Desalination breakthrough could bring fresh water to the world

Australian and Chinese researchers have found a way to make sea water evaporate faster than fresh water, in a breakthrough for desalination technology that should benefit billions of people worldwide. Their findings have been published in the journal Advanced Materials.

Up to 36% of the world’s eight billion people currently suffer from severe water shortages for at least four months of the year, and this could potentially increase to 75% by 2050. Seawater desalination is one of the most effective strategies to alleviate the impending scarcity, but existing processes consume massive amounts of energy, leaving a large carbon footprint.

Researchers at the University of South Australia (UniSA) have already demonstrated the potential of interfacial solar-powered evaporation as an energy-efficient alternative to current desalination methods, but they are still limited by a lower evaporation rate for sea water compared to pure water due to the negative effect of salt ions on water evaporation. UniSA materials science researcher Professor Haolan Xu has now collaborated with researchers from China on a project to develop a simple yet effective strategy to reverse this limitation.

By introducing various inexpensive and common clay minerals into a floating photothermal hydrogel evaporator, the team achieved seawater evaporation rates that were 18.8% higher than pure water. This is a significant breakthrough given that previous studies had found seawater evaporation rates were around 8% lower than pure water.

“The key to this breakthrough lies in the ion exchange process at the air–water interface,” Xu said.

“The minerals selectively enrich magnesium and calcium ions from sea water to the evaporation surfaces, which boosts the evaporation rate of sea water. This ion exchange process occurs spontaneously during solar evaporation, making it highly convenient and cost-effective.”

According to the researchers, the hydrogel evaporator maintained its performance even after months of immersion in sea water. This is significant as even small declines in desalination performance can result in the loss of tens of millions of tons of clean water, due to the size of the global desalination market.

“This new strategy, which could be easily integrated into existing evaporation-based desalination systems, will provide additional access to massive amounts of clean water, benefiting billions of people worldwide,” Xu said.

The next steps will involve exploring more strategies that can make seawater evaporation faster than pure water evaporation and applying them to practical seawater desalination.

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