Titanium dioxide (TiO²) is a photocatalyst which exhibits strong oxidative property when exposed to ultraviolet (UV) light. TiO² is able to decompose harmful organic compounds, kill bacteria and eliminate odours.

TiO²’s reactivity is used in many environmentally beneficial applications including water treatment and purification, atmospheric NOx (nitrogen oxide) removal and self-cleaning building façade.

Titanium dioxide is non-toxic and therefore is used in cosmetic products (sunscreens, lipsticks, toothpaste) and in pharmaceutics (pills).

ReactionWhen TiO² absorbs UV light, electrons are promoted from the valence band to the conduction band, producing holes in the valence band.

The production of pairs of negative-electrons (e-) and positive-holes (h+) is called “photo-excitation”. The holes in the valence band react with hydroxides on the titanium dioxide surface, by subtracting it’s electron, as a result, oxidizing to form Hydroxyl radicals.

When a contaminant in the air is adsorbed onto the TiO², the hydroxyl radical attacks the contaminant, extracting a hydrogen atom from the contaminant. The hydroxyl radical oxidizes the contaminant, producing water, carbon dioxide and other harmless substances.

Hydroxyl radicals have much stronger oxidative power than chlorine or ozone which is used as a sterilizer.

Light; Which Light?

As above figure presents, Excitation can be achieved by adsorption of the Ultra-violet light wave length light,; The light energy is described as the photon-are currently best explained by wave-particle duality, exhibiting properties of both waves and particles.


When the light wave hits TiO2, the electron in the balance band transfers to the conduction band by given energy of the light wave;

By gaining high enough energy to pass up the barrier, which is called “Band Gap” as TiO2 has 3.2 electron Volt energy.

Thus, this energy can be described as = hc /λ ; the famous equation by Dr. Albert Einstein.; Here E is characteristic energy of Titanium Dioxide 3.2eV (3.2eV=3.2×1.6×10-19J)

Calculating with Light speed c:3.0×108m/s;  Planc’s constant h:6.63×10-34J・s; λ = 380nm

Which is considered as the UV wave length (closer to the Visible purple light wave length)



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