title: Synthesis and Characterization of Fe-doped Aluminosilicate Nanotubes with Enhanced Electron Conductive Properties.
abstract: The goal of the protocol is to synthesize Fe-doped aluminosilicate nanotubes of the imogolite type with the formula (OH)3Al2-xFexO3SiOH. Doping with Fe aims at lowering the band gap of imogolite, an insulator with the chemical formula (OH)3Al2O3SiOH, and at modifying its adsorption properties towards azo-dyes, an important class of organic pollutants of both wastewater and groundwater. Fe-doped nanotubes are obtained in two ways: by direct synthesis, where FeCl3 is added to an aqueous mixture of the Si and Al precursors, and by post-synthesis loading, where preformed nanotubes are put in contact with a FeCl3•6H2O aqueous solution. In both synthesis methods, isomorphic substitution of Al3+by Fe3+occurs, preserving the nanotube structure. Isomorphic substitution is indeed limited to a mass fraction of ~1.0% Fe, since at a higher Fe content (i.e., a mass fraction of 1.4% Fe), Fe2O3 clusters form, especially when the loading procedure is adopted. The physicochemical properties of the materials are studied by means of X-ray powder diffraction (XRD), N2 sorption isotherms at -196 °C, high resolution transmission electron microscopy (HRTEM), diffuse reflectance (DR) UV-Vis spectroscopy, and ζ-potential measurements. The most relevant result is the possibility to replace Al3+ions (located on the outer surface of the nanotubes) by post-synthesis loading on preformed imogolite without perturbing the delicate hydrolysis equilibria occurring during nanotube formation. During the loading procedure, an anionic exchange occurs, where Al3+ions on the outer surface of the nanotubes are replaced by Fe3+ions. In Fe-doped aluminosilicate nanotubes, isomorphic substitution of Al3+by Fe3+is found to affect the band gap of doped imogolite. Nonetheless, Fe3+sites on the outer surface of nanotubes are able to coordinate organic moieties, like the azo-dye Acid Orange 7, through a ligand-displacement mechanism occurring in an aqueous solution.
authors.affiliation: Department of Applied Science and Technology, Politecnico di Torino.
authors.forename: Ehsan
authors.initials: E
authors.lastname: Shafia
authors.affiliation: Department of Civil and Mechanical Engineering, Università degli Studi di Cassino e del Lazio Meridionale.
authors.forename: Serena
authors.initials: S
authors.lastname: Esposito
authors.affiliation: Department of Applied Science and Technology, Politecnico di Torino.
authors.forename: Elnaz
authors.initials: E
authors.lastname: Bahadori
authors.affiliation: Department of Applied Science and Technology, Politecnico di Torino; Institute of Chemistry, Politecnico di Torino.
authors.forename: Marco
authors.initials: M
authors.lastname: Armandi
authors.affiliation: Department of Chemistry & NIS Interdepartmental Centre, University of Turin.
authors.forename: Maela
authors.initials: M
authors.lastname: Manzoli
authors.affiliation: Department of Applied Science and Technology, Politecnico di Torino; Institute of Chemistry, Politecnico di Torino; INSTM Unit of Torino-Politecnico, Politecnico di Torino; barbara.bonelli@polito.it.
authors.forename: Barbara
authors.initials: B
authors.lastname: Bonelli
mesh_terms: D004583:Electrons; D005290:Ferric Compounds; D046529:Microscopy, Electron, Transmission; D043942:Nanotubes; D014961:X-Ray Diffraction
chemical_list: D005290:Ferric Compounds