Alizarin complexone: an interesting ligand for designing TiO2-hybrid nanostructures

Abstract

Herein we report the characterization and photoelectrochemical behavior of nanocrystalline TiO₂ films modified with some alizarin derivatives. Particularly, alizarin complexone (3-[N,N-bis(carboxymethyl)-aminomethyl]-1,2-dihydroxyanthraquinone) and its Fe(II) and Fe(III) metal complexes have been examined. Based on UV-Visible and Raman spectroscopic studies we proposed that AC forms a tridentate complex with titanium dioxide involving the 2-OH and (methylimino) diacetate groups, while Fe(II) and Fe(III) AC-complexes bind to titanium dioxide through the carbonyl (CO) and hydroxyl (OH) groups at the 1,9 positions of the alizarin framework. These findings allow the design of different nanostructures with diverse photoelectrochemical behavior. Analysis of the j–V curves reveals a sign reversal at −90 mV and −100 mV upon the excitation of AC@TiO₂ and [Fe^IIIAC]@TiO₂ photoelectrodes, respectively, whereas [Fe^IIAC]@TiO₂ displays only anodic photocurrents. A description involving both electronic and geometric factors to account for these differences is proposed.