Autoinhibition of photocatalytic reduction of safranin and dichromate ions at anatase

The photocatalytic transformations of safranin and dichromate ion at titanium dioxide involve the formation of reduction products at the first stage. With increase in the concentration of catalyst the rate constant increases at E] 1 g/L and subsequently reaches a plateau in accordance with the Michaelis-Menten equation. With increase in the concentration of the substrate, however, the rate of the process increases, passes through a maximum, and then decreases. The retardation of the process is due to inhibition by the substrate or by the product of the photocatalytic transformation. The proposed equation predicts a hyperbolic dependence of the rate and the rate constant on E] and an extremal dependence of these kinetic parameters on the concentration of the substrate.