A humidity/thermal dual response 3D-fabric with porous poly(N-isopropyl acrylamide) hydrogel towards efficient atmospheric water harvesting

Superhygroscopic Aerogels with Hierarchical String-Bag Structure for Effective Humidity Control

Environmental humidity regulation is crucial for diverse applications ranging from healthcare, food preservation, drug storage, to electronics protection. Herein, we employed natural cellulose as the raw material to fabricate superhygroscopic aerogels with hierarchical string-bag structure for effective humidity control. The aggregation state of cellulose chains was regulated to fabricate micronano materials, including the cellulose nanofiber network (CNFN), dendritic microfibers (CDF), and pleated microfibers (CPF), via changing the precipitation process of cellulose/ionic liquid solutions. They immobilized hygroscopic salts (LiCl, CaCl2, and MgSO4) to form uniform aerogels featuring micrometer macropores and nanometer string-bags. The molecular-level distribution of metal salts along the macropore wall and nanofibers, combined with the high hydrophilicity of cellulose, enabled rapid moisture absorption from the environment and transportation within the hierarchical string-bag structure. Moreover, the micronano hierarchical structure was conducive to the water storage. CNFN/LiCl aerogel demonstrated exceptional moisture absorption performance, achieving a water uptake of 1.36 and 3.14 g/g at 30% and 70% RH, respectively. Such superhygroscopic materials could rapidly and effectively control the environmental humidity, indicating a huge potential in food preservation, healthcare, and environmental regulation.

Fabric Solar Evaporator Inspired by Jellyfish for Efficient and Continuous Water Desalination

The conversion of solar energy into heat for seawater desalination is emerging as a promising method. However, it requires further research on light absorption, thermal management, and salt deposition to improve water evaporation rates. This study introduces a 3D solar evaporator inspired by jellyfish utilizing honeycomb fabric (HF), which capitalizes on a synergistic effect between the periodically arranged concave unit structure and the Chinese ink and carbon black particles (ink@CB), achieving up to 98% light absorption with ink@CB-HF. Additionally, the insulating foam effectively separates the evaporating layer from the bulk water, thereby significantly reduces heat loss. Furthermore, the water transport channel and evaporation layer prepared by the hydrophilic flax yarns facilitate ion exchange and water transport, preventing salt accumulation in the photothermal layer during the evaporation. The results demonstrate that the evaporator exhibits an excellent evaporation rate of 1.854 kg m-2 h-1 and a high conversion efficiency of up to 92.2% under 1 sun illumination. It maintains efficient evaporation even under low sunlight or high ion concentration conditions. Notably, the ink@CB-HF-foam sustains its stability throughout 15 evaporation cycles. This work provides a new approach to design cost-effective, highly efficient, and durable solar evaporators for seawater desalination.

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.

A critical review of sodium alginate-based composites in water treatment

The global freshwater crisis is a pressing issue, especially in areas with little rainfall and inner continental regions. The growing attention to water scarcity has induced increased interest in research on advanced water treatment technologies. As an abundant bioactive material in nature, sodium alginate (SA) has been widely used in water management due to its outstanding water absorption and holding ability, reversible swelling property, and pollutant adsorption performance. Building on this, progress made in using various modified forms of SA to access clean water is addressed in this review. Covering studies concern the adsorption and separation of pollutants in wastewater by SA-based absorbents and freshwater harvesting by SA-based collectors. This review explores SA-based composites' composition-structure-construction designs and emphasizes the impact of materials like inorganic materials, functional polymers, and porous matrices and how they can be exploited for water treatment. It also highlights the mechanisms of contaminants adsorption and freshwater desorption of SA-based composites. Finally, the shortcomings and future orientation of SA-based composites are proposed, including performance optimization, structural modification, application expansion, and mechanism in-depth investigation. This review aims to offer a theoretical basis and technical guidance for the use of natural materials to respond to the shortage of freshwater resources.

Guar Gum-Based Macroporous Hygroscopic Polymer for Efficient Atmospheric Water Harvesting

Solar-driven atmospheric water harvesting technology has the advantage of not being limited by geography and has great potential in solving the freshwater crisis. Here, we first propose a purely natural and degradable superhydrophilic composite macroporous hygroscopic material by applying guar gum (GG) to atmospheric water harvesting. The material consists of GG-cellulose nanofibers (CNFs) as a porous substrate material, limiting the hygroscopic factor lithium chloride (LiCl) in its three-dimensional (3D) network structure, and carbon nanotubes (CNTs) play a photothermal conversion role. The composite material has a high light absorption rate of more than 95%, and the macroporous structure (20-60 μm) allows for rapid adsorption/desorption kinetics. At 35 °C and 90% relative humidity (RH), the moisture absorption capacity is as high as 1.94 g/g. Under 100 mW/cm2 irradiation, the absorbed water is almost completely desorbed within 3 h, and the water harvesting performance is stable in 10 cycles. Moreover, liquid water was successfully collected in an actual outdoor experiment. This work demonstrates the great potential of biomass materials in the field of atmospheric water collection and provides more opportunities for various energy and sustainable applications in the future.