Highly reactive visible-light-driven flower-like rutile-phase titanium nanoparticle (FTN) catalysts were prepared using a simple template-free hydrothermal method with different concentrations of hydrochloric acid (2 M–4M). The physicochemical properties of the catalysts were characterized via XRD, FESEM, FTIR, UV-DRS, N₂ adsorption-desorption, and via ESR. Catalytic testing of the photodegradation of methylene blue (MB) was performed using 0.25 mg L⁻¹ of catalyst for 90 min, which resulted in the following activity order: FTN-3M (98%) > FTN-4M (92%) > FTN-2M (86%). The remarkable photocatalytic performance shown by the FTN-3M catalyst was found to be due to its possession of the highest number of hydroxyl groups, oxygen vacancies, and titanium surface defects compared to other catalysts. The fastest reaction rate (4.49 × 10⁻² min⁻¹), which was achieved by the FTN-3M catalyst with values of k_r = 0. 1845 mg L⁻¹ min⁻¹ and k_LH = −0.1646 L mg⁻¹. These values suggested that the reaction occurred on the surface of the catalyst, and was most probably influenced by the previously mentioned, three important properties. In addition, the open structure of the flower-like structure provided more accessible active sites for the adsorption of MB, as well as enhanced light harvesting through multiple reflections between the extended nanospindle structures. The degradation pathway for MB was also investigated. The FTN-3M catalyst maintained their activities for up to five runs without experiencing severe deactivation of the catalyst. Mineralization measurements for MB using TOC and BOD₅ analyses, after 90 min of contact time, were 90.45% and 87.73%, respectively, using the FTN-3M sample. The cost-effectiveness of the FTN-3M catalyst proved that this photocatalytic process is greener and more sustainable than noun and should be implemented in industrial applications. It is expected that the extended light response range, in combination with the unique morphology of FTNs, could be exploited in the highly efficient treatment of wastewaters from the textile industry.