Water purification is critical for many industrial and energy applications but most importantly it is also critical for people who live in arid climates or do not have access to clean drinking water. There are many classes of materials that are utilized for water purification, but regardless of material, nearly all sorbents operate with the same physical principles, i.e. all known materials show increased water capacity with increasing humidity. We imagine how water could be purified if a material were able to adsorb water at low humidity and release at high humidity. We present here a material that does just that. We have discovered a newly developed class of carbon rods that adsorb water vapor at low humidity, and expel half of the adsorbed water as liquid droplets spontaneously as the humidity passes a 50–80% threshold. This water expulsion is unprecedented, but more remarkably it is a reversible physical process, where decreasing the humidity around the sample increases its uptake of water. The rods perform this marvel simply by changing their available surface area for water to adhere to as a function of humidity, where there is more available surface area at low humidity than at higher humidity. Such behavior provides new means for water purification and separation, where water could be harvested from a low humidity vapor stream and then collected as a liquid when exposed to a pure water vapor stream. We present the physical and spectroscopic evidence for this behavior and discuss new potential processes that can purify water using these carbon rods.

Anomalous carbon rods that adsorb water vapor at low humidity and release liquid droplets at higher humidity

251st National Meeting (2016)

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