Solar vapour generation is an efficient way of harvesting solar energy for the purification of polluted or saline water. However, water evaporation suffers from either inefficient utilization of solar energy or relies on complex and expensive light-concentration accessories. Here, we demonstrate a hierarchically nanostructured gel (HNG) based on polyvinyl alcohol (PVA) and polypyrrole (PPy) that serves as an independent solar vapour generator. The converted energy can be utilized in situ to power the vaporization of water contained in the molecular meshes of the PVA network, where water evaporation is facilitated by the skeleton of the hydrogel. A floating HNG sample evaporated water with a record high rate of 3.2 kg m h via 94% solar energy from 1 sun irradiation, and 18-23 litres of water per square metre of HNG was delivered daily when purifying brine water. These values were achievable due to the reduced latent heat of water evaporation in the molecular mesh under natural sunlight.

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Water purification by solar distillation is a promising technology to produce fresh water. However, solar vapor generation, is energy intensive, leading to a low water yield under natural sunlight. Therefore, developing new materials that can reduce the energy requirement of water vaporization and speed up solar water purification is highly desirable. Here, we introduce a highly hydratable light-absorbing hydrogel (h-LAH) consisting of polyvinyl alcohol and chitosan as the hydratable skeleton and polypyrrole as the light absorber, which can use less energy (<50% of bulk water) for water evaporation. We demonstrate that enhancing the hydrability of the h-LAH could change the water state and partially activate the water, hence facilitating water evaporation. The h-LAH raises the solar vapor generation to a record rate of ~3.6 kg m−2 hour−1 under 1 sun. The h-LAH-based solar still also exhibits long-term durability and antifouling functionality toward complex ionic contaminants.

Efficient solar water evaporation was achieved by antifouling hybrid hydrogels with capillarity facilitated water transport and heat concentration in a polymeric network.

Solid-state electrolytes have emerged as a promising alternative to existing liquid electrolytes for next generation Li-ion batteries for better safety and stability. Of various types of solid electrolytes, composite polymer electrolytes exhibit acceptable Li-ion conductivity due to the interaction between nanofillers and polymer. Nevertheless, the agglomeration of nanofillers at high concentration has been a major obstacle for improving Li-ion conductivity. In this study, we designed a three-dimensional (3D) nanostructured hydrogel-derived Li La TiO (LLTO) framework, which was used as a 3D nanofiller for high-performance composite polymer Li-ion electrolyte. The systematic percolation study revealed that the pre-percolating structure of LLTO framework improved Li-ion conductivity to 8.8×10 S cm at room temperature.

Solar vapor generation has presented great potential for wastewater treatment and seawater desalination with high energy conversion and utilization efficiency. However, technology gaps still exist for achieving a fast evaporation rate and high quality of water combined with low‐cost deployment to provide a sustainable solar‐driven water purification system. In this study, a naturally abundant biomass, konjac glucomannan, together with simple‐to‐fabricate iron‐based metal‐organic framework‐derived photothermal nanoparticles is introduced into the polyvinyl alcohol networks, building hybrid hydrogel evaporators in a cost‐effective fashion ($14.9 m−2 of total materials cost). With advantageous features of adequate water transport, effective water activation, and anti‐salt‐fouling function, the hybrid hydrogel evaporators achieve a high evaporation rate under one sun (1 kW m−2) at 3.2 kg m−2 h−1 out of wastewater with wide degrees of acidity and alkalinity (pH 2–14) and high‐salinity seawater (up to 330 g kg−1). More notably, heavy metal ions are removed effectively by forming hydrogen and chelating bonds with excess hydroxyl groups in the hydrogel. It is anticipated that this study offers new possibilities for a deployable, cost‐effective solar water purification system with assured water quality, especially for economically stressed communities.

demonstrated the possibility of directly collecting liquid water from air with the assistance of water condensation at ultrahigh relative humidity (RH = 100%, e.g., fog capture and dew collection). [3][4][5][6][7][8] Due to the dependence of RH on the temperature of the air, such a process requires either periodic temperature drop or artificial cooling systems to raise the RH to be supersaturated. [9] A recent report presents an AWH material functioning at low RH levels down to 20% to harvest moisture (water vapor) from air, enabling the moisture as a promising water source for potential next-generation AWH systems. [10] In view of the seasonal and climatic variation, the RH of the droughty region (such as the Namib Desert) varies between 30% and 90% for most of the years. [3,11] Since such modest RH (at given temperature and air pressure) indicates a relatively large water reservoir in the air, the highly efficient AWH toward this "rich ore" of water, which, however, remains elusive, is vital to both fundamental research and practical applications. In this context, hygroscopic materials based on surface water adsorption, such as molecular sieves, silica gels, and polymeric desiccants, can serve as the moisture absorber over a wide range of RH. [12][13][14] However, the hygroscopic materials designed for moisture capturing exhibit strong interaction with water that significantly hinders the water releasing, blunting their opportunity to be used as atmospheric water harvesters. [15,16] In line with the design of super water-absorbent gels, which are capable of absorbing tens of times its own weight in liquid water, [17,18] we present here a super moisture-absorbent gel (SMAG) that synergistically combines the moisture-absorbing hygroscopic polymer with the water-storing hydrophilic gel, which substantially outperforms other AWH materials. We demonstrate a rationally designed hybrid gel that integrates the hygroscopic chloride-doped polypyrrole (PPy-Cl) and the poly(Nisopropylacrylamide) (poly-NIPAM) with switchable hydrophilicity. [19][20][21] Such an SMAG realizes the polymeric-network-enabled moisture capturing, rather than active-surface-based vapor adsorption as in other AWH materials, and hence exhibits highly efficient AWH in broad humidity range. Moreover, to explore the potential application, we further demonstrate the outdoor experiments by a scalable SMAG prototype with low-cost accessories to simulate the AWH in the natural environment.The critical steps of SMAG-based AWH are (I) water capturing and (II) water releasing. As shown in Figure 1a, the Atmospheric water harvesting (AWH)-producing fresh water via collecting moisture from air-enables sustainable water delivery without geographical and hydrologic limitations. However, the fundamental design principle to prepare materials that can convert the water vapor in the air to collectible liquid water is still mostly unknown. Here, a super moisture-absorbent gel, which is composed of hygroscopic polypyrrole chloride penetrating in hydrophilicityswitchabl...

Conspectus Growing concern over water scarcity leads to increased research interest in advanced water purification technologies. Solar water purification, which uses solar energy to separate water and impurities through vaporization, enables the utilization of sustainable energy and potential freshwater resources to alleviate water scarcity. However, the essential process of solar water evaporation to remove impurities is energy intensive. Insufficient solar absorption and thermal loss limited the vapor generation rate and, thus, lowered the purified water yield. Diffuse natural sunlight cannot satisfy the intrinsic energy demand for rapid water vaporization. Therefore, developing new material platforms that can simultaneously provide high solar absorption, effective energy utilization, and low energy demand for water vaporization to achieve highly efficient solar water purification under natural sunlight is anticipated. In this Account, we review our recent progress on hydrogel-based evaporators for solar water purification in terms of material selection, molecular engineering, and structural design. First, we introduce the unique water state in hydrogels consisting of free, intermediate, and bound water, of which intermediate water has a reduced energy demand for water evaporation. Then, we describe the design principles of hydrogel-based solar evaporators, where the polymeric networks are tailored to regulate the water state. The water state in hydrogels defines the vaporization behavior of water. Thus, the polymer networks of hydrogels can be architected to tune the water state and, hence, to further reduce the evaporation enthalpy of water. Armed with fundamental gelation chemistry, we discuss synthetic strategies of hydrogels for efficient vapor generation. By incorporating solar absorbers with hydrophilic polymer networks, solar energy is harvested and converted to heat energy, which can be in situ utilized to power the vaporization of contained water in the molecular meshes, and the solar absorbers having strong interaction with hydrogels guide the formation of microstructure to reduce the energy loss and ensure adequate water transport of evaporative water. Regulating the vaporizing fronts, engineering the surface of hydrogels has been focused to favor the evaporationof water to further enhance the solar-to-vapor efficiency. By using hydrophilic polymers as building blocks, the hydrogel-based solar evaporators have also been endowed with multiple functionalities, such as antifouling, permselectivity, and thermal responsiveness, to improve water collection and purification abilities. Taking advantages of these merits, hydrogels have emerged as a promising materials platform to enable efficient solar water purification under natural sunlight. This Account serves to promote future efforts toward practical purification systems using hydrogel-based solar evaporators to mitigate water scarcity by improving their performance, scalability, stability, and sustainability.