Rochester professor Chunlei Guo and his team have developed a technique that can be used to collect sunlight to heat etched metal surfaces like the one featured here, which can then power an electrical generator for solar power. (Credit: University of Rochester photo/J. Adam Fenster)“This is a simple, durable, inexpensive way to address the global water crisis, especially in developing nations”Chunlei Guo
A team from the University of Rochester have shown a new approach to purifying water without wasting energy, a breakthrough that could help alleviate the serious global water crisis. Using lasers to etch metal with ultrashort laser bursts, they used sunlight to evaporate and purify contaminated water with more than 100% efficiency.
In addition to the lack of drinking water for nearly a third of the world’s population, the world is dealing with a pandemic that requires people to washing their hands more often, making supplies of clean water of huge importance, making this study, published in the journal Nature Sustainability [Singh et al. Nat. Sustain. (2020) DOI: 10.1038/s41893-020-0566-x], even more timely.
With bursts of femtosecond laser pulses, the surface of a sheet of aluminum was etched so that it attracted water and also became a super energy-absorbing material. In placing the material at a particular angle facing the sun, its surface was shown to pull a thin film of water upwards over the metal’s surface, retaining nearly all of the energy it absorbs from the sun to quickly heat the water. The technique alters the inter-molecular bonds of the water, substantially improving the efficiency of the evaporation process.
As well as the contaminant-heavy way of boiling water for purification, others have tried interfacial heating, where floating, multilayered absorbing and wicking materials are placed on top of water so that just water close to the surface has to be heated. However, a problem here is the materials have to float horizontally and not face the sun directly, as well as the wicking materials becoming clogged with contaminants remaining after evaporation, having to be replaced frequently.
However, these new panel avoids such inefficiencies by drawing a thin layer of water out of the reservoir and directly onto the solar absorber surface for heating and evaporation. As team leader Chunlei Guo points out, “This is a simple, durable, inexpensive way to address the global water crisis, especially in developing nations”. The method could also to help relieve water shortages in drought-stricken areas and in water desalinization projects.
The approach, which needs just a small amount of the heating energy to be used, reduced the presence of common contaminants, including detergent, dyes, urine, heavy metals, and glycerin, ensuring the water was safe to drink. To maximize energy absorption, the angle of the panels can be adjusted to make sure they directly face the sun as it moves across the sky.