Hierarchical Nanocapsules of Cu-Doped MoS2@H-Substituted Graphdiyne for Magnesium Storage.

Hierarchical nanocomposites, which integrate electroactive materials into carbonaceous species, are significant in addressing the structural stability and electrical conductivity of electrode materials in post-lithium-ion batteries. Herein, a hierarchical nanocapsule that encapsulates Cu-doped MoS2 (Cu-MoS2) nanopetals with inner added skeletons in an organic-carbon-rich nanotube of hydrogen-substituted graphdiyne (HsGDY) has been developed for rechargeable magnesium batteries (RMB). Notably, both the incorporation of Cu in MoS2 and the generation of the inner added nanoboxes are developed from a dual-template of Cu-cysteine@HsGDY hybrid nanowire; the synthesis involves two morphology/composition evolutions by CuS@HsGDY intermediates both taking place sequentially in one continuous process. These Cu-doped MoS2 nanopetals with stress-release skeletons provide abundant active sites for Mg2+ storage. The microporous HsGDY enveloped with an extended π-conjugation system offers more effective electron and ion transfer channels. These advantages work together to make this nanocapsule an effective cathode material for RMB with a large reversible capacity and superior rate and cycling performance.

Metal- and halide-free, solid-state polymeric water vapor sorbents for efficient water-sorption-driven cooling and atmospheric water harvesting.

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.

Solar Seawater Distillation by Flexible and Fully Passive Multistage Membrane Distillation.

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.

Designing a next generation solar crystallizer for real seawater brine treatment with zero liquid discharge.

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.

Simultaneous production of fresh water and electricity via multistage solar photovoltaic membrane distillation.

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.

Two-Dimensional Ti3C2Tx MXene Membranes as Nanofluidic Osmotic Power Generators.

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.

Spectrally Selective Smart Window with High Near-Infrared Light Shielding and Controllable Visible Light Transmittance.

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 (Cs xWO3) 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 Cs xWO3 under sunlight irradiation. The smart window exhibits fast optical switching, shows long-term operational stability, and can be made highly flexible. Under the experimental conditions in this work, the indoor temperature with the smart window is ∼21 °C lower than that with a regular single-layered glass window under one sun irradiation. The smart window design in this work is meaningful for further development of effective smart windows for energy saving in the build environment.

Solar Evaporator with Controlled Salt Precipitation for Zero Liquid Discharge Desalination.

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.

Hybrid Hydrogel with High Water Vapor Harvesting Capacity for Deployable Solar-Driven Atmospheric Water Generator.

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.

Dual-template engineering of triple-layered nanoarray electrode of metal chalcogenides sandwiched with hydrogen-substituted graphdiyne.

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.

Nature-Inspired, 3D Origami Solar Steam Generator toward Near Full Utilization of Solar Energy.

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.

Harvesting Water from Air: Using Anhydrous Salt with Sunlight.

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.