Pioneering research uses modified solar panels to remove salt from seawater, with potential to do so safely at scale.
As we face unprecedented heatwaves this summer, the advice is to stay out of the sun and ensure we are hydrated. But supplies of drinking water are limited.
The US Geological Survey estimates that 71% of the Earth’s surface is water, but more than 96% of it is saline – saltwater – which we can’t drink, use on crops or in other ways vital to life. Yes, there are ways to remove the salt from seawater, but it’s not easy or cheap to do at scale.
One challenge is that traditional desalination involves shallow amounts of water on wide surfaces that are either naturally or artificially heated. The pure water evaporates and is collected, but salt accumulates on the evaporator surfaces, making them less effective over time.
Another big problem is that as some water evaporates, there’s a higher concentration of salt in in the water left on the surface. The result is a highly salty resident called brine, which is deadly to sea life.
Now, researchers have devised an ingenious method to desalinate water that avoids both these problems – using specially etched solar panels.
Based at the Institute of Optics at the University of Rochester in New York, Luheng Tang, Subhash C Singh, Ran Wei, Tianshu Xu and Chunlei Guo used a highly accurate femtosecond laser to prepare the surface of solar panels to create a multifunctional superwicking black metal – known as SWBM.
- Real the full paper: ‘Additive-free and brine-discharge-free solar-thermal desalination with simultaneous complete mineral mining from ocean water’, published in the May issue of Light: Science and Applications.
The result is a little like the way a wick works in a candle: when you light the candle, the heat melts the wax, which the wick absorbs through capillary action and is then burned as fuel. In this case, the SWBM panel draws a thin layer of water up across its surface, against the force of gravity, absorbing almost all the solar radiation in the process to generate energy.
But what’s especially encouraging is that in doing so, the wicking action moves the crystallised salts to the edge of the SWBM panel, keeping the main surface clear to continue working. The salt can we developed a true sustainable and environmental-friendly solution for desalination and salt extraction of actual ocean water. Besides desalination, we envision that ABF-STIC can also be used to for a range of inorganic and organic solutions for solute separation and solvent recovery. Additionally, the active area of ABF-STIC could be functionalized with linker molecules to selectively collect desirable salts from ocean water or certain solutes from a solution. then be safely collected through an automated self-cleaning process.
The researchers found that deeper, wider grooves in the SWBM panels enabled self-cleaning even when treating real ocean water – they tested samples from different oceans around the world. What’s more, they report some 74% solar to vapour conversion efficiency plus almost 100% salt extraction.
‘This SWBM serves as an energy-efficient, self-maintained, and additive-free and brine-discharge-free solar-thermal interfacial crystallizer,’ say the authors – which they abbreviate to ‘ABF-STIC’. The result, ‘simultaneously produces fresh water and harnesses nearly all salts directly from ocean water.
‘We [have] developed a true sustainable and environmental-friendly solution for desalination and salt extraction of actual ocean water. Besides desalination, we envision that ABF-STIC can also be used to for a range of inorganic and organic solutions for solute separation and solvent recovery. Additionally, the active area of ABF-STIC could be functionalised with linker molecules to selectively collect desirable salts from ocean water or certain solutes from a solution.’
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