Solar Photomolecular Desalination

The use of solar energy for desalination is not a new idea, particularly solar thermal methods by evaporation of saline water and recondensation of the vapor into clean water. However, solar thermal evaporation has an overall low efficiency because it relies on breaking hydrogen bonds among individual water molecules, which is very energy-intensive. Chen and his lab recently discovered a photomolecular effect that could be a solution.

Hydrogen bonding is known to result in spontaneous clusters fluctuating in water. The bonds among water molecules inside a water cluster in liquid water are mostly hydrogen bonds. Chen discovered that a photon with energy larger than the bonding energy between the water cluster and the remaining water liquids can cleave off the water cluster at the water-air interface, colliding with air molecules and disintegrating into individual water molecules.

The catalyst for the process is a light-emitting diode (LED) that mimics the sun’s intensity by shining onto the water surface. The team plans to work on a system that efficiently traps light to achieve nearly 100% light absorption. The photomolecular effect causes water clusters to cleave off at the water-air interface, and forced air carries the molecular clusters to the condensing section. Here, the clusters will be efficiently collected. Because of the much smaller amount of heat released during condensation of clusters, the heat rejected during condensation will be recovered to improve the system efficiency. Professor Chen has already shown LEDs produce a photomolecular evaporation rate that can exceed pure thermal evaporation by ~ ten times.