Quantum efficiency of cyanide photooxidation with TiO2/SiO2 catalysts: Multivariate analysis by experimental design

Despite the large amount of work dealing with supported photocatalysts used to overcome the difficulties associated with the recovery of powdered titania after the photocatalytic treatments, few attempts have been made to calculate the quantum efficiency (η) of these materials. In this work the quantum efficiency for the photooxidation of cyanide with TiO2 and TiO2/SiO2 has been experimentally calculated using an approach based on the resolution of the radiative transfer equation inside the photoreactor. Due to the low absorption coefficient of the silica-supported material, a two-dimensional two-directional reactor model has been developed to describe the photon transport. The dependence of η on the incident radiation flux, the catalysts concentration and the cyanide concentration has been investigated. With both material suspensions, higher quantum efficiencies have been observed when lower radiation fluxes and higher cyanide concentrations are used. However, different trends in the quantum efficiencies are observed when increasing the catalyst concentration, leading to higher values when using powdered TiO2 and lower values for TiO2/SiO2 suspensions.