Ruthenium-Modified Titanate Nanowires for the Photocatalytic Oxidative Removal of Organic Pollutants from Water

Titanate elongated nanomaterials have been studied as promising catalysts for photoassisted oxidation processes, and various methods have been used to tailor their properties. In this context, the synthesis and photocatalytic evaluation of novel ruthenium-modified titanate nanowires is described. In this work, pristine (TNW) and modified nanowires (RuTNW) were obtained through the hydrothermal treatment of an amorphous precursor, and they were characterized by XRD, Raman, XRF, XPS, TEM, DRS, and PL. The results indicate some alterations on the structure and on the optical properties of these semiconductor nanoparticles, owing to ruthenium incorporation. Regarding the structure, several possible Ru positions can be anticipated: in the TiO6 octahedra, substituting Ti4+, or localized in interstitial sites, or in the interlayers, replacing some Na+. Anticipating their potential use for oxidation photocatalysis, namely, for pollutants removal, the samples were evaluated for hydroxyl radical production, using the probe molecule terephthalic acid. Both samples were catalytic for this photoactivated process, with RuTNW being the best photocatalyst. Afterward, the degradation of caffeine, used as a model pollutant, was evaluated under UV–vis and visible radiation. Regardless of the radiation type in use, a clear improvement on TNW photocatalytic performance was observed after Ru incorporation. In fact, RuTNW was the best catalyst for caffeine photodegradation (20 ppm; 0.13 g/L), with a complete pollutant removal after 60 min, using UV–vis radiation. Through the identification and quantification of the intermediates produced during irradiation, a longer time (more than 120 min) is however required to complete the degradation process. A proposal for the photogenerated charge-transfer mechanism in these photoactivated processes is also given and discussed.