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What is photocatalysis?
**What is Photocatalysis?**
Photocatalysis is a chemical process that uses light energy to trigger and accelerate reactions. The term "photocatalysis" comes from the Greek words "photo," meaning light, and "catalysis," referring to a substance that speeds up a chemical reaction without being consumed in the process. A photocatalyst is a material that remains unchanged during the reaction but helps convert light energy into chemical energy, enabling various transformations.
When exposed to light—whether natural sunlight or artificial sources like fluorescent lamps—the photocatalyst excites electrons within its structure. This excitation leads to the formation of highly reactive oxygen species, such as hydroxyl radicals and superoxide ions. These radicals are powerful oxidizing agents capable of breaking down organic pollutants, bacteria, and other harmful substances into harmless byproducts like water and carbon dioxide.
One of the most well-known examples of natural photocatalysis is photosynthesis in plants, where sunlight is used to convert carbon dioxide and water into glucose and oxygen. Similarly, synthetic photocatalysts, such as titanium dioxide (TiOâ‚‚), can be used to purify air, destroy bacteria, and degrade pollutants in water.
The concept of photocatalysis was first discovered in 1967 by Dr. Akira Fujishima while he was a graduate student at the University of Tokyo. In an experiment, he found that titanium dioxide, when illuminated, could split water molecules into hydrogen and oxygen—a phenomenon now known as the "Honda-Fujishima Effect." This discovery sparked global interest in using photocatalytic materials for renewable energy and environmental applications.
During the oil crisis of the 1970s, researchers saw great potential in using photocatalysis to produce hydrogen from water, which could serve as a clean energy source. Although large-scale hydrogen production proved challenging, the technology laid the foundation for future developments in green chemistry and sustainable materials.
In 1992, the International Conference on Titanium Dioxide Photocatalysts was held in Canada, where Japanese scientists presented groundbreaking research on the use of TiOâ‚‚ for air purification, particularly in removing nitrogen oxides. This led to a surge in patents and innovations related to photocatalytic technologies. From 1971 to June 2000, over 10,700 photocatalyst-related patents were filed worldwide, highlighting the growing importance of this field.
Today, photocatalysts are widely used in various applications, including antibacterial coatings, air purification systems, self-cleaning surfaces, and pollution control. Their ability to work under visible or UV light makes them ideal for both indoor and outdoor environments.
**Nano-TiOâ‚‚ Photocatalyst**
Modern advancements have led to the development of nano-sized photocatalysts, such as nano-TiOâ‚‚. These materials consist of particles ranging from 1 to 100 nanometers in size. Due to their small size, they have a very high surface area, allowing for greater interaction with pollutants and more efficient catalytic activity.
Nano-TiOâ‚‚ functions similarly to chlorophyll in plant photosynthesis. When exposed to light, it generates reactive oxygen species that can break down harmful substances. It is widely used in applications such as:
- **Antibacterial**: Effective against bacteria like *E. coli*, *Staphylococcus aureus*, *Klebsiella pneumoniae*, *Pseudomonas aeruginosa*, and viruses.
- **Air Purification**: Breaks down volatile organic compounds (VOCs), formaldehyde, benzene, ammonia, and other toxic gases.
- **Deodorization**: Removes odors from smoke, garbage, and body smells.
- **Mold and Algae Prevention**: Inhibits the growth of mold, algae, and scale.
- **Anti-fouling and Self-Cleaning**: Decomposes oils and dirt, allowing surfaces to remain clean.
**Key Features of Photocatalysts**
1. **Safety**: Many photocatalysts, especially TiOâ‚‚, are approved by regulatory agencies like the FDA and are considered safe for use in food, cosmetics, and medical products.
2. **Longevity**: Since photocatalysts do not get consumed in the reaction, they can last for many years, making them cost-effective and sustainable.
3. **Environmental Friendliness**: They help reduce pollution and improve air and water quality without producing harmful byproducts.
**Applications of Photocatalysts**
Photocatalysts are now used in a wide range of industries, including construction, healthcare, automotive, and consumer goods. They are incorporated into paints, coatings, textiles, and even air filters to enhance performance and sustainability.
As research continues, the future of photocatalysis looks promising, with new materials and methods being developed to make these processes even more efficient and accessible. Whether in nature or human-made systems, photocatalysis offers a powerful tool for creating a cleaner, healthier world.