Antimicrobial and photocatalytic technologies: Tile Files

By Noah Chitty

How do you innovate with a product like tile that has been around for centuries or even millennia? In recent years, we have seen some amazing new technologies, like inkjet printing and large, thin porcelain panels, that clearly show that the tile industry still has a few tricks up its sleeve. 

Another innovation that is providing new solutions to the tile end-user is the recent emergence of antimicrobial and photocatalytic tile products. While tile has always been seen as one of the most hygienic floor and wall options available due to its inert nature and ease of cleaning, new technologies are taking tile products to the next level. 

When it comes to antimicrobial solutions, tile has always been the best floor and wall surface option, because it does not provide an organic food source, which bacteria and other organisms need to grow. So, when these organisms come in contact with the surface of tile, they have no ability to thrive and multiply. Recent innovations have allowed manufacturers to apply antimicrobial metal compounds to tile surfaces. When these materials are employed with tile, bacterial growth is greatly reduced, destroying odor- and stain-causing organisms in the process. You may not know it, but most of the unpleasant smells associated with uncleanliness actually come from bacteria populating floor and wall surfaces. By eliminating the source, these treated tiles can eliminate the smell and stains, thus providing a much more pleasant and sanitary environment. 

In the past, in terms of smells and uncleanliness, floor and wall surfaces have either been part of the problem or innocent bystanders; now, antimicrobial tile products can be a tool to help provide a safer, cleaner, more hygienic environment. Antimicrobial metals have been touted and utilized for centuries because of their natural properties. Metals are either mixed with the glaze and then fired onto the surface of the tile or delivered as a coating to the surface of an already-fired tile, which is then re-fired to permanently fuse the materials to the face, making them an integral part of the tile product. The resulting products can provide a solution in healthcare, education and hospitality environments, where hygiene and cleanliness are critical.

You may ask, what about the grout? The grout makes up a small percentage of a floor or wall surface; therefore, having an antimicrobial tile surface serves as a solution for the majority of the floor or wall. But grouts have evolved with innovative solutions as well. Cement grouts are denser and less porous than they used to be, and some even incorporate antimicrobial additives that can provide a great solution. Epoxies, urethanes and other non-cementitious grouts can also provide greater functionality in this regard. 

Photocatalysts have not been around as long as antimicrobials, only about 15 to 20 years, and were first used to produce non-streaking window glass in Japan. This glass, when exposed to UV light, becomes hydrophilic (attracted to water) and the resulting sheeting of the water eliminates the streaks that commonly occur. Photocatalytic tile products generally use titanium dioxide (TiO₂) as the photocatalyst. TiO₂is a common material that is used in paint, food, toothpaste, make-up, and many other products as a whitening agent. Not all TiO₂ has photocatalytic properties, but there are certain forms that do; when exposed to UV light, these forms interact with oxygen and the moisture in the environment to produce reactive oxygen species, which essentially oxidize and mineralize organic compounds. This non-depleting reaction has the ability to provide self-cleaning and air-cleaning benefits. TiO₂ has started to get more mention in the press lately for the new ways this amazing technology is being used. Just a simple Internet search will yield information about its uses in water purification as well as its function as an air cleaner on the International Space Station. 

Exterior self-cleaning benefits are a function of three factors. First, the charged oxygen (O₂) that is created has the ability to decompose organics like algae and fungus that may form on an exterior wall. Second, the hydroxyl (OH) group that is produced provides an anti-static type effect, where a microscopic layer of water forms at the surface and reduces adhesion of contaminants on the surface of the tile product. Third, the hydrophilic effect causes water to spread on the surface and not bead, allowing rain or water to get behind contaminants and remove them from the surface. 

So, on the exterior of a building clad with photocatalytic tile, the organics are being broken down, the contaminants do not adhere strongly to the surface and, finally, when it rains, both the organics and the contaminants can be washed away. So the white building remains white; the need for costly pressure washing and cleaning is reduced or eliminated; and the use of harsh/environmentally unfriendly cleaning agents, often employed to eliminate dingy residues on building exteriors, is minimized.

Studies have shown that surfaces with a photocatalyst can contribute to a reduction in levels of nitrogen oxides (NO_X). Having building surfaces that can help reduce the amount of these harmful compounds can provide an environmental benefit, especially in urban areas where cars and factories produce a significant amount of NO_X and other pollutants. Tile cladding, once chosen for its aesthetic characteristics, can now provide cleaning of the surrounding environment. 

The difficulty in manufacturing both the antimicrobials and the photocatalyst products is how they are put in or on the products so that they become a permanent finish, and with the photocatalyst, it is key to provide a surface that does not become cloudy or milky when you apply the material. Crossville, for example, has licensed a technology from Toto called Hydrotect, which provides a delivery system for both of these technologies. For the exteriors it is a pure photocatalyst, and for the interiors it is a hybrid photocatalyst that combines both titanium dioxide and anti-microbial metals. 

The hybrid photocatalyst serves two functions. One, the titanium dioxide provides a stable platform for a consistently distributed delivery of the antimicrobials to the surface of the tile, where they must be in order to be most effective. Second, the photocatalyst provides the opportunity—in interiors with enough UV exposure through windows or with strong artificial light sources—for some photocatalytic effect to be realized, providing some of the above-described benefits. The amount of UV exposure in a given interior application is variable from project to project and may be less than is needed for full exploitation of the photocatalytic effect, so while it’s possible that some benefit from the photocatalyst might be achieved, the main interior benefits are derived from the antimicrobial metals that work in any lighting conditions or even in the dark. Combining the antimicrobials and the photocatalyst for interiors provides the best use of these powerful technologies. 

As more manufacturers begin to offer these types of tiles to their customers, it will be important to evaluate each product based on its testing and ability to deliver the functionality. Manufacturing a product employing these technologies is not simple, and formulation, method of application and production methods can produce varying levels of the benefits.

Related Topics:Crossville, Fuse Alliance, Fuse