Extreme Water Uptake of Hygroscopic Hydrogels through Maximized Swelling-Induced Salt Loading

All-regional highly efficient moisture capturing and sunlight driven steam generation

Utilizing solar energy to extract and purify potable water from atmospheric humidity offers a viable approach to combat water scarcity in diverse geographical areas. However, current technologies face challenges related to low efficiency due to the low intrinsic permeability and weak hydrophilicity of H2O, followed by ineffectiveness in diverse climatic conditions and long-lasting implementation. Herein, we develop a highly hygroscopic photothermal hydrogels consisting of chitosan polypyrrole (CP) copolymer matrix and zinc ions (Zn2+). The chelation of Zn2+ with CP avoids ionic leakage and endows the hierarchically porous hydrogel with strong hydration and moisture-absorbing properties. These hydrogels achieve an effective moisture capturing of up to 6.53 g g-1 in a wide humidity range of 30% to 90%, which are the reminiscence of environment including desert and lakes. Furthermore, the grafting of photothermal polypyrrole to chitosan allowed the sunlight-driven steam generation with 87% efficiency of solar energy without additional power input. The recyclable moisture adsorption and desorption procedures maintain without observable deduction in efficiency over 2 weeks. A potable device containing our sunlight-driven antibacterial hydrogels displays the production of 1.3 kg m-2 drinkable water per day, sufficient to meet the needs of a household. Its potential for application across diverse climatic conditions could refine water harvesting practices and guide future research on system optimization and scalability.

Material-to-system tailored multilayer-cyclic strategy toward practical atmospheric water harvesting

Solar-driven atmospheric water harvesting (AWH) presents a sustainable approach for freshwater production with sunlight as the sole energy input. To address challenges posed by diurnal moisture variations and diffusive sunlight, we present a system-wide approach that synergistically enhances moisture capture and solar energy utilization in an integrated water harvester. Moisture utilization at the bulk sorbent scale is improved through the hierarchical pore structure of scalable biomass gel sheets enabling rapid regeneration and is further upscaled to system-level performance through a kinetics-matched, continuously multicyclic operation protocol in a multilayered device. Solar energy utilization is enhanced by thermoresponsive hydrogels that lower the energy threshold for water desorption and by efficient thermal and mass flow management that increases energy efficiency. Our system delivers up to 235.09 mL d-1 of water with an energy efficiency as high as 26.4%, excluding solar panel power. This work offers an insight into developing energy-, material-, and space-efficient AWH systems from a cross-scale understanding of sorbent properties, device engineering, and operation protocol tailoring.

Encapsulated High-Salt but Corrosion-Resistant Hygroscopic Medium for Long-Term Passive Solar Cell Cooling

Cooling the solar panel with hygroscopic materials offers a potential solution to mitigate its thermal damage and photovoltaic efficiency reduction. However, the practical application of this approach is significantly hindered by the limited water storage capacity and the back electrode corrosion. In this study, it is demonstrated that encapsulating LiCl-loaded carbon felt in a superhydrophobic polytetrafluoroethylene membrane effectively preserves its high absorptivity while preventing the conventional corrosion issue. This approach ensures sustainable and long-term passive cooling of solar cells. The high-salt but corrosion-resistant (HSCR) material has extremely high water adsorption and storage capacities, which is characterized by the ability to absorb more than 5 times its weight of water within 8 h of incubation at 25 °C and 90% relative humidity (RH). Under 1 sun illumination, incorporating HSCR reduces the solar panel temperature by 17.8 °C while increasing the photovoltaic efficiency by 10.7%. More importantly, the salts encapsulated within the membrane remain leak-proof and the cooling performance can be effectively regenerated after multiple cycles. This work provides a promising solution for sustainable and passive solar panel cooling.

Fish Scale-Inspired β-Cyclodextrin Cross-Linked Polyacrylamide Hydrogels for Oil-Water Separation

Cyclodextrins (CDs), a low-polysaccharide class, possess a hydrophilic outer surface due to their hydroxyl groups, which can be functionalized for various applications. In this study, the hydroxyl groups on β-cyclodextrin were functionalized with acrylates (CD-A) and were subsequently used as a cross-linker in the copolymerization with acrylamide to form a polyacrylamide-cyclodextrin hydrogel (PAC). Compared with polyacrylamide (PAM), PAC exhibited enhanced water absorption abilities and mechanical strength. Inspired by fish scales' surface structural properties, microporous stainless steel meshes were coated with PAC, and we could demonstrate an excellent oil-water separation due to excellent superhydrophilicity and underwater superoleophobicity. The mesh effectively separated various oil-water mixtures by using gravity filtration, achieving separation efficiencies of over 99%. Repeated use with different oil types confirmed the durability and effectiveness of the hydrogel-coated mesh for practical applications in oil-water separation.

Reversible Swell-Shrink Hydrogel Microspheres for High-Selectivity Digital SERS Analysis of Nonvolatile Fentanyl in Simulated Breath Aerosols

In clinical diagnostics, human breath presents an alternative and more convenient sample than biofluids for detecting the ingestion of nonvolatile drugs. Surface-enhanced Raman spectroscopy (SERS) is a powerful vibrational spectroscopy technique with high sensitivity based on molecular fingerprinting. However, the low affinity of traditional SERS substrates for aerosols and the stochastic fluctuation of the SERS signal at low concentrations limit their application in breath aerosol analysis. In this study, we synthesized hydrogel microsphere SERS substrates with highly reversible swelling/shrinking properties that enhance target analyte accumulation in breath aerosols and promote plasmonic nanoparticle aggregation for intense Raman hotspot formation. Furthermore, these hydrogel microsphere SERS substrates function as a three-in-one system, enabling multilevel selectivity based on size, charge, and hydrophilicity for target molecules simultaneously without pretreatment. Notably, by "digitizing" the SERS signal of each individual hydrogel microsphere and calculating the proportion of positive microspheres, the hydrogel microspheres can serve as a digital SERS platform that circumvents the low stability issues resulting from fluctuations in SERS signal intensity. Consequently, the digital SERS platform achieved a detection limit of 0.5 ppm for fentanyl in simulated breath aerosols. This innovative sensing strategy not only demonstrates a promising approach for screening nonvolatile drugs but also simplifies the sampling process, holding great potential for clinical diagnosis of breath aerosols.

Bioinspired Conductivity-Enhanced, Self-Healing, and Renewable Silk Fibroin Hydrogel for Wearable Sensors with High Sensitivity

The development of silk fibroin-based hydrogels with excellent biocompatibility, aqueous processability, and facile controllability in structure is indeed an exciting advancement for biological research and strain sensor applications. However, silk fibroin-based hydrogel strain sensors that combine high conductivity, high stretchability, reusability, and high selectivity are still desired. Herein, we report a simple method for preparing double-network hydrogels including silk fibroin and poly(acrylic acid) sodium-polyacrylate (PAA-PAAS) networks. The conformation and aggregate of silk fibroin could be facilely tuned by both ions and pH resulting from the PAA-PAAS network. The optimized hydrogel exhibits intriguing properties, such as high conductivity (3.67 S/m) and transparency, high stretchability (1186%) with a tensile strength of 110 kPa, good adhesion properties, reversible compression, self-healing, and high sensitivity (GF = 10.71). This hydrogel strain sensor can detect large-scale and small human movements in real time, such as limb movements, heartbeats, and pulse. Additionally, its ability to adsorb water and recover effectiveness after losing water from air with 90% humidity along with the capability for low-temperature motion detection facilitated by ethylene glycol further enhance its practical utility. This work offers a novel and simple approach to design flexible bionic strain sensors.

Metal- and Halide-Free, Macroporous Hygroscopic Polymers for Efficient Atmospheric Water Harvesting

Hygroscopic materials based on highly hygroscopic salts are promising for atmospheric water harvesting (AWH), but the metal- or halide-containing highly hygroscopic salts often have leakage and corrosion issues. Here, the design and synthesis of metal- and halide-free, highly hygroscopic, and macroporous polymers from [2-(acryloyloxy)ethyl]trimethylammonium chloride simply via in situ foaming, solidification, and ion exchange are reported. The resulting polymers exhibit highly interconnected macroporous structure, robust compression, and leakage-free performance, and they also demonstrate relatively high moisture adsorption capacities (up to 1.24 g g-1 water at 85% relative humidity, accelerated adsorption rates, and efficient desorption. The polymers can harvest 0.76 g g-1 water per adsorption-desorption cycle and show high reusability, without obvious deterioration over 10 cycles of adsorption, desorption, and water collection. With the incorporation of carboxylic multi-walled carbon nanotubes into the hygroscopic polymers, solar-driven AWH is realized, without the requirement of additional energy. On the whole, the metal- and halide-free, highly hygroscopic polymers exhibit the advantages of ease of preparation, energy saving, environmental protection, and economic sustainability for AWH.

Bioinspired hydrophobic pseudo-hydrogel for programmable shape-morphing

Inspired by counterintuitive water "swelling" ability of the hydrophobic moss of the genus Sphagnum (Peat moss), we prepared a hydrophobic pseudo-hydrogel (HPH), composed of a pure hydrophobic silicone elastomer with a tailored porous structure. In contrast to conventional hydrogels, HPH achieves absorption-induced volume expansion through surface tension induced elastocapillarity, presenting an unexpected absorption-induced volume expansion capability in hydrophobic matrices. We adopt a theoretical framework elucidating the interplay of surface tension induced elastocapillarity, providing insights into the absorption-induced volume expansion behavior. By systematically programming the pore structure, we demonstrate tunable, anisotropic, and programmable absorption-induced expansion. This leads to dedicated self-shaping transformations. Incorporating magnetic particles, we engineer HPH-based soft robots capable of swimming, rolling, and walking. This study demonstrates a unusual approach to achieve water-responsive behavior in hydrophobic materials, expanding the possibilities for programmable shape-morphing in soft materials and soft robotic applications.

Composite Gel Polymer Electrolyte for High-Performance Flexible Zinc-Air Batteries

Enhancing ionic conductivity and electrolyte uptake is of significance for gel polymer electrolytes (GPEs) for flexible zinc-air batteries (FZABs). Herein, a composite mesoporous silica/polyacrylamide (5 wt.% mPAM) GPE is constructed with comparable ionic conductivity to aqueous electrolytes, where the ionic conductivity is up to 337 mS cm-1, and the weight loss after exposing in air 72 h is less than 18%, owing to the excellent electrolyte uptake and continuous ion migration network provided by the mesoporous silica fillers. When used as a quasi-solid-electrolyte, the rechargeable FZAB exhibited high electrochemical performance and structural stability, where the peak power density is up to 162.8 mW cm-2, and the initial charge-discharge potential gap is as low as 0.62 V, resulting in a long lifespan exceeding 110 h, showcasing the combination of high durability, cost-effectiveness and easy production for practical applications.

Tillandsia-Inspired Ultra-Efficient Thermo-Responsive Hygroscopic Nanofibers for Solar-Driven Atmospheric Water Harvesting

Sorption-based atmospheric water harvesting (SAWH) is a promising approach for supplying water in off-grid arid regions. However, it is difficult to improve the SAWH efficiency because water undergoes multiple phase transformations, such as water vapor-water (desorption and condensation) in the desorption phase. To address this issue, an ultrahygroscopic temperature-responsive hydrogel nanofiber inspired by Tillandsia is developed, comprising poly N-isopropylacrylamide, poly N-dimethylacetamide, and carbon nanotubes and impregnated with lithium chloride (PCP@LiCl). The hydrophobicity of the nanofiber membrane is enhanced with increasing temperature, facilitating water separation from the hydrogel in liquid form. Moreover, PCP@LiCl exhibits unique kinetics at 25 °C and 15%-30% relative humidity, capable of adsorbing moisture to saturation within 2 h, and oozing liquid water within 5 min under sunlight. Through global potential modeling, it is demonstrated that PCP@LiCl has potential applications in arid and semiarid regions. This study provides new insights into the design of high-performance composites for solar-powered atmospheric water harvesting.

Bifunctional Portable Powder for Freshwater Production With Moisture Harvesting and Undrinkable Water Purification

Freshwater scarcity threatens human survival, particularly in extreme environments like deserts, oceans, and space. Compatible atmospheric water harvesting and undrinkable water purification offer an affordable approach to solving freshwater scarcity in these extreme environments. Nonetheless, developing composite sorbent to attain efficient atmospheric water harvesting and undrinkable water purification remains challenging. Hence, a portable hybrid hygroscopic powder (HLC powder) consisting of hydroxypropyl chitosan, dibenzaldehyde-functional poly(ethylene glycol), lithium chloride (LiCl), and nano carbon black is proposed. The HLC powder with optimized LiCl load can capture moisture from the air, showing a high water uptake of 1.76 g g-1 at 34% relative humidity (RH) and appropriate over a wide humidity from 34% to 75% RH. pH-responsive sol-gel transition induced by Schiff base bonds transforms the HLC solution into hydrogel, inhibiting hydrated salt leakage. Meanwhile, to achieve efficient undrinkable water purification, the LiCl-free hybrid powder is utilized to convert the undrinkable water, including seawater, dye water, and human urine, to photothermal hydrogel evaporators with low evaporation enthalpies and high evaporation rates ranging from 1.81 to 2.05 kg m-2 h-1 under one sun. This strategy establishes a new path to conveniently obtaining freshwater, breaking hydrological restrictions.

Cobalt-Ion Superhygroscopic Hydrogels Serve as Chip Heat Sinks Achieving a 5 °C Temperature Reduction via Evaporative Cooling

In the rapidly advancing semiconductor sector, thermal management of chips remains a pivotal concern. Inherent heat generation during their operation can lead to a range of issues such as potential thermal runaway, diminished lifespan, and current leakage. To mitigate these challenges, the study introduces a superhygroscopic hydrogel embedded with metal ions. Capitalizing on intrinsic coordination chemistry, the metallic ions in the hydrogel form robust coordination structures with non-metallic nitrogen and oxygen through empty electron orbitals and lone electron pairs. This unique structure serves as an active site for water adsorption, beginning with a primary layer of chemisorbed water molecules and subsequently facilitating multi-layer physisorption via Van der Waals forces. Remarkably, the cobalt-integrated hydrogel demonstrates the capability to harvest over 1 and 5 g g-1 atmospheric water at 60% RH and 95% RH, respectively. Furthermore, the hydrogel efficiently releases the entirety of its absorbed water at a modest 40°C, enabling its recyclability. Owing to its significant water absorption capacity and minimal dehydration temperature, the hydrogel can reduce chip temperatures by 5°C during the dehydration process, offering a sustainable solution to thermal management in electronics.

In-situ synthesis and evaluation of anti-bacterial efficacy and angiogenesis of curcumin encapsulated lipogel dermal patch for wound healing applications

The development of synthetic hydrogels as a dermal patch offers unique advantage of providing moist environment around the wound site. The incorporation of curcumin in hydrogel plays a significant role in the healing process of chronic wounds. The present investigation aims to develop nano-formulated curcumin-fused lipogel to impart the dual advantages of sustained drug release and enhanced wound healing ability. The wound healing behaviour of the prepared lipogel has been assessed through series of techniques namely DPPH assay and bacterial inhibitory efficacy through the Kirby Bauer assay against E. coli and S. aureus. Further, the promotion of angiogenesis has been determined through an in-ovo CAM assay. The results obtained from the investigation revealed the enhanced solubility of curcumin in liposome formulation. Moreover, the encapsulation of curcumin in liposomes facilitated prolonged drug release and better antibacterial efficacy against the tested bacterial stains. The developed hydrogel also displayed good adhesion and water retention ability, which is an important prerequisite for better wound healing ability.

High-yield atmospheric water capture via bioinspired material segregation

Transforming atmospheric water vapor into liquid form can be a way to supply water to arid regions for uses such as drinking water, thermal management, and hydrogen generation. Many current methods rely on solid sorbents that cycle between capture and release at slow rates. We envision a radically different approach where water is transformed and directly captured into a liquid salt solution that is suitable for subsequent distillation or other processing using existing methods. In contrast to other methods utilizing hydrogels as sorbents, we do not store water within hydrogels-we use them as a transport medium. Inspired by nature, we capture atmospheric water through a hydrogel membrane "skin" at an extraordinarily high rate of 5.50 kgm[Formula: see text]d[Formula: see text] at a low humidity of 35%. and up to 16.9 kgm[Formula: see text]d[Formula: see text] at higher humidities. For a drinking-water application, calculated performance of a hypothetical one-square-meter device shows that water could be supplied to two to three people in arid environments. This work is a significant step toward providing new resources and possibilities to water-scarce regions.

Physics-based prediction of moisture-capture properties of hydrogels

Moisture-capturing materials can enable potentially game-changing energy-water technologies such as atmospheric water production, heat storage, and passive cooling. Hydrogel composites recently emerged as outstanding moisture-capturing materials due to their low cost, high affinity for humidity, and design versatility. Despite extensive efforts to experimentally explore the large design space of hydrogels for high-performance moisture capture, there is a critical knowledge gap on our understanding behind the moisture-capture properties of these materials. This missing understanding hinders the fast development of novel hydrogels, material performance enhancements, and device-level optimization. In this work, we combine synthesis and characterization of hydrogel-salt composites to develop and validate a theoretical description that bridges this knowledge gap. Starting from a thermodynamic description of hydrogel-salt composites, we develop models that accurately capture experimentally measured moisture uptakes and sorption enthalpies. We also develop mass transport models that precisely reproduce the dynamic absorption and desorption of moisture into hydrogel-salt composites. Altogether, these results demonstrate the main variables that dominate moisture-capturing properties, showing a negligible role of the polymer in the material performance under all considered cases. Our insights guide the synthesis of next-generation humidity-capturing hydrogels and enable their system-level optimization in ways previously unattainable for critical water-energy applications.

Enhanced continuous atmospheric water harvesting with scalable hygroscopic gel driven by natural sunlight and wind

Sorption-based atmospheric water harvesting (SAWH) has received unprecedented attention as a future water and energy platform. However, the water productivity of SAWH systems is still constrained by the slow sorption kinetics at material and component levels and inefficient condensation. Here, we report a facile method to prepare hygroscopic interconnected porous gel (HIPG) with fast sorption-desorption kinetics, high scalability and stability, and strong adhesion property for highly efficient SAWH. We further design a solar-wind coupling driven SAWH device with collaborative heat and mass enhancement achieving continuous water production. Concentrated sunlight contributes to enhancing the desorption and condensation synergistically, and natural wind is introduced to drive the device operation and improve the sorption kinetics. The device demonstrated record high working performance of 14.9 Lwater m-2 day-1 and thermal efficiency of 25.7% in indoor experiments and 3.5-8.9 Lwater m-2 day-1 in outdoor experiments by solar concentration without any other energy consumption. This work provides an up-and-coming pathway to realize highly efficient and sustainable clean water supply for off-grid and arid regions.

Solar-Driven Drum-Type Atmospheric Water Harvester Based on Bio-Based Gels with Fast Adsorption/Desorption Kinetics

Sorption-based atmospheric water harvesting is an attractive technology for exploiting unconventional water sources. A critical challenge is how to facilitate fast and continuous collection of potable water from air. Here, a bio-based gel (cellulose/alginate/lignin gel, CAL gel), resulting from the integration of a whole biomass-derived polymer network with lithium chloride is reported. A fast adsorption/desorption kinetics, with a water capture rate of 1.74 kg kg-1 h-1 at 30% relative humidity and a desorption rate of 1.98 kg kg-1 h-1, is simultaneously realized in one piece of CAL gel, because of its strong hygroscopicity, hydrophilic network, abundant water transport channels, photothermal conversion ability, and ≈200-µm-thick self-supporting bulky structure caused by multicomponent synergy. A solar-driven, drum-type, tunable, and portable harvester is designed that can harvest atmospheric water within a brief time. Under outdoor conditions, the harvester with CAL gels operates 36 switches (180°) per day realizes a water yield of 8.96 kg kggel -1 (18.87 g kgdevice -1). This portable harvester highlights the potential for fast and scalable atmospheric water harvesting in extreme environments.

Chemistries and materials for atmospheric water harvesting

Atmospheric water harvesting (AWH) is recognized as a crucial strategy to address the global challenge of water scarcity by tapping into the vast reserves of atmospheric moisture for potable water supply. Within this domain, sorbents lie in the core of AWH technologies as they possess broad adaptability across a wide spectrum of humidity levels, underpinned by the cyclic sorption and desorption processes of sorbents, necessitating a multi-scale viewpoint regarding the rational material and chemical selection and design. This Invited Review delves into the essential sorption mechanisms observed across various classes of sorbent systems, emphasizing the water-sorbent interactions and the progression of water networks. A special focus is placed on the insights derived from isotherm profiles, which elucidate sorbent structures and sorption dynamics. From these foundational principles, we derive material and chemical design guidelines and identify key tuning factors from a structural-functional perspective across multiple material systems, addressing their fundamental chemistries and unique attributes. The review further navigates through system-level design considerations to optimize water production efficiency. This review aims to equip researchers in the field of AWH with a thorough understanding of the water-sorbent interactions, material design principles, and system-level considerations essential for advancing this technology.

Biomimetic Aerogel Composite for Atmospheric Water Harvesting

Adsorption-based atmospheric water harvesting (AWH) with solar-driven photothermal desorption has become an effective means of solving freshwater scarcity in arid regions due to its low energy consumption and high efficiency. Moisture adsorption and desorption capacities are the most critical properties in AWH, and it is a challenge to improve the rate of moisture adsorption and desorption of composite adsorbents. Therefore, this paper reports a SA/carboxymethyl chitosan (CCS)/C/CaCl2-U composite aerogel adsorbents with simultaneously green, low-cost, degradable, and fast hygroscopicity and desorption kinetics. The composite adsorbent used water-soluble biomass materials sodium alginate (SA) and carboxymethyl chitosan (CCS) as the backbone of the aerogel, constructed a vertically aligned unidirectional pore structure by directional freezing, and introduced nanocarbon powder and moisture-absorbent salt calcium chloride (CaCl2) to improve the solar photothermal performance and water absorption, respectively. The results showed that the composite adsorbent had good water uptake capacity at 30-90% relative humidity (RH), the time to reach the water uptake of 1 g g-1 at 90% RH was only 2.5 h, and the final water uptake rate was up to 1.9 g g-1 within 12 h. Meanwhile, the composite sorbent can be heated and desorbed basically within 1 h at 80 °C and its evaporation efficiency is 1.3 times higher than that of the aerogel sorbent prepared by the conventional method when irradiated with 1000 W m-2 light intensity for 2 h. Therefore, the SA/CCS/C/CaCl2-U composite aerogel adsorbent of this study has a potential that can be applied in AWH due to its environmental friendliness, low cost, and faster hygroscopic desorption kinetics.

Nature-Inspired Molecular-Crowding Enabling Wide-Humidity Range Applicable, Anti-Freezing, and Robust Zwitterionic Hydrogels for On-Skin Electronics

Hydrogels are currently in the limelight for applications in soft electronics but they suffer from the tendency to lose water or freeze when exposed to dry environments or low temperatures. Molecular crowding is a prevalent occurrence in living cells, in which molecular crowding agents modify the hydrogen bonding structure, causing a significant reduction in water activity. Here, a wide-humidity range applicable, anti-freezing, and robust hydrogel is developed through the incorporation of natural amino acid proline (Pro) and conductive MXene into polyvinyl alcohol (PVA) hydrogel networks. Theoretical calculations reveal that Pro can transform "free water" into "locked water" via the molecular-crowding effect, thereby suppressing water evaporation and ice forming. Accordingly, the prepared hydrogel exhibits high water retention capability, with 77% and 55% being preserved after exposure to 20 °C, 28% relative humidity (RH) and 35 °C, 90% RH for 12 h. Meanwhile, Pro lowers the freezing temperature of the hydrogel to 34 °C and enhances its stretchability and strength. Finally, the PVA/Pro/MXene hydrogels are assembled as multifunctional on-skin strain sensors and conductive electrodes to monitor human motions and detect tiny electrophysiological signals. Collectively, this work provides a molecular crowding strategy that will motivate researchers to develop more advanced hydrogels for versatile applications.

Entangled Mesh Hydrogels with Macroporous Topologies via Cryogelation for Rapid Atmospheric Water Harvesting

Sorption-based atmospheric water harvesting (SAWH) is a promising technology to alleviate freshwater scarcity. Recently, hygroscopic salt-hydrogel composites (HSHCs) have emerged as attractive candidates with their high water uptake, versatile designability, and scale-up fabrication. However, achieving high-performance SAWH applications for HSHCs has been challenging because of their sluggish kinetics, attributed to their limited mass transport properties. Herein, a universal network engineering of hydrogels using a cryogelation method is presented, significantly improving the SAWH kinetics of HSHCs. As a result of the entangled mesh confinements formed during cryogelation, a stable macroporous topology is attained and maintained within the obtained entangled-mesh hydrogels (EMHs), leading to significantly enhanced mass transport properties compared to conventional dense hydrogels (CDHs). With it, corresponding hygroscopic EMHs (HEMHs) simultaneously exhibit faster moisture sorption and solar-driven water desorption. Consequently, a rapid-cycling HEMHs-based harvester delivers a practical freshwater production of 2.85 Lwater kgsorbents -1 day-1 via continuous eight sorption/desorption cycles, outperforming other state-of-the-art hydrogel-based sorbents. Significantly, the generalizability of this strategy is validated by extending it to other hydrogels used in HSHCs. Overall, this work offers a new approach to efficiently address long-standing challenges of sluggish kinetics in current HSHCs, promoting them toward the next-generation SAWH applications.

An Atmospheric Water-Harvester with Ultrahigh Uptake-Release Efficiency at Low Humidity

Atmospheric water harvesting is a practical strategy that is achieved by removing materials from air moisture to relieve global water scarcity. Here we design a water-harvester (i.e., MOF-303/thiolated polymer composite (MTC)) by using a metal-organic framework (MOF-303) and thiolated chitosan (TC) skeleton. Intermolecular hydrogen bonding between TC and MOF-303 facilitates porous structures with enlarged air-polymer interfaces for long cycling life and high capacity at low relative humidity. Benefiting from synergetic effects on porosity and anchorage for accelerating the uptake-release of moisture, MTC exhibits a rapid water uptake capacity of 0.135 g/g in 60 min under 12.5 RH% and ultrafast water desorption kinetics of 0.003 g/g/min at 8.5 RH%, which is superior to the as-reported MOF-303 based adsorbents. At low heat (∼40 °C), the water desorption and collection rate, respectively, are 0.0195 and 0.0168 g/g/min within 210 min, showing ultrahigh harvesting efficiency. These results highlight the enormous potential as promising materials for solving the world's water scarcity crisis. This study offers an insight into the design of AWH materials, which can be extended into applications in some realms, e.g., freshwater development for industry in arid areas, water engineering-related devices and systems, etc.

Macroporous, Highly Hygroscopic, and Leakage-Free Composites for Efficient Atmospheric Water Harvesting

Hygroscopic composites based on hygroscopic salts and hydrogels are promising for atmospheric water harvesting (AWH), but their relatively low water production and possible salt leakage hinder real applications. Here, we report highly hygroscopic and leakage-free composites from loading LiCl into emulsion-templated sodium alginate and poly(vinyl alcohol) hydrogels with macroporous structures and interpenetrating polymer networks. The resulting composites exhibited an enhanced moisture uptake (up to 3.4 g g-1) and leakage-free behavior even at an extremely high relative humidity (RH) of 90%. Moreover, the composites showed accelerated adsorption, with high adsorption (0.803 g g-1 water at 25 °C and 90% RH within 1 h) and desorption due to the emulsion-templated, highly interconnected macropores. The hygroscopic composites obtained 1.12 g g-1 water per adsorption-desorption collection cycle and showed high reusability, without obvious deterioration in adsorption, desorption, and collection after 10 cycles. With the presence of carbon nanotubes, solar-driven AWH could be realized, without the requirement of additional energy. The highly hygroscopic and leakage-free composites with enhanced and accelerated adsorption and desorption are excellent candidates for efficient AWH.

Intrinsic Water Transport in Moisture-Capturing Hydrogels

Moisture-capturing hydrogels have emerged as attractive sorbent materials capable of converting ambient humidity into liquid water. Recent works have demonstrated exceptional water capture capabilities of hydrogels while simultaneously exploring different strategies to accelerate water capture and release. However, on the material level, an understanding of the intrinsic transport properties of moisture-capturing hydrogels is currently missing, which hinders their rational design. In this work, we combine absorption and desorption experiments of macroscopic hydrogel samples in pure vapor with models of water diffusion in the hydrogels to demonstrate the first measurements of the intrinsic water diffusion coefficient in hydrogel-salt composites. Based on these insights, we pattern hydrogels with micropores to significantly decrease the required absorption and desorption times by 19% and 72%, respectively, while reducing the total water capacity of the hydrogel by only 4%. Thereby, we provide an effective strategy toward hydrogel material optimization, with a particular significance in pure-vapor environments.

Self-Healing and Wide Temperature-Tolerant Cellulose-Based Eutectogels for Reversible Humidity Detection

A kind of ionic conductive gel (also named eutectogel) is developed from an inorganic salt (ZnCl2)-based deep eutectic solvent (DES). The ternary DES consists of ZnCl2, acrylic acid, and water, and cotton linter cellulose is introduced into the DES system to tailor its mechanical and conductive properties. Enabled by the extensive hydrogen bonds and ion-dipole interactions, the obtained eutectogel displays superior ionic conductivity (0.33 S/m), high stretchability (up to 2050%), large tensile strength (1.82 MPa), and wide temperature tolerance (-40 to 60 °C). In particular, the water-induced coordination interactions can tune the strength of hydrogen/ionic bonds in the eutectogels, imparting them with appealing humidity sensing ability in complex and extreme conditions.

Phospholipid Bilayer Inspired Sandwich Structural Nanofibrous Membrane for Atmospheric Water Harvesting and Selective Release

Atmospheric water harvesting (AWH) has been broadly exploited to meet the challenge of water shortage. Despite the significant achievements of AWH, the leakage of hydroscopic salt during the AWH process hinders its practical applications. Herein, inspired by the unique selective permeability of the phospholipid bilayer, a sandwich structural (hydrophobic-hydrophilic-hydrophobic) polyacrylonitrile nanofibrous membrane (San-PAN) was fabricated for AWH. The hydrophilic inner layer loaded with LiCl could capture water from the air. The hydrophobic microchannels in the outer layer could selectively allow the free transmission of gaseous water molecules but confine the hydroscopic salt solution in the hydrophilic layer, achieving continuous and recyclable water sorption/desorption. As demonstrated, the as-prepared AWH devices presented high-efficient adsorption kinetics from 1.66 to 4.08 g g-1 at 30% to 90% relative humidity. Thus, this work strengthens the understanding of the water transmission process along microchannels and provides insight into the practical applications of AWH.

Hygroscopy as an Indicator of Specific Surface Area in Polymer Materials

Specific surface area (SSA) is an integral characteristic of the interfacial surface in poly-disperse systems, widely used for the assessment of technological properties in polymer materials and composites. Hygroscopic water content (Wh) is an obligate indicator of dispersed materials prior to any analysis of their chemical composition. This study links both indicators for the purpose of the express assessment of SSA using widely available Wh data, on the example of natural (starch, cellulose) and synthetic (acrylic hydrogels) polymer materials. The standard BET analysis of SSA using water vapor desorption was chosen as a reference method. In contrast to the known empirical correlations, this study is based on the fundamental thermodynamic theory of the disjoining water pressure for the connection of the analyzed quantities. The statistical processing of the results for the new methodology and the standard BET method showed their good compliance in a wide range of SSA from 200 to 900 m2/g. The most important methodological conclusion is the possibility of an accurate physically based calculation of hydrophilic SSA in polymer materials using their Wh data at a known relative humidity in the laboratory.