Under the unrelenting California sun, engineers at UC Riverside are exploring an invisible spectrum of light that could make solar desalination vastly more efficient. Their new experiments suggest that ultraviolet light, particularly in the deep UV range, can help separate salt from water without relying on heat.
The research team, led by Luat Vuong in the Marlan and Rosemary Bourns College of Engineering, discovered that aluminum nitride, a hard white ceramic, can act as a kind of molecular key. When exposed to deep UV wavelengths near 200 nanometers, the material appears to break the stubborn bonds holding salt and water together.
“To our knowledge, nobody else has yet articulated this deep UV channel for salt-water separation,” Vuong said. “We may be the first to really think about how you can leverage it for desalination.”
In the study, published in ACS Applied Materials & Interfaces, Vuong’s team placed ceramic wicks made of aluminum nitride in an enclosed chamber containing salt water. When illuminated with UV light, the rate of water evaporation surged compared with samples kept in darkness or exposed to visible and infrared light. The finding points to a new mechanism that could bypass traditional boiling-based desalination altogether.
Breaking Bonds Without Boiling
Conventional solar desalination depends on dark materials that absorb heat to evaporate water. But heating large volumes of liquid demands energy and creates thermal inefficiencies. Vuong’s approach may sidestep those limitations by targeting the bonds between salt and water molecules directly.
The researchers suspect a process known as photon upconversion may be at work. In this phenomenon, two or more low-energy photons merge to form one higher-energy photon, strong enough to disrupt chemical bonds. If confirmed, this would mean saltwater could be separated through light-matter interactions rather than heat, offering a non-photothermal route to freshwater.
“Aluminum nitride is well suited for emitting UV light due to its crystalline structure,” Vuong explained. “It is inexpensive, widely available, non-toxic, highly hydrophilic, and durable.”
Solar Solutions for a Thirsty Planet
Such a method could have major environmental advantages. Unlike reverse osmosis systems, which require high-pressure pumps and produce brine waste harmful to marine life, a light-based process would consume far less electricity and create minimal waste. The same principle could also apply to waste management, mineral harvesting in extreme environments, or even cooling systems that use salt water instead of fresh.
Still, Vuong cautions that the concept is in its early stages. While the experiments demonstrate proof of principle, further work is needed to confirm whether photon upconversion is occurring and to scale the system for real-world use. Yet the prospect is tantalizing: clean water drawn from the ocean, powered only by sunlight and the right kind of ceramic wick.
ACS Applied Materials & Interfaces: 10.1021/acsami.5c12331
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