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Clothes That Clean Themselves
I just put a load of clothing in my washer. I used to add a cup of detergent now the new technology calls for a tablespoon. If some researchers in China can perfect a technique that allows clothing to clean itself in simple sunlight we may not need detergent at all.
The science behind this amazing phenomenon is photo catalysts. These chemicals react to the wavelengths in sunlight. There are some that react to ultraviolet light but the trick was finding something you could coat clothing with that would react with sunlight. The chemicals they came up with are titanium dioxide (a key ingredient in white oil paints and interestingly tattoo ink) and silver iodide (used to seed clouds in early weather experiments). Titanium dioxide reacts with ultraviolet light and the Silver iodide reacts best with sunlight and is a catalyst.
All these chemical are safe in most circumstances but there is a danger. Inhaling titanium dioxide is a hazard. That means that the researchers have to find a way to make the chemical stick and stay through thick and thin, wind and snow, play and sleep, well you get the idea. Since cotton clothing is made of individual woven fibers they can coat the fibers and if this coating sticks it may just be the new wave of clothes cleaning.
The titanium dioxide works best in ultraviolet light and the silver iodide seems to speed up reactions in sunlight. We call a chemical that speeds up reactions a catalyst. These mighty chemicals speed boosters are useful in all sorts of manufacturing and even in reactions within your body.
Chemicals need a certain amount of energy to react, like combustion (reactions between a hydrocarbon and oxygen). A catalyst lowers the energy needed to get the reaction started. This energy is called activation energy. So, if you wanted the sunlight to react with a chemical and clean clothing you would benefit from a catalyst that would let that reaction start even with minimal sunlight.
There are cases where a catalyst only provides a surface for the reaction to happen on. The key is that in all of these reactions the catalyst is not changed. It remains the same where the two reacting chemicals form new compounds. The researchers did not report if the titanium dioxide gets depleted after a while and needs to be reapplied. Who knows, maybe a little bit goes a long way.
I remember an old social studies video that showed folks in Brazil cleaning clothing by beating them against rocks in a local river. That beating allowed the soap and water to penetrate the individual cotton fibers and I can imagine it is a bit exhausting. My grandmother used an old wringer washer where the washer agitated the clothing doing the same thing as the rocks and then two rollers wrung the water out of the clothing.
Letting the sunlight do the work sounds like science fiction.
Still it is intriguing to think that I could hang out my clothing and have the stains, dirt, smells and any bacteria be chemically whisked away by the sun.
A link to the research is below: