N. Hamidi, I. Williams, H. Hamidi, M. McKinney, E. Smalls, P.D. Ferguson
South Carolina State University,
Keywords: hygroscopic hydrogels, atmospheric water generation (AWG), freshwater,, thermoresponsive polymers
Summary:Recent innovative activities such as industrial, agricultural, rural developments, and defense endeavors require fresh water, and its resources are depleting quickly. The proposed solution for this problem is harvesting water from the air. The estimated amount of renewable water in Earth’s atmosphere reaches 12.4 trillion tons of vapor distributed worldwide with a fast refill. The vapor could be harvested as freshwater by emerging technology everywhere, including arid regions, land-locked areas, and remote communities. Materials that absorb fast vapor at room temperature and release it as a liquid at a slightly higher temperature are critical for atmospheric water harvesting. One of the promising materials is the flexible hybrid photothermal water sorbents composed of hygroscopic salt and hydrogel that possesses superior water sorption capacity even in low-humidity air. In these devices, the deliquescent salt, adsorbed to the hydrogel body, maintains its solid form after a significant amount of water is condensed in its structure. The condensed water could be released at temperatures below the boiling point of water (35 to 90 °C), a temperature that is achievable under sunlight via the photothermal effect. A sample of hygroscopic hydrogel with the embedded carbon nanotube was fabricated and tested under laboratory conditions. It absorbed up to 60% of its weight water, and its maximum water release rate was within 70 to 90 °C, a temperature achievable under direct sunshine. Environmental harvesting water devices made of these materials could become a complemental resource to reduce freshwater stresses.