Aluminum Nitride Wick Shows Promise in UV-Driven Water Purification

Associate Professor Luat Vuong from the University of California, Riverside’s Marlan and Rosemary Bourns College of Engineering, and her research team, have developed a promising method that could reshape the way solar desalination is approached. Their study, demonstrates how ultraviolet (UV) light; specifically in the deep-UV range may directly break the molecular bonds between salt and water, bypassing the need for high-temperature processes traditionally used to obtain fresh water from the sea.

Singh, N., Leung, J., Feng, J., González-Alcalde, A. K., Tolentino, A., Tuft, D., Guo, J., & Vuong, L. T. (2025). Spectrum Selective Interfaces and Materials toward Nonphotothermal Saltwater Evaporation: Demonstration with a White Ceramic Wick. ACS Applied Materials & Interfaces, 17(42), 58837–58845. https://doi.org/10.1021/acsami.5c12331

The work centers around the use of aluminum nitride (AlN), a hard, white ceramic known for its strong crystal structure, hydrophilic surface, and resistance to degradation. The team fabricated a wick made from this ceramic and tested it under various light conditions. Salt water absorbed by the wick was exposed to UV light, and the resulting evaporation rates were compared with those from samples kept in the dark or illuminated by visible and infrared light. The results showed a clear increase in evaporation when UV light was applied.

Associate Professor Luat Vuong from the University of California, Riverside’s Marlan and Rosemary Bourns College of Engineering stated,

“Other materials may be designed to be just as effective, but aluminum nitride is practical. It is inexpensive, widely available, non-toxic, highly hydrophilic, and durable”.

According to Vuong, this enhancement points to a little-explored mechanism within the UV spectrum, particularly wavelengths around 200 nanometers. While ultraviolet light in the 300–400 nanometer range is often used for sterilization and water disinfection, the deeper UV region is less studied due to its limited availability in natural sunlight and the difficulty in producing it artificially. Vuong’s team is among the first to propose and demonstrate that this wavelength range can be leveraged for salt-water separation.

The observed phenomenon could involve photon upconversion, where lower-energy photons combine to form a higher-energy photon capable of directly interacting with salt ions. This interaction may be sufficient to weaken or break the ionic bonds between sodium, chloride, and water molecules; an effect that would enable desalination without requiring the bulk of the water to be heated or boiled. If validated, this would represent a non-photothermal route to water purification, using light energy directly at the molecular level rather than converting it into heat.

Conventional solar desalination systems work by absorbing sunlight on a dark surface to heat and evaporate water, a process that inevitably requires large amounts of energy to overcome the latent heat of vaporization. In contrast, the UCR method focuses energy where it is most needed—at the interface between salt and water—minimizing waste heat and potentially lowering the overall energy demand of the system.

Vuong emphasized that aluminum nitride was selected for both practical and scientific reasons. The material is relatively inexpensive, non-toxic, durable, and highly hydrophilic, which helps the ceramic wick draw and retain water. It also exhibits favorable optical properties that may assist in generating or transmitting the deep-UV photons necessary for the effect. These qualities make it an accessible starting point for experimentation and potential engineering development.

During the team’s experiments, pairs of ceramic wicks were placed inside a sealed chamber designed to control environmental factors such as humidity and airflow. The researchers allowed each sample to reach equilibrium before introducing UV light. They noted that the salt water exposed to UV evaporated at a faster rate than that under red, yellow, or infrared illumination. While part of this effect could still be attributed to heat transfer, the data suggest that the deep-UV component plays a unique and dominant role.

If confirmed, this approach could provide a means of desalination that does not depend on boiling or high-pressure filtration, both of which are energy-intensive. Reverse osmosis systems, the most common form of desalination used today, rely on powerful pumps that force salt water through membranes to separate fresh water from brine. These systems consume substantial amounts of electricity and generate concentrated waste brine that is often discharged into the ocean, posing ecological risks to marine life. A UV-driven alternative could reduce both energy use and environmental impact.

There are, however, limitations and unanswered questions. One challenge lies in the fact that deep-UV light in the 200-nanometer range does not reach the Earth’s surface in large quantities, as the atmosphere absorbs most of it. To make the system work under natural sunlight, engineers will need to explore ways of generating or amplifying the necessary wavelengths—perhaps through coatings, materials that perform internal upconversion, or supplementary LED systems powered by solar cells.

Another issue is scalability. The laboratory experiments were conducted on small ceramic wicks and controlled light sources. To convert this into a practical desalination system, future designs would need to accommodate larger water volumes, varying salinity levels, and the complex heat and moisture dynamics of outdoor environments. Durability is another factor, as prolonged UV exposure and salt accumulation could degrade materials over time. Vuong and her colleagues are already investigating these aspects, developing optical and spectroscopic tools to analyze how light interacts with the wick material and the salt-water interface.

Despite these hurdles, the concept introduces a new direction in desalination research one that merges optical physics, materials science, and environmental engineering. If the mechanism can be optimized, UV-based desalination could complement or even replace parts of existing systems, offering a more modular and potentially off-grid option for water treatment in remote or arid areas.

In addition to producing freshwater, the approach could be adapted for other applications. Vuong’s team has suggested possibilities such as mineral recovery from concentrated brines, evaporation-based cooling systems that use saline water instead of freshwater, or waste management technologies for industries that deal with high-salinity effluents. The wicking principle could also be modified for chemical processing, where selective light absorption might drive reactions at the interface of different phases.

The next phase of the research will focus on improving the understanding of how the deep-UV interaction occurs within the aluminum nitride structure. The team plans to develop new architectures that increase surface area and optimize light penetration, along with experiments that more precisely isolate the effect of non-thermal evaporation from conventional heating. Spectroscopic studies are expected to reveal whether photon upconversion truly drives the process or whether another mechanism, such as localized charge excitation, plays a larger role.

Vuong remains cautious but optimistic. She noted that while aluminum nitride is practical and effective, it may not be the only viable material. Other ceramics or composites could potentially offer similar or even superior results once tailored for the deep-UV spectrum. The ultimate goal, she said, is to design a system that is both efficient and manufacturable—one that could be deployed in real-world desalination facilities or small-scale water purification units.

The study, titled Spectrum Selective Interfaces and Materials toward Non-photothermal Saltwater Evaporation: Demonstration with a White Ceramic Wick, adds to a growing body of research that seeks to rethink how light energy can drive molecular separations. Rather than relying solely on heat, the work explores a more direct coupling between light and matter; an idea that may one day change how engineers think about solar-powered water treatment.