Chinese invent self-cleaning cotton clothes
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Two material engineers from China may have stumbled across the greatest discovery since — well, the washing machine. By dunking cotton into a vat of specially-crafted nanoparticles, the researchers were able to create a material that self-cleans when exposed to sunlight. In an extreme test of the fabric’s self-cleaning abilities it was stained with an orange dye for 30 minutes — then, under simulated sunlight, the dye was broken down and could be rinsed off using water.
The chemistry behind the self-cleaning fabric is delightfully simple. The basis is titanium dioxide (aka titania), a very cheap, nontoxic powder that is used in white paint. Titanium dioxide is already used in solar panels (because it absorbs ultraviolet light), and in cleaning products and self-deodorizing socks because it can oxidize/break down organic compounds. The key, though, was finding a way to make the titania sensitive to more than just ultraviolet light — there’s some UV in sunlight, but not enough to trigger the self-cleaning mechanism.
To do this, they doped the titanium dioxide with nitrogen, and then finally a coating of silver iodide (a photosensitive chemical used in film photography). Both of these increased the sensitivity until the self-cleaning could be activated by visible daylight. The end result is a piece of cotton with a coating that is insoluble in water and can repeatedly break down dirt and stains — in other words, you could coat a pair of shoes in this material and, in theory, they would self-clean forever, irrespective of how wet they get.
Now, there are a couple of important factors to work out before we get too excited. First, silver iodide is toxic when ingested — and repeated contact with skin can give you argyria, where your skin turns blue. Second, we have no idea how commercially viable this process is. It sounds easy enough — you basically soak cotton in a mixture of chemicals for an hour — but it might be costly to prepare the solution, and silver iodide isn’t very cheap either.
Still, if self-cleaning cotton can be brought to market, just imagine the applications. For partying, you could don your self-cleaning shoes and shirt. For extended bouts of console gaming, how about some Cheetos-resistant pants? Teenage boys: self-cleaning underpants! How about napkins and towels in hotels and restaurants? Curtains in the living room, for when Little Timmy gets his first box of crayons? Most importantly, though, imagine the money savings — and reduction in greenhouse gases! — from not having to put everything through the washing machine and dryer.
I can’t see why the same titanium dioxide-nitrogen-silver-iodide compound couldn’t be used to keep mice and keyboards clean, too — assuming you actually get some sunlight in your computer room, of course.
Read more Applied Materials and Interfaces [PDF]
[Image credit: Monica Arellano-Ongpin]