  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.
