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Femtosecond Lasers Etch Superwicking Metal Surface for Water Purification System

Time:2020-08-08 | Author:

ROCHESTER, N.Y., Aug. 3, 2020 — Led by Chunlei Guo, a professor in the University of Rochester’s Institute of Optics, a team of scientists has demonstrated how ultrashort femtosecond laser pulses etch the surface of a sheet of metal (in this research, aluminum) into a super energy-absorbing material. The metal surface in the system is a broadband absorber, which increases the efficiency of the water evaporation process, demonstrating how sunlight can purify water of contaminants and make it safe for drinking.

In addition to absorbing light across a broad wavelength range, the surface of the energy-absorbing aluminum surface in the system is superwicking (hydrophilic). When researchers angled it to face a light source, the metal surface drew a thin film of water over itself in an upward direction against gravity. The surface retained nearly 100% of the light energy it absorbed. As it heated the water, evaporation intensified, and the water’s intermolecular bonds changed.

As water evaporates and becomes a gas, it loses many of the potentially harmful contaminants it may contain, such as heavy metals. This makes solar-based purification methods an appealing option for purification; simply boiling water fails to remove heavy metals and other harmful contaminants, as water does not enter a gaseous state.

Unfortunately, solar-based methods are not always efficient in practice. Volume heating, as its name suggests, involves heating a large quantity of water — though only to a point that its top layer evaporates. From start to finish, volume heating uses only a small amount of the generated heating energy.

Another method, interfacial heating, places floating, multilayered absorbing and wicking materials on top of water. Though only water near the surface must be heated, all materials involved in the process must face away from the sun, in a nonvertical position.

As a result, Guo said, durability is vital to the new technology.

“The biggest advantage,” he said, “is that the angle of the panels can be continuously adjusted to directly face the sun as it rises, and then moves across the sky before setting. There was simply nothing else resembling what we can do here.”

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