Photocatalysis promises an efficient conversion of abundant solar energy into usable chemical energy. Polyheptazine imides have some key structural and functional twists that make them especially interesting for photocatalysis. So far, there is only limited knowledge about how structural changes affect the electronic and optical properties of the many material candidates in this class. A team led by researchers from the Center for Advanced Systems Understanding (CASUS) at HZDR has now presented a reliable and reproducible theoretical method to solve this challenge that was confirmed by measurements done on genuine candidate materials.
Polyheptazine imides belong to the family of carbon nitrides, which are layered, graphene-like compounds composed of nitrogen-rich, ring-shaped units. Unlike graphene, which exhibits excellent electrical conductivity but lacks photocatalytic activity, polyheptazine imides possess band gaps suitable for visible-light absorption.
Carbon nitride-based materials impress due to their low production cost, nontoxicity and thermal stability. However, the first generation of such materials were not ideal photocatalysts as the materials possessed properties that hindered charge separation. If a material has a low charge separation, the electron excited by an incoming photon quickly recombines with the hole it was propelled from—and releases energy only as heat or light. No energy is available to drive chemical reactions.









