title: Surface properties of alumino-silicate single-walled nanotubes of the imogolite type.
abstract: An IR spectroscopy study is reported on the nature and accessibility of external and internal surfaces of single-walled alumino-silicate nanotubes (NTs) of the imogolite type. NTs form bundles with hexagonal symmetry, in which three kinds of surfaces may be figured out: surface A is the inner surface of NTs; surface B is that between three aligned NTs in the hexagonal packing; and surface C arises from slit mesopores between bundles. Two materials were considered: proper imogolite (IMO, (OH)3Al2O3SiOH) and its methylated analogue, (Me-IMO, (OH)3Al2O3SiCH3). The chemical nature of the outer surface of NTs is the same in both materials, i.e. a curved gibbsite sheet with both Al-OH-Al and Al-O-Al groups and an amphoteric character. The inner surface is very hydrophilic in IMO NTs, lined by closely packed silanols, and hydrophobic in Me-IMO, all silanols being replaced by -SiCH3 groups. The change in chemical composition is accompanied by an increment in pore size, about 1.0 nm in IMO, and ca. 2.0 nm in Me-IMO, which implies a change in the accessibility of the B surface, not available to any molecule in IMO, and accessible in Me-IMO to small molecules like water, due to larger pores between NTs. Aluminol species at the B surface display an acidic nature, in contrast with that of the same species at surface C, because of a confinement effect.
authors.affiliation: Department of Applied Science and Technology and INSTM Unit of Torino-Politecnico, Corso Duca degli Abruzzi, 24-Politecnico di Torino, Turin, I-10129, Italy. barbara.bonelli@polito.it
authors.forename: Barbara
authors.initials: B
authors.lastname: Bonelli
authors.forename: Marco
authors.initials: M
authors.lastname: Armandi
authors.forename: Edoardo
authors.initials: E
authors.lastname: Garrone
mesh_terms: D000535:Aluminum / Q000737:chemistry*; D043942:Nanotubes / Q000737:chemistry*; D017640:Silicates / Q000737:chemistry*; D013499:Surface Properties
chemical_list: D017640:Silicates; D000535:Aluminum