Skittles Titanium Dioxide-Why Does Titanium Dioxide Turn Yellow When Peroxide Is Added

Titanium dioxide (TiO2) is a white pigment commonly used in paints, plastics, and other products. When hydrogen peroxide (H2O2) is added to titanium dioxide, it can cause the compound to turn yellow. This color change is due to a chemical interaction between the titanium dioxide and the hydrogen peroxide.

The mechanism behind this involves the reduction of titanium dioxide by the hydrogen peroxide. Titanium dioxide exists in different crystal forms, with the most common being the rutile and anatase phases. Anatase is more reactive than rutile and is more likely to undergo changes when in contact with hydrogen peroxide.

Here’s a simplified explanation of what happens:

1. **Reduction of Titanium Dioxide**: When hydrogen peroxide comes into contact with titanium dioxide, it can reduce the titanium from a +4 oxidation state to a lower oxidation state, such as +3. This reduction process changes the electronic structure of the titanium dioxide particles.

2. **Surface Changes**: The reduction likely affects the surface of the titanium dioxide particles. The surface can become more reactive and may adsorb some of the peroxide or its breakdown products.

3. **Color Change**: The change in the electronic structure and the possible adsorption of peroxide or its degradation products can lead to a shift in the way the titanium dioxide absorbs and reflects light. Specifically, the material may absorb more light in the blue/violet part of the spectrum and reflect more light in the yellow part, resulting in a yellow appearance.

4. **Formation of Peroxide Complexes**: In some cases, hydrogen peroxide can form complexes with the titanium dioxide, which can also contribute to the yellowing effect.

It’s important to note that this yellowing is often considered an undesirable side effect in applications where the whiteness of titanium dioxide is crucial. However, in some cases, the yellowing effect can be harnessed for specific applications, such as in certain types of photochromic materials or in the development of self-cleaning surfaces.