69 The Effect of TiO₂ Nanoparticle Size on Photo-Catalytic Performance in Selective Propane Oxidation Available to Purchase

A high degree of control over the size of TiO₂ nano-particles at identical TiO₂ loading by growing them within the pores of an amorphous silica matrix TUD-1 were achieved. The photocatalytic behavior of this material was tested by oxidizing propane under narrowband ultraviolet light (335 nm), with simultaneous detection of adsorbed products by infrared spectroscopy. We present a detailed comparison of two samples of identical atomic composition but different texture, with narrow TiO₂ particle-size distributions centered at 4 and 7 nm. The initial reaction rate per incident photon is greater on the larger particles (by a factor of 4.8), despite the smaller TiO₂ surface area available in this material. However, the photochemical selectivity toward acetone (measured as the fraction of all adsorbed products) is 50% greater on the smaller particles at all stages of product accumulation. The lower photo-reactivity of the smaller particles is accompanied by luminescence that is several times more intense than from the larger TiO₂-particles, suggesting that the chemical benefits of reducing particle size (increased chemical selectivity) may come at the cost of a fundamentally lower photochemical quantum yield.