Humans need water to live. But the world’s fast-growing population and changing climate are putting the supply of this precious resource at risk. Removing salt from the seas is one way to relieve the thirst of millions of people in parched areas of the world. But today’s desalination technologies require a large amount of energy.
Researchers at the University of Waterloo have made a device that efficiently produces drinking water from saltwater by using solar energy. Their device mimics two natural processes: the natural water cycle of evaporation and condensation, and the transport of water in plants from roots to the leaves.
As reported in the journal Nature Communications, the device converts 93 percent of sunlight into usable energy, and produces 20 liters of fresh water per square meter daily. That’s the amount the World Health Organization recommends as the daily requirement for each person for basic drinking and hygiene.
Around 2.2 billion people worldwide have no access to clean water, according to the UN World Water Development Report 2024. Conventional desalination systems push seawater through special membranes that hold back salt and let fresh water through. But the process is energy-intensive. The expensive membranes also build up salt over time, requiring maintenance or replacement.
So the team of chemical engineers made a solar evaporation-based desalination device that cleans itself and does not require maintenance. They start with a porous piece of nickel foam and coat it with a layer of a conductive polymer called polydopamine (PDA).
Then they coat the bottom half of the foam piece with a layer of a heat-responsive polymer called sporopollenin. Sporopollenin is a mechanically tough and chemically stable biopolymer that is found in the outer walls of pollen grains and plant spores.
The researchers place the coated foam piece in seawater so that only the bottom part of the foam is immersed in water, and then cover it with a plastic dome-shaped condenser. During daytime, the top PDA layer soaks up sunlight and converts it into heat. At these high temperatures, a thin layer of seawater moves up along the PDA surface of the foam and evaporates, leaving behind salt. The water vapors condense on the plastic dome and trickle down along the sides for collection.
At night time, when temperatures drop, the lower half of the foam which is coated with sporopollenin draws water up through the nickel foam channels and wash away the accumulated salt. As a result, the self-cleaning device can continuously transport water up for evaporation and condensation.
“This new device is not only efficient but also portable, making it ideal for use in remote regions where access to fresh water is limited,” said co-author Yuning Li in a press release.
Source: Yi Wang et al. Thermo-adaptive interfacial solar evaporation enhanced by dynamic water gating. Nature Communications, 2024.
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