Seawater desalination advance could benefit billions of people

A novel approach to make seawater evaporate faster than freshwater has been hailed as a significant breakthrough in desalination technology that will benefit billions of people worldwide.

Up to 36% of the world’s 8 billion people currently suffer from severe freshwater shortages for at least four months of the year, and this could potentially increase to 75% by 2050, threatening the survival of humans.

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 from the University of South Australia (UniSA) have already demonstrated the potential of interfacial solar-powered evaporation as an energy-efficient, sustainable alternative to current desalination methods, but they are still limited by a lower evaporation rate for seawater 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. The findings have been published in the journal Advanced Materials.

By introducing 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 since previous studies all found seawater evaporation rates were around 8% lower than pure water.

The mineral materials used in the process included halloysite nanotubes, bentonite, zeolite, and montmorillonite in combination with carbon nanotubes and sodium alginate to form a photothermal hydrogel.

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

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

Considering the global desalination market—which numbers about 17,000 operational plants worldwide—even small declines in desalination performance can result in the loss of tens of millions of tons of clean water.

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

The researchers say the hydrogel evaporator maintained its performance even after months of immersion in seawater.

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