Hofmeister Effect-Enhanced Hydration Chemistry of Hydrogel for High-Efficiency Solar-Driven Interfacial Desalination

High-performance, salt-resistant, and stable wood-based solar evaporator equipped with sodium alginate-based functional skin

Harnessing renewable solar energy for photothermal evaporation and seawater desalination holds significant potential for alleviating freshwater scarcity. However, evaporators reported recently often suffer from limitations in environmental compatibility, salt resistance, and stability. Herein, we report a green and straightforward approach to fabricate a dual-layer solar evaporator (STF-wood) by equipping wood-based materials with a sodium alginate-based photothermal skin. The functional skin, synthesized through the chelation of tannic acid (TA), sodium alginate (SA), and Fe3+, not only exhibits excellent photothermal conversion efficiency but also forms a dense network that restricts the movement of free water, thereby enhancing the localized heat effect. Moreover, the positively charged surface of the skin can prevent the passage of salt ions through the Donnan effect, demonstrating superior salt resistance. STF-wood is capable of operating stably in seawater with an evaporation rate of 1.92 kg m-2 h-1 and maintains a similar rate even after undergoing 5-hour ultrasonic treatment. This work presents a sustainable and efficient solution to compensate for the shortcomings of environmental compatibility and operational stability for solar evaporator.

Cluster-directed ionic framework supramolecular hydrogel with high-temperature tolerability and enhanced water evaporation

Supramolecular hydrogels have been constructed with flexible 2D ionic framework assemblies comprised of a stick-shaped di-cationic pseudo-rotaxane and polyanionic nanoclusters through electrostatic interactions. This type of small-molecule hydrogel exhibits excellent thermal stability at high temperature and shows an efficient reduction of water evaporation enthalpy.

Ice-Confined Cryo-Polymerization of Sponge-Like Hydrogels with Self-Adapting Channel for Solar Water Purification

Polymer hydrogels are widely used in solar-driven water evaporation due to their controllable vaporization enthalpy, but the low water transport rates restrict their application. Here, a sponge-like polyacrylamide/carbon nanotube hydrogel is prepared by ice-confined cryo-polymerization, which possesses micro-size and non-swelling skeleton, and exhibits both hydrogel and sponge behaviors such as excellent squeezability and superior water transport capabilities about three orders of magnitude higher than that of conventional hydrogels. Moreover, the hydrogels can spontaneously regulate the size of internal channels to adjust the capillary force and thus they can support a water evaporation rate as high as 36.11 kg m-2 h-1 under collecting lens. Furthermore, the hydrogels show high water collection rate of 5.55 g g-1 under fog flow and the collected water can be quickly released by squeezing. The ice-confined cryo-polymerization provides a new way to develop distinctive materials combining the advantage of both hydrogel and sponge.

3D dual-network structure poly (vinyl alcohol)/cellulose nanofibers/MXene hydrogel evaporator with high-efficiency desalination for solar-driven water purification

Interfacial solar steam generation (ISSG) provides a sustainable solution to global water scarcity, yet achieving high efficiency, salt resistance, and long-term stability remains challenging. Here, we report a 3D umbrella-shaped poly (vinyl alcohol)/cellulose nanofiber (CNF)/MXene (PCM) hydrogel evaporator with a rigid-flexible dual-network structure for efficient solar desalination. The dual-network architecture, combining rigid CNF and flexible PVA chains, reduces water evaporation enthalpy by 18 % (from 2223.9 to 1825.2 J/g) through enhanced hydrogen bonding while improving mechanical strength by 68 %. The hierarchical porous structure enables rapid water transport and localized heat accumulation, achieving an evaporation rate of 2.09 kg m-2 h-1 with 86.37 % efficiency under one-sun irradiation. A self-regulating salt crystallization mechanism directs salt deposition to the hydrogel periphery, forming detachable rings that prevent performance degradation in 3.5-20 wt% brine. The evaporator demonstrates exceptional durability, maintaining >85 % efficiency over 8 weeks in 3.5 wt% brine through oxidation-resistant multilayer MXene (Ti3C2Tx) and CNF reinforcement. Outdoor testing yields a peak evaporation rate of 2.82 kg m-2 h-1 (34.7 % higher than lab-scale), with desalinated water meeting WHO drinking standards. This work provides a scalable, energy-efficient strategy for stable solar-driven water purification in diverse environments.

One-Step Enhances the Photothermal Performance of Lignin: Experimentation, Mechanism and Application

Solar-driven photothermal conversion technologies have gotten much attention for addressing the global freshwater crisis and energy shortage. However, several challenges remain regarding the applied materials with their single function, complex manufacturing process, and high raw material cost. Herein, the photothermal performance of the low-cost lignin was improved by the one-step hydroxymethyl modification with up to 52.16% of the maximum photothermal conversion efficiency of the modified lignin (Lg1-OH). The enhancement mechanism of the Lg1-OH was proposed by the structural analysis and simulation calculations. First, a larger hydrogen bond network strengthens the π-π stacking between the benzene rings and thus enhances the photothermal performance of lignin. Second, the conjugation effect of hydroxymethyl groups increases the electron cloud density of the benzene ring, ensuring more heat can be obtained by exciting more electrons under the same solar power. Subsequently, a photothermal gel (PG) was successfully prepared using Lg1-OH for solar-driven thermoelectric production and water purification. The thermoelectric device (TED) obtained the maximum power density of 20.85 W/m2 under 0.5 W/cm2 sun irradiation, and the evaporator reached a superior evaporation rate of 4.72 kg/(m2 h) under 0.3 W/cm2 sun irradiation. Additionally, no salt accumulation was found on the surface of the evaporator in a long period operation of 24 h. Besides, an outdoor solar-driven evaporation device achieved 8.58 kg/m2 of cumulative aquatic production in 9 h. This study offers a promising way for the commercial application of lignin in solar-driven electricity generation and water purification.

Dual Cross-Linking Coal Tar-Derived Phenolic Resin Porous Carbon-Based Hydrogel Solar Evaporators for Efficient Wastewater Purification

Porous carbon-based hydrogel evaporators show extensive application potential in the field of solar-driven water evaporation due to their wide availability, excellent hydrophilicity, and abundant porous structure. However, the closed pore structure of the single-molecule cross-linked hydrogel and the high production cost of the nanoporous carbon materials not only affect the salt resistance of the carbon-based hydrogel but also restrict its large-scale application. Herein, we developed a uniform porous APRC-PVA/PEG hydrogel evaporator by integrating poly(vinyl alcohol) (PVA)/polyethylene glycol (PEG) dual-network hydrogels with broadband solar-absorbing, cost-effective porous carbon nanosheets (APRC) derived from coal tar-based phenolic resin. The rich pores and three-dimensional double-network structure of the evaporator ensured excellent water transport performance and a high light absorption rate (≈98%). Meanwhile, the low thermal conductivity of the evaporator (dry: 0.09 W m-1 K-1; wet: 0.29 W m-1 K-1) reduces thermal loss to the bulk water, enabling a water evaporation rate of 1.45 kg m-2 h-1 under 1 sun irradiation and a low enthalpy of evaporation of 1614.605 J g-1. The evaporator also shows good potential in the field of brine, industrial wastewater, and organic dye wastewater.

Nanofibrous Hydrogel with Highly Salt-Resistant Radial/Vertical-Combined Structure for Efficient Solar Interfacial Evaporation

Hydrogel-based solar interfacial evaporators, featuring various channels such as random, unidirectional, and radial array, are considered effective for seawater desalination owing to their porous structure, lower evaporation enthalpy, and controllable water transport capacity. However, each individual array structure has its own strengths and limitations, influencing water transportation, thermal management, and salt rejection. By combining the benefits of each array configuration into a single evaporator, the evaporation performance can be maximized. Herein, the study develops a unique nanofibrous hydrogel-based solar evaporator featuring a combined radical/vertical array structure. This integrated structure with external radial and internal vertical channels endows this evaporator with excellent water transport capability and reduced heat loss, resulting in superior evaporation performance and high salty resistance. The addition of nanofibers into hydrogels not only enhances the hydrogel's stability but also facilitates water transport. Under 1 sun illumination, this evaporator can achieve an impressive evaporation rate of 4.62 kg m-2 h-1 with an energy efficiency of 149.57%. After 12 h of evaporation in a 20 wt.% NaCl solution, it still maintains an average evaporation rate of 3.98 kg m-2 h-1 with minimal salt accumulation, thereby exhibiting its exceptional salt resistance and durability.

Quantitative rationalization of the unexpectedly moderate water wettability of poly(vinyl alcohol) surfaces: thermodynamic evaluation and prediction of surface hydrogen bonding

In this work, a series of poly(vinyl alcohol) (PVA) films with defined but varied water wettability was prepared by curing as-prepared PVA films at systematically adjusted temperatures. The polar components of surface energy (γs,p) of the resulting PVA films were calculated and correlated with the molecular configurations of their surface OH groups-free OH (OHf), trans-hydrogen bonded OH (OHt), and gauche-hydrogen bonded OH groups (OHg)-with the aid of attenuated total reflectance Fourier transform infrared spectroscopy. By decomposing the γs,p values of the PVA films as a sum of the contributions from OHf, OHt, and OHg groups, the intrinsic γs,p components of and were calculated to be 8.0 mN m-1 and 9.8 mN m-1, respectively, which were substantially smaller than that of . This provided a thermodynamic foundation not only to rationalize the unexpectedly moderated surface hydrophilicity of PVA films but also to quantitatively predict the fHB component of hydrogen-bonded OH groups on their surfaces according to their water wettability.

Self-Generating Zwitterionic Polyurethane Foam for Solar-Driven Water Evaporation in Complex Environments

Solar-driven water evaporation has attracted increasing attention as an environmentally friendly method of water purification/desalination. However, the presence of biofouling and oil-fouling agents in natural water induces channel plugging and significantly decreases its efficiency. In this study, a self-generating zwitterionic polyurethane foam (ZPF) is fabricated by grafting a silylated hydrolysis-induced zwitterionic telomer (Si-HIZ), further spraying TiN/PDMS on the top as a solar evaporation device. The TiN/PDMS serves as a photothermal converter, and the ZPF serves as a water pump. The foam exhibits excellent evaporation performance, with a water evaporation rate of 1.51 kg m-2 h-1 and a photothermal conversion efficiency of 98.56%. When used underwater, the foam forms a hydration layer that effectively inhibits biofilm formation in the channels, allowing solar-driven water evaporation to occur normally after cocultivating in a bacterial suspension (Escherichia coli, Staphylococcus aureus, and Pseudomonas sp.) for 4 days. Moreover, it exhibits good anti-oil-fouling performance (underwater-oil contact angle = 151°) and resists 20 wt % NaCl solutions in solar-driven water evaporation. These results demonstrate that hydrolysis-induced zwitterionic polymers are promising materials for designing water purification/desalination devices, introducing new avenues for applications in complex environments.

Oil-Resistant and Wood-Inspired Superhydrophilic Poly(Vinyl Alcohol) Aerogel with Vertically Aligned Channels for Effective Solar Interfacial Desalination and Wastewater Treatment

Environmental pollution and sewage surges necessitate effective water purification methods. Solar interfacial evaporation offers a promising solution, which needs advancements in salt resistance, efficiency, and stability. Herein, inspired by the structure of wood, the unidirectional freeze-drying method was used to develop the vertically aligned channels and antioil-fouling poly(vinyl alcohol)-CNTs-waste carton fiber@polydopamine (PVA-CNTs-WCF@PDA) aerogel for desalination and wastewater treatment. The anisotropic three-dimensional porous structure of the aerogel enables it to rapidly transport water to the evaporation interface and resist salt deposition. Meanwhile, its unique structure is combined with CNTs and PDAs with excellent broadband spectral absorption capacity because the composite aerogels can interact with water molecules to reduce their water vaporization enthalpy. The composite aerogel shows an excellent photothermal evaporation rate (2.626 kg m-2 h-1) and efficiency (94.24%) under one-sun irradiation. Additionally, the composite aerogel interface evaporator can conduct 10 consecutive evaporations in 3.5% brine, indicating that it has the ability to desalination. Finally, it is also used to purify an oil-in-water emulsion and mine wastewater. It can be seen that there are no obvious oil droplets in the treated emulsion and that the treatment effect of mine wastewater reaches 89.13%. The composite aerogel showed excellent application prospects in the field of water purification.

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.

Integration of Bio-Enzyme-Treated Super-Wood and AIE-Based Nonwoven Fabric for Efficient Evaporating the Wastewater with High Concentration of Ammonia Nitrogen

The treatment of ammonia nitrogen wastewater (ANW) has garnered significant attention due to the ecology, and even biology is under increasing threat from over discharge ANW. Conventional ANW treatment methods often encounter challenges such as complex processes, high costs and secondary pollution. Considerable progress has been made in employing solar-induced evaporators for wastewater treatment. However, there remain notable barriers to transitioning from fundamental research to practical applications, including insufficient evaporation rates and inadequate resistance to biofouling. Herein, we propose a novel evaporator, which comprises a bio-enzyme-treated wood aerogel that serves as water pumping and storage layer, a cost-effective multi-walled carbon nanotubes coated hydrophobic/hydrophilic fibrous nonwoven mat functioning as photothermal evaporation layer, and aggregation-induced emission (AIE) molecules incorporated as anti-biofouling agent. The resultant bioinspired evaporator demonstrates a high evaporation rate of 12.83 kg m-2 h-1 when treating simulated ANW containing 30 wt% NH4Cl under 1.0 sun of illumination. AIE-doped evaporator exhibits remarkable photodynamic antibacterial activity against mildew and bacteria, ensuring outstanding resistance to biofouling over extended periods of wastewater treatment. When enhanced by natural wind under 1.0 sun irradiation, the evaporator achieves an impressive evaporation rate exceeding 20 kg m-2 h-1. This advancement represents a promising and viable approach for the effective removal of ammonia nitrogen wastewater.

A Fish-Gill-Inspired Biomimetic Multiscale-Ordered Hydrogel-Based Solar Water Evaporator for Highly Efficient Salt-Rejecting Seawater Desalination

Solar energy-driven steam generation is a renewable, energy-efficient technology that can alleviate the global clean water shortage through seawater desalination. However, the contradiction between resistance to salinity accretion and maintaining high water evaporation properties remains a challenging bottleneck. Herein, we have developed a biomimetic multiscale-ordered hydrogel-based solar water evaporator for efficient seawater desalination. The as-prepared solar water evaporator consists of highly ordered ultralong hydroxyapatite (HAP) nanowires as a supporting backbone and heat insulator, MXene as a sunlight absorber, and hydrophilic hyaluronic acid methacryloyl (HAMA) as an interfacial bonding agent, and a modifier to reduce the water evaporation enthalpy. The MXene/ultralong HAP nanowires/HAMA (MHH) photothermal hydrogel evaporator with the multiscale-ordered hierarchical structure mimics the fish-gill structure. The highly ordered alignment of ultralong HAP nanowires is realized at multiple scales, from the nanoscale to the microscale to the macroscale and from 1D to 2D to 3D in the as-prepared photothermal hydrogel evaporator. The high-performance MHH photothermal hydrogel water evaporator exhibits high efficiency of photothermal conversion, low water evaporation enthalpy, excellent heat management capability, and high solar water evaporation performance. The water evaporation enthalpy decreases from 2431 J g-1 (pure water) to 1113 J g-1 using the MHH photothermal hydrogel evaporator. As a result, the high-performance MHH hydrogel water evaporator can realize a high water evaporation rate of 6.278 kg m-2 h-1 under one sun illumination (1 kW m-2). Moreover, the as-prepared MHH hydrogel evaporator is able to achieve a water evaporation rate of 4.931 kg m-2 h-1 using the real seawater sample, exhibiting excellent salt-rejecting performance. It is expected that the as-prepared MHH hydrogel evaporator has promising applications in high-performance seawater desalination and wastewater purification using the sustainable solar energy.

Polyanionic Electrolyte Ionization Desalination Empowers Continuous Solar Evaporation Performance

Solar evaporation contributes to sustainable and environmentally friendly production of fresh water from seawater and wastewater. However, poor salt resistance and high degree of corrosion of traditional evaporators in brine make their implementation in real applications scarce. To overcome such deficiency, a polyanionic electrolyte functionalization strategy empowering excellent uniform desalination performance over extended periods of time is exploited. This 3D superhydrophilic graphene oxide solar evaporator design ensures stable water supply by the enhanced self-driving liquid capillarity and absorption at the evaporation interface as well as efficient vapor diffusion. Meanwhile, the polyanionic electrolyte functionalization implemented via layer-by-layer static deposition of polystyrene sodium sulfonate effectively regulates/minimizes the flux of salt ions by exploiting the Donnan equilibrium effect, which eventually hinders local salt crystallization during long-term operation. Stable evaporation rates in line with the literature of up to 1.68 kg m-2 h-1 are achieved for up to 10 days in brine (15‰ salinity) and for up to 3 days in seawater from Hangzhou Bay in the East China Sea (9‰ salinity); while, maintaining evaporation efficiencies of ≈90%. This work demonstrates the excellent benefits of polyanionic electrolyte functionalization as salt resistance strategy for the development of high-performance solar powered seawater desalination technology and others.

Considering Micro/nanostructures at the Surface of Photothermal Materials: A Game Changer in Correct Estimation of Evaporation Rate and Energy Conversion Efficiency in Interfacial Solar Vapor Generation Systems

Interfacial solar evaporator generation (ISVG) is a new, cost-effective, and eco-friendly emerging method for water desalination. Two main criteria for evaluating ISVG performance are evaporation rate (ṁ) and solar-to-vapor conversion efficiency (η). The main challenge of the previously presented models for the estimation of ṁ and η in 2D systems is that in most cases the calculated values are beyond the theoretical limits, ṁ > 1.47 kg m-2 h-1 and η > 100%, both of which are not acceptable from the thermodynamics viewpoint. Also, the recently presented strategy of reduced vaporization enthalpy for obtaining η < 100% is unacceptable from the thermodynamics approach for ISVG as a two-step continuous process. Therefore, this work aims to present a model and consequently new equations for the correct estimation of evaporation rate and energy conversion efficiency in two-dimensional (2D)-ISVG systems, which are consistent with their corresponding theoretical limits. The basis of the present model is discrimination between the projection area and evaporation area by considering the micro/nanostructures on the surface of interfacial support (photothermal material). This leads to the presentation of new equations for ṁ and η having consistency with thermodynamics laws. The presence of micro/nanostructures on the surface of photothermal material provides a higher evaporation area which is not considered in the previous models and led to theoretically inconsistent results. The results of the present study provide a theoretical basis for the correct estimation of the evaporation rate and energy conversion efficiency in 2D-ISVG systems in future works.

High-Performance Silicone Sponge Evaporators with Low Thermal Conductivity for Long-Term Solar Interfacial Evaporation and Freshwater Harvesting

Solar interfacial evaporation (SIE) has emerged as a highly promising approach for sustainable freshwater harvesting. However, maintaining a stable evaporation rate and achieving a high freshwater yield in high-salinity brines remain a significant challenge. In this study, we present the development of silicone sponge-based evaporators with a "free-salt" structure, designed to enhance the efficiency of SIE and freshwater collection. These evaporators, designated as PSS@Fe3O4/CNTs, were fabricated by grafting durable silicone onto a silicone sponge framework, followed by the incorporation of Fe3O4 nanoparticles and carbon nanotubes. The unique combination of exceptional photothermal properties and a controlled yolk-shell structure with low thermal conductivity enabled the PSS@Fe3O4/CNT evaporators to sustain a stable evaporation rate of 1.87 kg m-2 h-1 in real seawater over 200 h of continuous operation under 1 sun illumination. Importantly, no salt accumulation was observed on the evaporator surfaces, even when exposed to highly concentrated brines. In a closed system equipped with a condenser, these evaporators achieved freshwater production rates of 14.5 and 11.8 kg m-2 over 10 h from 10 and 20 wt % NaCl solutions, respectively, under 1 sun illumination. These values correspond to normalized production rates of 1.45 and 1.18 kg m-2 h-1, showcasing the consistent and efficient performance of the evaporators across varying salinity levels. Beyond salt rejection, the PSS@Fe3O4/CNT evaporators also demonstrated the ability to effectively remove various heavy metal ions (e.g., Cu2+ and Zn2+) and organic pollutants from contaminated water. This work provides valuable insights into innovative evaporator designs for efficient freshwater production from seawater and wastewater.

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.

Polyvinyl alcohol/sodium alginate hydrogels with tunable mechanical and conductive properties for flexible sensing applications

Despite the significant advantages of conductive hydrogels in flexible sensing, their further development is often hindered by limitations in strength and conductivity. In this work, the ionic conductive hydrogels with tunable mechanical and conductive properties were designed by utilizing sodium alginate (SA) to reinforce the polyvinyl alcohol (PVA) networks, followed by the respective introduction of Li2SO4, ZnSO4, and Fe2(SO4)3, leveraging the Hofmeister effect and metal coordination. Consequently, the mechanical properties (σ = 0.40-2.70 MPa) and conductivity (IC = 0.18-1.02 S/m) can be extensively tuned by adjusting the metal salts with varying oxidation states. Notably, Fe3+ ions can significantly enhance the mechanical properties, while Li+ ions more effectively improve conductivity. Interestingly, the PVA/SA/Zn2+ hydrogel achieves a balance between mechanical properties (σ = 1.86 MPa, ε = 1110 %) and conductivity (0.92 S/m), ascribing it to the multiple interactions including densification of polymer networks, formation of nanocrystalline domains, and ionic coordination effects. Furthermore, the conductive hydrogel also exhibits low strain detection limit (2.0 %), and demonstrated enormous potential in personal health monitoring and information transmission applications. This work presents a highly efficient and eco-friendly strategy for constructing hydrogels with tunable properties, while elucidating the mechanisms behind the enhanced mechanical and conductive performance.

Recent innovations in 3D solar evaporators and their functionalities

Interfacial solar evaporation (ISE) has emerged as a promising technology to alleviate global water scarcity via energy-efficient purification of both wastewater and seawater. While ISE was originally identified and developed during studies of simple double-layered two-dimensional (2D) evaporators, observed limitations in evaporation rate and functionality soon led to the development of three-dimensional (3D) evaporators, which is now recognized as one of the most pivotal milestones in the research field. 3D evaporators significantly enhance the evaporation rates beyond the theoretical limits of 2D evaporators. Furthermore, 3D evaporators could have multifaceted functionalities originating from various functional evaporation surfaces and 3D structures. This review summarizes recent advances in 3D evaporators, focusing on rational design, fabrication and energy nexus of 3D evaporators, and the derivative functions for improving solar evaporation performance and exploring novel applications. Future research prospects are also proposed based on the in-depth understanding of the fundamental aspects of 3D evaporators and the requirements for practical applications.

Solar-Driven Evaporator With "Starburst Turbine" Design Featuring Directional Salt Crystallization, Antibacterial, and Catalytic Multifunctionality for Efficient Water Purification

Facing the global challenge of water scarcity, solar-driven desalination is considered a sustainable technology for obtaining freshwater from seawater. However, issues such as uncontrolled salt crystallization and bacterial contamination limit its efficiency and practicality. This study proposes an innovative solar-driven evaporator designed to address these challenges using optimized shape design and advanced photothermal materials. Based on finite element analyses, cylindrical evaporators with a "Starburst Turbine" shape are designed and fabricated, achieving directional salt crystallization and a record-breaking water collection rate of 3.56 kg m-2 h-1 and an evaporation rate of 4.57 kg m-2 h-1 under one sun illumination. During continuous 60-h illumination tests, the evaporator maintained a stable evaporation rate, attributed to its excellent directional salt crystallization capability. Additionally, the evaporator demonstrates superior photodynamic antibacterial performance and photocatalytic degradation of organic pollutants. Under one sun illumination for 1 h, it achieves 100% sterilization of S. aureus and E. coli, and a 95.4% degradation of methylene blue (MB), demonstrating its potential to purify various wastewater types. These findings underscore the significant scientific and practical value of integrating antibacterial and photocatalytic functions into solar water purification materials, providing a sustainable solution to global water scarcity challenges and environmental protection.

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.

Dynamic Regulation of Hydrogen Bonding Networks and Solvation Structures for Synergistic Solar-Thermal Desalination of Seawater and Catalytic Degradation of Organic Pollutants

Although solar steam generation strategy is efficient in desalinating seawater, it is still challenging to achieve continuous solar-thermal desalination of seawater and catalytic degradation of organic pollutants. Herein, dynamic regulations of hydrogen bonding networks and solvation structures are realized by designing an asymmetric bilayer membrane consisting of a bacterial cellulose/carbon nanotube/Co2(OH)2CO3 nanorod top layer and a bacterial cellulose/Co2(OH)2CO3 nanorod (BCH) bottom layer. Crucially, the hydrogen bonding networks inside the membrane can be tuned by the rich surface -OH groups of the bacterial cellulose and Co2(OH)2CO3 as well as the ions and radicals in situ generated during the catalysis process. Moreover, both SO42- and HSO5- can regulate the solvation structure of Na+ and be adsorbed more preferentially on the evaporation surface than Cl-, thus hindering the de-solvation of the solvated Na+ and subsequent nucleation/growth of NaCl. Furthermore, the heat generated by the solar-thermal energy conversion can accelerate the reaction kinetics and enhance the catalytic degradation efficiency. This work provides a flow-bed water purification system with an asymmetric solar-thermal and catalytic membrane for synergistic solar thermal desalination of seawater/brine and catalytic degradation of organic pollutants.

Hofmeister Effect-Assisted Facile Fabrication of Self-Assembled Poly(Vinyl Alcohol)/Graphite Composite Sponge-Like Hydrogel for Solar Steam Generation

The use of hydrogel-based interfacial solar evaporators for desalination is a green, sustainable, and extremely concerned freshwater acquisition strategy. However, developing evaporators that are easy to manufacture, cheap, and have excellent porous structures still remains a considerable challenge. This work proposes a novel strategy for preparing a self-assembling sponge-like poly(vinyl alcohol)/graphite composite hydrogel based on the Hofmeister effect for the first time. The sponge-like hydrogel interfacial solar evaporator (PGCNG) is successfully obtained after combining with graphite. The whole process is environmental-friendly and of low-carbon free of freezing process. The PGCNG can be conventionally dried and stored. PGCNG shows impressive water storage performance and water transmission capacity, excellent steam generation performance and salt resistance. PGCNG has a high evaporation rate of 3.5 kg m-2 h-1 under 1 kW m-2 h-1 solar irradiation and PGCNG demonstrates stable evaporation performance over both 10 h of continuous brine evaporation and 30 cycles of brine evaporation. Its excellent performance and simple, scalable preparation strategy make it a valuable material for practical interface solar seawater desalination devices.

Hierarchical porous structure design and water activation in hydrogels containing hyperbranched peach gum polysaccharide for efficient solar water evaporation

Solar-powered interfacial evaporation is a developing and sustainable technique increasingly utilized in desalination and wastewater purification. This technology involves the creation of cellulose nanofiber (CNF)/polylactic acid (PLA) composite aerogels through the Pickering emulsion approach. Self-floating aero-hydrogel (E-VGP) with a hierarchical porous structure was formed on a viscous mixture containing polyvinyl alcohol (PVA), peach gum polysaccharide (PGP), and polypyrrole (PPy) via an in-situ polymerization process. Furthermore, by modifying the hydrolysis time of PGP with a hyperbranched polyhydroxy structure, VGP hybrid hydrogels of varying microscopic molecular sizes were produced. Additionally, solar vapor generators (SVG) with diverse macroscopic structures were fabricated using molds. The V8G4-12hP0.2 hybrid hydrogel, synthesized using PGP hydrolyzed for 12 h, exhibited an evaporation enthalpy of water at 1204 J g-1. This capacity effectively activates water and enables low enthalpy evaporation. Conversely, the macrostructural design allows the cylindrical rod raised sundial-shaped structure of SVG3 to possess an expanded evaporation area, minimize energy loss, and even harness additional energy from its nonradiative side. Consequently, this micro-macrostructural design enables SVG3 to attain an exceptionally high evaporation rate of 3.13 kg m-2 h-1 under 1 Sun exposure. Moreover, SVG3 demonstrates robust water purification abilities, suggesting significant potential for application in both desalination and industrial wastewater treatment.

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.

KOH Activated Carbon Coated 3D Wood Solar Evaporator with Highest Water Transport Height and Evaporation Rate for Clean Water Production

The water evaporation rate of 3D solar evaporator heavily relies on the water transport height of the evaporator. In this work, a 3D solar evaporator featuring a soil capillary-like structure is designed by surface coating native balsa wood using potassium hydroxide activated carbon (KAC). This KAC-coated wood evaporator can transport water up to 32 cm, surpassing that of native wood by ≈8 times. Moreover, under 1 kW m-2 solar radiation without wind, the KAC-coated wood evaporator exhibits a remarkable water evaporation rate of 25.3 kg m-2 h-1, ranking among the highest compared with other reported evaporators. The exceptional water transport capabilities of the KAC-coated wood should be attributed to the black and hydrophilic KAC film, which creates a porous network resembling a soil capillary structure to facilitate efficient water transport. In the porous network of coated KAC film, the small internal pores play a pivotal role in achieving rapid capillary condensation, while the larger interstitial channels store condensed water, further promoting water transport up more and micropore capillary condensation. Moreover, this innovative design demonstrates efficacy in retarding phenol from wastewater through absorption onto the coated KAC film, thus presenting a new avenue for high-efficiency clean water production.

Aerogel-Involved Triple-State Gels Resemble Natural Living Leaves in Structure and Multi-Functions

Natural plant leaves with multiple functions, for example, spectral features, transpiration, photosynthesis, etc., have played a significant role in the ecosystem, and artificial synthesis of plant leaves with multiple functions of natural ones is still a great challenge. Herein, this work presents an aerogel-involved living leaf (AL), most similar to natural ones so far, by embedding super-hydrophobic SiO2 aerogel microparticles in polyvinyl alcohol hydrogel in the presence of hygroscopic salt and chlorophyllin copper sodium to form solid-liquid-vapor triple-state gel. The AL shows a high spectral similarity with all sampled 15 species of natural leaves and exhibits ≈4-7 times transpiration speed higher than natural leaves. More importantly, AL can achieve several times higher photosynthesis than natural leaves without the energy provided by the respiratory action of natural ones. This work demonstrates the feasibility of creating ALs with natural leaf-like triple-state gel structures and multiple functions, opening up new avenues for energy conversion, environmental engineering, and biomimetic applications.

Enhancing Solar Steam Generation of Hydrogels via Silver Nanoparticle-Doped Cellulose Nanofibers

Solar steam generation (SSG) is regarded as an efficient approach for harnessing solar energy to purify polluted or saline water. Herein, we demonstrate a hydrogel composed of cellulose nanofibers (CNFs), polyethylenimine (PEI), and reduced graphene oxide (rGO) that functions as an independent solar steam generator, which shows enhanced solar water evaporation efficiency by incorporating silver nanoparticles (AgNPs). It presented that the presence of AgNPs increases the photothermal conversion efficiency and thermal conductivity of the evaporator and reduces the enthalpy of evaporation. As a result, an outstanding water evaporation rate of 3.62 kg m-2 h-1 and a photothermal conversion efficiency of 96.25% are successfully obtained under one sun illumination. Also, the resulting hydrogel exhibits exceptional mechanical properties, as well as outstanding desalination and salt-resistant abilities during prolonged seawater desalination. In oil/water mixtures, the evaporation of the hydrogel decreases to 2.94 kg m-2 h-1, owing to the oil layer barrier. This work paves a reference approach to produce easily addressed cellulose nanofiber (CNF)-based hydrogel evaporators with significantly enhanced evaporation rates.

Efficient Solar-Driven Interfacial Water Evaporator using Hydrogel Modified Carbon-Based Biomass with Abundant Microchannels

The conventional sea water desalination technologies are not yet adopted worldwide, especially in the third world countries due to their high capital cost as well as large energy requirement. To solve this issue in a sustainable way an interfacial solar water evaporation device is designed and proposed in this article using the branches of Prunus serrulata (PB). The PB has abundant microchannels and shows excellent photothermal conversion capability after carbonization. Moreover, the easy access to raw materials and the facile fabrication process makes the solar water evaporating device very cost effective for seawater desalination application. Experiments show that in the presence of the fabricated evaporator the evaporation rate of water can reach 3.5 kg m-2 h-1 under 1 sun, which is superior to many similar experimental devices. In addition, its advantages, such as effective sewage purification capability, low cost, and environmental friendliness, make this evaporator highly competitive in the extensive promotion of this technology and can be considered as a new sustainable solution for seawater desalination with great application potential and prospects.

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.

Sponge-like porous polyvinyl alcohol/chitosan-based hydrogel with integrated cushioning, pH-indicating and antibacterial functions

Developing a packaging material with integrated cushioning, intelligent and active functions is highly desired but remains challenging in the food industry. Here we show that a sponge-like porous hydrogel with pH-indicating and antibacterial additives can meet this requirement. We use polyvinyl alcohol and chitosan as the primary polymers to construct a hydrogel with hierarchical structures through a freeze-casting method in combination with salting-out treatment. The synergy of aggregated polymer chains and the sponge-like porous structure makes the hydrogel resilient and efficient in energy absorption. It also enables rapid movement of molecules/particles and fast reaction due to the large specific surface area of the pore structures and the large amount of free water in it, leading to a sensitive pH-indicating function. The hydrogel shows an obvious color variation within a wide pH range in 3 min. The silver nanoparticles are fixed in the dense polymer networks, enabling a lasting release of silver ions. The porous structure makes the silver ion reach the protected item in a short time, achieving an antibacterial effect against S. aureus and E. coli with little cytotoxicity. This work paves the way for fabricating multifunctional hydrogels for diverse advanced packaging systems.

MXene-Enhanced Ionovoltaic Effect by Evaporation and Water Infiltration in Semiconductor Nanochannels

In recent years, substantial attention has been directed toward energy-harvesting systems that exploit sunlight energy and water resources. Intensive research efforts are underway to develop energy generation methodologies through interactions with water using various materials. In the present investigation, we synthesized sodium vanadium oxide (SVO) nanorods with n-type semiconductor characteristics. These nanorods facilitate the initiation of capillary phenomena within nanochannels, thereby enhancing the interfacial area between nanomaterials and ions. The open-circuit voltage (VOC) was 0.8 V, and the short-circuit current (ISC) was 30 μA, which were continuously monitored at room temperature using a 0.1 M saltwater solution. Additionally, we achieved enhanced energy generation by efficiently converting light energy into thermal energy using MXene, a 2D material. This was accomplished through the photothermal effect, leveraging the inherent semiconductor characteristics. Under light exposure, the system exhibited improved performance attributed to heightened ion diffusion and increased conductivity. This phenomenon was a result of the concerted synergy between ions and electrons facilitated by a semiconductor nanofluidic channel. Ultimately, we demonstrated an application to showcase real-world viability. In this scenario, electricity was harvested through a smart buoy floating on the water, and, based on this, data from the surrounding environment was sensed and wirelessly transmitted.

Spontaneous thermal energy transfer and anti-gravitational water pumping using Al2O3 fiber-enhanced flexible nonwoven material as a high-performance and self-floating solar evaporator

Solar-driven evaporation is promising to address water scarcity. However, preserving the heat inside evaporators instead of allowing run-off, and synergistically utilizing it to wick water from the bulk, is still underexplored. Herein, a dual-functional bridge of longitudinal orientated channels of Al2O3 fibers (AOFs) embedded in a multi-layered nonwoven evaporator was proposed to create a buffer for spontaneous thermal conduction and anti-gravitational water pumping. As a self-floating system with high porosity and flexibility, benefiting from the strong water transporting ability and high thermal conductivity of the AOFs, a superhigh evaporation rate (2.79 kg m-2 h-1 under 1 sun) can be achieved with great stability and durability. This work highlights the potential of promoting thermal management using a large-scale vapour chamber and mass-producible nonwoven technology to prepare a high-performance evaporator for practical applications.

Cost-Effective 3D-Printed Bionic Hydrogel Evaporator for Stable Solar Desalination

Solar desalination using hydrogel evaporators is an eco-friendly, highly efficient means with natural sunlight for sustainable freshwater production. However, it remains challenging to develop a cost-effective and scalable method to prepare salt-resistant hydrogel evaporators for stable desalination. Here, inspired by tree transpiration and hierarchical porous structure, a 3D-printed bionic hydrogel evaporator (3DP-BHE) is designed for long-term solar desalination. Commercialized activated carbon (AC) is introduced into biomass starch skeleton as a solar light absorber to build 3DP-BHE in a cost-effective fashion ($10.14 m-2 of total materials cost). The bionic tree leaf layer for 94.01% light absorption and timely vapor diffusion. The bionic tree trunk layer with 3D printed bimodal porous structure for water transfer, thermal isolation, and salt ions convection and diffusion. With the unique bionic structure, the 3DP-BHE achieves a stable evaporation rate of 2.13 kg m-2 h-1 at ≈90.5% energy efficiency under one sun (1 kW m-2). During the 7-day desalination of 10 wt.% brine, a steady evaporation rate of 1.98 kg m-2 h-1 is maintained with a record-high cost-effectiveness (195.3 g h-1 $-1) manner. This 3DP-BHE will open significant opportunities for affordable solar desalination systems on multiple scales, from individual households to off-grid communities.

Well-designed lamellar reduced graphene oxide-based foam for high-performance solar-driven water purification

Although solar steam generation is promising for seawater desalination, it is less effective in purifying wastewater with both salt/heavy metal ions and organic contaminants. It is thus imperative to develop multifunctional integrated solar-driven water purification systems with high solar-thermal evaporation and photocatalytic degradation efficiencies. Herein, a lamellar reduced graphene oxide (L-RGO) foam with the vertical lamellar structure is fabricated by bidirectional-freezing, lyophilization, and slight chemical reduction for water purification. The unique vertical lamellar structure not only accelerates upward transport of water for facilitating water evaporation but also endows the L-RGO foam with superb high elasticity for tuning the interlayer distance and varying interactions between the oxygen-containing groups and water molecules to adjust water energy state. As a result, the L-RGO foam achieves a superb water evaporation rate of 2.40 kg m-2 h-1 along with an energy efficiency of 95.3 % under the compressive strain of 44.7 % under 1-sun irradiation. Equally importantly, the decoration of L-RGO foam with polypyrrole is capable of efficiently degrading organic pollutants while retaining high solar steam generation performances, exhibiting great potential in the comprehensive treatment of various water sources for relieving freshwater crisis.

Salt-rejecting 3D cone flowing evaporator based on bilayer photothermal paper for high-performance solar seawater desalination

Solar energy-driven water evaporation technology is a promising, low-cost and sustainable approach to alleviate the global clean water shortage, but usually suffers from low water evaporation rate and severe salt deposition on the water evaporation surface. In this work, a hydrophilic bilayer photothermal paper-based three-dimensional (3D) cone flowing evaporator was designed and prepared for stable high-performance seawater desalination with excellent salt-rejecting ability. The as-prepared bilayer photothermal paper consisted of MXene (Ti3C2Tx) and HAA (ultralong hydroxyapatite nanowires, poly(acrylic acid), and poly(acrylic acid-2-hydroxyethyl ester)). The accordion-like multilayered MXene acted as the efficient solar light absorber, and ultralong hydroxyapatite (HAP) nanowires served as the thermally insulating and supporting skeleton with a porous networked structure. A siphon effect-driven unidirectional fluid transportation unit in the 3D cone flowing evaporator could guide the concentrated saline flowing away from the evaporating surface to prevent salt deposition on the evaporation surface, avoiding severe deterioration of the performance in solar water evaporation. Furthermore, combining high solar light absorption and high photothermal conversion efficiencies, low water evaporation enthalpy (1838 ± 11 J g-1), and additional energy taken from the ambient environment, the as-prepared cone flowing evaporator exhibited a high water evaporation rate of 3.22 ± 0.20 kg m-2 h-1 for real seawater under one sun illumination (1 kW m-2), which was significantly higher than many values reported in the literature. This study provides an effective approach for designing high-performance solar energy-driven water evaporators for sustainable seawater desalination and wastewater purification.

Superhydrophobic sand evaporator with core-shell structure for long-term salt-resistant solar desalination

Solar-driven water evaporation, as an environmentally benign pathway, provides an opportunity for alleviating global clean water scarcity. However, the rapidly generated interfacial steam and localized heating could cause increased salt concentration and accumulation, deteriorating the evaporation performance and long-term stability. Herein, a novel superhydrophobic sand solar (FPPSD) evaporator with a core-shell structure was proposed through interface functionalization for continuous photothermal desalination. The collective behavior essence of the sand aggregate gave itself micron-scale self-organized pores and configurable shapes, generating desirable capillary force and supplying effective water-pumping channels. More importantly, combining the dopamine, polypyrrole (PPy), and 1H,1H,2H,2H-perfluorodecyltriethoxysilane (PFDTS) through π-π conjugation and multiple hydrogen bonding effects gave the FPPSD evaporator with stable superhydrophobic property and highly efficient photothermal conversion capability. Therefore, the FPPSD evaporator showed a continuous and stable photothermal performance even after 96 h continuous evaporation under 3-sun irradiation for 10 wt% saline solution, among the best values in the reported works of literature, demonstrating its excellent salt-resistance stability. Furthermore, this novel FPPSD evaporator displayed outstanding environmental stability that kept its initial water transport capacity even after being treated under harsh conditions for 30 days. With excellent salt-resistance ability and stable environmental stability, the FPPSD evaporator will provide an attractive platform for sustainable solar-driven water management.

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.

Natural lignocellulosic kapok fiber/MXene constructed hydrogel evaporators for high efficiency solar steam generation

Solar-driven interfacial evaporation (SDIE) is a green and sustainable technique for desalination. Hydrogel composite evaporators have been widely used for SDIE, but it is still challenging for the hydrogel evaporators to achieve uniform distribution of the light absorbing nanomaterials and at the same time possess satisfactory evaporation rate, durability and environmental applicability. We developed a 3D hydrogel evaporator with an asymmetric structure for high-efficiency SDIE. Natural kapok fibers, an important lignocellulosic plant fiber with a hollow structure, are decorated with MXene nanosheets for construction of one-dimensional photothermal conversion network. The top composite hydrogel serves as the light-absorption layer where MXene-modified kapok fibers are evenly dispersed in PVA hydrogel, while the bottom PVA hydrogel with an oriented structure acts as water delivery path. The evaporator exhibits a high solar evaporation rate and efficiency (2.49 kg·m-2·h-1 and 91.5 %, respectively) under one sun irradiation (1 kW·m-2). Even in a high salinity brine, emulsion and corrosive solutions, the evaporator can work normally with a slightly decreased evaporation rate. The 3D hydrogel evaporator with long-term stability and durability shows promising applications in purification of seawater and different waste water.

Bird's Nest-Shaped Sb2 WO6 /D-Fru Composite for Multi-Stage Evaporator and Tandem Solar Light-Heat-Electricity Generators

Herein, an integrated solar-thermal-power protocol is presented at a micro-nanoscopic level to maximize the energy utilization efficiency involving utilization period and utilization patterns, and the nexus of freshwater production and nanogeneration is realized. This sophisticated vaporization device is constructed with the merits of thermally confined evaporation space in favor of recycling latent heat of condensation and optimizing light absorption based on the local sunlight angle of incidence. Inspired by a bird's nest, Sb2 WO6 /D-Fructose composites are prepared as photothermal absorbers to achieve a superior water evaporation rate of 2.78 kg m-2  h-1 in the Multi-stage evaporator. In addition, a synergistic tandem photo thermal-electric device with a combination of solar-driven water evaporation and further waterflow-driven hydrovoltaic generation, which can output a stable voltage of up to 360.8 mV with effective utilization of steam energy and a limited water source, is exploited. Such integrated configurations pave a pathway for clean water production and renewable power generation simultaneously toward energy issues.

Making Nanofiber Membrane Stand on End to Construct Vertically Interfacial Evaporators for Efficient Solar Evaporation, Omnidirectional Solar Absorption, and Ultrahigh-Salinity Brine Desalination

Solar-driven interfacial desalination is widely considered to be a promising technology to address the global water crisis. This study proposes a novel electrospun nanofiber-based all-in-one vertically interfacial solar evaporator endowed with a high steam generation rate, steady omnidirectional evaporation, and enduring ultrahigh-salinity brine desalination. In particular, the electrospun nanofiber is collected into the tubular structure, followed by spraying with a dense crosslinked poly(vinyl alcohol) film, which renders them sufficiently strong for the preparation of a vertically array evaporator. The integrated evaporator made an individual capillary as a unit to form multiple thermal localization interfaces and steam dissipation channels, realizing zone heating of water. Thus a high steam generation rate exceeding 4.0 kg m-2 h-1 in pure water is demonstrated even under omnidirectional sunlight, and outperforms existing evaporators. Moreover, salt ions in the photothermal layer can be effectively transported to the water in capillaries and subsequently exchanged with the bulk water due to the strong action of capillary force, which ensures an ultrahigh desalination rate (≈12.5 kg m-2 h-1 under 3 sun) in 25 wt% concentration brine over 300 min. As such, this work provides a meaningful roadmap for the development of state-of-the-art solar-driven interfacial desalination.

Interfacial Solar Evaporation: From Fundamental Research to Applications

In the last decade, interfacial solar steam generation (ISSG), powered by natural sunlight garnered significant attention due to its great potential for low-cost and environmentally friendly clean water production in alignment with the global decarbonization efforts. This review aims to share the knowledge and engage with a broader readership about the current progress of ISSG technology and the facing challenges to promote further advancements toward practical applications. The first part of this review assesses the current strategies for enhancing the energy efficiency of ISSG systems, including optimizing light absorption, reducing energy losses, harvesting additional energy, and lowering evaporation enthalpy. Subsequently, the current challenges faced by ISSG technologies, notably salt accumulation and bio-fouling issues in practical applications, are elucidated and contemporary methods are discussed to overcome these challenges. In the end, potential applications of ISSG, ranging from initial seawater desalination and industrial wastewater purification to power generation, sterilization, soil remediation, and innovative concept of solar sea farm, are introduced, highlighting the promising potential of ISSG technology in contributing to sustainable and environmentally conscious practices. Based on the review and in-depth understanding of these aspects, the future research focuses are proposed to address potential issues in both fundamental research and practical applications.

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.

A Self-Adaptive and Regenerable Hydrogel Interfacial Evaporator with Adjustable Evaporation Area for Solar Water Purification

Solar-driven interfacial evaporation is a potential water purification solution. Here, a novel regenerable hydrogel interfacial evaporator is designed with tunable water production. Such an evaporator is fabricated by readily mixing hydroxypropyl chitosan (HPCS) and dibenzaldehyde-functional poly(ethylene glycol) (DF-PEG) at ambient conditions. Dynamic Schiff base bonds bestow on the HPCS/DF-PEG hydrogel (HDH) evaporator self-adaptivity and pH responsiveness. The as-prepared HDH is enabled to spontaneously change shape to adapt to different molds, endowing the evaporator with adjustable evaporation area. The water production performance of the intelligent evaporator is first evaluated using tunable evaporation index (TEI, the tunable evaporated water mass per hour), which can be altered from 0 kg h-1 to 3.21 kg h-1 under one sun. Besides, the large-scale evaporator can be expediently fabricated by virtue of the self-adaptivity. Benefiting from the pH responsiveness, the HDH evaporator is successfully regenerated with the removal of organic dye by the liquefaction-dialysis-regeneration operations. Meanwhile, the re-created evaporator maintains the self-adaptive characteristic and almost constant water evaporation rate compared to that of the initial evaporator. Therefore, this distinctive concept provides a facile strategy to develop smart and recyclable solar-driven interfacial evaporators for flexible water purification.

Amphibious Polymer Materials with High Strength and Superb Toughness in Various Aquatic and Atmospheric Environments

Herein, the fabrication of amphibious polymer materials with outstanding mechanical performances, both underwater and in the air is reported. A polyvinyl alcohol/poly(2-methoxyethylacrylate) (PVA/PMEA) composite with multiscale nanostructures is prepared by combining solvent exchange and thermal annealing strategies, which contributes to nanophase separation with rigid PVA-rich and soft PMEA-rich phases and high-density crystalline domains of PVA chains, respectively. Benefiting from the multiscale nanostructure, the PVA/PMEA hydrogel demonstrates excellent stability in harsh (such as acidic, alkaline, and saline) aqueous solutions, as well as superior mechanical behavior with a breaking strength of up to 34.8 MPa and toughness of up to 214.2 MJ m-3 . Dehydrating the PVA/PMEA hydrogel results in an extremely robust plastic with a breaking strength of 65.4 MPa and toughness of 430.9 MJ m-3 . This study provides a promising phase-structure engineering route for constructing high-performance polymer materials for complex load-bearing environments.

Ionization Engineering of Hydrogels Enables Highly Efficient Salt-Impeded Solar Evaporation and Night-Time Electricity Harvesting

Interfacial solar evaporation holds immense potential for brine desalination with low carbon footprints and high energy utilization. Hydrogels, as a tunable material platform from the molecular level to the macroscopic scale, have been considered the most promising candidate for solar evaporation. However, the simultaneous achievement of high evaporation efficiency and satisfactory tolerance to salt ions in brine remains a challenging scientific bottleneck, restricting the widespread application. Herein, we report ionization engineering, which endows polymer chains of hydrogels with electronegativity for impeding salt ions and activating water molecules, fundamentally overcoming the hydrogel salt-impeded challenge and dramatically expediting water evaporating in brine. The sodium dodecyl benzene sulfonate-modified carbon black is chosen as the solar absorbers. The hydrogel reaches a ground-breaking evaporation rate of 2.9 kg m-2 h-1 in 20 wt% brine with 95.6% efficiency under one sun irradiation, surpassing most of the reported literature. More notably, such a hydrogel-based evaporator enables extracting clean water from oversaturated salt solutions and maintains durability under different high-strength deformation or a 15-day continuous operation. Meantime, on the basis of the cation selectivity induced by the electronegativity, we first propose an all-day system that evaporates during the day and generates salinity-gradient electricity using waste-evaporated brine at night, anticipating pioneer a new opportunity for all-day resource-generating systems in fields of freshwater and electricity.

Visible Light Locking in Mineral-Based Composite Phase Change Materials Enabling High Photothermal Conversion and Storage

Fully stimulating the capacity of light-driven phase change materials (PCMs) for efficient capture, conversion, and storage solar energy requires an ingenious combination of PCMs, supporting structural materials, and photothermal materials, therefore motivating the synergistic effects between the components. Herein, this work thoroughly explores the interaction forces between PCMs and supporting structural materials and the synergy between PCMs and photothermal materials in photothermal conversion. Rejoicingly, when capitalizing on the prepared directional channel structure of hierarchically porous composite aerogel (PEPG) as a supporting structural material, a superior paraffin wax (PW) encapsulation rate of 85.11% is achieved, and the prepared PEPG2-PW has a high phase change enthalpy of 182.9 J/g. The van der Waals force and Lewis acid-base action between PEPG and PW molecules reveal the excellent stabilities of PEPG-PW. More importantly, the PEPG2-PW has an ultrahigh photothermal conversion efficiency of 95.2% under 1 sun irradiation and durability. Most importantly, the COMSOL Multiphysics software calculations demonstrate that transparent PW can anchor sunlight on the surface of graphite nanoplates, converting it into heat by enhancing the loss of graphite backbone lattice vibrations, and the accumulated heat is then stored in molten PW. This work provides some design principles for high-efficiency solar-thermal conversion materials.

Synergistic Dual-Mechanism Localized Heat Channeling and Spectrum-Tailored Liquid Metal Hydrogels for Efficient Solar Water Evaporation and Desalination

Photothermal hydrogels featuring broadband light absorption abilities and highly hydrated networks provide an appealing mass-energy transfer platform for water evaporation by using solar energy. However, the targeted delivery of solar heat energy to power the water evaporation process remains challenging. Herein, enlightened by metal-phenolic coordination chemistry and camouflaged architecture, photothermal hydrogels with dual-mechanism vaporization structure are tactfully designed via a rational interfacial engineering and integration strategy to enable near-µm heat confinement and highly efficient light-to-heat conversion ability. The spectrum-tailored liquid metal droplet (LMGAs-FeIII ) and optimized carbon-wrapped silver nanowire sponge (Ag@C750 ) are integrally built as photothermal promotors/channels and jointly embedded into a highly hydratable poly(vinyl alcohol) hydrogel, denoted as PALGH, to synergistically boost water molecule activation and interfacial vaporization behavior by triggering robust photothermal performance. As a result, under one sun irradiation, the all-embracing PALGH hydrogel evaporation system achieves a brine evaporation rate to a high level of 3.47 kg m-2 h-1 , and >19 L m-2 clean water of PALGH is ideally delivered daily when purifying natural seawater. This work offers not only a rational design principle to create sophisticated photothermal materials but also replenishes insight into solar heat generation and water transportation in a cross-media system.

Simultaneous Solar-Thermal Desalination and Catalytic Degradation of Wastewater Containing Both Salt Ions and Organic Contaminants

Although solar steam generation is promising in generating clean water by desalinating seawater, it is powerless to totally degrade organic contaminants in the seawater. Herein, solar steam generation and catalytic degradation are integrated to generate clean water by simultaneous solar-driven desalination and catalytic degradation of wastewater containing both salt ions and organic contaminants. Stepwise decoration of three-dimensional nickel foam with polypyrrole, reduced graphene oxide (RGO), and cobalt phosphate is realized to obtain polypyrrole/RGO/cobalt phosphate/nickel foam (PGCN) hybrids for solar-driven desalination and catalytic degradation of wastewater containing antibiotics and salt ions. The oxygen-containing groups of the RGO integrated with the porous nickel foam make the porous PGCN hybrid hydrophilic and ensure the upward transport of water to the evaporation surface, and the oxygen vacancies of the cobalt phosphate allow the PGCN to generate abundant highly active singlet oxygen that could still exhibit excellent catalytic degradation performances in the high salinity and highly alkaline environment of seawater. In addition to the high solar light absorbance and satisfactory solar-thermal conversion efficiency of polypyrrole and RGO, the thermally conductive nickel foam skeleton can effectively transfer the heat generated by the solar-thermal energy conversion to the adjacent cobalt phosphate catalyst and nearby wastewater, achieving a solar-thermal-promoted catalytic degradation of organic contaminants. Therefore, a high pure water evaporation rate of 2.08 kg m-2 h-1 under 1 sun irradiation and 100% catalytic degradation of Norfloxacin and dyes are achieved. The PGCN hybrid is highly efficient in purifying seawater containing 10 ppm Norfloxacin and simultaneously achieves a high purification efficiency of 100 kg m-2 h-1.