Photocatalytic degradation of methyl red by TiO2: Comparison of the efficiency of immobilized nanoparticles versus conventional suspended catalyst

The photocatalytic efficiency of supported TiO2 nanoparticles (mean size 6 nm), immobilized onto the inner walls of a cylindrical glass photoreactor was compared versus the performance of conventional TiO2 Degussa P25 catalyst. For this purpose the degradation of methyl red dye was used as evaluation test. The obtained results showed that the TiO2 Degussa P25 catalyst is more efficient than the supported nanoparticles. The poorer performance of the nanosized catalyst can be ascribed to the fact that the immobilization procedure turns out, in spite of the extremely high surface to volume ratio, in an overall reduction of active surface area available for target molecule adsorption, due to the low porosity of the supported catalyst layer. The kinetics of the investigated processes were monitored and a study on the reaction products and intermediates was carried out in order to evaluate possible difference in the reaction pathway in presence of immobilized nanoparticles versus suspended catalyst. The results demonstrate that the mechanisms of parent dye degradation in presence of supported TiO2 nanoparticles are the same as those occurring in presence of TiO2 Degussa P25 catalyst. The present work describe the results obtained on the feasibility of scaling up the colloidal nanocrystal-based photocatalysis experiment: the comparison with a well standardized degradation method performed with a known material can allow a realistic evaluation of the advantages and the limits of the investigated nanoparticle towards the ultimate technology transfer. © 2006 Elsevier B.V. All rights reserved.