Cornell researchers say specially dyed wool could provide a low-cost, biodegradable material for producing fresh water from salt water using sunlight.
The study tested wool treated with polydopamine, a light-absorbing polymer inspired by melanin, in a process known as interfacial solar vapor generation. The method heats water at its surface, converts it to vapor and then condenses the vapor into potable water.
Larissa Shepherd, an assistant professor in Cornell's Department of Human Centered Design, led the research. The work was published Sept. 6 in Advanced Science, with Kyuin Park as lead author.
Researchers said wool offers an advantage over synthetic materials because it is renewable and biodegradable and does not create persistent microplastics. The team tested both polydopamine-dyed wool and an ultrablack version created through plasma etching.
The ultrablack material was inspired by the deep-black feathers of a bird of paradise. Etching creates tiny fibers that trap light, while the polydopamine converts near-infrared light into heat.
Researchers tested three wool structures in horizontal, one-sided vertical and two-sided vertical configurations under a solar simulator. Mirrors were used behind the material in the two-sided setup.
Ultrablack wool in the two-sided vertical system produced 2.43 kilograms of water per square meter of fabric each hour. Wool treated only with polydopamine produced 2.21 kilograms, with both rates nearly twice those of traditional horizontal evaporation systems.
The material also operated for 10 continuous hours without a buildup of salt. Shepherd said salt levels in the collected water were well below the World Health Organization's drinking-water standard.
Shepherd said the smaller performance gain from plasma etching may not justify the extra manufacturing step in every application, though the additional output could become meaningful over a year or longer.
Future studies will test the material with rainwater and wastewater and explore improved collection designs. The National Science Foundation, Cornell Atkinson Center for Sustainability and AATCC Foundation supported the work.
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