Due to its high intrinsic efficiency, heterogeneous catalysis is widely used in waste water treatments employing mixed catalysts. However, in this kind of catalysis it is extremely difficult to separate the suspended catalyst from the solution at the end of the procedure due to the small dimension of the particles. In environmental applications, the most used catalyst is titanium dioxide because of its great catalytic efficiency. The present research concerns the efficiency evaluation of TiO2 catalysts, estimated on the extent of photodegradation of target molecules after a radiation treatment (solar, UV, microwave) carried out in a dedicated apparatus. Experimental variables are: 1) catalyst type (TiO2 particles of different size), 2) catalyst concentration (0.1, 0.2, 0.5, 1.0 g/L), 3) exposure time (45 and 90 min), and 4) target molecules (five industrial textile dyes: Acid Blue 29, Alizarin Red S, Procion Red MX-5B, Reactive Blue 2, Acid Green 25). The efficiency of the photodegradation process has been evaluated by a UV/ Vis spectrophotometry comparing the spectra of the target substances obtained before and after the degradation process itself, therefore monitoring the cracking of the chromophore groups. Obtained data matrix was analysed with chemometric tools. The aim of this work was to identify the correlation between photodegradation efficiency and experimental variables. It has been also evaluated the possibility of substituting nanomaterial catalysts with catalysts characterized by bigger particle size keeping the degradation efficiency unaltered: this evaluation has been performed because the non- nanoparticles are more easily separable from suspension, making the water clarification post-processes easier.