Surface Functionalization of Nanostructured Fe₂O₃ Polymorphs: From Design to Light-Activated Applications

Nanostructured iron­(III) oxide deposits are grown by chemical vapor deposition (CVD) at 400–500 °C on Si(100) substrates from Fe­(hfa)₂TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethylenediamine), yielding the selective formation of α-Fe₂O₃ or the scarcely studied ε-Fe₂O₃ polymorphs under suitably optimized preparative conditions. By using Ti­(OPrⁱ)₄ (OPrⁱ = iso-propoxy) and water as atomic layer deposition (ALD) precursors, we subsequently functionalized the obtained materials at moderate temperatures (<300 °C) by an ultrathin titanomagnetite (Fe_3–<i>x</i>Ti_<i>x</i>O₄) overlayer. An extensive multitechnique characterization, aimed at elucidating the system structure, morphology, composition and optical properties, evidenced that the photoactivated hydrophilic and photocatalytic behavior of the synthesized materials is dependent both on iron oxide phase composition and ALD surface modification. The proposed CVD/ALD hybrid synthetic approach candidates itself as a powerful tool for a variety of applications where semiconductor-based nanoarchitectures can benefit from the coupling with an ad hoc surface layer