Researchers from Tokyo Metropolitan University have discovered key clues behind the workings of "single-atom" catalysts based on iron-pyridine sites in a carbon matrix. They firstly developed a new, simple synthesis method for a catalyst that activate peroxymonosulfate, highly effective in breaking down pollutants that do not easily biodegrade. They discovered that "high-spin" state iron sites strongly correlated with catalyst performance thanks to two distinct chemical pathways.