Photocatalytic activity of transition metal and metal ions impregnated TiO2 nanostructures for iodide oxidation to iodine formation

Transition metal and metal ions such as Fe, Cu, Ag, Au and Cr dispersion into TiO2 matrix was done by impregnation and NaBH4 reduction in aqueous solution. These metal-TiO2 composites were characterized by XRD, SEM, TEM, EDS, diffuse reflectance spectral analysis and magnetic susceptibility and are tested for iodine formation. Metal loading results in red shift of absorption band along with characteristic surface plasmon band for Ag (∼460 nm) and Au (∼570 nm). TEM images reveal the fairly uniform metal deposition with size range of 6–15 nm depending upon the nature of metal. High concentration of Fe3+ loading led to agglomeration of TiO2 particles due to high magnetic properties. X-ray diffraction shows the shift of 2θ angle of (1 0 0), (1 0 1) and (2 0 0) lattice planes of TiO2 to lower value and increase in activity is attributed to change in the lattice parameters and cell volume on high Fe3+ concentration. The co-catalysis of 10 wt.% Fe3+ and Fe0 makes a large difference in iodine formation rate. Metal loading significantly enhance the photooxidation of iodide ion under UV light in order Fe3+ > Cr6+ > Ag > Au > Cu depending upon their oxidation state, nature, electron capturing tendency, work function, etc.

The effect of metal/metal ions (Fe, Cr, Cu, Ag, and Au) dispersion into TiO2 on the photocatalytic oxidation of iodide ion was studied. The highest yield of iodine is achieved during 2.5 h irradiation of aqueous suspension of 10 wt.% Fe3+-TiO2 and 0.2 M KI solution. The X-ray diffraction angle 2θ = 25.3388° and 48.0804° for (1 0 1) and (2 0 0) anatase lattice plane and 2θ = 27.5184° for (1 1 0) rutile lattice planes are blue shifted to 2θ = 24.9186°, 47.6865° and 27.072°, respectively, due to the lattice substitution of Ti4+ ions with Fe3+ ions. These structural defects in TiO2 by Fe3+ incorporation significantly improved the TiO2 photoactivity for iodide oxidation. The relative co-catalytic ability for iodide photooxidation by different metals-TiO2 follows the order: Fe3+ > Cr6+ > Ag > Au > Cu.Figure optionsDownload high-quality image (66 K)Download as PowerPoint slideHighlights
► Fe3+ doping led to blue shift in the 2θ values of TiO2 lattice planes.
► Crystal parameters and cell volume increased with Fe3+ incorporation.
► Co-catalytic activity follows Fe > Cr > Ag > Au > Cu for I2 formation.
► Fe3+ (10 wt.%)-TiO2 exhibits optimum production (14.2 μmol) of I2.
► Metal ions always have superior co-catalytic activity than M0 loading.