A Proposal for the Quantitative Assessment of Heterogeneous Photocatalytic Processes

A critical assessment of the parameters needed for the correct comparison of activity and efficiency of various heterogeneous photocatalytic systems is presented in the present paper. Two parameters are to be evaluated in order to compare different photocatalytic systems. The first parameter, the "intrinsic reaction rate" (ri), allows one to have information on the specific catalytic reactivity, while the second one, the "rate of photon absorption" (rpa), allows the evaluation of the capacity of absorbing photons. From the knowledge of these two parameters the "quantum yield" (qy), which indicates the efficiency of the absorbed photons for promoting a reaction event, can be determined. The phenol photodegradation reaction, carried out in aqueous dispersions of polycrystalline (anatase) TiO2, has been used as a test reaction in order to determine the ri, rpa, and qy values of powdered specimens from different preparation methods and sources.