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.
