The new water purification technique involves draping a sheet of carbon-dipped paper in an upside-down “V.” The paper’s bottom edges soak up water, while the carbon coating absorbs solar energy and transforms it into heat for evaporation. Credit: Credit: Huaxiu Chen
An upgrade to a 2,000-year-old purifying technique could yield clean drinking water in remote regions or areas decimated by natural disasters.
Researchers from the University of Buffalo have tapped into the ancient idea of using energy from the sun to evaporate and purify water for sanitation, and upgraded it by draping black, carbon-dipped paper into a triangular shape and using it to both absorb and vaporize water.
“Our technique is able to produce drinking water at a faster pace than is theoretically calculated under natural sunlight,” lead researcher Qiaoqiang Gan, PhD, associate professor of electrical engineering in the University at Buffalo School of Engineering and Applied Sciences, said in a statement. “Usually, when solar energy is used to evaporate water, some of the energy is wasted as heat is lost to the surrounding environment.
“This makes the process less than 100 percent efficient. Our system has a way of drawing heat in from the surrounding environment, allowing us to achieve near-perfect efficiency.”
The researchers have launched Sunny Clean Water, a startup focusing on the new technology, hoping to integrate the new system into a prototype of a solar still—a sun-powered water purifier. The team is hopeful that a solar still the size of a miniature refrigerator could generate 10-to-20 liters of clean water a day.
Solar stills use the sun’s heat to evaporate water, leaving salt, bacteria and dirt behind. The water vapor then cools and returns to a liquid state, at which point it is collected in a clean container.
While the new technique is simple and taps into an abundant source of power, solar still models are still inefficient at vaporizing water.
The researchers were able to increase the efficiency of the system by cooling it down using the sheet of carbon-dipped paper that is folded into an upside-down “V” shape. The bottom edges of the paper hang in a pool of water, soaking up the fluid like a napkin, while the carbon coating absorbs solar energy and transforms it into heat for evaporation.
Most of the carbon-coated paper stays under room temperature, enabling it to draw in heat from the surrounding area and compensate for the regular loss of solar energy that occurs during the vaporization process.
The researchers were able to evaporate the equivalent of 2.2 liters of water per hour for every square meter of area illuminated by the Sun.
“Most groups working on solar evaporation technologies are trying to develop advanced materials, such as metallic plasmonic and carbon-based nanomaterials,” Gan said. “We focused on using extremely low-cost materials and were still able to realize record-breaking performance.
“Importantly, this is the only example I know of where the thermal efficiency of the solar evaporation process is 100 percent when you consider solar energy input. By developing a technique where the vapor is below ambient temperature, we create new research possibilities for exploring alternatives to high-temperature steam generation.”
The study was published in Advanced Science.
