Freshwater scarcity has always been a factor in human mortality. Today, it remains one of the greatest logistical and humanitarian challenges. Our planet Earth is 70% covered in water, but most of it is salty or very difficult to access. This leaves a large part of humanity with problems supplying drinking water, which is essential for life.
Nearly 4 billion people suffer from water shortages for at least one month each year. This is why, even at the beginning of the 21st century, scientists are still searching for sustainable and accessible solutions to obtain drinking water. For a long time, desalinating seawater seemed like the logical answer—after all, we are surrounded by the sea—but it had too many limitations. However, thanks to a collaboration between the University of South Australia (UniSA) and several Chinese researchers, technology has advanced to such an extent that desalinating water for drinking purposes may become accessible.
Modern methods—and their limitations
Historically, water desalination was carried out using two technologies: thermal distillation and reverse osmosis. Although both methods work, they also have serious drawbacks that prevent their large-scale and sustainable use. Conventional desalination has always required high energy consumption, to the point where it was not even viable as an alternative.
Given that these facilities had to be installed in remote locations with little infrastructure, this energy ended up being generated from fossil fuels, which created a large carbon footprint and was counterproductive to the desalination process. To make matters worse, desalination plants produce a highly concentrated by-product known as “toxic brine.” This brine contains harmful chemicals that damage the ecosystem when discharged back into the ocean.
This led to the idea of finding an alternative method of desalination. That is how scientists came up with Interfacial Solar Evaporation (ISE), which only requires sunlight as an energy source.
How does ISE technology work?
Interfacial solar evaporation is a passive process inspired by the natural water cycle, but it accelerates it dramatically through materials engineering. To do this, it needs a central component, which is the floating photothermal evaporator. This is a device made of a porous, multi-layer structure that floats on the water source to be desalinated. This system is 100% solar-powered, as it uses photothermal materials on the upper part of the evaporator. These are dark materials—such as carbon variants, nanometals, or polymers—and have a very high capacity to absorb sunlight.
Once the light is absorbed, it is efficiently converted into heat. It is the heat localization mechanism that makes ISE technology so efficient: since the photothermal material floats and has low thermal conductivity, the heat is confined exclusively to the very thin layer of surface water that is in contact with the evaporator. This water rises to the surface through capillary action through the pores of the material, where it turns into water vapor. This vapor rises through the capillary, leaving behind all mineral salts and non-volatile contaminants, so it is collected and condensed to obtain fresh drinking water.
Drinking water with a simple—and affordable—mechanism
One of the greatest merits of this mechanism is its use of passive energy (such as sunlight) and common, inexpensive materials. To further improve the design, the collaboration between UniSA and China decided to add clay minerals to the evaporator structure. Thanks to zeolite and bentonite, the mechanism selectively concentrates certain ions, allowing pure water to evaporate 18.8 percent faster.
Not only does this improve the mechanism’s performance, but it also makes the system more durable. Researchers claim that the hydrogel maintains its high performance even months after being installed in seawater, suggesting a long potential lifespan. For now, we will have to wait and see when this technology will be commercially available on a large scale.