Abstract:

The micro-structure and photocatalytic activity of natural  rutile, which was heated and annealed under hydrogen
atmosphere, was studied here. Several conventional mineralogical  test methods were used, such as X-ray diffraction  (XRD),
environmental scanning electron microscopy  (ESEM), UV-vis diffusive  reflectance absorption spectral analysis and structural
refinement using GSAS software with Rietveld method. The natural rutile samples used in this study are found in a metamorphic
deposit and collected from Shanxi province, China. The experimental results indicate that V, Fe and other impurities exist in the
crystal  lattice of natural  rutile as  isomorphous substitution  for Ti  ions, which causes distortion of crystal  lattice and effectively
enhances  the photocatalytic activity of  the specimens. As  the  temperature  increased, parts of  the  isomorphous substituted  ferric
ions were gradually reduced to divalent and elemental iron. On one hand, the unit cell parameters of rutile decreased because of
escaping of ions from the lattice, which have larger ionic radii than Ti⁴⁺ion. On the other hand, the unit cell parameters would be
increased because of thermal expansion caused by the heat treatment. Therefore, no significant change in the unit cell parameters
was observed. At the same time, the visible light response abilities of heated rutile samples were largely improved with increasing
temperature. Compared  to  the original  sample RZM,  the  light absorption  intensity of  sample, which was  subjected  to heat
treatment at 900℃, was enlarged by 147.2 % at 600 nm. Rietveld refinements suggested that a small amount of simple substance
iron appeared when the heating temperature reached 800 ℃ and 900 ℃. Iron is a metallic conductor and has lower Fermi level.When  iron was  in contact with semiconductor rutile particles,  the photo-induced electrons could be  transferred rapidly,  thereby
enhancing the visible light response ability of the system.

Key words: natural rutile, hydrogen heat treatment, simple substance iron, visible light response