Molecular deposition of a macrocyclic cobalt catalyst on TiO2 nanoparticles

•Hybrid photocatalysts are prepared by depositing a molecular Co catalyst on TiO2.•Terminal TiOH groups are essential for molecular deposition of the catalyst.•Electron transfer occurs from TiO2 to the molecular catalyst for CO2 reduction.•EPR studies reveal the catalyst’s coordination geometry and interaction with CO2.

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.

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