Under the relentless California sun, engineers at UC Riverside are investigating an unseen spectrum of light that could significantly enhance solar desalination efficiency. Their recent experiments indicate that ultraviolet light, especially in the deep UV spectrum, can assist in separating salt from water without the need for heat.
The research team, led by Luat Vuong from the Marlan and Rosemary Bourns College of Engineering, found that aluminum nitride, a solid white ceramic, serves as a sort of molecular key. When subjected to deep UV wavelengths close to 200 nanometers, this material seems to sever the tenacious bonds that hold salt and water together.
“To our knowledge, no one else has articulated this deep UV approach for salt-water separation,” Vuong stated. “We might be the pioneers in contemplating how to utilize it for desalination.”
In the study published in *ACS Applied Materials & Interfaces*, Vuong’s team positioned ceramic wicks made from aluminum nitride in a sealed chamber filled with salt water. When exposed to UV light, the water evaporation rate escalated dramatically compared to samples kept in darkness or those exposed to visible and infrared light. This discovery indicates a novel mechanism that might eliminate the need for conventional boiling-based desalination altogether.
Severing Bonds Without Boiling
Traditional solar desalination relies on dark materials that absorb heat to vaporize water. However, heating significant quantities of liquid requires energy and results in thermal inefficiencies. Vuong’s method may avoid those drawbacks by directly targeting the bonds between salt and water molecules.
The researchers suspect that a phenomenon called photon upconversion could be at play. In this process, two or more low-energy photons combine to generate one higher-energy photon, powerful enough to disrupt chemical bonds. If validated, this would imply that saltwater can be separated through light-matter interactions rather than heat, presenting a non-photothermal pathway to freshwater.
“Aluminum nitride is ideally suited for emitting UV light thanks to its crystalline structure,” Vuong clarified. “It is affordable, abundantly available, non-toxic, highly hydrophilic, and durable.”
Solar Solutions for a Water-Strapped Planet
Such a technique could offer significant environmental benefits. Unlike reverse osmosis systems, which rely on high-pressure pumps and produce brine waste detrimental to marine ecosystems, a light-based method would require considerably less electricity and generate minimal waste. The same principle might also be applicable in waste management, mineral extraction in harsh conditions, or even cooling systems utilizing salt water rather than fresh.
Nonetheless, Vuong warns that the idea is still in its infancy. While the experiments demonstrate proof of concept, additional research is necessary to confirm the occurrence of photon upconversion and to scale the system for practical applications. Yet the potential is enticing: pure water sourced from the ocean, powered solely by sunlight and the appropriate ceramic wick.
[ACS Applied Materials & Interfaces: 10.1021/acsami.5c12331](https://doi.org/10.1021/acsami.5c12331)
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