Photochemistry is the study of chemical reactions that occur as a result of light absorption. Photochemical systems that use sunlight to drive key chemical reactions or generate electricity are extremely significant for the development of sustainable energy sources. The underlying process for all of photobiology is photochemistry. A molecule's electrical structure changes when it absorbs a photon of light, and it responds differently with other molecules as a result. The absorbed energy from light might cause photochemical changes in the absorbing molecule or in a nearby molecule (e.g., photosensitization).
Photocatalysis is a photo-activated chemical reaction that occurs when free radical mechanisms are triggered when a substance comes into contact with photons with adequate energy levels. The term photocatalyst is made up of two words: photo, which refers to a photon, and catalyst, which refers to a chemical that changes the rate of a reaction when it is present. Photocatalysts are materials that, when exposed to light, change the rate of a chemical reaction. Photocatalysis is the term for this occurrence. Photocatalysis is the use of light and a semiconductor to catalyse processes. A photocatalyst is a substrate that absorbs light and functions as a catalyst for chemical reactions.
A photoreactor is a chemical reactor that interacts with photons, a photocatalyst, and reactants, as well as accumulates reaction products resulting from physicochemical transformations.