Water Research

Water Research

At EIL, we focus on advancing atmospheric water harvesting, purification, and mineral recovery systems that are efficient, scalable, and tailored for resource-limited or off-grid environments, additionally, we design hygroscopic material for thermochemical energy storage (TCES) systems Our primary research thrust is atmospheric water harvesting (AWH), where we develop sorbent-based systems capable of capturing water vapor from ambient air. We explore the thermodynamics of sorption, transport resistance imposed by swelling polymer networks, and cyclic device performance in variable relative humidity environments. Our approach integrates materials such as salt-hydrogel composites, with system-level engineering, including multicycle regeneration schemes and solar-thermal or waste heat integration. We also investigate how material microstructure, diffusivity, and hysteresis behavior influence device efficiency and water yield.

Salt creeping: the migration and crystallization of salts beyond the evaporating liquid front, is a ubiquitous yet poorly understood phenomenon that affects diverse fields, from agriculture and building durability to maritime systems and art preservation. Despite its detrimental impacts, the same process also holds promise for controlled mineral recovery, desalination, and wastewater treatment if it can be properly understood and managed. Our research employs in situ X-ray microscopy to visualize the onset of salt creeping with single-crystal resolution, offering an unprecedented view into its microscale physics. We directly observed the nucleation of the very first salt crystal that becomes pinned at the solid–liquid interface, puncturing the liquid meniscus and extending it outward. This initial event triggers a self-sustaining cascade of crystallization, as new crystals precipitate from the extended meniscus formed by the first pinned crystal.

Through thermodynamic analysis, we discovered that this onset is governed by a critical contact angle, a precise geometrical condition that determines when a crystal can stabilize and grow through the meniscus. Together, these results reveal the microscopic origin of salt creeping and establish a quantitative framework to predict and control its dynamics. By connecting interfacial geometry, capillary forces, and crystallization kinetics, this work lays the foundation for manipulating salt growth in both preventive applications (e.g., corrosion and damage mitigation) and beneficial ones such as evaporative water treatment, mineral extraction, and self-assembling materials.

Our work focuses on designing hydrogel–salt composites that combine the strong hygroscopicity of salts with the flexibility and tunability of polymer networks. The schematic illustrates how water molecules are absorbed within the hydrogel’s interconnected structure, where salt ions act as binding sites and the polymer matrix provides mechanical stability and rapid vapor diffusion pathways. This coupling of chemistry and structure allows the composite to achieve high water uptake even at low humidity, while preventing salt crystallization or leakage that often limits traditional sorbents. The accompanying data demonstrate how our PAM–LiCl hydrogel exceeds the performance of conventional materials such as MOFs, carbon-based hybrids, and other polymer–salt systems, particularly under arid conditions. These results underscore the potential of polymer-engineered sorbents to serve as robust, low-temperature materials for scalable atmospheric water harvesting.

Swelling Kinetics of Hydrogels

Our research introduces a new class of hygroscopic hydrogel–salt composites designed for low-temperature thermochemical energy storage (TCES). Traditional TCES materials, such as zeolites, salt hydrates, and metal hydrides, offer high reaction enthalpies but face critical material limitations: high regeneration temperatures, salt leakage, and structural degradation over repeated cycling.

We overcome these challenges by engineering the polymer matrix to regulate water–salt interactions at the molecular level. The hydrogel framework suppresses deliquescence and crystallization, allowing the embedded hygroscopic salts to retain high activity while remaining physically confined within a flexible, porous network. This design enables rapid sorption kinetics, tunable thermal conductivity, and long-term structural stability even under repeated hydration–dehydration cycles. The composite exhibits exceptionally high-water uptake and energy density, exceeding 200 Wh L⁻¹ when loaded with 4 grams of LiCl per gram of polymer, while requiring only 40–80 °C for regeneration. Its softness, chemical stability, and low processing cost make it uniquely scalable for integration into solar, HVAC, and waste-heat recovery systems.

To probe durability, we performed extended vapor-phase cycling, revealing consistent water uptake and morphology over thousands of cycles. Advanced image-based swelling analysis confirmed that the polymer network maintains reversible volume change without microstructural fatigue. Together, these results position the hydrogel–salt composite as a robust, low-temperature alternative to conventional solid sorbents for thermochemical energy storage.

Related References

  • J. P. Mooney, O. R. Caylan, J. Gao, J. Punch, V. Egan, B. El Fil*, and L. Zhang “In Situ X-ray Microscopy Unraveling the Onset of Salt Creeping at a Single-Crystal Level “Langmuir 2025 41 (27), 17741-17748 DOI: 10.1021/acs.langmuir.5c01460
  • C.T. Wilson, C.D. Diaz, J. P. Colque, J.P. Mooney, B. El Fil*, “Solar-driven atmospheric water harvesting in the Atacama Desert through physics-based optimization of a hygroscopic hydrogel device”. Device, Volume 3, Issue 8, 100798 (2025). https://doi.org/10.1016/j.device.2025.100798.
  • X. Li#, B. El Fil#*, B. Li, G. Graeber, A.C. Li, Y. Zhong, M. Alshrah, C.T. Wilson, E.Lin. “Design of a Compact Multicyclic High-Performance Atmospheric Water Harvester for Arid Environments”. ACS Energy Letters (2024) 9 (7), 3391-3399. https://doi.org/10.1021/acsenergylett.4c01061.
  • Y. Zhong, L. Zhang, X. Li, B. El Fil, C. D. Díaz-Marín, A. C. Li, X. Liu, A. LaPotin, E. N. Wang Bridging materials innovations to sorption-based atmospheric water harvesting devices. Nat Rev Mater 9, 681–698 (2024). https://doi.org/10.1038/s41578-024-00665-2
  • C.T. Wilson, H. Cha, Y. Zhong, A. C. Li ∙ E. Lin ∙ B. El Fil*, “Design considerations for next-generation sorbent-based atmospheric water-harvesting devices”. Device, Volume 1, Issue 2, 100052 (2024). https://doi.org/10.1016/j.device.2023.100052.
  • G. Graeber, C. D. Díaz-Marín, L. C. Gaugler, B. El Fil. “Intrinsic Water Transport in Moisture-Capturing Hydrogels”. Nano Lett. (2024), 24, 3858−3865. https://doi.org/10.1021/acs.nanolett.3c04191.
  • B. El Fil*, X.  Li, C. Jacobucci, C. D. Díaz-Marín, L. Zhang “Significant Enhancement of Sorption Kinetics via Boiling-Assisted Channel Templating”. Cell Reports Physical Science, Volume 4, Issue 9, (2023) 101549. https://doi.org/10.1016/j.xcrp.2023.101549.
  • E. Lin, C.T. Wilson, A. Leroy, B. El Fil* “High energy density entrainment-based catalytic micro-combustor for portable devices” Applied Energy, Volume 285, (2023), 117014. https://doi.org/10.1016/j.enconman.2023.117014.
  • G. Graeber, C. D. Díaz-Marín, L. C. Gaugler, Y. Zhong, B. El Fil, X. Liu, and E N. Wang “Extreme Water Uptake of Hygroscopic Hydrogels Through Maximized Swelling-Induced Salt Loading” Adv. Mater., Special Edition Hygroscopic Materials. (2024), 36, 2211783. https://doi.org/10.1002/adma.202211783.
  • X. Liu, L. Zhang, B. El Fil, C.D. Díaz-Marín, Y. Zhong, X. Li, S. Lin, and E.N. Wang (2023), Unusual Temperature Dependence of Water Sorption in Semi-Crystalline Hydrogels. Adv. Mater.  2211763. https://doi.org/10.1002/adma.202211763