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 degrees C on Si(100) substrates from Fe(hfa)(2)TMEDA (hfa = 1,1,1,5,5,5-hexafluoro-2,4-pentanedionate; TMEDA = N,N,N',N'-tetramethylethylenediamine), yielding the selective formation of alpha-Fe2O3 or the scarcely studied epsilon-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 degrees C) by an ultrathin titanomagnetite (Fe3-xTixO4) 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.