Thermoresponsive hydrogel technology for efficient atmospheric water harvesting

Background

Rapidly growing global water scarcity and the need for decentralized, energy-efficient water collection have driven the search for atmospheric water harvesting systems that can overcome limitations in conventional approaches.

Traditional fog capture or dew condensation methods often depend on high humidity levels, while existing sorbent-based techniques such as silica gels, zeolites, and conventional polymeric hydrogels face challenges including low water uptake, high energy requirements for regeneration, and slow vapor sorption kinetics. Furthermore, modifications like incorporating hygroscopic salts into thermoresponsive hydrogels can lead to issues such as salt leakage, diminished swelling capacity, and elevated desorption temperatures—all of which hinder effective water release and long-term operational stability.

Technology overview

A bifunctional polymer network combines hygroscopic zwitterionic units with thermoresponsive NIPAM moieties, enabling stable water uptake, controlled low-temperature release, and rapid sorption-desorption cycles. The hydrogel, synthesized via in situ free-radical polymerization and subsequently loaded with LiCl, forms amorphous microgels in the 50-100 μm range. By immobilizing hygroscopic sites within the polymer matrix, the design circumvents problems such as salt leakage and reduced swelling. The incorporation of photothermal absorbers like Ppy:PSS enhances solar absorption across a broad spectrum, facilitating efficient, solar-driven water release. This approach ensures effective atmospheric water harvesting even at low relative humidities by relying on confined hydration mechanisms and optimized swelling behavior.

Benefits

• Energy efficiency: The hybrid microgels enable water release at lower temperatures using mild heating or solar radiation, in contrast to conventional salt-infused hydrogels (e.g., LiCl- or CaCl₂-doped systems) that require high-energy input for desorption.
• Rapid sorption-desorption kinetics: The microgel configuration shortens water diffusion distances, achieving ultrafast uptake and release compared to traditional polymeric hydrogels like PNIPAM, which typically exhibit slower kinetics.
• Enhanced stability and reduced ion leakage: The confined hydration strategy immobilizes hygroscopic sites, preventing uncontrolled salt liquefaction and leakage—a common drawback in conventional salt-infused hydrogels.
• Broad humidity range operation: The technology efficiently harvests water even in low relative humidity environments, overcoming the limitations of fog capture and dew condensation methods that require high humidity conditions.
• Improved solar absorption: By incorporating photothermal absorbers such as Ppy:PSS, the system achieves nearly complete solar absorption, enhancing water release efficiency compared to conventional materials that lack integrated photothermal conversion.
• Scalability and versatility: The microgel-based design supports application in thin-layer sorbent beds or fluidized beds, offering greater flexibility and potential for commercial deployment versus more rigid existing sorbent materials like silica gels and zeolites.

Applications

• Atmospheric water harvesting for potable water production: The novel hydrogel efficiently captures and releases water from the atmosphere using low-temperature and solar-driven methods, making it ideal for decentralized, energy‐efficient, and reliable drinking water generation in arid or remote environments.
• Solar-driven water release
• Rapid sorption-desorption kinetics
• Energy-efficient water release