Molecular deposition of a macrocyclic cobalt catalyst on TiO₂ nanoparticles

Hybrid photocatalysts consisting of molecular catalysts and solid-state surfaces have demonstrated great potential as robust and efficient systems in solar fuel production. Based on our prior work, we synthesized hybrid photocatalysts by depositing a macrocyclic Co(III) complex on three different TiO₂ nanomaterials via a microwave method. The hybrid photocatalysts were tested in CO₂ reduction and were thoroughly characterized with spectroscopic (UV–vis, FTIR and EPR) and microscopic (TEM) techniques. The presence of terminal OH groups on TiO₂ surfaces was essential for the molecular deposition of catalytically active Co(III) sites. On a TiO₂ material without such terminal OH groups, the Co(III) complex formed amorphous aggregates, which hindered interfacial electron transfer from photoactivated TiO₂ to the surface molecular complex. EPR studies further revealed important information regarding the coordination geometry and interaction with CO₂ of surface cobalt sites in the hybrid photocatalysts.