Tailoring Photocatalytic Activity of TiO₂ Nanosheets by ⁵⁷Fe

TiO₂ nanosheets were modified by two different procedures (volume and surface modification) with 0.5 wt % of ⁵⁷Fe toward Ti. In the case of volume modification, the ⁵⁷Fe (in the form of ⁵⁷Fe­(NO₃)₃·nH₂O solution) was added at the beginning of preparation of TiO₂ nanosheets while the surface modified sample was prepared from the aqueous suspension of undoped TiO₂ nanosheets annealed at 800 °C and solution of ⁵⁷Fe­(NO₃)₃·nH₂O via impregnation method. The volume modified sample was later annealed at 650, 800, and 950 °C; no further annealing was done on the surface modified sample. Both types of prepared materials were characterized by electron microscopy, X-ray powder diffraction, surface and porosity measurements, thermal analysis, FTIR and Raman spectroscopies, and Mössbauer spectroscopy. Photocatalytic activity was characterized from the results of 4-chlorophenol (4-CP) decomposition. The surface modified sample exhibited highly effective photocatalytic decomposition of a model pollutant under UV irradiation. On the other hand, the volume modification proved to suppress photocatalytic activity under UV. The visible light activity of 4-CP decomposition was negligible for both volume and surface modified samples. Mössbauer spectroscopy measurements confirmed the presence of iron atoms in the TiO₂ structure. The surroundings of the iron atoms exhibit a structure close to that of mixed oxides (Fe_1–xTi_2–xO₅ and Fe_2–xTi_xO₃) in solid solution.