Rochester Scientists Develop Brine-Free Solar Desalination System

Billions of people worldwide lack access to safe drinking water, prompting increased reliance on desalination technologies in water-scarce regions ranging from California to the Middle East. However, conventional methods such as reverse osmosis and thermal distillation are energy-intensive and produce highly concentrated brine, which can harm marine ecosystems when discharged back into the ocean.

Addressing these challenges, scientists at the University of Rochester’s Institute of Optics have developed a solar thermal desalination system that eliminates liquid brine waste. The study, led by Chunlei Guo, a professor of optics and physics, was published in Light: Science & Applications.

The system utilizes solar panels composed of black metal treated with femtosecond lasers—ultrafast pulses lasting one quadrillionth of a second. This precise treatment creates microscopic structures that enable the metal to absorb nearly all incoming sunlight and exhibit superwicking properties, allowing seawater to spread rapidly across the surface rather than beading up.

As sunlight heats the thin layer of seawater on the panel, it evaporates, leaving salts and dissolved minerals behind. To prevent these minerals from clogging the active surface, the researchers engineered microscopic grooves that guide the deposits toward untreated “passive” regions at the panel’s edges. This process leverages the “coffee ring effect,” a physical phenomenon where evaporating liquid transports suspended particles to its perimeter.

Guo noted that previous solar desalination devices often performed well in labs using simple sodium chloride solutions but struggled with real seawater. Natural seawater contains magnesium, calcium, and other compounds that form dense, hard crystalline deposits similar to limescale, which can impede water flow and reduce efficiency.

In tests using actual seawater collected from the Pacific, Atlantic, and Indian Oceans, the self-cleaning panels maintained their desalination efficiency while successfully directing salts into the passive regions. Unlike traditional methods, the system extracts nearly 100 percent of dissolved salts in solid form, converting potential waste into a resource.

Beyond freshwater production, the technology offers a pathway for recovering valuable minerals. In a separate study published in the Journal of Materials Chemistry A, the team demonstrated that embedding hydrogen titanate nanoparticles into the panel’s grooves allows for the selective isolation of lithium from the salt mixture. Lithium is a critical component in batteries for electric vehicles and electronics, and earth mining for the material is energetically taxing and environmentally damaging.

Using samples from the Great Salt Lake, researchers recovered approximately 50 percent of the lithium present in the desalination byproducts. Guo suggested that extracting lithium directly from saltwater could become a significant future source for the material.

While the technology is currently in the proof-of-concept stage with small-scale devices, Guo stated that the design is inherently scalable. If successful at larger scales, the system could simultaneously address global freshwater shortages and reduce the environmental impact of both desalination waste and mineral extraction.

The research received support from the National Science Foundation, the Bill & Melinda Gates Foundation, and the Worldwide Universities Network. Contributing researchers from the Institute of Optics included Senior Scientist Subash Singh, alumnus Ran Wei, and PhD students Luheng Tang and Tainshu Xu, along with Mingjiang Ma.