Titanium Dioxide as a Photocatalyst

from Wikipedia

As a photocatalyst

TiO fibers and spirals.

Titanium dioxide, particularly in the anatase form, is a photocatalyst under ultraviolet light. Recently it has been found that titanium dioxide, when spiked with nitrogen ions or doped with metal oxide like tungsten trioxide, is also a photocatalyst under visible and UV light. The strong oxidative potential of the positive holes oxidizes water to create hydroxyl radicals. It can also oxidize oxygen or organic materials directly. Titanium dioxide is thus added to paints, cements, windows, tiles, or other products for its sterilizing, deodorizing and anti-fouling properties and is used as a hydrolysis catalyst. It is also used in the Graetzel cell, a type of chemical solar cell.

The photocatalytic properties of titanium dioxide were discovered by Akira Fujishima in 1967^[18] and published in 1972.^[19] The process on the surface of the titanium dioxide was called the Honda-Fujishima effect.^[18] Titanium dioxide has potential for use in energy production: as a photocatalyst, it can

• carry out hydrolysis; i.e., break water into hydrogen and oxygen. Were the hydrogen collected, it could be used as a fuel. The efficiency of this process can be greatly improved by doping the oxide with carbon.^[20].
• Titanium dioxide can also produce electricity when in nanoparticle form. Research suggests that by using these nanoparticles to form the pixels of a screen, they generate electricity when transparent and under the influence of light. If subjected to electricity on the other hand, the nanoparticles blacken, forming the basic characteristics of a LCD screen. According to creator Zoran Radivojevic, Nokia has already built a functional 200-by-200-pixel monochromatic screen which is energetically self-sufficient.

In 1995 Fujishima and his group discovered the superhydrophilicity phenomenon for titanium dioxide coated glass exposed to sun light.^[18] This resulted in the development of self-cleaning glass and anti-fogging coatings.

TiO₂ incorporated into outdoor building materials, such as paving stones in noxer blocks or paints, can substantially reduce concentrations of airborne pollutants such as volatile organic compounds and nitrogen oxides.^[21]

A photocatalytic cement that uses titanium dioxide as a primary component, produced by Italcementi Group, was included in Time‘s Top 50 Inventions of 2008.^[22]

TiO₂ offers great potential as an industrial technology for detoxification or remediation of wastewater due to several factors.

1. The process occurs under ambient conditions very slowly; direct UV light exposure increases the rate of reaction.
2. The formation of photocyclized intermediate products, unlike direct photolysis techniques, is avoided.
3. Oxidation of the substrates to CO₂ is complete.
4. The photocatalyst is inexpensive and has a high turnover.
5. TiO₂ can be supported on suitable reactor substrates.