Goethite–titania composite: disinfection mechanism under UV and visible light

Goethite–titania (α-FeOOH–TiO(2)) composites were prepared by co-precipitation and mechanical milling. The structural, morphological and optical properties of as-synthesized composites were characterized by X-ray powder diffraction, scanning electron microscopy and UV-Vis diffuse reflectance spectroscopy, respectively. α-FeOOH–TiO(2) composites and TiO(2)-P25, as reference, were evaluated as photocatalysts for the disinfection of Escherichia coli under UV or visible light in a stirred tank reactor. α-FeOOH–TiO(2) exhibited better photocatalytic activity in the visible region than TiO(2)-P25. The mechanical activation increased the absorption in the visible range of TiO(2)-P25 and the photocatalytic activity of α-FeOOH–TiO(2). In the experiments with UV light and α-FeOOH–TiO(2), mechanically activated, a 5.4 log-reduction of bacteria was achieved after 240 min of treatment. Using visible light the α-FeOOH–TiO(2) and the TiO(2)-P25 showed a 3.1 and a 0.7 log-reductions at 240 min, respectively. The disinfection mechanism was studied by ROS detection and scavenger experiments, demonstrating that the main ROS produced in the disinfection process were superoxide radical anion, singlet oxygen and hydroxyl radical.