title: Synthesis of Hollow Nanotubes of Zn2SiO4 or SiO2: Mechanistic Understanding and Uranium Adsorption Behavior.
abstract: We report a facile synthesis of Zn2SiO4 nanotubes using a two-step process consisting of a wet-chemical synthesis of core-shell ZnO@SiO2 nanorods followed by thermal annealing. While annealing in air leads to the formation of hollow Zn2SiO4, annealing under reducing atmosphere leads to the formation of SiO2 nanotubes. We rationalize the formation of the silicate phase at temperatures much lower than the temperatures reported in the literature based on the porous nature of the silica shell on the ZnO nanorods. We present results from in situ transmission electron microscopy experiments to clearly show void nucleation at the interface between ZnO and the silica shell and the growth of the silicate phase by the Kirkendall effect. The porous nature of the silica shell is also responsible for the etching of the ZnO leading to the formation of silica nanotubes under reducing conditions. Both the hollow silica and silicate nanotubes exhibit good uranium sorption at different ranges of pH making them possible candidates for nuclear waste management.
authors.affiliation: Materials Research Centre, Indian Institute of Science , Bangalore 560012, India.
authors.forename: Shalini
authors.initials: S
authors.lastname: Tripathi
authors.affiliation: Department of Atomic Energy, Atomic Minerals Directorate for Exploration and Research , Nagrabhavi, Bangalore 560012, India.
authors.forename: Roopa
authors.initials: R
authors.lastname: Bose
authors.affiliation: Materials Research Centre, Indian Institute of Science , Bangalore 560012, India.
authors.forename: Ahin
authors.initials: A
authors.lastname: Roy
authors.affiliation: Department of Atomic Energy, Atomic Minerals Directorate for Exploration and Research , Nagrabhavi, Bangalore 560012, India.
authors.forename: Sajitha
authors.initials: S
authors.lastname: Nair
authors.affiliation: Materials Research Centre, Indian Institute of Science , Bangalore 560012, India.
authors.forename: N
authors.initials: N
authors.lastname: Ravishankar
keywords: Kirkendall diffusion; hollow; in situ TEM; silicate nanotube; surface charge; uranyl species