Rational Design of a High Performance and Robust Solar Evaporator via 3D-Printing Technology

Construction of Nanocellulose Aerogels with Environmental Drying Strategy without Organic Solvent Displacement for High-Efficiency Solar Steam Generation

Solar desalination is one of the effective means to alleviate water scarcity, in which aerogel-like evaporators have attracted extensive attention in the field of efficient desalination. However, the current preparation methods for aerogels still mainly rely on high-cost solutions, such as freeze-drying or supercritical drying. Herein, a preparation scheme for aerogels that can be realized under atmospheric pressure conditions is reported. In this paper, a foam skeleton template (FST) strategy is proposed, in which flake graphite is entangled by cellulose nanofibers (CNFs) and codispersed between the foam cell walls, and subsequently connected with the nascent Ca2+ in the inner wall to form a tough and stable three-dimensional network structure, which can effectively avoid the structural collapse caused by atmospheric drying. The cellulose/graphite aerogel (CGA) prepared using the FST strategy possesses lightweight (36 mg cm-3) and porous (porosity >97%) properties. The 3D porous structure and wetting characteristics of the CGA provided excellent energy management, rapid water transport capability, and a reduced enthalpy of evaporation, which enabled it to achieve a fast water evaporation rate of 3.8 kg m-2 h-1 with 98.4% energy efficiency. This FST strategy provides a solution for the low-cost development of aerogel and desalination.

Honeycomb-like Microthermal Traps on a Photothermal Surface for Highly Efficient Solar Evaporation

Solar evaporation is an ecofriendly and practical method for seawater desalination. The photothermal layer, which absorbs solar energy and converts it to thermal energy, plays a crucial role in enhancing the efficiency of the evaporator. However, structural design methods for photothermal layers are often complex and energy-intensive. This work reports a simple and efficient strategy for fabricating a necklace-like beaded nanofiber self-organized honeycomb-structured photothermal material. The honeycomb-like cavities form numerous microscale thermal traps, achieving thermal localization while maintaining high energy utilization efficiency, which not only increases light absorption but also facilitates the diffusion and escape of steam. Besides, the hydrophobic honeycomb layer separates the photothermal layer and the interface water, which reduces considerable heat conduction loss and achieves an effective antisalting performance. These functional features endow the evaporator with an evaporation efficiency of 92.9%, and the evaporation rate reaches 2.11 kg m-2 h-1 at 1 sun irradiance, demonstrating its great potential for practical solar-driven seawater desalination under natural sunlight.

Bifunctional Janus Membranes for Multicomponent Contaminated Seawater Separation and Recovery

Solar-driven interface desalination has emerged as a promising strategy to address the global freshwater shortage crisis. However, the separation and recovery of multicomponent oil-contaminated seawater remain a key challenge. This study reports a novel high-strength Janus photothermal membrane with a unique reverse wettability design. On one side, the membrane has hydrophilic and oleophobic properties, while on the other, it has hydrophobic and oleophilic characteristics. The Janus membrane demonstrates dual functionality: solar desalination and oil-water separation. This dual functionality enables efficient separation and recovery of four components from contaminated seawater: purified water, salt crystals, light oil, and heavy oil. As a result, the Janus membrane achieves an evaporation rate of 2.06 kg m-2 h-1 under 1.0 sun. The ion (Na+, K+, Ca2+, and Mg2+) removal rate approaches 100% with nearly complete recovery of salt crystals. Furthermore, various types of oils can be accurately separated, with separation efficiency approaching 100%. An integrated separation device successfully separates and recovers the four components. This research presents significant potential for efficient separation and recovery of complex components in oil-contaminated seawater.

Development Status of Solar-Driven Interfacial Steam Generation Support Layer Based on Polymers and Biomaterials: A Review

With the increasing shortage of water resources and the aggravation of water pollution, solar-driven interfacial steam generation (SISG) technology has garnered considerable attention because of its low energy consumption, simple operation, and environmental friendliness. The popular multi-layer SISG evaporator is composed of two basic structures: a photothermal layer and a support layer. Herein, the support layer underlies the photothermal layer and carries out thermal management, supports the photothermal layer, and transports water to the evaporation interface to improve the stability of the evaporator. While most research focuses on the photothermal layer, the support layer is typically viewed as a supporting object for the photothermal layer. This review focuses on the support layer, which is relatively neglected in evaporator development. It summarizes existing progress in the field of multi-layer interface evaporators, based on various polymers and biomaterials, along with their advantages and disadvantages. Specifically, mainly polymer-based support layers are reviewed, including polymer foams, gels, and their corresponding functional materials, while biomaterial support layers, including natural plants, carbonized biomaterials, and other innovation biomaterials are not. Additionally, the corresponding structure design strategies for the support layer were also involved. It was found that the selection and optimal design of the substrate also played an important role in the efficient operation of the whole steam generation system. Their evolution and refinement are vital for advancing the sustainability and effectiveness of interfacial evaporation technology. The corresponding potential future research direction and application prospects of support layer materials are carefully presented to enable effective responses to global water challenges.

Fluid Unidirectional Transport Induced by Structure and Ambient Elements across Porous Materials: From Principles to Applications

Spontaneous or nonspontaneous unidirectional fluid transport across multidimension can occur under specific structural designs and ambient elements for porous materials. While existing reviews have extensively summarized unidirectional fluid transport on surfaces, there is an absence of literature summarizing fluid's unidirectional transport across porous materials. This review introduces wetting phenomena observed on natural biological surfaces or porous structures. Subsequently, it offers an overview of diverse principles and potential applications in this field, emphasizing various physical and chemical structural designs (surface energy, capillary size, topographic curvature) and ambient elements (underwater, under oil, pressure, and solar energy). Applications encompass moisture-wicking fabric, sensors, skincare, fog collection, oil-water separation, electrochemistry, liquid-based gating, and solar evaporators. Additionally, significant principles and formulas from various studies are compelled to offer readers valuable references. Simultaneously, potential advantages and challenges are critically assessed in these applications and the perspectives are presented.

Developing Salt-Rejecting Evaporators for Solar Desalination: A Critical Review

Solar desalination, a green, low-cost, and sustainable technology, offers a promising way to get clean water from seawater without relying on electricity and complex infrastructures. However, the main challenge faced in solar desalination is salt accumulation, either on the surface of or inside the solar evaporator, which can impair solar-to-vapor efficiency and even lead to the failure of the evaporator itself. While many ideas have been tried to address this ″salt accumulation″, scientists have not had a clear system for understanding what works best for the enhancement of salt-rejecting ability. Therein, for the first time, we classified the state-of-the-art salt-rejecting designs into isolation strategy (isolating the solar evaporator from brine), dilution strategy (diluting the concentrated brine), and crystallization strategy (regulating the crystallization site into a tiny area). Through the specific equations presented, we have identified key parameters for each strategy and highlighted the corresponding improvements in the solar desalination performance. This Review provides a semiquantitative perspective on salt-rejecting designs and critical parameters for enhancing the salt-rejecting ability of dilution-based, isolation-based, and crystallization-based solar evaporators. Ultimately, this knowledge can help us create reliable solar desalination solutions to provide clean water from even the saltiest sources.

Facile fabrication of 3D Janus foams of electrospun cellulose nanofibers/rGO for high efficiency solar interface evaporation

Solar-powered interfacial evaporation is one of the most efficient state-of-the-art technologies for producing clean water via desalination. Herein, we report a novel bio-based nanofibrous foam for high efficiency solar interface evaporation. To this end, a hybrid membrane of cellulose nanofibers/graphene oxide (GO) is first fabricated by electrospinning coupled with in situ layer-by-layer self-assembly technique. After that, the membrane is subjected to a foaming process in an aqueous NaBH4, which effectively transforms the 2D membrane into a 3D foam. This structure can improve the photothermal conversion efficiency and also facilitate the water transport at the gas-water interface. In the meantime, the GO is converted to the reduced GO (rGO) with a higher light absorption efficiency. Finally, one side of the foam is hydrophobically modified via spray-coating with a fluorocarbon resin (FR) to obtain the Janus type 3D foam, namely FR@EC/rGO. The resultant 3D foam combines the functions of solar energy absorption in the upper layer and water pumping capability in the lower layer. It exhibits an extraordinary solar vapor conversion efficiency of 94.2 % and a fast evaporation rate of 1.83 kg m-2 h-1, showing high potential in future seawater desalination.

Multifunctional Solar Evaporator with Adjustable Island Structure Improves Performance and Salt Discharge Capacity of Desalination

Interfacial solar steam generation (ISSG) is the main method to get fresh water from seawater or wastewater. The balance between evaporation rate and salt resistance is still a major challenge for ISSG. Herein, a wood aerogel island solar evaporator (WAISE) with tunable surface structure and wettability by synthesizing poly(n-isopropylacrylamide)-modified multi-walled carbon nanotube photothermal layers. Compared to dense surface structure evaporators, interfacial moisture transport, thermal localization, and surface water vapor diffusion of WAISE are greatly promoted, and the evaporation rate of WAISE increased by 87.64%. WAISE allows for record performance of 200 h continuous operation in 20% NaCl solution without salt accumulation. In addition, the photo-thermal-electric device is developed based on WAISE with continuous water purification, power generation, and irrigation functions. This work provides a new direction for the development of multifunctional water purification systems.

One-step fabrication of all-in-one three-dimensional porous polypyrrole/polydopamine structure for efficient solar vapor generation

High-quality solar evaporators with all-in-one design are highly desirable for vapor generation, but relevant research is scarce. In this study, a three-dimensional (3D) porous polypyrrole/polydopamine (PPY/PDA) structure was fabricated via a simple heating-assisted rapid oxidative polymerization method. The obtained evaporator has multiple features, and can simultaneously provide rapid water transport channels (average pore sizes ∼ 18.37 nm), low thermal conductivity (0.071 W m-1 K-1), high solar absorbance (97.08%), and good mechanical properties. When it is employed as an evaporator, the calculated water evaporation rate is approximately 2.12 kg m-2h-1, which is comparable to other reported 3D evaporators. Additionally, the evaporator displays great potential for purification toward various nonpotable water, as well as reliable pure water yields in an outdoor application (from 8:00 am to 5:00 pm, the evaporator can produce at least 13.95 L of drinkable water for a 1 m2 sample). We believe that the proposed strategy to fabricate all-in-one evaporators has great significance for scientific research and practical applications.

Solar-Powered Interfacial Evaporation and Deicing Based on a 3D-Printed Multiscale Hierarchical Design

Solar-powered interfacial heating has emerged as a sustainable technology for hybrid applications with minimal carbon footprints. Aerogels, hydrogels, and sponges/foams are the main building blocks for state-of-the-art photothermal materials. However, these conventional three-dimensional (3D) structures and related fabrication technologies intrinsically fail to maximize important performance-enhancing strategies and this technology still faces several performance roadblocks. Herein, monolithic, self-standing, and durable aerogel matrices are developed based on composite photothermal inks and ink-extrusion 3D printing, delivering all-in-one interfacial steam generators (SGs). Rapid prototyping of multiscale hierarchical structures synergistically reduce the energy demand for evaporation, expand actual evaporation areas, generate massive environmental energy input, and improve mass flows. Under 1 sun, high water evaporation rates of 3.74 kg m-2 h-1 in calm air and 25.3 kg m-2 h-1 at a gentle breeze of 2 m s-1 are achieved, ranking among the best-performing solar-powered interfacial SGs. 3D-printed microchannels and hydrophobic modification deliver an icephobic surface of the aerogels, leading to self-propelled and rapid removal of ice droplets. This work shines light on rational fabrication of hierarchical photothermal materials, not merely breaking through the constraints of solar-powered interfacial evaporation and clean water production, but also discovering new functions for photothermal interfacial deicing.

Graphene-Encapsulated Bifunctional Catalysts with High Activity and Durability for Zn-Air Battery

Carbon-based electrocatalysts with both high activity and high stability are desirable for use in Zn-air batteries. However, the carbon corrosion reaction (CCR) is a critical obstacle in rechargeable Zn-air batteries. In this study, a cost-effective carbon-based novel material is reported with a high catalytic effect and good durability for the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER), prepared via a simple graphitization process. In situ growth of graphene is utilized in a 3D-metal-coordinated hydrogel by introducing a catalytic lattice of transition metal alloys. Due to the direct growth of few-layer graphene on the metal alloy decorated 3d-carbon network, greatly reduced CCR is observed in a repetitive OER test. As a result, an efficient bifunctional electrocatalytic performance is achieved with a low ΔE value of 0.63 V and good electrochemical durability for 83 h at a current density of 10 mA cm^-2 in an alkaline media. Moreover, graphene-encapsulated transition metal alloys on the nitrogen-doped carbon supporter exhibit an excellent catalytic effect and good durability in a Zn-air battery system. This study suggests a straightforward way to overcome the CCR of carbon-based materials for an electrochemical catalyst with wide application in energy conversion and energy storage devices.

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.

A robust and 3D-printed solar evaporator based on naturally occurring molecules

The interfacial solar desalination has been considered a promising method to address the worldwide water crisis without sophisticated infrastructures and additional energy consumption. Although various advanced solar evaporators have been developed, their practical applications are still restricted by the unsustainable materials and the difficulty of precise customization for structure to escort high solar-thermal efficiency. To address these issues, we employed two kinds of naturally occurring molecules, tannic acid and iron (III), to construct a low-cost, highly efficient and durable interfacial solar evaporator by three-dimensional (3D) printing. Based on a rational structural design, a robust and 3D-printed evaporator with conical array surface structure was developed, which could promote the light harvesting capacity significantly via the multiple reflections and anti-reflection effects on the surface. By optimizing the height of the conical arrays, the 3D-printed evaporator with tall-cone structure could achieve a high evaporation rate of 1.96 kg m^-2 h^-1 under one sun illumination, with a photothermal conversion efficiency of 94.4%. Moreover, this evaporator was also proved to possess excellent desalination performance, recycle stability, anti-salt property, underwater oil resistance, as well as adsorption capacity of organic dye contaminants for multipurpose water purification applications. It was believed that this study could provide a new strategy to fabricate low-cost, structural regulated solar evaporators for alleviating the dilemma of global water scarcity using abundant naturally occurring building blocks.

Superelastic 3D Assembled Clay/Graphene Aerogels for Continuous Solar Desalination and Oil/Organic Solvent Absorption

Superelastic, arbitrary-shaped, and 3D assembled clay/graphene aerogels (CGAs) are fabricated using commercial foam as sacrificial skeleton. The CGAs possess superelasticity under compressive strain of 95% and compressive stress of 0.09-0.23 MPa. The use of clay as skeletal support significantly reduces the use of graphene by 50%. The hydrophobic CGAs show high solvent absorption capacity of 186-519 times its own weight. Moreover, both the compression and combustion methods can be adopted for reusing the CGAs. In particular, it is demonstrated a design of 3D assembled hydrophilic CGA equipped with salt collection system for continuous solar desalination. Due to energy recovery and brine transport management promoted by this design, the 3D assembled CGA system exhibits an extremely high evaporation rate of 4.11 kg m-2  h-1 and excellent salt-resistant property without salt precipitation even in 20 wt% brine for continuous 36 h illumination (1 kW m-2 ), which is the best reported result from the solar desalination devices. More importantly, salts can be collected conveniently by squeezing and drying the solution out of the salt collection system. The work provides new insights into the design of 3D assembled CGAs and advances their applications in continuous solar desalination and efficient oil/organic solvent adsorption.

Sustainable Interfacial Evaporation System Based on Hierarchical MXene/Polydopamine/Magnetic Phase-Change Microcapsule Composites for Solar-Driven Seawater Desalination

Solar photothermal-driven interfacial evaporation is a promising technology with great potential for wastewater purification and seawater desalination. However, intermittent solar illumination and salt accumulation are still the major roadblocks of interfacial evaporation in practical applications. Herein, we developed a novel interfacial evaporation system based on the hierarchical MXene/polydopamine (PDA)/magnetic phase-change microcapsule composites (hereafter named "MXene/PDA@TiO₂/Fe₃O₄@C₂₂-HMC") integrated with natural wood. The microcapsule composites were fabricated by microencapsulating n-docosane as a phase-change material (PCM) core in a TiO₂/Fe₃O₄ composite shell and then coating a PDA layer, followed by surface-attaching with MXene nanosheets. The obtained MXene/PDA@TiO₂/Fe₃O₄@C₂₂-HMC exhibits a good optical absorption ability, high heat energy-storage capacity, and good hydrophilicity. This enables the MXene/PDA@TiO₂/Fe₃O₄@C₂₂-HMC-based evaporator to gain a high water evaporation rate of 2.09 kg m^-2 h^-1 under one-sun illumination. A combination of the microchannels in natural wood and the tiny gap between the microcapsules results in a rapid water transportation within the evaporation system, which effectively resists salt accumulation during the evaporating process. As a result, there was no salt crystal observed from the evaporator surface in a 10 wt % NaCl solution under three-sun illumination for 8 h. More importantly, the introduction of Fe₃O₄ nanoparticles into the TiO₂ shell endows the MXene/PDA@TiO₂/Fe₃O₄@C₂₂-HMC with magnetism, greatly enhancing the reusability and separability of the developed evaporator to undertake multicycle salt accumulation and washing processes for long-term desalination use. The latent heat release of the n-docosane core offers the developed evaporator a large amount of heat energy for continuous evaporation on a semi-cloudy day, increasing the total water production by 1.17 kg m^-2 compared to the conventional evaporator without a PCM. This study provides an effective solution for intermittent solar energy utilization and salt accumulation in the solar-driven interfacial evaporation systems of seawater desalination.

Solar Interface Evaporation System Assisted by Mirror Reflection Heat Collection Based on Sunflower Chasing the Sun

In this study, a photothermal material, C-CP/MnO₂, was prepared by compounding corrugated paper (CP) and MnO₂, with excellent photothermal conversion efficiency. The porous structure and the presence of oxygen-containing functional groups enabled the material to have a good water transport function and a fast vapor escape rate. The special semihollow structure also allowed C-CP/MnO₂ to have better thermal management and an evaporation rate that could reach 2.563 kg m^-2 h^-1 with an efficiency of 98.82% under 1 sun. The continuous arch structure inside C-CP/MnO₂ was able to induce the Marangoni effect to achieve continuous desalination of high-concentration brine. The mirror heat collector achieved efficient light capture on the material surface through multiple reflections of light. This could increase the amount of radiation on the material surface by nearly 80%, and the evaporation rate could reach 4.314 kg m^-2 h^-1 under 1 sun. Moreover, this study demonstrated the light propagation path by simulating the light using Zemax to verify the correctness of the experimental results. Inspired by the sunflower chasing the sun, we designed a chasing heat collection system powered by solar panels to achieve efficient evaporation outdoors. This provided new ideas for further development of solar interface evaporation and also provided guidance for other industrial applications.

3D Hydrogel Evaporator with Vertical Radiant Vessels Breaking the Trade-Off between Thermal Localization and Salt Resistance for Solar Desalination of High-Salinity

Delivering sufficient water to the evaporation surface/interface is one of the most widely adopted strategies to overcome salt accumulation in solar-driven interfacial desalination. However, water transport and heat conduction loss are positively correlated, resulting in the trade-off between thermal localization and salt resistance. Herein, a 3D hydrogel evaporator with vertical radiant vessels is prepared to surmount the long-standing trade-off, thereby achieving high-rate and stable solar desalination of high-salinity. Experiments and numerical simulations reveal that the unique hierarchical structure, which consists of a large vertical vessel channel, radiant vessels, and porous vessel walls, facilitates strong self-salt-discharge and low longitudinal thermal conductivity. With the structure employed, a groundbreaking comprehensive performance, under one sun illumination, of evaporation rate as high as 3.53 kg m^-2  h^-1 , salinity of 20 wt%, and a continuous 8 h evaporation is achieved, which thought to be the best reported result from a salt-free system. This work showcases the preparation method of a novel hierarchical microstructure, and also provides pivotal insights into the design of next-generation solar evaporators of high-efficiency and salt tolerance.

Inspired by the Nature: A Post-Printed Strategy to Efficiently Elaborate Parahydrophobic Surfaces

The lack of drinkable water is one of the most significant risks for the future of the humanity. Estimates show that in the near future, this risk will become the origin of massive migrations leading to humanitarian disaster. As consequence, the development of solutions to provide water is becoming ever more critical, and a significant effort is devoted to identifying new sources of water. Among the developed strategies, fog harvesting, which takes advantage of atmospheric water to provide potable water, is a solution of interest due to its potential in sustainable development. Unfortunately, this approach suffers from low yield. In the present work, we take inspiration from living species to design and elaborate surfaces with high potential for water harvesting applications. This work takes advantage of 3D-printing and post-printing functionalization to elaborate a strategy that allows modelling, printing, and functionalization of surfaces to yield parahydrophobic behavior. The roughness and surface morphology of the prepared surfaces were investigated. These characteristics were then related to the observed wettability and potential of the functionalized interfaces for water harvesting applications. This work highlights significant variations in surface wettability via surface modification; strong hydrophobic behavior was observed via modification with linear carboxylic acids particularly for surfaces bearing vertical blades (plate with vertical blades and grid with vertical blades).

Layer-by-Layer Assembled Smart Antibacterial Coatings via Mussel-Inspired Polymerization and Dynamic Covalent Chemistry

Bacterial colonization on the surface of medical implanted devices and bacterial infection-induced biofilm have been a lethal risk for patients of clinical treatment. While antibacterial coatings fabricated by layer-by-layer (LBL) assembly techniques have been well explored, the facile preparation of substrate-independent smart antibacterial coatings with on-demand antibiotics release profile and excellent antibacterial performance is still urgently needed. In this work, this goal is addressed by LBL assembly fabrication of robust antibacterial coatings using naturally occurring and commercially available building blocks (i.e., aminoglycosides, 5,6-dihydroxyindole, and formylphenylboronic acid) via the subsequentially performed mussel-inspired polymerization and dynamic covalent chemistries. The resulting antibacterial coatings on different substates all presente a dynamic feature (i.e., pH-responsive), on-demand antibiotics release properties, and highly effective antibacterial performance both in vitro and in vivo. It is envisioned that this work can expand the scope of LBL assembly technique toward the next generation of robust and universal antibacterial coating materials by using natural building blocks and readily available chemistries.