Question

Describe two photocatalytic methods that can destroy organic wastes.

Short answer

Two methods are: Titanium Dioxide and Zinc Oxide photocatalysis.

Step-by-step solution

Titanium Dioxide Photocatalysis

Titanium dioxide (TiO2) is a widely used photocatalyst that can destroy organic wastes. When TiO2 is exposed to ultraviolet (UV) light, it generates electron-hole pairs. These reactive species can degrade organic pollutants through oxidative reactions. TiO2 is particularly effective for breaking down complex molecules into harmless end-products like CO2 and H2O.

Zinc Oxide Photocatalysis

Zinc oxide (ZnO) is another photocatalyst similar to TiO2 in its action mechanisms. Like TiO2, ZnO also requires exposure to UV light to create reactive electron-hole pairs. These reactive pairs can effectively oxidize and decompose organic compounds, transforming them into non-toxic byproducts. ZnO is often chosen for its cost-effectiveness and its ability to absorb a wider spectrum of light.

Key concepts

Titanium Dioxide Photocatalysis

Titanium dioxide (TiO2) photocatatalysis is a popular technique in the field of environmental cleanup. TiO2 is a stable and non-toxic semiconductor that when exposed to ultraviolet (UV) light, gets activated. This activation leads to the formation of electron-hole pairs. These pairs create a highly reactive environment ideal for breaking down pollutants.
The major advantage of TiO2 is its efficiency in degrading complex pollutants. Upon activation, TiO2 can convert harmful chemicals into harmless substances like carbon dioxide (CO2) and water (H2O). This makes it an excellent option for treating contaminated water or air.
Some key benefits of using titanium dioxide include:

• High stability under various environmental conditions.
• Ability to degrade a wide range of organic pollutants.
• No secondary pollution as it breaks down pollutants into non-toxic end products.

UV Light Activation

UV light activation plays a crucial role in initiating the photocatalytic reactions. Both titanium dioxide and zinc oxide require UV light to activate their photocatalytic properties. The energy from UV light is necessary to excite electrons, thereby creating reactive species that can interact with organic pollutants.
The interaction of UV light with the photocatalyst leads to the generation of electron-hole pairs. Electrons, energized by UV light, jump from the valence band to the conduction band of the photocatalyst, leaving behind electron vacancies or 'holes'. This process can be summarized as follows:

• The energy from UV light is absorbed by the photocatalyst.
• Electrons are excited from the valence band to the conduction band.
• Reactive electron-hole pairs form, initiating the degradation of pollutants.

Most UV light sources used in photocatalysis mimic the portion of sunlight that naturally contains UV rays. Utilizing these sources helps initiate and maintain the photocatalytic processes beneficially.

Zinc Oxide Photocatalysis

Zinc oxide (ZnO) is another effective photocatalyst used in degrading organic pollutants. While similar to titanium dioxide, zinc oxide offers a unique advantage in its ability to absorb a broader spectrum of light. This quality can make ZnO preferable in certain environmental conditions.
The mechanism of zinc oxide photocatalysis mirrors that of titanium dioxide. Under UV light, it generates electron-hole pairs. These pairs are highly reactive, initiating oxidative reactions that break down organic compounds into simple, non-toxic molecules.
Some merits of using zinc oxide include:

• Cost-effective compared to other photocatalysts.
• Efficient in absorbing and utilizing a wider range of light, enhancing its catalytic activity.
• Capabilities of transforming numerous toxic organic substances.

Despite its advantages, the performance of zinc oxide can be affected by factors such as crystal structure, surface area, and preparation methods, which require careful consideration for optimization in practical applications.