Room-Temperature Synthesis of Iron-Doped Anatase TiO₂ for Lithium-Ion Batteries and Photocatalysis

Iron-doped nanocrystalline particles of anatase TiO₂ (denoted <i>x</i>% Fe-TiO₂, with <i>x</i> the nominal [Fe] atom % in solution) have been successfully synthesized at room temperature by a controlled two-step process. Hydrolysis of titanium isopropoxide is first achieved to precipitate Ti­(OH)₄ species. A fine control of the pH allows one to maintain (i) soluble iron species and (ii) a sluggish solubility of Ti­(OH)₄ to promote a dissolution and condensation of titanium clusters incorporating iron, leading to the precipitation of iron-doped anatase TiO₂. The pH does then influence both the nature and crystallinity of the final phase. After 2 months of aging at pH = 2, well-dispersed nanocrystalline iron-doped TiO₂ particles have been achieved, leading to 5–6 nm particle size and offering a high surface area of ca. 280 m²/g. This dissolution/recrystallization process allows the incorporation of a dopant concentration of up to 7.7 atom %; the successful incorporation of iron in the structure is demonstrated by X-ray diffraction, high-resolution transmission electron microscopy, and Mössbauer spectroscopy. This entails optical-band-gap narrowing from 3.05 to 2.30 eV. The pros and cons effects of doping on the electrochemical properties of TiO₂ versus lithium are herein discussed. We reveal that doping improves the power rate capability of the electrode but, in turn, deserves the electrolyte stability, leading to early formation of SEI. Finally, we highlight a beneficial effect of low iron introduction into the anatase lattice for photocatalytic applications under standard AM1.5G visible-light illumination