Chemists at the Leibniz Institute for Catalysis in Rostock discovered the molecular mechanism of a photocatalyst that completely breaks down organic contaminants in wastewater with the help of sunlight. Worldwide, for example, more and more residues of drugs such as anti-inflammatory drugs, antibiotics or contraceptives are entering treatment systems where they are difficult to remove. Laboratories are increasingly working on photocatalytic solutions, but knowledge of the active principles is incomplete. Researchers around Angelika Brückner and Jabor Rabeah at LIKAT have therefore observed photocatalysts live at work, so to speak, and have explained the basics of how they work.