When materials come in contact with natural air, they are coated with a thin layer of molecules that alter their properties. This molecular dirt has been found to be very difficult for scientists, and some have theorized that the coating is simply a layer of water molecules.
To investigate this, researchers from the Vienna University of Technology have developed a new method of pure ice in a vacuum chamber and then it melts. This allowed the scientists to create the world's cleanest water droplets on titanium dioxide surfaces.
Using this technique, the researchers discovered that the molecular soil changes the properties of titanium dioxide surfaces consists of two organic acids, acetic acid and formic acid, in a layer that is a single molecule thick. This was unexpected since these acids are only found in small amounts in the air.
Titanium dioxide (TiO2) plays an important role in a variety of technical applications, including self-cleaning surfaces. Experts around the world had previously observed an unknown molecule that adhered to titanium dioxide surfaces when exposed to water.
The two acids identified in the current study as the TiO2 coating are simple organic acids produced by plants. The traces of these acids in the air are tiny, with only a few acid molecules per billion air molecules. While these molecules are not very common in the air, they adhere to the metal oxide surface and change their behavior.
"In order to avoid such impurities, such experiments have to be carried out in a vacuum," states the study. Author Ulrike Diebold. "That's why we had to create a drop of water that never came into contact with the air, then place the drop on a titanium dioxide surface that's exactly at the atomic scale."
The research team found the molecules appeared on the sample only when it had contact with the air. In addition, the same molecules were discovered in very different parts of the world ̵
"This result shows us how careful we must be when performing such experiments," said Diebold. "Sometimes even tiny traces in the air, which could be considered insignificant, are crucial."
The study appears in the journal Science .
By Chrissy Sexton Earth.com Employee Writer
Credit: TU Vienna