Effect of TiO2 hydrodynamic particle sizes and catalyst loading on the optical properties of three commercial photocatalysts has been analyzed (P25 Aeroxide (R) P25/20 VP Aeroperl (R) and P90 Aeroxide (R)). These catalysts, characterized by similar structural and electronic properties, but with singular differences in morphology and aggregation particle sizes, have been studied to understand the corresponding crossed effects on their final photo-efficiencies throughout organic matter removal in aqueous suspensions, with a pollutant such as phenol, where photo-oxidation is regularly described as mediated by an indirect photo-mechanism via HO center dot radicals. Reflectance measurements in the range of visible wavelength, close to TiO2 absorption edge, could be comparable to extinction coefficient in the UV-A range and may well be suitable to optimize catalyst loadings. Phenol photocatalytic efficiency followed P25 > P90 > P25/20 order, emphasizing that increases in TiO2 hydrodynamic particle sizes are detrimental to phenol photo-efficiency, and highlighting that radiation photocatalyst interactions are essential but not enough to guarantee an improved photodegradation rate. Finally, the higher values of HO center dot found in sonicated P25/20 catalyst could corroborates its better performance in phenol photo degradation, as a consequence of lowest hydrodynamic particle sizes in reaction media, which take advantage of light as a result of a significant increase in exposed surface area.