Modulating the Conduction Band of MOFs by Introducing Tiny TiO₂ Nanoparticles for Enhanced Photocatalytic Performance: Importance of the Loading Position

The preparation of TiO2 and metal-organicframework(MOF) into composite photocatalysts has been proven to be a matureand effective strategy to achieve stronger catalytic activity. Inthis work, we focus on exploring the significant effects and mechanismsof the relative positions of decorated titanium oxide nanoparticlesand MOFs on the final catalytic activity. We first used a simple insitu method to encapsulate tiny TiO2 nanoparticles intoa Zr-MOF (PCN-222), where Zr-Ti bonds were created at the interfaceof the two components. Thanks to the strong interfacial interactionforces, band bending occurred in TiO2@PCN-222 and a morenegative conduction band (& UDelta; = 0.26 V) with better electron transportproperties was obtained. The results of photocatalytic CO2 reduction experiments under visible light showed a 78% increase(142 & mu;mol g(-1) h(-1)) in theproduction rate of HCOO-. Surprisingly, the loadingof TiO2 nanoparticles on the MOF surface (TiO2@PCN-222) resulted in a significant decrease of 56% in the catalystyield activity due to poor adsorption and electron transfer properties.This work demonstrates the possibility of tuning the band structureand catalytic activity of MOFs with the help of changing the positionof the dopant and shows the importance of the rational design of MOF-basedcomposites. The interaction effect andmechanism between TiO2 and PCN-222 were explored when TiO2 was encapsulatedwithin PCN-222 or loaded on the surface. The above mechanism was confirmedby photocatalytic CO2RR experiments and photoelectrochemicalmeasurements. The results showed that the encapsulation of TiO2 nanoparticles in the PCN-222 exhibited stronger interfacialinteraction and a better generation rate of formate.