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New Carbon Nanotube Device Harvests Water from Air

Jun 12, 2014 06:21 AM EDT
hygroscopic scaffold
A sample of hygroscopic scaffold made from a forest of carbon nanotubes at Rice University collects and stores water molecules from even arid air. The molecules sink into the forest from the top down, filling up to 80 percent of the scaffold in humid conditions (left), and less in temperate (center) and dry (right) conditions.
(Photo : Ajayan Group/Rice University)

A team of researchers at the Rice University have built a new device that harvests water from arid air like the Namib Desert beetle.

The Stenocara beetle or Namib Desert beetle survives in the arid landscape by using its wings to collect water molecules from the early morning fog.

The researchers call this forest of carbon nanotubes "hygroscopic scaffold".

They created the carbon nanotube forest using a technique called water-assisted chemical vapor deposition. The nanotube cup has a hydrophilic (water loving) top and a super-hydrophobic (water-repelling) bottom.

The water droplets are collected by the water-loving part of the device via capillary action and gravity. Once few molecules of water are collected at the bottom, they start attracting more water molecules. The water droplets are then drawn into the nanotubes and stored in the super-hydrophobic bottom.

"It doesn't require any external energy and it keeps water inside the forest," said graduate student and first author Sehmus Ozden, according to a news release. "You can squeeze the forest to take the water out and use the material again."

The amount of water collected by the nanotube device depends on the humidity of the air, researchers said. An 8 milligram sample (with a 0.25-square-centimeter surface) attracted around 27.4 percent of its weight of water over an 11-hour period and 80 percent in humid air.

Creation of large-scale carbon nanotube forests could help trap water from fog in arid regions, researchers said. Producing a carbon nanotube is expensive, which is limiting its use on a commercial scale.

Harvesting water from fog isn't a new idea. Researchers at the Massachusetts institute of Technology had demonstrated in 2011 that water droplets from air could be collected using fence-like mesh panel. Recently, MIT scientists had shown practical application of the device in Chile.

An ad agency in Lima, Peru recently put up a billboard that produces around 100 liters of water a day (about 26 gallons) from fog.

The U.S. Department of Defense and the U.S. Air Force Office of Scientific Research Multidisciplinary University Research Initiative supported the research and it is published in the journal Applied Materials and Interfaces. 

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