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Some windows are just hard to clean. Staking its claim on the world map for beneficiating titanium, South African nanomaterials can soon make light work of cleaning ceiling windows such as this in a museum in Vienna. Photograph by Janice Limson

South Africa currently has the second-largest global reserves of titanium. With plans afoot to construct a 4.2 billion rand plant to manufacture titanium dioxide particles, Jan Kruid reports on a practical application of nanosized titanium dioxide particles for the modern-day landscape.

Imagine never having to clean your windows again, because they clean themselves. Technology has made self-cleaning windows a reality through the application of titanium dioxide (TiO₂) coatings. Ordinary glass panes are coated with transparent layers of TiO₂ tens of nanometres thick. This cheap and durable coating has sterilising, anti-fouling, anti-fogging, and anti-pollutant properties. This technology offers great advantage for windows in hard-to-reach places, such as those in skyscrapers.

Glass coated with TiO₂ has the two properties required to achieve self-cleaning capabilities: firstly, the ability to break down the organic compounds that make windows dirty and secondly, the capacity to improve the hydrophilic (water-loving) properties of the glass surface. The ability to degrade organic materials arises from the properties of  TiO₂ that, when irradiated by UV light found in sunlight, generates free radicals on the glass surface which break down organic materials, pollutants, and bacterial membranes to water, carbon dioxide and debris.

Simultaneously, the TiO₂ dramatically improves the wettability of the glass by making the surface superhydrophilic. This means that water touching the surface of the glass spreads evenly along the surface, instead of forming droplets. Water falling on these types of windows spreads evenly, washing away the organic debris while leaving hardly any streaks behind. Windows are thus cleaned by rainfall and sunlight alone.

Writer: Jan Kruid