Photocatalysis is a fantastic way to clean facilities, houses, and living environments.  By modifying and further developing this technology, we can reduce pollution in our air and water.  We can even reduce the spread of infections and diseases such as SARS in hospitals.  This cleaner way of life would benefit everyone around the world.

The word photocatalysis is composed of two parts:

1. The prefix photo, defined as "light",

2. Catalysis is the process where a substance participates in modifying the rate of a chemical transformation of the reactants without being altered in the end.  This substance is known as the catalyst which increases the rate of a reaction by reducing the activation energy.

Hence, photocatalysis is a reaction which uses light to activate a substance which modifies the rate of a chemical reaction without being involved itself.

Today, semiconductors are usually selected as photocatalysts, because semiconductors have a narrow gap between the valence and conduction bands.  In order for photocatalysis to proceed, the semiconductors need to absorb energy equal to or more than its energy gap.  This movement of electrons forms e^-/h⁺ or negatively charged electron/positively charged hole pairs. The hole can oxidize donor molecules.

Among the possible semiconductors, TiO₂, or Titanium Dioxide, (E_g = 3.2 eV) is most extensively used because it has many advantages.  It is inert and resistant to corrosion, and it requires little post-processing, making it inexpensive.  Finally, it can react under mild-operating conditions.  However, it currently needs to use ultraviolet light for photocatalysis to occur.

Visible-Light Photocatalysis: A Cleaner Way of Life