New and fast route to black TiO2 based on hollow cathode H2 plasma.

In this work, we demonstrate a new method to produce black TiO2 from pristine anatase TiO2 films. It consists on the immersion of TiO2 films in a hollow cathode H2 RF plasma for a few minutes, resulting in an efficient blackening of TiO2. In this study, the pristine anatase TiO2 films were grown by magnetron sputtering onto cover glass and c-Si substrates and then annealed at 450 {\deg}C for 2 h. Before and after the hollow cathode H2 plasma treatment, the samples were characterized by profilometry, UV-Vis spectrophotometry, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, field emission scanning electron and atomic force microscopies, and four-point probe measurements. The results show that the obtained black TiO2 thin films have a significant light absorption on the whole solar spectrum, a very low sheet resistance, and also a relatively high surface area when compared to the pristine TiO2. All these characteristics lead to an important improvement on their photocatalytic activity, as measured by the degradation rate of methylene blue under UV irradiation.