The photocatalytic properties of anatase TiO2 nanorods (NRs) and noble metal–semiconductor nanocomposites (TiO2 NRs/Ag) prepared by colloidal chemistry routes and immobilized onto suitable substrates were investigated. Photocatalytic experiments were performed under UV irradiation in order to test the degradation of a target compound (the azo dye, methyl red) in aqueous solution using TiO2 P25 Degussa as a reference material. Absorbance spectroscopy and liquid chromatography/mass spectrometry (LC/MS) measurements pointed out that, according to pH conditions, TiO2 NRs and TiO2 NRs/Ag presented a photoactivity up to 1.3 and 2 times higher than TiO2 P25 Degussa, respectively. Notably, the TiO2 NRs/Ag-based catalysts demonstrated a photocatalytic activity 2-fold higher than bare TiO2 NRs. Remarkably, only a negligible dependence on pH conditions was detected for the nanocomposite catalyst, whereas both TiO2 NRs and TiO2 P25 Degussa showed much higher photoactivity at acidic pH. In all the investigated cases, the identified byproducts pointed out the occurrence of the same reaction mechanism, basically relying on the hydroxyl radical attaching on the benzene ring and on the homolytic rupture of the nitrogen–carbon bond of the dimethyl-amino moiety.