They say this material is cheap and can pull “ 13 liters in areas with up to 30% relative humidity” …
Now I’m wondering if you could use this stuff like crazy in hot, humid places and whether (a) it could pull enough water to be useful for drinking or irrigation, and (b) whether it’s possible to “locally” lower the ambient humidity (like the reverse of the urban heat island effect).
Getting the water out from the spongy material could pose a challenge in hot environments.
According to the paper, they use heating (60°C) to extract the water. In hot environments, however, ambient temperatures get quite close to that already (see India at the moment).
The answer to b) would be a no. The technique doesn't work in high humidity environments.
With a somewhat different material, optimized for that situation, could this be made to work well in hot, humid environments?
If so, then I'm smelling a plausible solar-powered, cheap, modular "emergency life support" system for people threatened by extreme web bulb temperature conditions.
According to the paper, it's the absolute temperature that matters. The desorption is optimal at about 60°C to 70°C, meaning the absorption-desoprition cycle wouldn't work anymore if the ambient temperature is too high. The absorption phase took place at 25°C ambient - the provided data suggests that the desorption would dominate over the absorption above about 50°C.
In conclusion, if the environment is 50°C or hotter, the sponge cannot absorb much water from the atmosphere, because the kinetics imply that the water would evaporate too quickly.
Now I’m wondering if you could use this stuff like crazy in hot, humid places and whether (a) it could pull enough water to be useful for drinking or irrigation, and (b) whether it’s possible to “locally” lower the ambient humidity (like the reverse of the urban heat island effect).