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We would like to thank the King Abdullah University of Science and Technology (KAUST) and Saudi Aramco for generous funding to support this project (RGC/3/3577-01-01).

Solar-assisted distillation is considered promising to solve the freshwater supply for off-grid communities. In this work, a passive and flexible multistage membrane distillation (F-MSMD) device is devised to produce freshwater via solar distillation with the latent heat of vapor condensation being recycled to enhance its energy efficiency. By designing a siphon effect, source water is continuously wicked into the evaporation layer and the concentrated brine flows out of the device before reaching saturation, which successfully solves the otherwise challenge of salt accumulation inside the device. To achieve such siphon flow, the recycled paper is prepared from spent copy paper and used as the evaporation layer for efficient water delivery owing to its large pore size and high hydrophilicity. An eight-stage F-MSMD device exhibits a stable clean water production rate at 3.61 kg m-2 h-1 in the newly designed siphon-flow mode. This work provides a green route for designing a solar-assisted distillation device.

Quick fever screening at a mass scale is proven effective during a pandemic to single out the ones with suspected symptoms of infectious diseases. However, achieving affordable and real-time fever alert at an individual level, although more preferable, remains elusive. Herein, we report an inexpensive and highly sensitive fever detector, which possesses a sharp color transition temperature window tailor-tuned for fever screening. The sensing component of the detector is rationally designed thermoresponsive agarose@poly(N-isopropylacrylamide)-co-acrylamide hydrogel. The hydrogel turns from transparent to opaque white when its temperature is higher than its cloud point. As a proof of concept of its practical applicability, a wearable fever monitoring device was fabricated in the form of a wristband. When the wrist temperature is higher than the threshold of a human fever, the device shows a remarkable color change, alerting an elevated body temperature. The wearable detector provides a promising strategy for real-time fever alert monitoring and is capable of making contributions to inhibit the spread of infectious diseases during a pandemic.

Proper disposal of industrial brine has been a critical environmental challenge. Zero liquid discharge (ZLD) brine treatment holds great promise to the brine disposal, but its application is limited by the intensive energy consumption of its crystallization process. Here we propose a new strategy that employs an advanced solar crystallizer coupled with a salt crystallization inhibitor to eliminate highly concentrated waste brine. The rationally designed solar crystallizer exhibited a high water evaporation rate of 2.42 kg m−2 h−1 under one sun illumination when treating real concentrated seawater reverse osmosis (SWRO) brine (21.6 wt%). The solar crystallizer array showed an even higher water evaporation rate of 48.0 kg m−2 per day in the outdoor field test, suggesting a great potential for practical application. The solar crystallizer design and the salt crystallization inhibition strategy proposed and confirmed in this work provide a low-cost and sustainable solution for industrial brine disposal with ZLD., Proper disposal of industrial brine remains a critical environmental challenge. Here, the authors devise a solar crystallizer and propose a salt crystallization inhibition strategy, which together provide a low-cost and sustainable solution for industrial brine disposal with zero liquid discharge.

The shortage and contamination of local water resources have long been a challenge especially for off-grid communities without centralized water supply. The emerging solar photothermal distillation lacks the capability of handling polluted source water with a wide range of common environmental pollutants. Based on water vapor harvesting, this work reports a Simple Water Extraction Apparatus with Pollutant Shielding (SWEAPS) design which is able to efficiently produce clean water from various polluted liquid water sources and the atmosphere. SWEAPS is fabricated by encapsulating a water vapor sorbent by an omniphobic fabric. The omniphobicity of the encapsulation fabric endows SWEAPS with self-floating capability and the ability to screen out the contaminants in the source water. The self-floating properties of SWEAPS allow it to harvest clean water vapor right above the source-water–air interface where the relative humidity is close to 100%, leading to its much higher water harvesting capacity than that of the same material harvesting water vapor from the ambient atmosphere. Due to the chemical and physical stability, anti-bacterial, pollution and corrosion shielding effects of SWEAPS, it is demonstrated to produce clean water meeting the WHO drinking water standard from various polluted water resources, such as seawater, contaminated water, and amazingly untreated real domestic wastewater. SWEAPS has the potential to produce clean water for point of consumption at a decentralized scale and thus to improve the quality of life for those who need water most.

Metal- and halide-free, solid-state water vapor sorbents are highly desirable for water-sorption-based applications, because most of the solid sorbents suffer from low water sorption capacity caused by their rigid porosity, while the liquid sorbents are limited by their fluidity and strong corrosivity, which is caused by the halide ions. Herein, we report a novel type of highly efficient and benign polymeric sorbent, which contains no metal or halide, and has an expandable solid state when wet. A group of sorbents are synthesized by polymerizing and crosslinking the metal-free quaternary ammonium monomers followed by an ion-exchange process to replace chloride anions with benign-anions, including acetate, oxalate, and citrate. They show significantly reduced corrosivity and improved water sorption capacity. Importantly, the water sorption capacity of the acetate paired hydrogel is among the best of the literature reported hygroscopic polymers in their pure form, even though the hydrogel is crosslinked. The hydrogel-based sorbents are further used for water-sorption-driven cooling and atmospheric water harvesting applications, which show improved coefficient of performance (COP) and high freshwater production rate, respectively. The results of this work would inspire more research interest in developing better water sorbents and potentially broaden the application horizon of water-sorption-based processes towards the water-energy nexus.

More than 600 GW of photovoltaic panels are currently installed worldwide, with the predicted total capacity increasing very rapidly every year. One essential issue in photovoltaic conversion is the massive heat generation of photovoltaic panels under sunlight, which represents 75–96% of the total absorbed solar energy and thus greatly increases the temperature and decreases the energy efficiency and lifetime of photovoltaic panels. In this report we demonstrate a new and versatile photovoltaic panel cooling strategy that employs a sorption-based atmospheric water harvester as an effective cooling component. The atmospheric water harvester photovoltaic cooling system provides an average cooling power of 295 W m–2 and lowers the temperature of a photovoltaic panel by at least 10 °C under 1.0 kW m–2 solar irradiation in laboratory conditions. It delivered a 13–19% increase in electricity generation in a commercial photovoltaic panel in outdoor field tests conducted in the winter and summer in Saudi Arabia. The atmospheric water harvester based photovoltaic panel cooling strategy has little geographical constraint in terms of its application and has the potential to improve the electricity production of existing and future photovoltaic plants, which can be directly translated into less CO2 emission or less land occupation by photovoltaic panels. As solar power is taking centre stage in the global fight against climate change, atmospheric water harvester based cooling represents an important step toward sustainability. Photovoltaic panel conversion generates heat that reduces the energy efficiency and lifetime of the panel. A photovoltaic panel cooling strategy by a sorption-based atmospheric water harvester is shown to improve the productivity of electricity generation with important sustainability advantages.

Energy & fresh water have both become scarce resources in the modern era of human society. Sorption-based technology is environmentally friendly and energy-efficient and can be driven by low-grade energy to transfer energy and produce fresh water. Here, we report a solid sorbent fabricated by encapsulating a hygroscopic salt, lithium chloride (LiCl), inside micro-sized hollow-structured SiO2. This composite sorbent (LiCl@HS) exhibits 6 times faster water vapor sorption kinetics than pure LiCl and a water vapor sorption capacity of 1.7 kg kg-1 at a relative humidity (RH) of 50%, which is the highest ever reported for any solid sorbent in the literature. The low regeneration temperature (

Salinity-gradient is emerging as one of the promising renewable energy sources but its energy conversion is severely limited by unsatisfactory performance of available semipermeable membranes. Recently, nanoconfined channels, as osmotic conduits, have shown superior energy conversion performance to conventional technologies. Here, ion selective nanochannels in lamellar Ti3C2Tx MXene membranes are reported for efficient osmotic power harvesting. These subnanometer channels in the Ti3C2Tx membranes enable cation-selective passage, assisted with tailored surface terminal groups, under salinity gradient. A record-high output power density of 21 W·m-2 at room temperature with an energy conversion efficiency of up to 40.6% is achieved by controlled surface charges at a 1000-fold salinity gradient. In addition, due to thermal regulation of surface charges and ionic mobility, the MXene membrane produces a large thermal enhancement at 331 K, yielding a power density of up to 54 W·m-2. The MXene lamellar structure, coupled with its scalability and chemical tunability, may be an important platform for high-performance osmotic power generators.

The energy shortage and clean water scarcity are two key challenges for global sustainable development. Near half of the total global water withdrawals is consumed by power generation plants while water desalination consumes lots of electricity. Here, we demonstrate a photovoltaics-membrane distillation (PV-MD) device that can stably produce clean water (>1.64 kg·m−2·h−1) from seawater while simultaneously having uncompromised electricity generation performance (>11%) under one Sun irradiation. Its high clean water production rate is realized by constructing multi stage membrane distillation (MSMD) device at the backside of the solar cell to recycle the latent heat of water vapor condensation in each distillation stage. This composite device can significantly reduce capital investment costs by sharing the same land and the same mounting system and thus represents a potential possibility to transform an electricity power plant from otherwise a water consumer to a fresh water producer., The increasing demand for energy and clean water has become a grand global challenge. Here the authors develop a membrane-distillation device that exploits sunlight and the heat dissipated by an integrated solar cell unit, enabling simultaneous efficient production of electricity and drinkable water.

The application of solar-driven water evaporation process in clean water production via solar distillation is recently intensively investigated. The phase change and mass transfer processes during the solar-driven water evaporation process can directly leave behind the salts, heavy metals, organic dyes, etc and simultaneously produce the clean water vapor. However, if the water source is contaminated by volatile organic compounds (VOCs), solar-driven water evaporation may accelerate VOCs volatile and enrich them in the condensate. In this work, the enrichment of VOCs in distillate water was first demonstrated and a multi-functional honeycomb ceramic plate was fabricated by coating a layer of CuFeMnO4 on the surface of a cordierite honeycomb ceramic substrate. The honeycomb structure was beneficial for light trapping and energy recycling and thus to improve the solar-to-water evaporation efficiency. The CuFeMnO4 coating layer acted as both the photothermal material for solar-driven water evaporation process and the catalyst for VOCs removal via heterogeneous photon-Fenton reaction. With the integration of photo-Fenton reaction into the solar distillation process, the clean distillate water was produced with efficient removal of the potential VOCs from the contaminated water sources.

A smart material with switchable surface wettability is highly desired for the practical application in removing oil from oily wastewater. In this work, we developed a robust and simple method to f...

A sustainable supply of clean water is essential for the development of modern society, which has become increasingly dependent on desalination technology since 96.5% of the water on Earth is salt water. Thousands of desalination plants are producing massive waste brine as byproduct, and the direct discharge of brine raises serious concerns about its ecological impact. The concept of zero liquid discharge (ZLD) desalination is regarded as the solution, but the current ZLD technologies are hampered by their intensive use of energy and high cost. In this work, a 3D cup shaped solar evaporator was fabricated to achieve ZLD desalination with high energy efficiency via solar distillation. It produces solid salt as the only byproduct and uses sunlight as the only energy source. By rationally separating the light absorbing surface from the salt precipitation surface, the light absorption of the 3D solar evaporator is no longer affected by the salt crust layer as in conventional 2D solar evaporators. Therefore, it can be operated at an extremely high salt concentration of 25 wt % without noticeable water evaporation rate decay in at least 120 h. This new solar evaporator design concept offers a promising technology especially for high salinity brine treatment in desalination plants to achieve greener ZLD desalination as well as for hypersaline industrial wastewater treatment.

Solar steam generation, due to its capability of producing clean water directly by solar energy, is emerging as a promising eco-friendly and energy-efficient technology to address global challenges of water crisis and energy shortage. Although diverse materials and architectures have been explored to improve solar energy utilization, high efficiency in solar steam generation could be accomplished only with external optical and thermal management. For the first time, we report a deployable, three-dimensional (3D) origami-based solar steam generator capable of near full utilization of solar energy. This auxetic platform is designed based on Miura-ori tessellation and is able to efficiently recover radiative and convective heat loss as well as to trap solar energy via its periodic concavity pattern. The 3D solar steam generator device with a nanocarbon composite of graphene oxide and carbon nanotubes being photothermal component in this work shows a very strong dependence between its solar energy efficiency and surface areal density. The device yields an extraordinary solar energy efficiency close to 100% under 1 sun illumination at a highly folded configuration. The 3D origami device can withstand a great number of folding and unfolding cycles and shows unimpaired solar steam generation performances. The unique structural feature of the 3D origami structure offers a new insight into the future development of highly efficient and easily deployable solar steam generator.

Hybrid nanostructures integrating electroactive materials with functional species, such as metal-organic frameworks, covalent organic frameworks, graphdiyne etc., are of significance for both fundamental research and energy conversion/storage applications. Here, hierarchical triple-layered nanotube arrays, which consist of hydrogen-substituted graphdiyne frameworks seamlessly sandwiched between an outer layer of nickel–cobalt co-doped molybdenum disulfide nanosheets and an inner layer of mixed cobalt sulfide and nickel sulfide (Co9S8/Ni3S2), are directly fabricated on conductive carbon paper. The elaborate triple-layered structure emerges as a useful hybrid electrode for energy conversion and storage, in which the organic hydrogen-substituted graphdiyne middle layer, with an extended π-conjugated system between the electroactive nanomaterials, provides built-in electron and ion channels that are crucial for performance enhancement. This dual-template synthetic method, which makes use of microporous organic networks to confine a self-template, is shown to be versatile and thus provides a promising platform for advanced nanostructure-engineering of hierarchical multi-layered nanostructures towards a wide range of electrochemical applications., Multi-shelled nanomaterials offer interesting electrochemical properties, but have been limited in composition. Here the authors use dual templating to integrate electroactive metal chalcogenide layers with hydrogen-substituted graphdiyne, achieving electrocatalytic activity for hydrogen evolution.

Summary The energy efficiency in solar steam generation by 2D photothermal materials has approached its limit. In this work, we fabricated 3D cylindrical cup-shaped structures of mixed metal oxide as solar evaporator, and the 3D structure led to a high energy efficiency close to 100% under one-sun illumination due to the capability of the cup wall to recover the diffuse reflectance and thermal radiation heat loss from the 2D cup bottom. Additional heat was gained from the ambient air when the 3D structure was exposed under one-sun illumination, leading to an extremely high steam generation rate of 2.04 kg m −2 h −1 . The 3D structure has a high thermal stability and shows great promise in practical applications including domestic wastewater volume reduction and seawater desalination. The results of this work inspire further research efforts to use 3D photothermal structures to break through the energy efficiency limit of 2D photothermal materials.

Solar-driven water distillation by photothermal materials is emerging as a promising way of renewable energy-driven clean water production. In designing photothermal materials, light absorption, photo-to-thermal conversion efficiency, and ability to localize thermal energy at the water–air interface are three important considerations. However, one additional consideration, regenerability, has so far slipped out of the photothermal material designs at status quo. This work reveals that there is a fouling layer formed during photothermal evaporation of real seawater (Red Sea water) and domestic wastewater, which once formed would be difficult to remove. Herein, we synthesize a SiC–C composite monolith as an effective photothermal material where carbon acts as photothermal component and SiC serves as a heat conductor and strong structural support. The high mechanical strength of the monolithic composite makes it able to withstand repeatedly high strength physical cleaning by brush scrubbing and sonication, a...

Solar-driven water evaporation is emerging as a promising solar-energy utilization process. In the present work, a highly stable, flexible and washable nonwoven photothermal cloth is prepared by electrospinning for efficient and durable solar steam evaporation. The cloth is composed of polymeric nanofibers as the matrix and inorganic carbon black nanoparticles encapsulated inside the matrix as light absorbing components. The photothermal cloth with an optimized carbon loading shows desirable underwater black properties, absorbing 94% of the solar spectrum and giving rise to a state-of-the-art solar energy utilization efficiency of 83% during the pure water evaporation process. Owing to its compositions and special structural design, the cloth possesses anti-photothermal-component-loss properties and is highly flexible, mechanically strong, and chemically stable in various harsh environments such as strong acid, alkalis, organic solvents and salty water. It can be hand-washed more than 100 times without degrading its performance and thus offers a potential mechanism for foulant cleaning during practical solar steam generation and distillation processes. The results of this work stimulate more research in durable photothermal materials aiming at real world applications.

Rapid cleanup of heavy oil spills is always considered a great challenge because conventional porous oil sorbents cannot efficiently remove them due to the high viscosity of heavy oil (>103 mPa s). In this work, we take advantage of the photothermal effect to heat heavy oil by using sunlight as the energy source to significantly reduce its viscosity and thus to achieve a fast heavy oil cleanup. A carbon nanotube (CNT) modified polyurethane sponge was fabricated as a photothermal sorbent that exhibited superhydrophobicity and superoleophilicity, as well as outstanding absorption capacity for heavy oil. Thanks to the excellent photothermal effect of CNTs, the modified sponge achieved nearly full sunlight absorption (99%). The resulting solar heating effectively reduced the viscosity of the heavy oil, which enabled the modified sponge to quickly absorb 20 times its own weight of heavy oil under sun illumination. This solar-assisted heavy oil sorbent design is promising for future remediation of viscous oil-spills.

Salinity-gradient is emerging as one of the promising renewable energy sources but its energy conversion is severely limited by unsatisfactory performance of available semipermeable membranes. Recently, nanoconfined channels, as osmotic conduits, have shown superior energy conversion performance to conventional technologies. Here, ion selective nanochannels in lamellar Ti

This project is based upon work supported by the King Abdullah University of Science and Technology (KAUST) Center Applied Research Fund (CAF) awarded to the Water Desalination and Reuse Center (WDRC).

Clean water shortage has long been a challenge in remote and landlocked communities especially for the impoverished. Atmospheric water is now considered as an unconventional but accessible fresh water source and sorption-based atmospheric water generator (AWG) has been successfully demonstrated a reliable way of harvesting atmospheric water. The water vapor sorbents with high water uptake capacity and especially fast vapor sorption/desorption kinetics have become the bottleneck to a desirable clean water productivity in AWG. In this work, we developed a new nano vapor sorbent composed of a nano carbon hollow capsule with LiCl inside the void core. The sorbent can capture water vapor from ambient air as much as 100% of its own weight under RH 60% within 3 h and quickly release the sorbed water within just half hour under 1 kW/m2 sunlight irradiation. A batch-mode AWG device was able to conduct 3 sorption/desorption cycles within 10 h during one day test in the outdoor condition and produced 1.6 kgwater/kgsorbent. A prototype of continuous AWG device was designed, fabricated, and successfully demonstrated, hinting a possible way of large-scale deployment of AWG for practical purposes.

Smart windows with high near-infrared (NIR) light shielding and controllable visible light transmittance are highly sought after for cooling energy saving in buildings. Herein, we present a rationally designed spectrally selective smart window which is capable of shielding 96.2% of the NIR irradiation from 800 to 2500 nm and at the same time permitting acceptable visible light (78.2% before and 45.3% after its optical switching) for indoor daylighting. The smart window synergistically integrates the highly selective and effective NIR absorption based photothermal conversion of cesium tungsten bronze (CsxWO3) with the transparent thermoresponsive poly(N-isopropyl acrylamide) (PNIPAM) microgel–polyacrylamide (PAM) hydrogel. Optical switching of the smart window is a direct result of the phase transition of PAM–PNIPAM hydrogel, which in turn is induced by the photothermal effect of CsxWO3 under sunlight irradiation. The smart window exhibits fast optical switching, shows long-term operational stability, and ...

The Earth's atmosphere holds approximately 12 900 billion tons of fresh water distributed all over the world with fast replenishment. Atmospheric water harvesting is emerging as a promising strategy for clean water production in arid regions, land-locked areas, and remote communities. The water vapor sorbent is the key component for atmospheric water harvesting devices based on absorbing-releasing process. In this work, a flexible hybrid photothermal water sorbent composed of deliquescent salt and hydrogel was rationally fabricated. It possesses superior water sorption capacity even in low humidity air thanks to the deliquescent salt and maintains a solid form after it sorbs a large amount of water owing to the hydrogel platform. The harvested water could be easily released under regular sunlight via the photothermal effect, and it can be directly reused without noticeable capacity fading. An "easy-to-assemble-at-household" prototype device with 35 g of the dry hydrogel was tested outdoors under field conditions and delivered 20 g of fresh water within 2.5 h under natural sunlight. It is estimated that the material cost of making such a device to supply minimum daily water consumption for an adult (i.e., 3 kg) is only $3.20 (USD). This type of atmospheric water generator (AWG) is cheap and affordable, works perfectly with a broad range of humidity, does not need any electricity, and thus is especially suitable for clean water production in remote areas.

Water condensation is an important phase change phenomenon whose applications range from power generation to water desalination. In the present study, we compared condensation occurring on two different substrates (namely square and strip) and demonstrated the effect of substrate geometry on water condensation. It is found that condensation on different regions of the same substrate is dramatically different due to different local vapor flux. In general, the condensation rate is linearly proportional to vapor flux while average vapor flux can be improved by creating geometrical discontinuity (strip substrate) within rigid substrates. Experimental result of water collection confirms that the condensation rate is increased by around 40% on the strip substrate compared to the square substrate. This study demonstrates that water condensation can be enhanced by rationally tuning the geometry of the condensation substrate. Performance of water condensation of a specific substrate can be predicated by simulating the vapor flux over the substrate.

In this work, a simple and facile approach was developed to modify hydrophobic polyvinylidene fluoride (PVDF) microfiltration membrane with superhydrophilicity and excellent underwater anti-oil adhesion properties. The approach involves a rapid deposition of tannic acid (TA) on the membrane surface followed by its oxidation by sodium periodate (NaIO4). The modified membrane not only showed a promising oil/water separation (greater than 98%) with an average water flux ranging from 38 ± 13 to 401 ± 97 L/m2-h for different kinds of surfactant-stabilized oil-in-water emulsions driven by vacuum pressure but also exhibited excellent recyclability and chemical stability. The modification method is versatile, can be applied on different types of substrate materials, such as non-woven textile and mesh, and thus has a great potential to fabricate materials at large-scale for industrial oily wastewater treatment.

Atmospheric water is an abundant alternative water resource, equivalent to 6 times the water in all rivers on Earth. This work screens 14 common anhydrous and hydrated salt couples in terms of their physical and chemical stability, water vapor harvesting, and release capacity under relevant application scenarios. Among the salts screened, copper chloride (CuCl2), copper sulfate (CuSO4), and magnesium sulfate (MgSO4) distinguish themselves and are further made into bilayer water collection devices, with the top layer being the photothermal layer, while the bottom layer acts as a salt-loaded fibrous membrane. The water collection devices are capable of capturing water vapor out of the air with low relative humidity (down to 15%) and releasing water under regular and even weakened sunlight (i.e., 0.7 kW/m2). The work shines light on the potential use of anhydrous salt toward producing drinking water in water scarce regions.

Condensed water droplet jumping on superhydrophobic surfaces has been a hot research topic during the last decade for various applications including enhancing condensation, antifogging, self-cleaning, electrostatic energy harvesting, and anti-icing/frosting surfaces. In the present work, a superhydrophobic nano-cone array is prepared by simple chemical bath reaction followed by silane modification. The tip of an individual nano-cone is only around 10 nm. The nano-cone array is also characterized by cavities among cones with varying sizes due to the imperfect alignment of individual nano-cones to the substrate. We demonstrate theoretically and experimentally that water condensation preferentially occurs within larger cavities among hydrophobized nano-cone arrays. After extrusion from cavities, droplets form a partial Cassie state which is a prerequisite of coalescence induced jumping. Moreover, growth rates of droplets extruded from larger cavities are larger than those from smaller cavities. Droplet jumping is observed at the very first coalescence and after multiple coalescence events under a microscope. The jumping droplet size is at tens of microns, demonstrating that droplets can be efficiently removed from the nano-cone array. In general, it is indicated that condensation can be controlled by purposely designing nano-scale structures, which would provide valuable suggestion for applications involving water condensation.

This work was supported by the King Abdullah University of Science and Technology (KAUST) center competitive fund (CCF) awarded to Water Desalination and Reuse Center (WDRC).