A four factor three level Box-Benkhen design (BBD) was developed to describe the photocatalytic degradation of phenol in an aqueous media. The four process variables under consideration in BBD model included titanium dioxide (TiO2) catalyst size, TiO2 concentration, dissolved oxygen (DO) concentration and phenol concentration. The model predicted a maximum degradation rate (0.083 min(-1)) with conditions set at 9.091 nm TiO2 particle size, 1.0 g/l TiO2, 31.0 mg/l DO and 40 mg/l phenol. A response outcome computed using experimental data for the 10 nm nanoparticle size catalyst was 13% less than the maximum value. The data suggest that small catalytic particle size augmented the quantum yield in the photocatalytic degradation process with the maximum located at an approximate catalyst size of 10 nm. The photocatalytic degradation rate constant followed an Arrhenius dependency with activation energy of 13.55 kJ/mol K for the 10 nm TiO2 particles. (C) 2008 Elsevier B.V. All rights reserved.