Modulating the Conduction Band of MOFs by Introducing Tiny TiO 2 Nanoparticles for Enhanced Photocatalytic Performance: Importance of the Loading Position.

The preparation of TiO 2 and metal-organic framework (MOF) into composite photocatalysts has been proven to be a mature and effective strategy to achieve stronger catalytic activity. In this work, we focus on exploring the significant effects and mechanisms of the relative positions of decorated titanium oxide nanoparticles and MOFs on the final catalytic activity. We first used a simple in situ method to encapsulate tiny TiO 2 nanoparticles into a Zr-MOF (PCN-222), where Zr-Ti bonds were created at the interface of the two components. Thanks to the strong interfacial interaction forces, band bending occurred in TiO 2 @PCN-222 and a more negative conduction band (Δ = 0.26 V) with better electron transport properties was obtained. The results of photocatalytic CO 2 reduction experiments under visible light showed a 78% increase (142 μmol g -1 h -1 ) in the production rate of HCOO - . Surprisingly, the loading of TiO 2 nanoparticles on the MOF surface (TiO 2 @PCN-222) resulted in a significant decrease of 56% in the catalyst yield activity due to poor adsorption and electron transfer properties. This work demonstrates the possibility of tuning the band structure and catalytic activity of MOFs with the help of changing the position of the dopant and shows the importance of the rational design of MOF-based composites.