellent electromagnetic shielding properties, and the electromagnetic interface shielding effectiveness exceeded 63 dB from 9 kHz to 1.5 GHz. The modified paper also had excellent self-cleaning properties and a better corrosion resistance. The unique three-dimensional interweaving structure between the cellulose fibers in the filter paper is fully utilized, and the substitution reaction between the silver ion and the copper coating produces a coral reef-like structure, which provides a new strategy for promoting the wide application of paper-based materials.

Laser Fabrication of Bioinspired Graphene Surfaces With Superwettability

The past decades have seen growing research interest in developing efficient fabrication techniques for preparing bioinspired graphene surfaces with superwettability. Among the various fabrication methods, laser fabrication stands out as a prominent one to achieve this end and has demonstrated unique merits in the development of graphene surfaces with superwettability. In this paper, we reviewed the recent advances in this field. The unique advantages of laser fabricated graphene surfaces have been summarized. Typical graphene surfaces with superwettability achieved by laser fabrication, including superhydrophobic graphene surfaces, oil/ water separation, fog collection, antibacterial surfaces, surface enhanced Raman scattering (SERS), and desalination, have been introduced. In addition, current challenges and future perspectives in this field have been discussed. With the rapid progress of novel laser physical/ chemical fabrication schemes, graphene surfaces with superwettability prepared by laser fabrication may undergo sustained development and thus contribute greatly to the scientific research and our daily life.

Laser Direct Structuring of Bioinspired Spine with Backward Microbarbs and Hierarchical Microchannels for Ultrafast Water Transport and Efficient Fog Harvesting

Achieving effective dropwise capture and ultrafast water transport is essential for fog harvesting. In nature, cactus uses the conical spine with microbarbs to effectively capture fog, while Sarracenia utilizes the trichome with hierarchical microchannels to quickly transport water. Herein, we combined their advantages to present a novel configuration, a spine with barbs and hierarchical channels (SBHC), for simultaneous ultrafast water transport and high-efficient fog harvesting. This bioinspired SBHC exhibited the fastest water transport ability and the highest fog harvesting efficiency in comparison with the spine with hierarchical channels (SHCs), the spine with barbs and grooves (SBG), and the spine with barbs (SB). Based on the fundamental SBHC unit, we further designed and fabricated a two-dimensional (2D) spider-web-like fog collector and a three-dimensional (3D) cactus-like fog collector using direct laser structuring and origami techniques. The 2D spider-web and 3D cactus-like fog collectors showed high-efficient fog collection capacity. We envision that this fundamental understanding and rational design strategy can be applied in fog harvesting, heat transfer, liquid manipulation, and microfluidics.

Micro-/Nanostructured Interface for Liquid Manipulation and Its Applications

Understanding the relationship between liquid manipulation and micro-/nanostructured interfaces has gained much attention due to the wide potential applications in many fields, such as chemical and biomedical assays, environmental protection, industry, and even daily life. Much work has been done to construct various materials with interfacial liquid manipulation abilities, leading to a range of interesting applications. Herein, different fabrication methods from the top-down approach to the bottom-up approach and subsequent surface modifications of micro-/nanostructured interfaces are first introduced. Then, interactions between the surface and liquid, including liquid wetting, liquid transportation, and a number of corresponding models, together with the definition of hydrophilic/hydrophobic, oleophilic/olephobic, the definition and mechanism of superwetting, including superhydrophobicity, superhydrophilicity, and superoleophobicity, are presented. The micro-/nanostructured interface, with major applications in self-cleaning, antifogging, anti-icing, anticorrosion, drag-reduction, oil-water separation, water collection, droplet (micro)array, and surface-directed liquid transport, is summarized, and the mechanisms underlying each application are discussed. Finally, the remaining challenges and future perspectives in this area are included.

Water Harvesting of Bioinspired Microfibers with Rough Spindle-Knots from Microfluidics

Heterostructure rough spindle-knot microfibers (HRSFs) are fabricated via a flexible parallel-nozzle microfluidic method. In this method, the bioinspired HRSF with a roughness gradient between spindle-knots and joints, can be manufactured in large-scale, and with which the size of the spindle-knots and joints can be precisely adjusted by regulating flow rates. The HRSFs, fabricated with chitosan and calcium alginate, have strong mechanical properties and corrosion resistance in acid environment (pH = 5) and alkaline environment (pH = 9), respectively. More attractively, under controlled treatment conditions, the morphology of the spindle-knots on the HRSFs can be effectively managed by changing the composite content of calcium chloride in the fluid. During the water collection process, tiny droplets of moisture can be captured on the surface of the HRSFs, subsequently, the droplets can coalesce and be transported from joint to spindle-knot sections. It is demonstrated that the surface morphology of spindle-knots directly influences the water collection efficiency, where a higher roughness gradient generates higher water collection efficiency. This parallel-nozzle microfluidic technology provides a low-cost and flexible method to manufacture high biocompatibility bioinspired rough spindle-knot microfibers, which has many potential applications in large-scale water collection, sustained drug release, and directional water collection.

Integrative Bioinspired Surface with Wettable Patterns and Gradient for Enhancement of Fog Collection

A novel integrative bioinspired surface with wettable patterns and gradient (WPGS) is proposed for fog collection via a novel anodic oxidation strategy. We study the water collection behaviors on WPGS with different parameters. Quantitative force analysis is presented, providing evidence for the underlying mechanism leading to the directional motion of the droplet, which is consistent with the experimental results. Such a surface can not only improve the fog droplet capture performance effectively owing to wettable patterns but also accelerate surface regeneration by taking full advantage of the cooperation of multidriving forces, leading to a further fog collection enhancement.