Herein, a one-step solvothermal method was applied to produce CuBi2O4/CuO heterojunctions containing nanocolumns with small platelike nanoparticles homogeneously distributed over its surface. The photocatalytic activity of the heterojunctions was evaluated through the photodegradation of Methylene Blue (MB) dye and Metronidazole (MTZ) under simulated solar light and visible light irradiation, respectively. The heterojunction CuBi2O4/CuO-b showed an enhanced photocatalytic performance with 98% removal of MB (@2 sun simulated solar irradiation) and 36% removal of MTZ (@1 sun visible light) within 60 min of irradiation, compared to the results obtained with the pristine materials (CuO and CuBi2O4) or the other composite synthesized CuBi2O4/CuO-a. The apparent quantum efficiency for MB photocatalytic degradation using the optimized photocatalyst and 180 min of light irradiation is ∼2.1%, under the excitation wavelength of 540 nm. This enhanced photocatalytic performance is a result of an effective charge separation through a type-II heterojunction, indicating that photoinduced electrons transfer from CuBi2O4 to CuO nanoparticles and the photoholes migrate in the opposite direction. The main reactive species responsible for the photocatalytic degradation of the organic pollutant molecules were the photogenerated holes. Finally, the best photocatalysts were reused and presented good stability over three cycles, endorsing their promise as candidates for photocatalytic applications.

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Black TiO2 materials have been quite widely explored due to their large solar absorption and superior photocatalytic activity. In this paper, the blackening process of titanium dioxide (TiO2) thin film using the hollow cathode hydrogen plasma (HCHP) technique is reported. First, pristine anatase TiO2 films were grown by magnetron sputtering onto silicon and cover glass substrates and then annealed at 450 °C for 2 h. Then, the as-grown TiO2 films were treated with HCHP for 15 min. The physical, chemical and morphological properties of the films were analyzed by profilometry, X-ray diffraction (XRD), UV-Vis spectrophotometry, Raman spectroscopy, X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) techniques. Electrical and photocatalytic measurements were performed by four-point probe and methylene blue UV degradation assays, respectively. The results showed that the black TiO2 film is highly absorbent in the UV-visible region, has low electrical resistance and greater surface area compared to the non-treated TiO2 film. These properties of black TiO2 film, as well as its performance as a photocatalytic agent, were investigated, indicating the superior quality of this material in thin film form and the promising potential of the HCHP treatment to produce hydrogenated TiO2 in short process time.