Synthesis and Visible-Light-Driven Photocatalytic Activity of Ta4+ Self-Doped Gray Ta2O5 Nanoparticles

C-impregnated/Ta4+ self-doped ultrafine Ta2O5 nanoparticles (NPs) were prepared by a one-step solvothermal method through reaction of Ta­(V) chloride with benzyl alcohol. These NPs showed a large specific surface area of 253.4 m2 g–1, mean diameter of 2–3 nm, and superior photocatalytic activity in the photodegradation of Rhodamine B dye (RhB), compared to TiO2 (P25) and Ta2O5 commercial NPs. The obtained materials were annealed at different temperatures and their structure, morphology and optical and photocatalytic properties were investigated in detail. The C-impregnated Ta4+ self-doped Ta2O5 NPs presented enhanced and extended absorption in the visible range of the solar spectrum, increasing significantly their photocatalytic activity. The best photocatalyst could completely remove RhB after only 12 min of UV irradiation and yielded 68% and 43% of RhB photodegradation after 120 min of simulated sunlight and visible irradiation, respectively, with an apparent quantum efficiency of 3.6% at 447 nm. This enhanced photocatalytic performance is ascribed to the combined effects of better light harvesting properties, high surface area and longer electron lifetimes in the excited sub-band, due to the presence both of oxygen vacancies neighboring Ta4+ and Ta–O–C on the Ta2O5 surface. The photocatalyst systems presented good stability, confirming their promise as candidates for photocatalytic applications.