In 1951, Alec Guinness, a famous British actor at the time, role played a film about a man who wore a magical white suit. This film, so called “The man in the white suit” featured a fabric that never get dirty, wrinkles and completely impervious to the elements. After 60 years later, the fiction is becoming a reality, as many scientists all around the world, are getting close to make a fabric that can actually clean itself.
Burning the stains at the nanoscale
This fascinating feat is only possible due to special class of nanomaterial called photocatalysts. These materials can perform catalytic activity when excited by light. The most widely used photocatalyst are nanomaterials of Titanium dioxide (TiO2) and Zinc oxide (ZnO).
Photocatalysis occur when light (photons) having a frequency above certain limit is absorbed by the nano particle and produce electron hole pairs. This electron and hole migrate in to the nanoparticle surface and take reactions with the surface bound water molecules to produce free radicals. These highly unstable radicals will attack anything on their path. If there are organic stains in the vicinity of the photocatalyst, free radicals will attack the organic stains until they are converted to, elementary, carbon dioxide and water. This appears much like stains get vanished in to thin air as both carbon dioxide and water escape from the surface leaving no traces behind.
Photocatalytic reaction is very similar to burning where organic compounds react with oxygen to form carbon dioxide and water. Stain removal by photocatalysts is just like burning the stains in the nanoscale but without a flame.
The nano twist
Scientists make self cleaning fabrics by coating a thin layer of photocatalytic nanoparticles like TiO2 on the surface of the fibers. These nanoparticles get activated with UV light and initiate photocatalysis when fabrics are exposed to sunlight. Radicals generated in this way can attack and decompose any stains in the fabric essentially making it a self cleaning cloth. These radicals can also attack harmful bacteria that may grow on the fiber, damaging their cell wall. So the fabric surface is no longer a safe haven for pathogenic microorganisms.
This photocatalyst layer also provide some protection to wearer from harmful UV radiation as these nanoparticles absorb UV preventing it penetrating through the fabric. Scientists have also shown that this technique is quite capable in removing wine stains and removing deodorant stains, which are proven tough stains even to harshest washing detergents.
Many experts agree that self cleaning fabrics will be a standard issue in the future. It has already entered market especially in areas where the hygiene and prevention of pathogenic infections is quite important as textile surfaces are known hiding places for harmful microorganisms.
- Linsebigler, Amy L.; Lu, Guangquan.; Yates, John T. (1995). “Photocatalysis on TiO2 Surfaces: Principles, Mechanisms, and Selected Results”. Chemical Reviews 95 (3): 735.doi:10.1021/cr00035a013
- Cushnie TPT, Robertson PKJ, Officer S, Pollard PM, Prabhu R, McCullagh C, Robertson JMC (2010). “Photobactericidal effects of TiO2 thin films at low temperature”. Journal of Photochemistry and Photobiology A: Chemistry 216 (2-3): 290–294.doi:10.1016/j.jphotochem.2010.06.027
- Linsebigler, A. L.; G. Lu; J.T. Yates (1995). “Photocatalysis on TiO2 Surfaces: Principles, Mechanisms, and Selected Results”. Chemical Review 95 (3): 735–758.doi:10.1021/cr00035a013
- Realizing Visible-Light-Induced Self-Cleaning Property of Cotton through Coating N-TiO2 Film and Loading AgI Particles, Deyong Wu and Mingce Long, ACS Applied Materials & Interfaces 2011 3 (12), 4770-4774,DOI: 10.1021/am201251d