Written by Wonjin Ko '26
Edited by David Han '24
Sanitation is no stranger to our society. Since ancient times, people have understood the importance of cleanliness in daily life, helping prevent the outbreak of disease and infection. Proper sanitary conditions have been stressed for decades in hospitals, schools, or any public facility. Basic sanitary habits such as washing one’s hands have been ingrained for generations. In the past couple of years, however, these everyday sanitary habits have suddenly become a necessity. Once given weird side-eyes for carrying around the pocket-sized Purell hand-sanitizers, people are praised and supported for sanitizing their hands every minute. And this is all with due cause; the Coronavirus pandemic has effectively changed our lives and our habits, probably indefinitely. Our society has become clean-freaks, basically overnight.
Given the abundance of sanitary concerns nowadays, many technologies have been developed to ensure the safety and health of the general public — including the “antimicrobial” green handles on our toilets. However, most cleaning products only cleanse the surface temporarily and require constant reapplication. Hence, a “self-cleaning” surface has been created to ensure sanitation 24/7.
This self-cleaning surface is driven by photochemical reactions by a chemical compound called titanium dioxide. As obscure as it may sound, titanium dioxide is actually very common in everyday life. It is an important ingredient in sunscreen, medications, cosmetics, food colorants, M&Ms, chewing gum, and many other products. However, this new application of titanium dioxide has potential to have a greater, more innovative impact on health and sanitation.
There are two main ways in which titanium dioxide-derived surfaces self-clean. Titanium dioxide is an abundant, environmentally friendly chemical that acts as an oxidative photocatalyst, making it an effective antimicrobial agent. In other words, it reacts chemically under light and releases harmful products that destroy cell membranes of bacteria. When titanium dioxide is irradiated with sufficient energies of protons (light energy) under oxidative conditions, electrons are released and subsequently bind to nearby oxygen atoms, forming superoxide ions. These ions can degrade organic material as well as increase the permeability of cell membranes to free radicals. These free radicals are highly energetic chemical agents that disrupt cell functions, making them dangerous to cell life. Under light conditions, titanium dioxide also produces highly reactive hydroxyl radicals that attack cell walls and the cytoplasmic membrane of bacterial cells. These radicals are able to penetrate the membranes of invading cells and cause lysis, leading to cell death.
There are many advantages to using photocatalytic cleaning surfaces as opposed to other antimicrobial cleaning agents. Primarily, photocatalytic surfaces are able to function without electricity or other chemical reagents— the only required reagents are light, oxygen, and water. Unlike many other chemical reagents, titanium dioxide is not poisonous and are environmentally safe. These characteristics make titanium dioxide surfaces the ideal choice for maintaining sanitary conditions.
As such, many companies, including San Gobain Bioclean™, Pilkington Active™, Sunclean™, and Nanotouch™, have already started using titanium dioxide surfaces to manufacture self-cleaning windows, lamps, and filters. The applications of titanium dioxide surfaces are limitless, given its accessibility and efficiency.
References
1. How It Works [Internet]. [cited 2022 Nov 17]. Available from: https://nanotouch.com/how-it-works/.
2. Foster HA, Ditta IB, Varghese S, Steele A. Photocatalytic disinfection using titanium dioxide: spectrum and mechanism of antimicrobial activity. Appl Microbiol Biotechnol. 2011;90(6):1847–68.
3. Prakash J, Cho J, Mishra YK. Photocatalytic TiO2 nanomaterials as potential antimicrobial and antiviral agents: Scope against blocking the SARS-COV-2 spread. Micro and Nano Engineering. 2022 Apr 1;14:100100.
4. Unraveling titanium dioxide’s self-cleaning ability [Internet]. Cornell Chronicle. [cited 2022 Nov 17]. Available from: https://news.cornell.edu/stories/2018/08/unraveling-titanium-dioxides-self-cleaning-ability
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