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Cleaning clothes usually requires soap and water to remove stains and smells, and a tumble in the dryer or an afternoon on the clothesline to dry. The time and energy needed to turn a heap of dirty laundry into a pile of clean clothes might make people wish for clothes that just clean themselves.
That wish is a step closer to coming true. Recent experiments show that cotton fabric coated with the right mixture of chemicals can dissolve stains and remove odors after only a few hours in the sun. "The technology can be applied to all kinds of fabrics and their related products," says materials scientist Mingce Long. He helped develop the treated cotton with his colleague Deyong Wu.
The handy fabric gets its self-cleaning abilities from a chemical mixture that coats the cotton threads. The coating includes substances known as photocatalysts, which trigger chemical reactions in light. One of those photocatalysts, called titanium dioxide (二氧化钛), helps sunscreen block the sun. Another, called silver iodide (碘化银), is used for developing photographs.
Researchers have previously shown that titanium dioxide mixtures could remove stains in clothes—but with exposure to ultraviolet, not visible, light. (The waves of ultraviolet light are more energetic and shorter than those of visible light.) Other studies have demonstrated that silver iodide can speed up chemical reactions in sunlight.
"We knew that self-cleaning cotton fabrics with titanium dioxide coating had already been developed, but they cannot work, or they work weakly, under sunlight," Long says. "If we want to use the fabrics in daily life, we must develop cotton that cleans itself under daylight." Long and Wu created just such a fabric, working for years to perfect the recipe for a liquid dip that left cotton coated with the titanium dioxide mixture. Then they added particles of silver iodide, which boosted the fabric’s self-cleaning ability in the sun. In laboratory tests, their creation was nearly seven times better at removing stains than titanium dioxide alone.
The scientists can’t start selling their self-cleaning cotton just yet; they still need to make sure the coated cotton won’t harm those who wear it. Although titanium dioxide is used in some foods, recent experiments have shown that it can cause health problems if it gets in the lungs. So before the material can be worn, scientists need to find a way to make it safe. What is the major topic of the passage