Fog Collection Research Articles

High-efficient and robust fog collection through topography modulation

Janus wettable material is considered one of the most promising candidates for fog collection. However, the applications of fog collectors are confined by many weaknesses nowadays, such as tedious fabrication methods, low mechanical stability and durability, and poor collecting efficiency. Among them, improving fog harvesting efficiency is a big challenge to be overcome. Herein, a series of hydrophobic-superhydrophilic Janus system has been successfully fabricated by a facile and eco-friendly method including etching and interface modification. Importantly, under the inspiration of natural creatures, the topography of hydrophobic surface in Janus system can be modulated by modifying substances with different low surface energy, effectively improving the fog collecting performance, and obtaining an excellent fog harvesting efficiency of 3718 mg·cm−2·h−1 in unenclosed fog environment. The underlying mechanism is designed to discuss the enhancement of fog collection in terms of fog capture, drop coalescence and drop transportation. Meanwhile, it is recyclable and durable even maintained for at least 5 months. Moreover, it exhibits good stability during mechanical, thermal and ultraviolet (UV) resistance testing. Overall, the findings open up a new avenue to design Janus materials for efficient fog harvesting by regulating micromorphology and promote a promising candidate for addressing water scarcity.

Development of gradient-wetting Janus wood membrane with high-efficiency fog collection and oil-water separation

Conventional preparation of Janus membranes with asymmetric wettability focuses on the preparation of extreme hydrophilic side and hydrophobic side, but suffers from pore clogging, low liquid transfer and collection efficiency and short service life. In this study, Janus wood (JW) with a continuous wettability gradient was created throughunidirectional vacuum impregnation of a hydrophobic solvent after the delignification of wood. Digital image correlation (DIC) and layer-by-layer contact angle assessment were utilized to examine the thickness-dependent wettability gradient of the JW membrane. The JW membrane completed the modification of the cell walls without blocking the cell lumens. The presence of wettability gradient in the JW membrane effectively reduced the capillary force of liquid penetration, resulting in decreased adhesion and stagnation of liquid on the membrane surface, and increased flow rate and transport efficiency. Based on the continuous wettability change of the JW membrane, the JW membrane was endowed with the ability to act as a “unidirectional valve” to enable continuous and rapid directional transport of liquids. The mechanical properties of the JW membrane prepared by the unidirectional introduction method were significantly improved, rendering them highly stable and environmentally durable. The fog collection efficiency of the JW membrane was maintained at 97.7% over 10 repeated use cycles. For light oil/water and heavy oil/water mixtures, JW membrane maintained an efficiency of 99.6% or higher. Unlike conventional surface modification methods, the unidirectional introduction method proved practical and effective for modifying the JW membrane in the thickness direction. Furthermore, the prepared JW membrane was sustainable, inexpensive, durable, and environmentally friendly. This study provides a wide range of potential applications in fields such as droplet manipulation, multi-liquid separation, industrial wastewater purification, and microfluidics.

Biomimetic 3D efficient fog harvester by synergistic wettability effect

By collecting water in the air, it is an important way to solve the problem of water shortage in arid and semi-arid areas. Improving the efficiency of fog harvesting is still a great challenge to be overcome. The use of 3D structure is an excellent strategy, here, a Multiple-biomimetic 3D hydrophilic and superhydrophobic fog harvester with a hump-valley structure was prepared by the combination of thermal processing and spraying. Inspired by biological water collection in nature, a 3D porous sponge surface with hydrophilic valley and superhydrophobic hump was obtained by two-step treatment. This surface structure showed excellent fog harvesting performance, which was 185 % higher than the original sponge. This structure accelerates the capture, transfer and transport of droplets during the fog harvesting process and greatly improves the efficiency of fog harvest. The results show that the chemical gradient and structural gradient actuation we constructed on the melamine sponge surface can effectively improve the fog collection efficiency. A surface with a linear hump-valley mixed wettability pattern is designed, and it is proved that fog collection efficiency can be effectively improved at the droplet capture and transfer stage and transport stage respectively. This study highlights a simple and cheap integrated fog harvester material design.

Preparation of a Bioinspired Conical Needle for Rapid Directional Water Transport and Efficient Fog Harvesting

Water shortages have become a serious issue that threatens the survival of humans, particularly in arid regions. Collecting fog from the air environment is an effective approach to obtaining freshwater resources. Herein, inspired by cactus spines, we fabricated a superhydrophilic conical copper needle by the combination of electrochemical etching and the SiO2 colloidal self-assembly method for water transportation and fog collection. It was found that a water film would be formed on the surface of the as-prepared copper needle once a water droplet was transported from the tip to the base, which acted as a lubricating film to reduce the frictional resistance between the following water droplets and the copper needle and promote the self-propelled movement of the droplets. As a result, the transport velocity and the longest transport distance of a single water droplet on the as-prepared copper needle were high up to 142 mm/s and 42 mm, respectively. Besides, the results reveal that the droplet transport distance decreased with the increase of apex angles, whereas it increased with the increase of droplet volume and tilt angles. Additionally, the as-prepared copper needle exhibited an outstanding water collection rate of ∼1700 mg/h for a single copper needle, which is five times that of the original copper needle. This work provides a facile and low-cost method to fabricate conical copper needles for water droplet manipulation and efficient fog collection, showing great application potential in the fields of microfluid, desalination, and freshwater collection.

Efficient Water Mist Collector with Both a Kirigami Structure and Chemical Modification.

The shortage of freshwater resources is a common problem faced by people all over the world. Water mist collection provides a feasible solution to this problem. In this paper, three kinds of foggers with a kirigami structure and chemical modification were prepared. Their fog collection efficiencies were 3.04, 3.17, and 3.54 g·h-1·cm-2, respectively, which were 1.57, 1.63, and 1.82 times that of the original zinc sheet. Then, the fog collector of sample 3 with the highest fogging efficiency was analyzed and discussed. In order to evaluate the practical application of the sample, durability and ultraviolet (UV) resistance tests of the sample were carried out. The experimental results show that the surface of sample 3 has better durability and excellent UV resistance. In addition, the fog collector design incorporating readily available materials and a straightforward preparation process showcases outstanding efficiency. As such, it presents a novel approach for the development of high-performance fog collection systems in the future.

RETRACTED: Temperature and pH endurable self-assembled camellia-like nanostructure achieved on zinc sheet with superamphiphobicity for fog harvesting

Easy-implement and low-cost fabrication of super-hydrophobic/super-oleophobic materials is vital for efficient fog harvesting. In this study, we introduce a simple two-step procedure based on Cu/1-octadecanethiol (ODT) self-assembled monolayer (SAM) modified zinc plates. Intriguingly, the process emulates the natural blooming of flowers: copper particle deposition and subsequent SAM formation lead to the progressive expansion of the surface, culminating in camellia-like nanostructures. The ensuing materials display water contact angle (WCA) and oil contact angle (OCA) of 160 ± 1° and 159 ± 1°, respectively. The formation of a layered petal structure that effectively traps air is recognized as the crucial factor in achieving superamphiphobicity. In addition to enhanced fog collection, the materials exhibit exceptional performance in acidic and basic environments (1 ≤ pH ≤ 14) as well as artificial seawater conditions. Furthermore, they demonstrate remarkable wear resistance and self-cleaning capabilities. The combination of these attributes ensures the robustness and stability necessary for efficient fog collection.

Potential Solutions for the Water Shortage Using Towers of Fog Collectors in a High Andean Community in Central Ecuador

The lack of water is a fundamental issue for survival of peasant communities located at heights above 3200 masl in the Andean highlands, such as in the case of the Galte-Yaguachi community in central Ecuador. The social balance, agricultural development as well as animal subsistence and finally the economic income is pending on the availability of hydric resources. Therefore, a three-dimensional fog collector system was constructed with Urku Yaku material in order to provide water for the close-by community. Simultaneously, we determined the quality of the collected water per square meter of the mesh, during the period of the highest annual precipitations. The installed nets yielded a gain of at least 2.63 L/m2 and a minimum of 0.65 L/m2 per day. The analyzed water quality reflected the suitability for human consumption. As water collection has been successful, an expansion of the proposed system may provide this fundamental good also to other communities with similar characteristics. Fog catcher towers will produce 26,577.84 m3/year of water, fulfilling crops’ needs, and the economic analysis proves it is worth the investment, as demonstrated by a benefit cost ratio of 1.90.

Super-Fast Fog Collector Based on Self-Driven Jet of Mini Fog Droplets.

Freshwater scarcity crisis threatens human life and economic security. Collecting water from the fog seems to be an effective method to defuse this crisis. Nonetheless, the existing fog collection methods have the limitations of the low fog collection rate and efficiency because of their gravity-based droplet shedding. Here, the aforementioned limitations are resolved by proposing a new fog collection method based on the self-driven jet phenomenon of the mini fog droplets. A prototype fog collector (PFC) composed of a square container that is filled with water is first designed. Both sides of the PFC are superhydrophobic but covered with superhydrophilic pore array. The mini fog droplets touching the side wall are easily captured and spontaneously and rapidly penetrate into the pores to form jellyfish-like jets, which greatly increases the droplet shedding frequency, guaranteeing a higher fog collection rate and efficiency compared with the existing fog collection methods. Based on this, a more practical super-fast fog collector is finally successfully designed and fabricated which is assembled by several PFCs. This work is hoping to resolve the water crisis in some arid but foggy regions.

Efficient fog collector with superhydrophobic coated surface

In this work, we developed a novel harp structure that collects water directly from fog in comparison with conventional Raschel mesh. Polyethylene (PE) monofilament was used as a collector’s element in the harp. The Raschel mesh in its particular design is quite anisotropic, shows elastic behavior breadth-wise while no stiffness is exhibited in transverse direction. A comparison of fog collection yield for the harp signifies that fog harvesting rate is four times higher than Raschel mesh, suggesting some alterations in monofilament diameter and collector element. Therefore, harp technology with cylindrical monofilaments can be deployed commercially to increase the efficiency of fog collectors, where mass and velocity of fog are inappropriate for Raschel mesh. In addition, silane-coated harp showed that surface hydrophobicity further enhances fog collection efficiency. The fog collector element (FCE) after silane coating significantly enhanced fog water collection yield. Samples were characterized by high resolution scanning electron microscope (HR-SEM), energy-dispersive x-ray (EDX) and atomic force microscope (AFM). Hydrophobicity was analyzed by static water contact angle and water collection yield.

Enhanced fog collection of hydrogel-coated wires inspired by water film-trapping characteristics of Tillandsia

Fog collection has been widely studied to collect fresh water in arid regions. With the demand of optimizing the design of fog collectors, removing the pinned droplets and accelerating the water drainage have become a challenge. To address this challenge, we propose a fog collection method utilizing calcium alginate hydrogel-coated wires inspired by the water film-trapping characteristics of Tillandsia. Maintaining the effective wire diameter by water film trapped on the hydrogel, the fog collection performance of our hydrogel-coated wire precedes that of a bare wire in collection efficiency (up to 136 % higher) under different flow speed conditions. Significantly, retaining the inter-distance between dual-wires, the collection efficiency of hydrogel-coated dual-wires is 1.2 ∼ 1.7 times higher than that of two bare dual-wires. Moreover, the hydrogel-coated wires prevent the formation of water bridges between wires by removing the deposited droplets promptly, which opens different perspectives on designing the hydrogel-coated wires for the purpose of water harvesting, sustainable engineering, and ecofriendly technology.

Analysis of Architectural Needs for Passive Low-Tech Fog and Dew Collector Building Design: A Narrative Literature Review

Global warming and climate change have negative effects on life on earth. One of the consequences is a water crisis or water scarcity, both in quantity and quality. Indonesia also cannot avoid this problem. Therefore it is necessary to prepare an alternative water supply solution, one of which is from water vapor (atmospheric water), especially in the form of dew and fog. This study aimed to formulate the design requirements for passive low-tech dew and fog collector building by comparing several technologies and projects in the world that have been realized recently that have a relationship with architectural science. This research used qualitative research with a narrative literature review approach. This research produced design requirements in the form of principles and technical requirements in designing and realizing dew and fog collector building, especially in terms of function, construction, and appearance.Keywords: dew collector, fog collector, low-tech, water scarcity, architecture

From capture to transport: A review of engineered surfaces for fog collection

AbstractCollecting microscale water droplets suspended in the wind, that is, fog, using permeable surfaces is a promising solution to the worldwide problem of water scarcity and is of great interest to industries, such as mist elimination and recapturing water in cooling towers. In the past few decades, this topic has attracted a drastically increasing number of researchers across a wide range of subjects. However, many aspects remain unclear, such as the definition and process of fog collection, fog collection determined from the perspectives of both the fog capture process and the liquid transport process, and how surface characteristics affect fog collection performance. In this review, we introduce and discuss fog collection from the perspectives of aerodynamics‐governed fog‐capturing processes and interfacial‐phenomena‐determined liquid transport processes. Then, an emphasis is given to the design and engineering of permeable surfaces at different length scales to optimize the fog collection performance, including the dimension, morphology, and arrangement of wires at the millimetric scale, unidirectional spreading, and Laplace pressure gradient induced by asymmetric surface geometry and nano‐/microstructures. At last, a brief outlook of future research directions is provided.

Back Cover, Volume 2, Number 2, April 2023

Back Cover: The cover image is based on the Review Article From capture to transport: A review of engineered surfaces for fog collection by Jiang et al. This cover image demonstrates that the collection of fog from an incoming fog-laden wind includes the aerodynamics-governed fog-capturing process and interfacial-phenomena-determined liquid transport process. This review introduces and discusses the definition of fog collection, fog capture process, liquid transport process, the effects of surface characteristics on fog collection performance, and the optimization of a fog collector. (DOI: 10.1002/dro2.55)

Improved Liquid Collection on a Dual‐Asymmetric Superhydrophilic Origami (Adv. Mater. 17/2023)

Bioinspired Interfaces Bioinspired fluid transporting interfaces provide a promising strategy to simplify the current systems. In article number 2211596, Moyuan Cao and co-workers present superhydrophilic origami with dual-asymmetric channels to realize a spontaneous, unidirectional, adaptive, and gravity-independent fluid-collection process. The further integration of a radiative layer can improve fog and steam collection, proving a potential application in water reusage.

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 1451mg 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 2.42kg m-2 h-1 under 1 Sun illumination. Consequently, a daily yield of ≈35kg 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.

Temperature and pH endurable self-assembled camellia-like nanostructure achieved on zinc sheet with superamphiphobicity for fog harvesting

Easy-implement and low-cost fabrication of super-hydrophobic/super-oleophobic materials is of great significance for efficient fog harvesting. Herein, we propose a simple two-step procedure based on Cu/1-octadecanethiol (ODT) self-assembled monolayer (SAM) modified zinc plates. Interestingly, the whole process mimics the blooming process of flowers in nature: the deposition of copper particle and the subsequent formation of SAM drives the surface undergo gradually stretches and finally blooms to camellia-like nanostructures. The water contact angle (WCA) and oil contact angle (OCA) reach 160 ± 1° and 159 ± 1° respectively, as a result of the formation of layered petal structure that traps air effectively, which is attributed as one of the most important factors for the superamphiphobic effect. In addition to much enhanced facility in fog collection, the materials maintain excellent performance in acid/base environments (1 ≤ pH ≤ 14), broad temperature conditions ranging from −18 °C to 240 °C, and the artificial sea environment, and exhibit capable wear resistance as well as self-cleaning property. The cooperation of all these multiple properties ensures the robustness and stability for efficient fog collection.

Load-responsive bionic kirigami structures for high-efficient fog harvesting

Harvesting fog is a charming approach to alleviating the global water shortage crisis. However, it is extremely challenging to design fog collectors with high efficiency due to the scarce geometric driving structures. Herein, we develop a 3D kirigami structure inspired by the new corrugated driving structures in the Bird's Nest Fern, which can be fabricated by simple shearing and stretching. Its water collection ratio increases with the external load, forming the unique load responsiveness. The kirigami structure owns a 3D array configuration to enhance flow velocity for the efficient droplet condensation rate and has geometric and wetting gradients to transport condensate droplets spontaneously and quickly, contributing to a high water collection efficiency. The water collection ratio can reach 3.45 times that of a pure iron sheet by only changing the geometric structure, and the highest ratio can even reach 4.58 times with the assistance of wetting gradients.

Potential Analysis of Atmospheric Water Harvesting Technologies from the Perspective of “Trading-in Energy for Water”

An applicable, high-volume, and sustainable water uptake technology can alleviate freshwater shortages, improve the energy utilization rate and promote the development of energy technology. Traditional seawater desalination, fog water, and dew collection are limited by the geographical environment, and the water resource transportation cost is high, or the water uptake volume is limited, so they cannot be used on a large scale. There are potential safety problems with wastewater reuse and recycled water. Atmospheric water harvesting technology uses energy for direct condensation or uses adsorbent to absorb water, which is characterized by strong sustainability, high applicability, decentralization, and stable water uptake. This study summarizes the working principle of mainstream atmospheric water harvesting technologies, mainly including condensation, absorption, and desorption water harvesting, and some active dew and fog collection technologies. It also theoretically analyzes the energy consumption of condensation and adsorption and desorption water harvesting technologies. Aiming at the problems of difficult condensing for direct condensation and long adsorption/desorption cycle of adsorption and desorption water harvesting, it summarizes the countermeasures of multi-stage condensation and multi-cycle adsorption and desorption. The development prospect of atmospheric water harvesting technologies is also discussed

An Efficient Fog Collector Achieved by Optimal Hierarchical Surface Patterns and Wetting Gradient

AbstractWith the decrease in fresh water resources, fog collection has become a promising way to obtain fresh water. This paper presents an efficient fog collector that combines wettability and spokes geometry. Water droplets move along a fixed route on the mist collector and can easily overcome the pinning effect at the end of the structure to detach from the surface and then be collected. Its fog collecting efficiency can be 1.82 times that of a planar zinc sheet, which provides a new idea for the design of subsequent fog collectors.

Water harvesting through fog collectors: a review of conceptual, experimental and operational aspects

Abstract In water-scarce regions where fog is abundant, the population can rely on this resource to obtain fresh water. The potential to harvest fog is confirmed by Large Fog Collector projects worldwide, which are reviewed. Mostly maintenance issues due to environmental and complex social factors compromise the sustainability of such projects. The researchers endeavour to resolve these issues by developing enhanced materials, while others use biomimetic design, hence creating innovative collectors. The objective of this paper is to survey and review the state of the art and develop a framework of different types of innovative fog collectors, including conceptual, experimental and operational aspects.