Water scarcity is a growing global concern that is driving increasing efforts to conserve, re-use and treat water. Desalination of seawater is a known technology to combat water shortages, but it is an energy-intensive process. Solar-powered evaporation can be a more energy-efficient desalination process, as demonstrated by researchers from the University of South Australia (UniSA; www.unisa.edu.au). The salt in seawater, however, limits the achievable evaporation rate. Studies reportedly found seawater evaporation rates to be about 8% lower than those for pure water.
A desalination plant (Source: Shutterstock)
Professor Haolan Xu, a materials science researcher at UniSA, in collaboration with researchers from China, has developed a simple strategy to overcome this limitation. The team was able to achieve seawater evaporation rates 18.8% higher than for pure water by introducing common clay minerals into a floating photothermal hydrogen evaporator. According to the researchers, the hydrogen evaporator maintained its performance for months after immersion in seawater. The mineral materials used in the process included halloysite nanotubes (HNTs), bentonite (BN), zeolite (ZL) and montmorillonite (MN) in combination with carbon nanotubes (CNTs) and sodium alginate (SA) to form a photothermal hydrogel.
“The key to this breakthrough lies in the ion exchange process at the air-water interface,” 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.”
This work has been published in the journal Advanced Materials.