Carbon Materials for Solar Water Evaporation and Desalination

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.

Three-Dimensional Double-Layer Multi-Stage Thermal Management Fabric for Solar Desalination

Water scarcity is a serious threat to the survival and development of mankind. Interfacial solar steam generation (ISSG) can alleviate the global freshwater shortage by converting sustainable solar power into thermal energy for desalination. ISSG possesses many advantages such as high photothermal efficiency, robust durability, and environmental friendliness. However, conventional evaporators suffered from huge heat losses in the evaporation process due to the lack of efficient thermal management. Herein, hydrophilic Tencel yarn is applied to fabricate a three-dimensional double-layer fabric evaporator (DLE) with efficient multi-stage thermal management. DLE enables multiple solar absorptions, promotes cold evaporation, and optimizes thermal management. The airflow was utilized after structure engineering for enhanced energy evaporation efficiency. The evaporation rate can reach 2.86 kg·m-2·h-1 under 1 sun (1 kW·m-2), and 6.26 kg·m-2·h-1 at a wind speed of 3 m·s-1. After a long duration of outdoor operation, the average daily evaporation rate remains stable at over 8.9 kg·m-2, and the removal rate of metal ions in seawater reaches 99%. Overall, DLE with efficient and durable three-dimensional multi-stage thermal management exhibits excellent practicality for solar 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.

Manipulating 2D Membrane Interlayer Channels with Accelerated Mass-Transfer Behavior to Boost Solar Desalination

The scarcity of fresh water necessitates sustainable and efficient water desalination strategies. Solar-driven steam generation (SSG), which employs solar energy for water evaporation, has emerged as a promising approach. Graphene oxide (GO)-based membranes possess advantages like capillary action and Marangoni effect, but their stacking defects and dead zones of flexible flakes hinders efficient water transportation, thus the evaporation rate lag behind unobstructed-porous 3D evaporators. Therefore, fundamental mass-transfer approach for optimizing SSG evaporators offers new horizons. Herein, a universal multi-force-fields-based method is presented to regularize membrane channels, which can mechanically eliminate inherent interlayer stackings and defects. Both characterization and simulation demonstrate the effectiveness of this approach across different scales and explain the intrinsic mechanism of mass-transfer enhancement. When combined with a structurally optimized substrate, the 4Laponite@GO-1 achieves evaporation rate of 2.782 kg m-2 h-1 with 94.48% evaporation efficiency, which is comparable with most 3D evaporators. Moreover, the optimized membrane exhibits excellent cycling stability (10 days) and tolerance to extreme conditions (pH 1-14, salinity 1%-15%), verifies the robust structural stability of regularized channels. This optimization strategy provides simple but efficient way to enhance the SSG performance of GO-based membranes, facilitating their extensive application in sustainable water purification technologies.

Tree-Inspired Aerogel Comprising Nonoxidized Graphene Flakes and Cellulose as Solar Absorber for Efficient Water Generation

As global freshwater shortages worsen, solar steam generation (SSG) emerges as a promising, eco-friendly, and cost-effective solution for water purification. However, widespread SSG implementation requires efficient photothermal materials and solar evaporators that integrate enhanced light-to-heat conversion, rapid water transportation, and optimal thermal management. This study investigates using nonoxidized graphene flakes (NOGF) with negligible defects as photothermal materials capable of absorbing over 98% of sunlight. By combining NOGF with cellulose nanofibers (CNF) through bidirectional freeze casting, we created a vertically and radially aligned solar evaporator. The hybrid aerogel exhibited exceptional solar absorption, efficient solar-to-thermal conversion, and improved surface wettability. Inspired by tree structures, our design ensures rapid water supply while minimizing heat loss. With low NOGF content (∼10.0%), the NOGF/CNF aerogel achieves a solar steam generation rate of 2.39 kg m-2 h-1 with an energy conversion efficiency of 93.7% under 1-sun illumination, promising applications in seawater desalination and wastewater purification.

Green Synthesis of Polyurethane Sponge-Grafted Calcium Alginate with Carbon Ink Aerogel with High Water Vapor Harvesting Capacity for Solar-Driven All-Weather Atmospheric Water Harvesting

Atmospheric water harvesting (AWH) technology is a new strategy for alleviating freshwater scarcity. Adsorbent materials with high hygroscopicity and high photothermal conversion efficiency are the key to AWH technology. Hence, in this study, a simple and large-scale preparation for a hygroscopic compound of polyurethane (PU) sponge-grafted calcium alginate (CA) with carbon ink (SCAC) was developed. The PU sponge in the SCAC aerogel acts as a substrate, CA as a moisture adsorber, and carbon ink as a light adsorber. The SCAC aerogel exhibits excellent water absorption of 0.555-1.40 g·g-1 within a wide range of relative humidity (40-80%) at 25 °C. The SCAC aerogel could release adsorbed water driven by solar energy, and more than 92.17% of the adsorbed water could be rapidly released over a wide solar intensity range of 1.0-2.0 sun. In an outdoor experiment, 57.517 g of SCAC was able to collect 32.8 g of clean water in 6 h, and the water quality meets the drinking water standards set by the World Health Organization. This study suggests a new approach to design promising AWH materials and infers the potential practical application of SCAC aerogel-based adsorbents.

Adaptive Thermal Management Radiative Cooling Smart Window with Perfect Near-Infrared Shielding

The architectural window with spectrally selective features and radiative cooling is an effective way to save building energy consumption. However, architectural windows that combine both functions are currently based on micro-nano photonic structures, which undoubtedly hinder their commercial application due to the complexity of manufacture. Herein, a novel tunable visible light transmittance radiative cooling smart window (TTRC smart window) with perfect near-infrared (NIR) shielding ability is manufactured via a mass-producible scraping method. TTRC smart window presents high luminous transmittance (Tlum = 56.8%), perfect NIR shielding (TNIR = 3.4%), bidirectional transparency adjustment ability unavailable in other transparent radiative coolers based on photonic structures (ΔTlum = 54.2%), and high emittance in the atmospheric window (over 94%). Outdoor measurements confirm that smart window can reduce 8.2 and 6.6 °C, respectively, compared to ordinary glass and indium tin oxide (ITO) glass. Moreover, TTRC smart window can save over 20% of annual energy in the tropics compared to ITO and ordinary glass. The simple preparation method employed in this work and the superior optical properties of the smart window have significantly broadened the scope of application of architectural windows and advanced the commercialization of architectural windows.

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.

Confined and spontaneously transformed oxidation structures due to the intrinsic heterogeneous surface morphology of C3N monolayer

Identifying the oxidation structure of two-dimensional interfaces is crucial to improve surface chemistry and electronic properties. Beyond graphene with only phenyl rings, a novel carbon-nitrogen material, C3N, presents an intrinsic heterogeneous surface morphology where each phenyl ring is encircled by six nitrogen atoms, yet its atomistic oxidation structure remains unclear. Here, combining a series of density functional theory calculations and ab initio molecular dynamics simulations, we demonstrate that thermodynamically favorable oxidation loci are confined to the phenyl ring, and kinetic transformations of oxidation structures are feasible along the phenyl ring, whereas those toward nitrogen atoms are proven to be extremely difficult. These results are attributed to the lower barrier of oxygen atom migration along the phenyl ring, while the significantly high barriers toward nitrogen atoms are due to the heterogeneous potential energy surface for oxygen-C3N interaction. This work highlights the significance of surface morphology on the characteristics of oxidation structure, offering insights into tunable electronic properties via confined interfacial oxidation.

In situ MIL-101 growth on cotton cloth to fabricate multifunctional phase change composites driven by solar and magneto-thermal for all-day desalination

It is certainly one of the most feasible ways to extract fresh water from seawater in the face of the current depletion of fresh water resources. Although solar energy as a heat source for desalination is the cleanest and most abundant way, its intermittent and seasonal also poses an obstacle to its practical application. In order to solve the above-mentioned issues, we prepared a series of phase change composites (PCCs) with excellent light-absorbing and magnetic properties by growing MIL-101(Fe) in situ on cotton fabric. All-day desalination through the synergistic action of phase change material (PCM) and magnetic particles. The evaporation rate of PCC can reach 2.76 kg m-2h-1 with an evaporation efficiency of 90.19 % under one sunlight condition. The evaporation rate of sea water under the synergistic effect of magnetic particles and PCM reached 4.53 kg m-2h-1 in the absence of sunlight. This paper provides a new approach to all-day desalination without contact heating.

A Solar Evaporator Based on Polypyrrole Coated 3D Carbon Nanotube Materials for Efficient Solar-Driven Vapor Generation

Highly porous light absorbers are fabricated based on polypyrrole (PPy)-coated carbon nanotube (CNT). Carbon nanotube sponge (CNTS) or carbon nanotube array (CNTA) with three-dimensional (3D) network structure is the framework of porous light absorbers. Both PPy@CNTS and PPy@CNTA composites exhibit excellent light absorption of the full solar spectrum. The CNTS and CNTA with porous structures have extremely large effective surface area for light absorption and for water evaporation that has great practical benefit to the solar-driven vapor generation. The PPy layer on CNT sidewalls significantly improves the hydrophilicity of porous CNTS and CNTA. The good wettability of water on CNT sidewalls makes water transport in porous CNT materials highly efficient. The PPy@CNTS and PPy@CNTA light absorbers achieve high water evaporation rates of 3.35 and 3.41 kg m-2 h-1 , respectively, under 1-sun radiation. The orientation of nano channels in CNTA-based light absorbers also plays an important role in the solar-driven vapor generation. The water transport and vapor escape are more efficient in CNTA-based light absorbers as compared to the CNTS-based light absorbers due to the relatively short path for the water transport and the vapor escape in CNTA-based light absorbers.

Performance enhancement of the solar still using textiles and polyurethane rollers

The acquisition of clean drinking water in regions with limited power sources has been a challenge of paramount concern. Solar stills have emerged as a popular and sustainable option for obtaining clean water in such regions. This process involves employing solar radiation to heat up water, which is then condensed to obtain potable water. The present study introduces a solar still system that is both cost-effective and energy-efficient, while simultaneously ensuring sustainability. Fabric-coated polyurethane rollers with capillary action enhance evaporation area, leading to notable performance improvements. Water vapour condensed on the cooling chamber's inclined aluminium plate and collected in the distillate chamber within the solar still. The thermal, energetic, and economic performance and productivity of the proposed model were evaluated. The fabricated solar still boasted maximum instantaneous system efficiency and exergy efficiency of approximately 62.16% and 7.67%, respectively. This system's cost-effectiveness and performance improvements are particularly noteworthy. The daily average distillate productivity of the proposed still was estimated at 1.14 L/m2, resulting in an annual production rate of 416.54 L/year. The estimated cost of producing 1 L of distillate was 0.023 $.

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.

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.

Bacterially synthesized superfine tellurium nanoneedles as an antibacterial and solar-thermal still for efficient purification of polluted water

Bacterial biosynthesis of nanomaterials has several advantages (e.g., reduced energy inputs, lower cost, negligible environmental pollution) compared with traditional approaches. Various nanomaterials have been produced by bacteria. However, reports on using the bacterial biosynthesis of nanomaterials for applications with solar-thermal agents are scarce due to their narrow optical absorption. Herein, for the first time, we proposed a bacterial biosynthesis of broad-absorbing tellurium nanoneedles and demonstrated their effectiveness for solar-thermal evaporation and antibacterial applications. By simple biosynthesis within bacteria (Shewanella oneidensis MR-1), tellurium nanoneedles achieved a superfine configuration with a length-to-diameter ratio of nearly 20 and broad-spectrum absorbance. After integrating tellurium nanoneedles into a porous polyvinyl-alcohol scaffold, a solar-thermal still named TSAS-3 realized a high evaporation rate of 2.25 kg m-2 h-1 and solar-thermal conversion efficiency of 81% upon 1-Sun illumination. Based on these unique properties, the scaffold displayed good performances in seawater desalination, multiple wastewater treatment, and antibacterial applications. This work provides a simple and feasible strategy for the use of microbial-synthesized nanomaterials in solar-driven water purification and antibacterial applications.

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.

JUJUNCAO-Stem-Based Interfacial Solar-Driven Evaporator with Natural Two-Phase Composite Structures of Functional Partition and Inherent Ultralow Vaporization Enthalpy of Water for Stable and Efficient Steam Production

The interfacial solar-driven evaporation has been deemed as an environmentally friendly approach for freshwater generation. Nevertheless, there is still a challenge to obtain solar evaporators with efficient vapor production from low-cost and renewable biomass through a simple preparation process. Herein, the JUJUNCAO stem was selected as the substrate material, and a kind of interfacial solar-driven evaporator with natural two-phase composite structures and inherent ultralow water vaporization enthalpy was constructed by a dip-coating process. The natural two-phase composite structures were utilized as independent functional partition: the low-tortuosity and hydrophilic vascular bundles served as hierarchical channels for rapid water transportation and continuous steam escape, and the honeycomb-like parenchyma cells were considered natural heat insulators for effective thermal management. Furthermore, the JUJUNCAO stem exhibited inherent ultralow water vaporization enthalpy which was only 1.15 kJ g-1. Benefiting from the natural two-phase composite structures of functional partition and inherent ultralow water vaporization enthalpy, the C-Js evaporator could achieve an evaporation rate of 2.77 kg m-2 h-1 with an efficiency of 85.6% under 1 sun illumination. Meanwhile, the C-Js exhibited a stable and ideal evaporation performance and metal ion rejection behavior in the actual brine desalination process. Owing to the cost-effective and simple pretreatment process, the C-Js evaporator has the potential for freshwater generation in undeveloped areas.

Electrochemical Biosensor for Protein Concentration Monitoring Using Natural Wood Evaporation for Power Generation

A high-sensitivity, low-cost, self-powered biomass electrochemical biosensor based on the "evaporating potential" theory is developed for protein detection. The feasibility of experimental evaluation methods was verified with a probe protein of bovine serum albumin. The sensor was then used to detect lung cancer marker CYFRA21-1, and the potential of our sensor for clinical diagnosis was demonstrated by serum analysis. This work innovatively exploits the osmotic power generation capability of natural wood to construct a promising electrochemical biosensor that was driven by kinetics during testing. The detection methods used for this sensor, chronoamperometry and AC impedance, showed potential for quantitative analysis and specific detection, respectively. Furthermore, the sensor could facilitate new insights into the development of high-sensitivity, low-cost, and easy-to-use electrochemical biosensors.

MXene nanosheets coated conjugated microporous polymers hollow microspheres incorporating with phase change material for continuous desalination

The inevitable intermittency of solar illumination during the interfacial evaporation process can cause a reduction in the evaporation performance of solar evaporators. Here, we report the fabrication of a new solar-driven interfacial evaporator using MXene nanosheets as the photothermal layer, modifying them with conjugated microporous polymer hollow microspheres, and then compounding them with the phase change material, in this case, cetyl alcohol, to form a composite evaporator (CE) that can perform all-weather solar interfacial evaporation. By combining interfacial evaporation photothermal conversion with energy storage, the evaporator achieves an evaporation rate of 1.57 kg⋅m-2⋅h-1 at a light intensity of 1 kW⋅m-2 and 2.79 kg⋅m-2⋅h-1 at a light intensity of 2 kW⋅m-2. In addition, the evaporator attains an excellent solar evaporation efficiency of over 91% in both cases and even in salt water. In addition, interestingly, our CE exhibits excellent continuous evaporation ability, e.g., the mass of evaporated water was increased by 0.36 kg⋅m-2 at a light intensity of 2 kW⋅m-2 compared to the cavity evaporator without the phase change material (PCM) when solar light was turned off. These results could be attributed to the fact that the energy released by the incorporated phase change material allows the evaporator to maintain stable evaporation under conditions of insufficient or intermittent solar irradiation, potentially providing a new opportunity for addressing the intermittent problem of evaporation at the solar interface due to unstable light intensity, thus showing great potential for practical continuous desalination.

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.

3D porous β-cyclodextrin grafted graphene oxide/sodium alginate superhydrophilic natural polysaccharide-based aerogel for solar steam generation

Solar steam generation (SSG) emerges as a paramount technology for efficient and sustainable desalination and wastewater purification. The innovative development of porous aerogel materials for solar steam generation heralds a new era in photothermal materials. In this study, a category of β-cyclodextrin-grafted graphene oxide/sodium anionic polysaccharide alginate composite aerogels (named GO-CD/SA) with solar steam generation behavior and wastewater purification properties is developed. GO-CD/SA demonstrates remarkable properties, including an impressive solar absorption efficiency of approximately 97.4 %, a low thermal conductivity of just 0.124 W m-1 K-1 in a wetted state, and exceptional superhydrophilicity. These attributes collectively contribute to GO-CD/SA achieving an evaporation rate of 1.79 kg m-2 h-1 when utilized with pure water. Furthermore, GO-CD/SA features an abundant three-dimensional porous structure (88.07 % porosity) and superhydrophilic properties that promote the rapid reflux of salt solution between the pore channels. This, in turn, enables excellent salt resistance, with no noticeable salt crystals precipitating during continuous evaporation in 20 % high concentration brine for 6 h. GO-CD/SA also demonstrates outstanding purification capabilities for organic dye wastewater and heavy metal ion wastewater. Therefore, this work combines the advantages of salt tolerance and wastewater treatment, paving the way for the exploration of natural polysaccharide-based photothermal materials.

Macroscopic assembly of 2D materials for energy storage and seawater desalination

Since the discovery of graphene in 2004, two-dimensional (2D) materials have attracted widespread attention due to their excellent physical and chemical properties in the fields of energy, environment, catalysis, and optoelectronics. However, there are still many key problems in the process of practical application. To further promote the potential of 2D materials for practical applications, macroscopic assembly of 2D materials is crucial for the continued development of 2D materials, especially in the fields of energy storage and seawater desalination. Therefore, this review focuses on the latest progress and current status related to the macroscopic assembly of 2D materials, including 1D fibers, 2D films, and 3D architectures. In addition, the application of macroscopic bodies assembled based on 2D materials in the fields of energy storage and seawater desalination is also introduced. Finally, future directions for the macroscopic assembly of 2D materials and their applications are prospected.

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.

Water Activation in Solar-Powered Vapor Generation

Solar-powered vapor evaporation (SVG), based on the liquid-gas phase conversion concept using solar energy, has been given close attention as a promising technology to address the global water shortage. At molecular level, water molecules escaping from liquid water should overcome the attraction of the molecules on the liquid surface layer to evaporate. For this reason, it is better to reduce the energy required for evaporation by breaking a smaller number of hydrogen bonds or forming weak hydrogen bonds to ensure efficient and convenient vapor production. Many novel evaporator materials and effective water activation strategies have been proposed to stimulate rapid steam production and surpass the theoretical thermal limit. However, an in-depth understanding of the phase/enthalpy change process of water evaporation is unclear. In this review, a summary of theoretical analyses of vaporization enthalpy, general calculations, and characterization methods is provided. Various water activation mechanisms are also outlined to reduce evaporation enthalpy in evaporators. Moreover, unsolved issues associated with water activation are critically discussed to provide a direction for future research. Meanwhile, significant pioneering developments made in SVG are highlighted, hoping to provide a relatively entire chain for more scholars who are just stepping into this field.

Plant Transpiration-Inspired Biomass-Based Device with Underwater Oleophobicity for Efficient General-Purpose Solar-Driven Oily Wastewater Purification

The remediation of wastewater containing oily pollutants is imperative to mitigate the serious threats posed to the safety of fresh water, human well-being, and the environment. Current membrane separation technologies are severely restricted by their limitations for separating various types of oily pollutants with low sustainability. Herein, by imitating the plant transpiration in nature, we designed a solar-driven device composed of natural biomass sugar cane stem, chitosan/carboxymethyl cellulose, and graphite powders to separate versatile oily pollutants from the wastewater. Owing to its superior solar absorption capacity, microchannels for water transportation, and underwater oleophobicity, the resultant evaporator not only exhibited an excellent evaporation rate of 1.41 kg m-2 h-1 but also demonstrated an admirable purification efficiency of 99.9% for oily wastewater. Moreover, the device can maintain a stable evaporation rate and the original structure even in oily wastewater containing strong acid, alkali, or hypersaline components. Therefore, this work provides an effective approach to producing clean water from versatile wastewater.

Tunable 1D and 2D Polyacrylonitrile Nanosheet Superstructures

Carbon superstructures are widely applied in energy and environment-related areas. Among them, the flower-like polyacrylonitrile (PAN)-derived carbon materials have shown great promise due to their high surface area, large pore volume, and improved mass transport. In this work, we report a versatile and straightforward method for synthesizing one-dimensional (1D) nanostructured fibers and two-dimensional (2D) nanostructured thin films based on flower-like PAN chemistry by taking advantage of the nucleation and growth behavior of PAN. The resulting nanofibers and thin films exhibited distinct morphologies with intersecting PAN nanosheets, which formed through rapid nucleation on existing PAN. We further constructed a variety of hierarchical PAN superstructures based on different templates, solvents, and concentrations. These PAN nanosheet superstructures can be readily converted to carbon superstructures. As a demonstration, the nanostructured thin film exhibited a contact angle of ∼180° after surface modification with fluoroalkyl monolayers, which is attributed to high surface roughness enabled by the nanosheet assemblies. This study offers a strategy for the synthesis of nanostructured carbon materials for various applications.

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

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

Hierarchical Tantalum Oxide Composite for Efficient Solar-Driven Water Purification

Applying solar energy to generate drinking water is a clean and low-energy exhaust route to address the issue of water purification. The current challenge with solar vapor generation is constructing nano/micro-hierarchical structures that can convert solar irradiation into exploitable thermal energy with high efficiency. Although various structures and material designs have been reported in recent years, solar vapor conversion can be improved by integrating light harvesting, thermal concentration, and water diffusion. Because of the optimized solar harvesting, enhanced heat capacity, and specified diffusive path endowed by the hierarchical composite structure, amorphous tantalum oxide/carbon-based yolk-shell structures (α-Ta2O5/C YS) for highly efficient solar vapor generation under 1 sun illumination are applied in this study. As a result, the α-Ta2O5/C YS realized a water evaporation rate of 3.54 kg m-2 h-1 with a solar-thermal conversion efficiency of 91% under one sun irradiation (1 kW m-2) with excellent evaporation stability. The collected water from seawater meets the World Health Organization drinking water standard. Importantly, reactive oxygen species enabled by α-Ta2O5 could be produced for water sterilization, exhibiting a facile way for application in various scenarios to acquire drinkable water.

Petroleum Coke Embedded in Cigarette Butts: All Waste-Derived Solar Evaporator for Effective Water Evaporation

Solar-driven interfacial evaporation is an eco-friendly solution for tackling the impending water scarcity the world is facing in our century. In this work, a solar-driven interfacial evaporator was prepared from cigarette butts loaded with petroleum coke powder (Filter-PetCoke), a by-product of the oil refinery processes, for the improvement of the absorption of the incident solar light. A comparison between a flat 2D and a 3D evaporator with a surface composed of orderly patterned protrusions of 2.1 cm was carried out to assess the influence of the evaporator configuration on the evaporation performance. The 3D evaporator (3D Filter-PetCoke) achieved by far the best performance (evaporation rate: 1.97 ± 0.08 kg m-2 h-1 and solar conversion efficiency: 93.2 ± 5.4%) among the prepared samples (3D Filter-PetCoke, 3D Filter, 2D Filter-PetCoke, and 2D Filter). In addition, this configuration seems to be adaptable for real and more massive operation because of the geometry of the evaporator. The high efficiency was ascribed to the good heat generation of the petroleum coke and the excellent heat management of the 3D structure of the evaporator. Moreover, this evaporator was resistant to multiple repeated usages without significant efficiency loss and capable of producing drinking water from seawater and Escherichia coli (E. coli)-contaminated water. The findings in this work indicate that this evaporator is pertinent to real situations to supply safe freshwater very efficiently from chemically/biologically contaminated water.

Overview of Solar Steam Devices from Materials and Structures

The global shortage of freshwater supply has become an imminent problem. The high energy consumption of traditional desalination technology cannot meet the demand for sustainable energy development. Therefore, exploring new energy sources to obtain pure water has become one of the effective ways to solve the freshwater resource crisis. In recent years, solar steam technology which utilizes solar energy as the sole input source for photothermal conversion has shown to be sustainable, low-cost, and environmentally friendly, providing a viable low-carbon solution for freshwater supply. This review summarizes the latest developments in solar steam generators. The working principle of steam technology and the types of heating systems are described. The photothermal conversion mechanisms of different materials are illustrated. Emphasis is placed on describing strategies to optimize light absorption and improve steam efficiency from material properties to structural design. Finally, challenges in the development of solar steam devices are pointed out, aiming to provide new ideas for the development of solar steam devices and alleviate the shortage of freshwater resources.

CO2-laser-induced carbonization of calcium chloride-treated chitin nanopaper for applications in solar thermal heating

Remarkable progress has been made in the development of carbonized chitin nanofiber materials for various functional applications, including solar thermal heating, owing to their N- and O-doped carbon structures and sustainable nature. Carbonization is a fascinating process for the functionalization of chitin nanofiber materials. However, conventional carbonization techniques require harmful reagents, high-temperature treatment, and time-consuming processes. Although CO₂ laser irradiation has progressed as a facile and second-scale high-speed carbonization process, CO₂-laser-carbonized chitin nanofiber materials and their applications have not yet been explored. Herein, we demonstrate the CO₂-laser-induced carbonization of chitin nanofiber paper (denoted as chitin nanopaper) and investigate the solar thermal heating performance of the CO₂-laser-carbonized chitin nanopaper. While the original chitin nanopaper was inevitably burned out by CO₂ laser irradiation, CO₂-laser-induced carbonization of the chitin nanopaper was achieved by pretreatment with calcium chloride as a combustion inhibitor. The CO₂-laser-carbonized chitin nanopaper exhibits excellent solar thermal heating performance; its equilibrium surface temperature under 1 sun irradiation is 77.7 °C, which is higher than those of the commercial nanocarbon films and the conventionally carbonized bionanofiber papers. This study paves the way for the high-speed fabrication of carbonized chitin nanofiber materials and their application in solar thermal heating toward the effective utilization of solar energy as heat.

Improved Photo-Excited Carriers Transportation of WS2 -O-Doped-Graphene Heterostructures for Solar Steam Generation

Two-dimensional (2D) transition metal dichalcogenides and graphene have revealed promising applications in optoelectronic and energy storage and conversion. However, there are rare reports of modifying the light-to-heat transformation via preparing their heterostructures for solar steam generation. In this work, commercial WS₂ and sucrose are utilized as precursors to produce 2D WS₂ -O-doped-graphene heterostructures (WS₂ -O-graphene) for solar water evaporation. The WS₂ -O-graphene evaporators demonstrate excellent average water evaporation rate (2.11 kg m^-2  h^-1 ) and energy efficiency (82.2%), which are 1.3- and 1.2-fold higher than WS₂ and O-doped graphene-based evaporators, respectively. Furthermore, for the real seawater with different pH values (pH 1 and 12) and rhodamine B pollutants, the WS₂ -O-graphene evaporators show great average evaporation rates (≈2.08 and 2.09 kg m^-2  h^-1 , respectively) for producing freshwater with an extremely low-grade of dye residual and nearly neutral pH values. More interestingly, due to the self-storage water ability of WS₂ -O-graphene evaporators, water evaporation can be implemented without the presence of bulk water. As a result, the evaporation rate reaches 3.23 kg m^-2  h^-1 , which is ≈1.5 times higher than the regular solar water evaporation system. This work provides a new approach for preparing 2D transition metal dichalcogenides and graphene heterostructures for efficient solar water evaporation.

A Magneto-Heated Silk Fibroin Scaffold for Anti-Biofouling Solar Steam Generation

Macroscopic 3D porous materials are ideal solar evaporators for water purification. However, the limited sunlight intensity and penetrating depth during solar-driven evaporation cannot prevent the biofouling formation by photothermal effect, thus leading to the deterioration of evaporation rate. Herein, a magnetic heating strategy is reported for anti-biofouling solar steam generation based on a magnetic silk fibroin (SF) scaffold with bi-heating property. Under one sun, the solar-heated top surface of magnetic SF scaffolds accelerates water evaporation at 2.03 kg m^-2 h^-1 , while the unheated inner channels suffer from the formation of biofilm. When exposed to alternating magnetic field (AMF), the magnetic SF scaffold can be integrally heated, leading to an efficient inner temperature to prevent biofouling in channels for water transportation. Accordingly, magneto-heated scaffolds show steady water evaporation rates after exposure to S. aureus and E. coli, which maintained 93.6-94.6% of original performance. In contrast, the evaporation rates of the scaffolds without AMF treatment are reduced to 1.31 (S. aureus) and 1.32 (E. coli) kg m^-2 h^-1 , decreased by 35.5% and 35.0%, respectively. In addition, the magneto-heated scaffold inhibits biofouling formation in natural lake water, maintaining 99.5% original performance.

Chitin-Derived Nitrogen-Doped Carbon Nanopaper with Subwavelength Nanoporous Structures for Solar Thermal Heating

Sustainable biomass-derived carbons have attracted research interest because of their ability to effectively absorb and convert solar light to thermal energy, a phenomenon known as solar thermal heating. Although their carbon-based molecular and nanoporous structures should be customized to achieve enhanced solar thermal heating performance, such customization has insufficiently progressed. In this study, we transformed a chitin nanofiber/water dispersion into paper, referred to as chitin nanopaper, with subwavelength nanoporous structures by spatially controlled drying, followed by temperature-controlled carbonization without any pretreatment to customize the carbon-based molecular structures. The optimal carbonization temperature for enhancing the solar absorption and solar thermal heating performance of the chitin nanopaper was determined to be 400 °C. Furthermore, we observed that the nitrogen component, which afforded nitrogen-doped carbon structures, and the high morphological stability of chitin nanofibers against carbonization, which maintained subwavelength nanoporous structures even after carbonization, contributed to the improved solar absorption of the carbonized chitin nanopaper. The carbonized chitin nanopaper exhibited a higher solar thermal heating performance than the carbonized cellulose nanopaper and commercial nanocarbon materials, thus demonstrating significant potential as an excellent solar thermal material.

Photothermal-Photocatalytic CSG@ZFG Evaporator for Synergistic Salt Rejection and VOC Removal during Solar-Driven Water Distillation

Sunlight-driven interfacial photothermal evaporation has been considered as a promising strategy for addressing global water crisis. Herein, we fabricated a self-floating porous triple-layer (CSG@ZFG) evaporator using porous fibrous carbon derived from Saccharum spontaneum (CS) as a photothermal material. The middle layer of the evaporator is composed of hydrophilic sodium alginate crosslinked by carboxymethyl cellulose and zinc ferrite (ZFG), whereas the top hydrophobic layer consists of fibrous (CS) integrated benzaldehyde-modified chitosan gel (CSG). Water is transported to the middle layer through the bottom elastic polyethylene foam using natural jute fiber. Such a strategically designed three-layered evaporator exhibits a broad-band light absorbance (96%), excellent hydrophobicity (120.5°), a high evaporation rate of 1.56 kg m^-2 h^-1, an energy efficiency of 86%, and outstanding salt mitigation ability under the simulated sunlight of intensity 1 sun. Adding ZnFe₂O₄ nanoparticle as a photocatalyst has been proved to be capable of restricting the evaporation of volatile organic contaminants (VOCs) like phenol, 4-nitrophenol, and nitrobenzene to ensure the purity of evaporated water. Such an innovatively designed evaporator offers a promising approach for the production of drinking water from wastewater and seawater.

3D Printing of Solar Crystallizer with Polylactic Acid/Carbon Composites for Zero Liquid Discharge of High-Salinity Brine

Zero liquid discharge (ZLD) is a technique for treating high-salinity brine to obtain freshwater and/or salt using a solar interface evaporator. However, salt accumulation on the surface of the evaporator is a big challenge to maintaining stable water evaporation. In this study, a simple and easy-to-manufacture evaporator, also called a crystallizer, was designed and fabricated by 3D printing. The photothermal layer printed with polylactic acid/carbon composites had acceptable light absorption (93%) within the wavelength zone of 250 nm–2500 nm. The micron-sized voids formed during 3D printing provided abundant water transportation channels inside the crystallizer. After surface hydrophilic modification, the crystallizer had an ultra-hydrophilic channel structure and gravity-assisted salt recovery function. The results revealed that the angles between the photothermal layers affected the efficacy of solar evaporation and the yield of solid salt. The crystallizer with the angle of 90° between two photothermal layers could collect more solid salt than the three other designs with angles of 30°, 60°, and 120°, respectively. The crystallizer has high evaporation and salt crystallization efficiency in a high-salinity brine environment, which is expected to have application potentials in the zero liquid discharge of wastewater and valuable salt recovery.

Dual-Functional Solar-to-Steam Generation and SERS Detection Substrate Based on Plasmonic Nanostructure

Solar-to-steam (STS) generation based on plasmonic materials has attracted significant attention as a green method for producing fresh water. Herein, a simple in situ method is introduced to fabricate Au nanoparticles (AuNPs) on cellulose filter papers as dual-functional substrates for STS generation and surface-enhanced Raman spectroscopy (SERS) sensing. The substrates exhibit 90% of broadband solar absorption between 350 and 1800 nm and achieve an evaporation rate of 0.96 kg·m^-2·h^-1 under 1-sun illumination, room temperature of 20 °C, and relative humidity of 40%. The STS generation of the substrate is stable during 30 h continuous operation. Enriched SERS hotspots between AuNPs endow the substrates with the ability to detect chemical contamination in water with ppb limits of detection for rhodamine 6G dye and melamine. To demonstrate dual-functional properties, the contaminated water was analyzed with SERS and purified by STS. The purified water was then analyzed with SERS to confirm its purity. The developed substrate can be an improved and suitable candidate for fresh water production and qualification.

Heteropoly Blue/Carbon Nanotubes Nanocomposites as High-Performance Photothermal Conversion Materials

To realize the direct and full use of the widely distributed solar energy, developing novel materials with superb photothermal conversion capability is essential. Although heteropoly blue has intrinsic outstanding solar absorption and photothermal conversion properties, its spectral absorption in the infrared region is weak. Here, composites of heteropoly blue and carbon nanotubes (HPB/CNTs) are synthesized depending on electrostatic interactions by facile microwave sonication and freeze-drying. The doped CNTs can dramatically improve the spectral absorption performance of HPB ontology in the infrared region. As a result, the light absorption of the optimized HPB/CNTs (20 %) reaches more than 95 % in the range of 200-2400 nm, showing promising prospects as high-performance photothermal conversion material in the applications of solar desalination and wastewater treatment.

Synergistic Solar-Driven Freshwater Generation and Electricity Output Empowered by Wafer-Scale Nanostructured Silicon

Electricity generation triggered by the ubiquitous water evaporation process provides an intriguing way to harvest energy from water. Meanwhile, natural water evaporation is also a fundamental way to obtain fresh water for human beings. Here, a wafer-scale nanostructured silicon-based device that takes advantage of its well-aligned configuration that simultaneously realizes solar steam generation (SSG) for freshwater collection and hydrovoltaic effect generation for electricity output is developed. An ingenious porous, black carbon nanotube fabric (CNF) electrode endows the device with sustainable water self-pumping capability, excellent durable conductivity, and intense solar spectrum harvesting. A combined device based on the CNF electrode integrated with nanostructured silicon nanowire arrays (SiNWs) provided an aligned numerous surface-to-volume water evaporation interface that enables a recorded continuous short-circuit current 8.65 mA and a water evaporation rate of 1.31 kg m^-2 h^-1 under one sun illumination. Such wafer-scale SiNWs-based SSG and hydrovoltaic integration devices would unchain the bottleneck of the weak and discontinuous electrical output of hydrovoltaic devices, which inspires other sorts of semiconductor-based hydrovoltaic device designs to target superior performance.

A novel TiO2-x/TiN@ACB composite for synchronous photocatalytic Cr(VI) reduction and water photothermal evaporation under visible/infrared light illumination

Relatively large band-gap, fast charge carriers recombination, and mono-functionality of photocatalytic materials are still representing stumbling hurdles against their optimal usage for water cleaning. Herein, a novel black titanium oxide/plasmonic titanium nitride@activated coconut biochar (TiO2-x/TiN@ACB) composite was designed to have both photocatalytic and photothermal functions. Intermediate states of black TiO2-x, plasmonic effect of TiN, and high electrons (e-) capacity of biochar enhanced band-gap narrowing, light absorbance extension, and charge carriers separation respectively. Black TiO2-x and plasmonic TiN sensitization via visible/infrared (Vis/IR) portion of photonic spectrum in addition to the confirmed close contact of composite constituents explained the demonstrated major role of e- in photocatalytic mechanism through efficient excitation and facile transfer. Thanks to black photocatalytic semiconductor and carbonic materials for their ultimate photons harnessing and efficient photothermal conversion where the composite exhibited a remarkable photothermal water evaporation upon Vis/IR illumination as well. TiO2-x/TiN@ACB composite revealed 92.8 and 89.7% photocatalytic reduction of hexavalent chromium (Cr(VI)) and water evaporation efficiencies up to 92.9 and 51.1% upon IR and Vis light illumination respectively. This study proposes a new approach for efficient water cleaning by coupling of oxygen deficient and plasmonic semiconductors supported on naturally derived carbonic material as a broad spectrum harvester and bi-functional photocatalytic and photothermal material.

Water Harvesting Strategies through Solar Steam Generator Systems

Solar steam generator (SSG) systems have attracted increasing attention, owing to its simple manufacturing, material abundance, cost-effectiveness, and environmentally friendly freshwater production. This system relies on photothermic materials and water absorbing substrates for a clean continuous distillation process. To optimize this process, there are factors that are needed to be considered such as selection of solar absorber and water absorbent materials, followed by micro/macro-structural system design for efficient water evaporation, floating, and filtration capability. In this contribution, we highlight the general interfacial SSG concept, review and compare recent progresses of different SSG systems, as well as discuss important factors on performance optimization. Furthermore, unaddressed challenges such as SSG's cost to performance ratio, filtration of untreatable micropollutants/microorganisms, and the need of standardization testing will be discussed to further advance future SSG studies.

Progress on TiO2-based materials for solar water interfacial evaporation

Solar water interfacial evaporation (SWIE) has attracted much attention for harvesting clean water. Over the last few decades, researchers have developed an innovative photo-thermal material for high-performance solar water interfacial evaporation. For higher evaporation performance, TiO2-based materials gain attention as a promising photo-thermal material due to their light absorption capacity. This study compared conceptual designs of TiO2-based materials for SWIE. Structural design and engineering strategies for improving evaporation rates and higher thermal conversion efficiency were reviewed. In addition, the material’s thermal stability and heat management were analyzed. This review provides an overview of the current advances in photo-thermal TiO2 materials to motivate research and translation efforts from the laboratory to large-scale solar water clean water production. Additional benefits of TiO2 materials on solar water interfacial evaporation should be investigated beyond containers to solve interconnected water, environmental, and energy progression.

Three-dimensional open architecture enabling salt-rejection solar evaporators with boosted water production efficiency

Direct solar desalination exhibits considerable potential for alleviating the global freshwater crisis. However, the prevention of salt accumulation while maintaining high water production remains an important challenge that limits its practical applications because the methods currently employed for achieving rapid salt backflow usually result in considerable heat loss. Herein, we fabricate a solar evaporator featuring vertically aligned mass transfer bridges for water transport and salt backflow. The 3D open architecture constructed using mass transfer bridges enables the evaporator to efficiently utilize the conductive heat that would otherwise be lost, significantly improving the water evaporation efficiency without compromising on salt rejection. The fabricated evaporator can treat salt water with more than 10% salinity. Moreover, it can continuously and steadily work in a real environment under natural sunlight with a practical solar-to-water collection efficiency of >40%. Using the discharged water from reverse osmosis plants and sea water from the Red Sea, the evaporator demonstrates a daily freshwater generation rate of ~5 L/m², which is sufficient to satisfy individual drinking water requirements. With strong salt rejection, high energy efficiency, and simple scalability, the 3D evaporator has considerable promise for freshwater supply for water-stressed and off-grid communities.

Conventional salt-rejection evaporators typically exhibit low evaporation rate due to large heat loss. Here, authors demonstrate a solar evaporator featuring vertically aligned mass transfer bridges that takes advantage of the conductive heat to enable optimized water transport and salt backflow.

Hygroscopic Porous Polymer for Sorption-Based Atmospheric Water Harvesting

Sorption-based atmospheric water harvesting (SAWH) holds huge potential due to its freshwater capabilities for alleviating water scarcity stress. The two essential parts, sorbent material and system structure, dominate the water sorption-desorption performance and the total water productivity for SAWH system together. Attributed to the superiorities in aspects of sorption-desorption performance, scalability, and compatibility in practical SAWH devices, hygroscopic porous polymers (HPPs) as next-generation sorbents are recently going through a vast surge. However, as HPPs' sorption mechanism, performance, and applied potential lack comprehensive and accurate guidelines, SAWH's subsequent development is restricted. To address the aforementioned problems, this review introduces HPPs' recent development related to mechanism, performance, and application. Furthermore, corresponding optimized strategies for both HPP-based sorbent bed and coupling structural design are proposed. Finally, original research routes are directed to develop next-generation HPP-based SAWH systems. The presented guidelines and insights can influence and inspire the future development of SAWH technology, further achieving SAWH's practical applications.

MXene-Based Porous Monoliths

In the past decade, a thriving family of 2D nanomaterials, transition-metal carbides/nitrides (MXenes), have garnered tremendous interest due to its intriguing physical/chemical properties, structural features, and versatile functionality. Integrating these 2D nanosheets into 3D monoliths offers an exciting and powerful platform for translating their fundamental advantages into practical applications. Introducing internal pores, such as isotropic pores and aligned channels, within the monoliths can not only address the restacking of MXenes, but also afford a series of novel and, in some cases, unique structural merits to advance the utility of the MXene-based materials. Here, a brief overview of the development of MXene-based porous monoliths, in terms of the types of microstructures, is provided, focusing on the pore design and how the porous microstructure affects the application performance.

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

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