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If you don't want to die in the desert, learn from desert beetles or carry a carbon nanotube cup with you. According to reports recently organized by the Physicists Organization Network, scientists from Rice University in the United States have shown their latest achievement, the "absorbent rack" produced by the modified carbon nanotube forest, which can collect water molecules in the dry desert air and store them for use. Use it in the future. The related papers were published in the recently published American Journal of Chemical Society, Applied Materials and Interfaces.
"Carbon nanotube forest" is an elongated array of carbon nanotubes grown by a process called water-assisted chemical vapor deposition. Nanotubes are only a few nanometers in diameter and are about 1 cm long. There is a hydrophilic layer on the top surface and a super hydrophobic layer on the bottom surface so that the water molecules are trapped inside the nanotubes.
Pryker Ajayan, a scientist in materials science at Rice University, discovered a method for simulating the desert beetle (Stenocara beetle). This beetle can spread its wings to capture the rare water molecules in the desert morning fog to quench its thirst and survive in the desert. The researchers improved the growth process of the carbon nanotube forest by first depositing a super hydrophobic layer on top of the carbon nanotube forest, and then peeling them off the silicon base and turning it over to add a layer of hydrophilic polymer.
In the experiment, water molecules bind to the hydrophilic tip and enter the interior of the material due to the capillary effect and gravity of the nanotube forest. When the water droplets stick to the hydrophilic side, the water molecules are pulled into the interior by van der Waals forces, hydrogen bonding forces, and bipolar effects, extending to the entire nanotube, and then the water molecules absorb more water.
They also experimented with several different carbon nanotubes. Only those with a hydrophilic layer at the top will scatter in the moist air, because there is nothing at the bottom to connect them together; there are hydrophilic layers at the top and bottom, the nanotube forests will be connected, but the water will leak out The nanotube forest, where the water-repellent layer is made at the bottom and the hydrophilic layer is topped, can still be kept intact after absorbing up to 80% of its own weight.
How much water vapor the material can absorb depends on the air humidity. In dry air, an 8 milligram sample (0.25 square centimeter in surface area) absorbs 27.4% of its own weight in 11 hours, and 80% of its own weight in 13 hours in moist air. Further tests have also shown that nanotube forests can significantly slow the evaporation of their absorbed water.
Researchers say that carbon nanotube forests are easy to manufacture, and if they can be produced on a large scale, they will become an efficient water collection device. "It does not require any external energy to keep the water in the nanotube forest," said the paper's first author and graduate student Hemus Ozden. "You can squeeze the nanotubes out of the water, and then Use the material repeatedly.†(Chang Lijun)
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