Photocatalysts are substances that accelerate chemical reactions when exposed to light, typically ultraviolet or visible light. They work by absorbing light energy, which excites electrons and creates reactive species that can drive various chemical processes. Common materials used as photocatalysts include titanium dioxide and zinc oxide, which are often employed in environmental applications like air purification and water treatment. These materials can help break down pollutants and harmful substances, making them valuable in addressing environmental challenges. Photocatalysts are also being explored for use in solar energy conversion and hydrogen production, as they can facilitate reactions that generate clean energy from sunlight.