Hollow spheric Ag–Ag₂S/TiO₂ composite and its application for photocatalytic reduction of Cr(VI)

Graphical abstract: - Highlights: • Hollow spheric Ag–Ag₂S/TiO₂ composites were prepared. • Ag–Ag₂S/TiO₂ composite shows prior UV and visible photocatalytic activities. • Schottky barrier between Ag and Ag₂S (TiO₂) promotes the photocatalytic activity. • Low bandgap of Ag₂S gives Ag–Ag₂S/TiO₂ a good visible photocatalytic activity. • The photocatalytic activity of Ag–Ag₂S/TiO₂ is maintained well after recycled. - Abstract: Hollow spheric Ag–Ag₂S was prepared by in-situ chemical transforming of sacrificial Cu₂S templates with AgNO₃ solution. Hollow spheric Ag–Ag₂S/TiO₂ composites were then prepared by assembling TiO₂ grains around the Ag–Ag₂S spheres with hydrothermal treatment of Ag–Ag₂S with Ti precursor at 180 °C. X-ray diffraction (XRD), scanning electron microscope (SEM), transmission electron microscopy (TEM), Inductively coupled plasma-atomic emission spectroscopy (ICP-AES) were adopted to characterize the as-prepared composite. Ag–Ag₂S/TiO₂ composite has obvious absorption at both UV and visible regions, and shows prior photocatalytic activity for the reduction of Cr(VI) under both UV and visible irradiation. Particularly, the Ag–Ag₂S/TiO₂-5 and Ag–Ag₂S/TiO₂-10 show the highest activity for the photocatalytic reduction of Cr(VI) under UV and visible irradiation, respectively. The Schottky barrier between Ag and Ag₂S (and TiO₂ as well) and the heterojunction between the Ag₂S and TiO₂ are suggested as the main reasons that enhance the photocatalytic reduction of Cr(VI). The photocatalytic activity of Ag–Ag₂S/TiO₂ composite is maintained well after being recycled several times