A kinetic model for evaluating the dependence of the quantum yield of nano-TiO2 based photocatalysis on light intensity, grain size, carrier lifetime, and minority carrier diffusion coefficient: Indirect interfacial charge transfer

A model based on spherical TiO2 nanoparticles was developed to study heterogeneous photocatalysis based on TiO2 in the case of indirect interfacial charge transfer. In this model, the effect of light intensity (I0), grain size (r0), carrier lifetime (τp), and minority carrier diffusion coefficient (Dp) on the quantum yield (QY) of photocatalytic reactions was investigated in detail. Under conditions of sufficiently low incident-light intensity, the QY was found to be ∝I0, while it decreased rapidly with an increase in I0. In addition, the QY went to zero at a critically high light intensity. Furthermore, the QY was found to decrease with increasing r0 due to the bulk-recombination loss, and the effect of r0 on the QY became increasingly stronger with the increase in I0. The QY decreased with the decrease in τp and Dp, which was more apparent at the critically high I0. Under conditions of low [(RH2)aq], the QY increased with an increase in [(RH2)aq], while it remained nearly constant at high [(RH2)aq] due to the fact that the photoinduced electron interfacial transfer became the limiting step for photocatalytic reactions in the case of high [(RH2)aq].