Bioinspired Self-Standing, Self-Floating 3D Solar Evaporators Breaking the Trade-Off between Salt Cycle and Heat Localization for Continuous Seawater Desalination

Bioinspired Structured Metal-Insulator-Metal Metamaterials with Gradient Resonator for High Efficiency and Solar Selective Absorption

Efficient utilization of solar energy is crucial in addressing energy challenges. Solar selective absorption materials, like metal-insulator-metal (MIM) absorbers, are highly efficient in converting solar energy to heat due to their strong solar absorption and minimal radiation loss. However, traditional planar MIM absorbers have narrow solar absorption bands and limited spectral tuning, restricting their practical use. Inspired by marine diatoms, this study designs and fabricates a structured MIM metamaterial (SMM) to achieve omnidirectional and polarization-insensitive selective absorption. The SMM features a concave-structured design with gradient resonance cavities, significantly expanding absorption across the solar spectrum and enabling tailored electromagnetic responses for selective absorption in different wavelength bands. With a thickness of just 180 nm, the SMM absorber shows outstanding selective absorption, reaching up to 91% absorptivity in the 0.3-2.5 µm and emissivity only 0.09 in the infrared range. The SMM absorber also exhibits size insensitivity, reducing design constraints in practical applications. In terms of photothermal conversion, the SMM absorber demonstrates stable performance, achieving a surface temperature of 165 °C under 3 sun illumination. Compared to planar MIM structures, this structured design significantly enhances solar absorption without affecting infrared emissivity, offering a novel approach to improving selective absorption performance.

Biomass-Derived Gradient and Aligned Structured Aerogel for Sustainable Agricultural Irrigation

Interface evaporation-driven hydroelectric systems integrating water purification and energy collection offer the potential for sustainable agricultural irrigation. However, achieving high evaporation rates and efficient energy harvesting poses challenges, particularly in optimizing evaporation and water transport. This study develops a gradient-aligned structured aerogel (GA aerogel), composed of biomass materials such as cellulose and chitosan, which utilizes efficient water transport through aligned cellulose channels, unique ion management in nanoscale channels, and chitosan's ability to reduce evaporation energy consumption, thereby enhancing water and energy harvesting performance. The GA aerogel achieves a solar absorption rate of 91.4%, an evaporation rate of 2.5 kg m-2 h-1, an output power of 680 nW cm-2, and stable operation for over 120 h. Furthermore, by integrating a series array with capacitive energy storage, the system utilizes harvested electrical energy to irrigate plants with purified water, promoting sustainable agriculture and providing insights for designing biomass-based solar evaporators.

Solar Evaporators for Saline Water: Sustainable Clean Water Harvesting and Critical Mineral Resources Extraction

Solar-driven interfacial water evaporation (SIWE) can efficiently utilize solar energy to separate or extract various ions from saline water, providing an environmentally friendly, economical, and sustainable approach to clean water and critical mineral resources harvesting. However, for ongoing practical implementation, solid salt accumulation at the interface will inevitably impair the SIWE performance, while direct disposal of residual concentrated brine poses significant environmental risks. As such, advancing solar evaporators for sustainable clean water harvesting and critical mineral resources extraction is pivotal in the resources-energy-environment nexus. Critically, this review spotlights the latest research progress in engineering nonselective salt-rejecting solar evaporators (NS-SRSEs) for sustainable desalination, emphasizing interfacial structural design and surface modification. We then delineate our endeavors aimed at the construction strategies of selective salt-extraction solar evaporators (S-SESEs) for getting access to critical mineral resources such as uranium and lithium. Finally, current challenges and opportunities are outlined in the high-value saline water utilization of NS-SRSE and S-SESE for real-world applications that balance high efficiency, durability, and adaptability with a low environmental impact. Looking ahead, we anticipate ongoing advancements in promoting solar evaporators from laboratory research to practical applications, contributing to global efforts in sustainable water management and critical mineral resources recovery.

Advancing Efficiency in Solar-Driven Interfacial Evaporation: Strategies and Applications

Solar-driven interfacial evaporation (SDIE) has emerged as a promising technology for addressing global water scarcity by utilizing solar-thermal conversion and evaporation at the air/material/water interface. The exceptional performance of these systems has attracted significant interest; it is imperative to establish rigorous and scientific standards for evaluating effectiveness, optimizing system design, and ensuring efficient practical applications. In this Review, we propose consensus criteria for accurately assessing system performance and guiding future advancements. We then explore the fundamental mechanisms driving system synergy, emphasizing how material compositions, microscopic hierarchical material structures, and macroscopic three-dimensional spatial architecture designs enhance solar absorption and photothermal conversion; balance heat confinement with water pathway optimization; manage salt resistance; and regulate enthalpy during vaporization. These matched coordination strategies are crucial for maximizing the target SDIE efficiency. Additionally, we investigate the practical applications of SDIE technologies, focusing on cutting-edge progress and versatile water purification, combined with atmospheric water harvesting, salt collection, electric generation, and photothermal deicing. Finally, we highlight the challenges and exciting opportunities for advancing research, emphasizing future efforts to integrate fundamental principles, system-level collaboration, and application-driven approaches to boost sustainable and highly efficient water and energy technologies. By linking system performance evaluation with optimization strategies for influencing factors, we offer a comprehensive overview of the field and a future outlook that promotes highly efficient clean water production and synergistic applications.

An All-Passive and Macropatterned Architecture Design for Water Harvesting

Solar evaporation designs show great promise in water harvesting without electricity inputs. Unfortunately, they have been heavily limited by a low water yield. To overcome this challenge, we introduced a new architecture featuring both system-level and materials-level designs. At the system level, we implemented a macropatterned architecture with a decoupled design for water evaporation and condensation to enhance water yield efficiency. This design also ensures that condensed water droplets do not block the solar evaporation process. At the materials level, solar selective heating and radiative cooling were applied to improve passive water yield performance. As a proof of concept, our design showed an indoor water collection rate of 2.06 kg m-2 h-1 under one sun and an average outdoor water collection rate of 1.85 kg m-2 h-1 over five consecutive days. The decoupled, all-passive, and macropatterned architecture offers substantial potential for commercial water collection applications toward mitigating global water scarcity.

Making Interfacial Solar Evaporation of Seawater Faster than Fresh Water

Interfacial solar evaporation-based seawater desalination is regarded as one of the most promising strategies to alleviate freshwater scarcity. However, the solar evaporation rate of real seawater is significantly constricted by the ubiquitous salts present in seawater. In addition to the common issue of salt accumulation on the evaporation surface during solar evaporation, strong hydration between salt ions and water molecules leads to a lower evaporation rate for real seawater compared to pure water. Here a facile and general strategy is developed to reverse this occurrence, that is, making real seawater evaporation faster than pure water. By simply introducing specific mineral materials into the floating photothermal evaporator, ion exchange at air-water interfaces directly results in a decrease in seawater evaporation enthalpy, and consequently achieves much higher seawater evaporation rates compared to pure water. This process is spontaneously realized during seawater solar evaporation. Considering the current enormous clean water production from evaporation-based desalination plants, such an evaporation performance improvement can remarkably increase annual clean water production, benefiting millions of people worldwide.

Antibacterial Janus cellulose/MXene paper with exceptional salt rejection for sustainable and durable solar-driven desalination

The scarcity of freshwater resources and increasing demand for drinking water have driven the development of durable and sustainable desalination technologies. Although MXene composites have shown promise due to their excellent photothermal conversion and high thermal conductivity, their high hydrophilicity often leads to salt precipitation and low durability. In this study, we present a novel Cellulose (CF)/MXene paper with a Janus hydrophobic/hydrophilic configuration for long-term and efficient solar-driven desalination. The paper features a dual-layer structure, with the upper hydrophobic layer composed of CF/MXene paper exhibiting convexness to serve as a photothermal layer with exceptional salt rejection properties. Simultaneously, the bottom porous layer made of CF acts as an efficient thermal insulation. This unique design effectively minimizes heat loss and facilitates efficient water transportation. The Janus CF/MXene paper demonstrates a high evaporation rate of 1.11 kg m-2h-1 and solar thermal conversion efficiency of 82.52 % under 1 sun irradiation. Importantly, even after 2500 h of operation in a simulated seawater environment, the paper maintains a stable evaporation rate without significant salt deposition and biodegradation due to an antibacterial rate exceeding 90 %. These findings highlight the potential of the Janus CF/MXene paper for scalable manufacturing and practical applications in solar-driven desalination.

Highly efficient solar steam evaporation via elastic polymer covalent organic frameworks monolith

Three-dimensional solar steam evaporators with efficient water purification performance have received increasing attention recently. Herein, elastic polymer covalent organic frameworks (PP-PEG) containing PEG chains with intriguing adaptability to guests are prepared by forming porphyrin rings. PP-PEG foams demonstrate full spectrum absorbance and excellent photothermal conversion properties. Through well-designed thermal management and optimization of the hydrophilicity and PEG chain length, we obtain a highly efficient solar evaporator with an evaporation rate of 4.89 kg m-2 h-1 under 1 sun in self-contained mode. The optimized solar evaporation rate is increased to 18.88 kg m-2 h-1 under 1 sun with a facile truncated cone reflector, exceeding all known solar steam evaporators. This innovative design holds immense promise for desalination and water purification owing to its simple preparation, high efficiency and durability.

Spatial Confinement Engineered Gel Composite Evaporators for Efficient Solar Steam Generation

Recently, solar-driven interfacial evaporation (SDIE) has been developed quickly for low-cost and sustainable seawater desalination, but addressing the conflict between a high evaporation rate and salt rejection during SDIE is still challenging. Here, a spatial confinement strategy is proposed to prepare the gel composite solar evaporator (SCE) by loading one thin hydrogel layer onto the skeleton of a carbon aerogel. The SCE retains the hierarchically porous structure of carbon aerogels with an optimized water supply induced by dual-driven forces (capillary effects and osmotic pressure) and takes advantage of both aerogels and hydrogels, which can gain energy from air and reduce water enthalpy. The SCE has a high evaporation rate (up to 4.23 kg m-2 h-1 under one sun) and excellent salt rejection performance and can maintain structural integrity after long-term evaporation even at high salinities. The SDIE behavior, including heat distribution, water transport, and salt ion distribution, is investigated by combining theoretical simulations and experimental results. This work provides new inspiration and a theoretical basis for the development of high-performance interfacial evaporators.

Hofmeister effect induced water activation of hydrogel and its applications for the accelerated solar evaporation in brine

Solar-driven desalination has emerged as a promising approach to address water scarcity caused by the decreasing supply of freshwater. Reducing the enthalpy of water vaporization is crucial for enhancing the efficiency of solar-powered desalination. In this study, inspired by the Hofmeister effect, we developed a highly hydratable network hydrogel evaporator to achieve a superior evaporation rate in brine compared with pure water. The evaporator comprised a carbonized layer as the photothermal layer and a chitosan aerogel hydrogel as the hydratable matrix. The hydrogel exhibited a dramatically reduced vaporization enthalpy of 1397 J/g and a significant evaporation rate of 2.38 kg m-2 h-1 when exposed to seawater. These results demonstrated the superior performance of hydrogel compared with pure water (1.91 kg m-2 h-1). Excellent evaporation rates and outstanding salt resistance ensured efficient coordination for practical long-term desalination applications. Further investigations revealed that the remarkable evaporation performance of the carbonized chitosan (CCS) hydrogel in brine environments was attributed to its hydrability, which was regulated by Cl-. According to the Hofmeister effect, Cl- accelerated the hydration chemistry in CCS and suppressed the associated crystallinity, which resulted in a lower enthalpy of vaporisation owing to a higher amount of intermediate water. With its superior evaporation performance in brine and comprehensive theoretical simulation analysis, this study presents an achievable and economical strategy for simultaneously addressing the water and energy crises.

Simultaneous Salt Rejection and Heat Localization Via Engineering Macrochannels in Morning Glory-Shaped 3D Evaporator

Solar desalination is a promising solution for alleviating water scarcity due to its low-cost, environmentally friendly, and off-grid capabilities. However, simultaneous salt rejection and heat localization remain challenging, as the rapid salt convection often results in considerable heat loss. Herein, this challenge is overcome via a facile design: i) isolating high-temperature and high-salt zones by rationally designing morning glory-shaped wick structures and ii) bridging high-salt zones and bulk water with low-tortuosity macrochannels across low-temperature surfaces. The salinity gradient in the macrochannels passively triggers convective flow, facilitating the rapid transfer of salt ions from the high-salt zone to the bulk water. Meanwhile, the macrochannels are spatially isolated from the high-temperature zone, preventing heat loss during salt convection and thereby achieving a high evaporation rate (≈3 kg m-2 h-1) and superior salt rejection even in highly concentrated real seawater. This work provides new insights into salt rejection strategies and advances practical applications for sustainable seawater desalination.

Interface Structure Strengthening of a Mesoporous Silicon/Expanded Perlite Microevaporator for Efficient Solar-Driven Interfacial Evaporation

Solar-driven interfacial evaporation is one of the cutting-edge technologies for seawater desalination and wastewater purification. Herein, a floating carbon-coated silica microsphere/expanded perlite integrated interfacial microevaporator (HEPCL) is reported. The carbon nanolayer allows the HEPCL to have better broadband light absorption performance than natural graphite and graphene oxide. Through the low density of expanded perlite, HEPCL particles can self-float on the water surface and self-aggregate into an integrated whole under surface tension, which enhances the heat collection capacity. The hierarchical porous structure of the HEPCL has a continuous water absorption capacity. Notably, water molecules adsorbed in the HEPCL have a high desorption energy, which reduces the water evaporation enthalpy (1621 kJ/kg), making it easy to remove with external energy. Thanks to the design merits, the HEPCL achieves a water evaporation rate of 1.551 kg m-2 h-1 (efficiency of 94.85%) under 1 sun irradiation and may inspire a practicable solution of water scarcity.

Dual-Interface Solar Evaporator with Highly-Efficient Thermal Regulation via Suspended Multilayer Design

Facing the increasing global shortage of freshwater resources, this study presents a suspended multilayer evaporator (SMLE), designed to tackle the principal issues plaguing current solar-driven interfacial evaporation technologies, specifically, substantial thermal losses and limited water production. This approach, through the implementation of a multilayer structural design, enables superior thermal regulation throughout the evaporation process. This evaporator consists of a radiation damping layer, a photothermal conversion layer, and a bottom layer that leverages radiation, wherein the bottom layer exhibits a notable infrared emissivity. The distinctive feature of the design effectively reduces radiative heat loss and facilitates dual-interface evaporation by heating the water surface through mid-infrared radiation. The refined design leads to a notable evaporation rate of 2.83 kg m-2 h-1. Numerical simulations and practical performance evaluations validate the effectiveness of the multilayer evaporator in actual use scenarios. This energy-recycling and dual-interface evaporation multilayered approach propels the design of high-efficiency solar-driven interfacial evaporators forward, presenting new insights into developing effective water-energy transformation systems.

Thermo-adaptive interfacial solar evaporation enhanced by dynamic water gating

Solar-driven evaporation offers a sustainable solution for water purification, but efficiency losses due to heat dissipation and fouling limit its scalability. Herein, we present a bilayer-structured solar evaporator (SDWE) with dynamic fluidic flow mechanism, designed to ensure a thin water supply and self-cleaning capability. The porous polydopamine (PDA) layer on a nickel skeleton provides photothermal functionality and water microchannels, while the thermo-responsive sporopollenin layer on the bottom acts as a switchable water gate. Using confocal laser microscopy and micro-CT, we demonstrate that this unique structure ensures a steady supply of thin water layers, enhancing evaporation by minimizing latent heat at high temperatures. Additionally, the system initiates a self-cleaning process through bulk water convection when temperature drops due to salt accumulation, thus maintaining increased evaporation efficiency. Therefore, the optimized p-SDWE sample achieved a high evaporation rate of 3.58 kg m-2 h-1 using 93.9% solar energy from 1 sun irradiation, and produces 18-22 liters of purified water per square meter of SDWE per day from brine water. This dynamic water transport mechanism surpasses traditional day-night cycles, offering inherent thermal adaptability for continuous, high-efficiency evaporation.

Self-Flipping Solar Seesaw Evaporators Leverage Scaling to De-Scale

Salt scaling poses a significant obstacle to the practical implementation of solar-driven evaporation for desalination. Attempts to mitigate scaling by enhancing mass transfer often lead to a compromise in evaporation efficiency due to associated heat loss. In the present work, a novel seesaw evaporator with a Janus structure to harness scaling for periodic self-descaling is reported. The seesaw evaporators are facilely fabricated by delignifying balsa wood and subsequently single-sided spray-coating it with soot and polydimethylsiloxane (PDMS). This unique Janus structure enables the evaporator to float on the brine while ensuring an ample supply of solution for evaporation. During evaporation, salt ions are transported directionally toward the cocked end of the evaporator to form scaling, triggering the seesaw evaporator to flip once a threshold is reached. The accumulated salts re-dissolve back into the solution. By adjusting the tilt angle, the evaporator can achieve an impressive evaporation rate of up to 2.65 kg m-2 h-1 when evaporating an 8 wt.% NaCl solution. Remarkably, these evaporators maintain a stable evaporation rate during prolonged 120 h operation and produce ≈3.93-6.35 L m⁻2·day⁻¹ of freshwater from simulated brines when assembled into an evaporation device.

Kirigami enabled reconfigurable three-dimensional evaporator arrays for dynamic solar tracking and high efficiency desalination

A kirigami-engineered composite hydrogel membrane is exploited for the construction of three dimensional (3D) solar-tracking evaporator arrays with outstanding evaporation performance and salt tolerance. The hybrid nanofiber network in the hydrogel membrane offers favorable water transport dynamics combined with excellent structural robustness, which are beneficial for the engineering of 3D dynamic structures. Periodic triangular cuts patterned into the membrane allow formation and reconfiguration of 3D conical arrays controlled by uniaxial stretching. With these structures, the tilt angles of the membrane surface are actively tuned to follow the solar trajectory, leading to a solar evaporation rate ~80% higher than that of static planar devices. Furthermore, the tapered 3D flaps and their micro-structured surfaces are capable of localized salt crystallization for prolonged solar desalination, enabling a stable evaporation rate of 3.4 kg m-2 hour-1 even in saturated brine. This versatile design may facilitate the implementation of solar evaporators for desalination and provide inspirations for other soft functional devices with dynamic 3D configurations.

Photoreaction Drives Efficient, Precise, and Sustainable Additive Manufacturing

Additive manufacturing, normally referred to as three-dimensional (3D) printing, has been maturing rapidly in recent years and widely utilized in various industrial fields, because it can create predesigned functional products with sophisticated structures that are basically difficult to achieve using traditional methods. Among all 3D printing technologies, vat photopolymerization has attracted much attention because of its outstanding advantages such as fast printing speed, high precision, and ease of formulating. In recent years, many breakthroughs in photopolymerization based 3D printing have been achieved by photoreaction design regarding photopolymerizable monomers, photoinitiating systems, inhibition functions, light sourcs, etc., but challenges remain. This Perspective attempts to highlight these great advances regarding the promotion of printing efficiency, accuracy, and sustainability. At the end, several challenges, such as longer-wavelength printing, printing of functional materials, and multimaterial printing, are discussed, which must be carefully addressed to meet the increasing requirements of future high-performance additive manufacturing.

Versatile GO/ANFs Aerogel for Highly Efficient Solar-Powered Water Purification in Wide Environments

Solar-driven interfacial evaporation is a very promising choice for producing clean water. Despite the considerable investigation of pure NaCl brine purification, solar-driven complex water purification, such as real-world seawater desalination as well as domestic and industrial wastewater treatment, has rarely been investigated, mainly due to its compositions being much more complicated than NaCl brine. Herein, we developed a graphene oxide/aramid nanofiber (GO/ANFs) aerogel by a freeze-drying process. The GO/ANFs aerogel combined opened porous microchannels, superhydrophilicity, anti-oil-fouling capacity, enhanced broad-spectrum light absorption (more than 92%), and good solar/heat management. These integrated properties enabled the GO/ANFs aerogel to be an advanced solar interfacial evaporator for efficient freshwater production with the characteristics of localized heat conversion, quick water transport, and salt crystallization inhibition, and the rate of steam production rate was as high as 2.25 kg m-2 h-1 upon exposure to 1 solar irradiation. Importantly, the high-water-vapor generation rate was maintained even under complicated conditions, including real-world seawater, dye water, emulsions, and corrosive liquid environments. Considering its promising adaptability to a wide range of environments, this work hopes to inspire the development of brine desalination, wastewater purification, clean water production, and solar energy utilization.

Gradient Graphene Spiral Sponges for Efficient Solar Evaporation and Zero Liquid Discharge Desalination with Directional Salt Crystallization

Solar desalination is a promising strategy to utilize solar energy to purify saline water. However, the accumulation of salt on the solar evaporator surface severely reduces light absorption and evaporation performance. Herein, a simple and eco-friendly method to fabricate a 3D gradient graphene spiral sponge (GGS sponge) is presented that enables high-rate solar evaporation and zero liquid discharge (ZLD) desalination of high-salinity brine. The spiral structure of the GGS sponge enhances energy recovery, while the gradient network structures facilitate radial brine transport and directional salt crystallization, which cooperate to endow the sponge with superior solar evaporation (6.5 kg m-2 h-1 for 20 wt.% brine), efficient salt collection (1.5 kg m-2 h-1 for 20 wt.% brine), ZLD desalination, and long-term durability (continuous 144 h in 20 wt.% brine). Moreover, the GGS sponge shows an ultrahigh freshwater production rate of 3.1 kg m-2 h-1 during the outdoor desalination tests. A continuous desalination-irrigation system based on the GGS sponge for crop growth, which has the potential for self-sustainable agriculture in remote areas is demonstrated. This work introduces a novel evaporator design and also provides insight into the structural principles for designing next-generation solar desalination devices that are salt-tolerant and highly efficient.

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.

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.

Anisotropic MXene/Poly(vinyl alcohol) Composite Hydrogels with Vertically Oriented Channels and Modulated Surface Topography for Efficient Solar-Driven Water Evaporation and Purification

Hierarchical structure and surface topography play pivotal roles in developing high-performance solar-driven evaporators for clean water production; however, there exists a notable gap in research addressing simultaneous modulation of internal microstructure and surface topography in hydrogels to enhance both solar steam generation performance and desalination efficiency. Herein, anisotropic poly(vinyl alcohol)/MXene composite hydrogels for efficient solar-driven water evaporation and wastewater purification are fabricated using a template-assisted directional freezing approach followed by precise surface wettability modulation. The resultant composite hydrogels exhibit vertically oriented channels that ensure fast water supply during evaporation, and their poly(vinyl alcohol) skeletons can reduce the vaporization enthalpy of the water in the hydrogels. The incorporation of MXene sheets enables efficient solar light absorption and solar-thermal conversion while providing structural reinforcement to the hydrogels. More importantly, the as-created undulating solar-thermal surface, featuring modulated hydrophilic troughs and hydrophobic crests, significantly enhances solar-thermal conversion efficiency, thereby boosting solar evaporation performances. As a result, the fabricated hydrogel-based evaporator exhibits an impressive evaporation rate of 2.55 kg m-2 h-1 under 1 sun irradiation, coupled with long-term durability and desalination stability. Notably, the outstanding mechanical robustness of the hydrogel further enables high portability through a readily achievable process of reversible dehydration/hydration.

3D-Printed Liquid Metal-in-Hydrogel Solar Evaporator: Merging Spectrum-Manipulated Micro-Nano Architecture and Surface Engineering for Solar Desalination

Solar desalination driven by interfacial heating is considered a promising technique to alleviate the freshwater shortage crisis. However, its further extension and application are confined by factors such as highlighted salt accumulation, inferior energy efficiency, and poor durability. Herein, a microsized eutectic gallium-indium (EGaIn) core-shell nanodroplet (denoted as LMTE) with photo-cross-linking and photothermal traits, stabilized by allyl glycidyl ether (AGE)-grafting tannic acid (TA), is explored as the solar absorber for broadband light absorbing and localized micro-nano heat channeling. The LMTE nanodroplets are formulated directly with highly hydrated polymers and photosensitive species to successfully develop a water-based photothermal ink suitable for digital light processing (DLP) 3D printing. As a demonstration, the LMTE composite hydrogel-forged milli-conical needle arrays with metal-phenolic network (MPN)-engineered wettability and photothermal enhancement can be printed by the digital light processing (DLP) technique and designed rationally via a bottom-up strategy. The 3D-printing hydrogel evaporator is composed of spectrum-tailored EGaIn nanodroplets for efficient photon harvesting and MPN-coated milli-cone arrays for water supplying with micro-nano channeling, which function cooperatively to bestow the 3D solar evaporator with superior solar-powered water evaporation (2.96 kg m-2 h-1, 96.93% energy efficiency) and excellent solar desalination (salt cycle and site-specific salt crystallization). Furthermore, a robust steam generating/collecting system of the 3D solar evaporator is demonstrated, providing valuable guidance for building a water-energy-agriculture nexus.

Boosting the Viable Water Harvesting in Solar Vapor Generation: From Interfacial Engineering to Devices Design

Continuously increasing demand for the life-critical water resource induces severe global water shortages. It is imperative to advance effective, economic, and environmentally sustainable strategies to augment clean water supply. The present work reviews recent reports on the interfacial engineering to devices design of solar vapor generation (SVG) system for boosting the viability of drinkable water harvesting. Particular emphasis is placed on the basic principles associated with the interfacial engineering of solar evaporators capable of efficient solar-to-thermal conversion and resulting freshwater vapor via eliminating pollutants from quality-impaired water sources. The critical configurations manufacturing of the devices for fast condensation is then highlighted to harvest potable liquid water. Fundamental and practical challenges, along with prospects for the targeted materials architecture and devices modifications of SVG system are also outlined, aiming to provide future directions and inspiring critical research efforts in this emerging and exciting field.

Rational Design of a Hydrophilic Core-Hydrophobic Shell Yarn-Based Solar Evaporator with an Underwater Aerophilic Surface for Self-Floating and High-Performance Dynamic Water Purification

Interfacial solar vapor generation holds great promise for alleviating the global freshwater crisis, but its real-world application is limited by the efficiently choppy water evaporation and industrial production capability. Herein, a self-floating solar evaporator with an underwater aerophilic surface is innovatively fabricated by weaving core-shell yarns via mature weaving techniques. The core-shell yarns possess capillary water channels in the hydrophilic cotton core and can trap air in the hydrophobic electrospinning nanofiber shell when submerged underwater, simultaneously realizing controllable water supplies, stable self-flotation, and great thermal insulation. Consequently, the self-floating solar evaporator achieves an evaporation rate of 2.26 kg m-2 h-1 under 1 sun irradiation, with a reduced heat conduction of 70.18 W m-2. Additionally, for the first time, a solar evaporator can operate continuously in water with varying waveforms and intensities over 24 h, exhibiting an outdoor cumulative evaporation rate of 14.17 kg m-2 day-1.

A Lotus Seedpods-Inspired Interfacial Solar Steam Generator with Outstanding Salt Tolerance and Mechanical Properties for Efficient and Stable Seawater Desalination

Interfacial solar steam generators (ISSGs) can capture solar energy and concentrate the heat at the gas-liquid interface, resulting in efficient water evaporation. However, traditional ISSGs have limitations in long-term seawater desalination processes, such as limited light absorption area, slow water transport speed, severe surface salt accumulation, and weak mechanical performance. Inspired by lotus seedpods, a novel ISSG (rGO-SA-PSF) is developed by treating a 3D warp-knitted spacer fabric with plasma (PSF) and combining it with sodium alginate (SA) and reduces graphene oxide (rGO). The rGO-SA-PSF utilizes a core-suction effect to achieve rapid water pumping and employs aerogel to encapsulate the plasma-treated spacer yarns to create the lotus seedpod-inspired hydrophilic stems, innovatively constructing multiple directional water transport channels. Simultaneously, the large holes of rGO-SA-PSF on the upper layer form lotus seedpod-inspired head concave holes, enabling efficient light capture. Under 1 kW m-2 illumination, rGO-SA-PSF exhibits a rapid evaporation rate of 1.85 kg m-2  h-1 , with an efficiency of 96.4%. Additionally, it shows superior salt tolerance (with no salt accumulation during continuous evaporation for 10 h in 10% brine) and self-desalination performance during long-term seawater desalination processes. This biomimetic ISSG offers a promising solution for efficient and stable seawater desalination and wastewater purification.

Hierarchical nanofibrous and recyclable membrane with unidirectional water-transport effect for efficient solar-driven interfacial evaporation

Solar-driven interfacial evaporation technology has attracted significant attention for water purification. However, design and fabrication of solar-driven evaporator with cost-effective, excellent capability and large-scale production remains challenging. In this study, inspired by plant transpiration, a tri-layered hierarchical nanofibrous photothermal membrane (HNPM) with a unidirectional water transport effect was designed and prepared via electrospinning for efficient solar-driven interfacial evaporation. The synergistic effect of the hierarchical hydrophilic-hydrophobic structure and the self-pumping effect endowed the HNPM with unidirectional water transport properties. The HNPM could unidirectionally drive water from the hydrophobic layer to the hydrophilic layer within 2.5 s and prevent reverse water penetration. With this unique property, the HNPM was coupled with a water supply component and thermal insulator to assemble a self-floating evaporator for water desalination. Under 1 sun illumination, the water evaporation rates of the designed evaporator with HNPM in pure water and dyed wastewater reached 1.44 and 1.78 kg·m-2·h-1, respectively. The evaporator could achieve evaporation of 11.04 kg·m-2 in 10 h under outdoor solar conditions. Moreover, the tri-layered HNPM exhibited outstanding flexibility and recyclability. Our bionic hydrophobic-to-hydrophilic structure endowed the solar-driven evaporator with capillary wicking and transpiration effects, which provides a rational design and optimization for efficient solar-driven applications.

Shape-Memory Three-Dimensional Evaporators with High Portability for Efficient Solar-Driven Freshwater Production

Solar-driven water evaporation can alleviate the severe water scarcity situation in a nonpolluting and sustainable manner. Although the design of integrated three-dimensional (3D) solar evaporators has been proven to be effective in achieving ultrahigh evaporation rates and energy efficiency, their scalable application is still hindered by complex manufacturing processes and poor portability. Herein, we report a highly portable shape-memory 3D solar evaporator by depositing MXene on low-cost lignin-cellulosic sponges for freshwater production. When not in use, the 3D evaporator can be compressed into a thin film with up to 89.3% volume reduction, ensuring minimal space occupation and high portability. When needed, due to the shape-memory effect, the 3D structure can be rapidly restored by swelling the compressed film in water, resulting in an efficient 3D solar evaporator. This 3D evaporator exhibits not only a high evaporation rate of 2.48 kg m-2 h-1 under 1 sun illumination but also excellent long-term stability and recyclability. In addition, the 3D evaporator itself can serve as a water reservoir without requiring a continuous water supply during evaporation, showing remarkable application flexibility. This work opens a new perspective for manufacturing highly portable and efficient 3D solar evaporators and may facilitate their progress from the laboratory to commercial applications.

Three-Dimensional Spiral Evaporator with Side Channels for Efficient Solar-Driven Water Purification

Solar evaporators have the advantages of not consuming fossil fuels, being environmentally friendly, and nonpolluting, offering a promising sustainable method to obtain fresh water and alleviate the worldwide freshwater shortage crisis. In this work, we report that high-performance solar evaporators can be facilely fabricated by processing a cost-effective polypyrrole (PPy)-coated nonwoven fabric (PCNF) into a three-dimensional (3D) spiral structure and introducing side channels for vapor escape. The coated PPy layer ensures excellent photothermal properties and the chemical stability of the evaporator. Meanwhile, the as-created spiral structure of the evaporator can significantly increase the effective evaporation area and harvest energy from the environment, greatly stimulating the evaporation. The side opening channels can effectively facilitate the escape of vapor generated inside the 3D spiral structure, avoid the internal vapor accumulation, and ultimately promote the evaporation of the inner surface, leading to a boost of the evaporation performance. Combining these features, the resulting evaporator exhibits an ultrahigh evaporation rate of 3.26 kg m-2 h-1 and an energy efficiency of 138% under 1-sun irradiation. More importantly, we show that this evaporator can also be used to collect fresh water from soil and sand, demonstrating its great applicability for obtaining potable water in arid areas.

A hierarchical porous aerohydrogel for enhanced water evaporation

Natural solar-powered steam generation provides a promising strategy to deal with deteriorating water resources. However, the practical applications of this strategy are limited by the tedious manufacturing of structures at micro-nano levels to concentrate heat and transport water to heat-localized regions. Herein, this work reports the fabrication of hierarchically porous aerohydrogel with enhanced light absorption and thermal localization at the air-solid interface. This aerohydrogel steam generator is fabricated by a simple yet controllable micropore generation approach to assemble air and hydrogel into hierarchically porous gas-solid hybrids. The tunable micropore size in a wide range from 99±49µm to 316±58μm not only enables contrasting sunlight absorptance (0.2 - 2.5µm) by reducing the reflection of solar light but also harnesses water transportation to the heating region via a capillary force-driven liquid flow. Therefore, a solar-vapor conversion efficiency of 91.3% under one sun irradiation was achieved using this aerohydrogel evaporator, reaching a ready evaporation rate of 2.76kg m-2 h-1 and 3.71kg m-2 h-1 under one and two sun irradiations, respectively. Our work provides a versatile and scalable approach to engineering porous hydrogels for highly efficient steam generation and opens an avenue for other potential practical applications based on this aerohydrogel.