World’s cleanest drop of water reveals why nothing is ever truly clean | Artificial intelligence
In a bid to find out where molecular dirt comes from researchers have created the world’s cleanest water.
No matter how clean you try to make something a thin layer of molecules always ends up coating the surface, but identifying them can be tricky.
To learn more, Ulrike Diebold at the Vienna University of Technology and colleagues investigated when a piece of titanium dioxide would become dirty under controlled conditions.
There were several theories about what the dirt might be, including a new form of ice or carbonic acid from the air. “There were four papers from four teams, all with different explanations, and all of them were wrong,” says Diebold.
In an ultra-high vacuum chamber the team tested different suspects. These included arguably the world’s cleanest water, made by further purifying commercially available ultrapure water, soda water – a mixture of carbon dioxide and water, and air. Only exposure to air resulted in molecular dirt accumulating on the surface of the titanium dioxide.
A chemical analysis revealed why: the smut is made of acetic acid and formic acid. Produced by plants, they are only present in a few parts per billion in air. But their chemistry gives them a strong affinity for titanium dioxide. Diebold says this patina may contribute to the material’s self-cleaning properties.
Journal reference: Science, DOI: 10.1126/science.aat6752
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