Hollowing Sn-Doped TiO₂ Nanospheres via Ostwald Ripening

Abstract

The well-known physical phenomenon Ostwald ripening in crystal growth has been widely employed in template-free fabrication of hollow inorganic nanostructures in recent years. Nevertheless, all reported works so far are limited only to stoichiometric phase-pure solids. In this work we describe the first investigation of doped (nonstoichiometric) materials using Ostwald ripening as a means of creating interior space. In particular, we chose the xSnO2-(1 - x)TiO2 binary system to establish preparative principles for this approach in synthesis of structurally and compositionally complex nanomaterials. In this study, uniform Sn-doped TiO2 nanospheres with hollow interiors in 100% morphological yield have been prepared with an aqueous inorganic route under hydrothermal conditions. Furthermore, our structural and surface analyses indicate that Sn4+ ions can be introduced linearly into TiO2, and preferred structural phase(s) can also be attained (e.g., either anatase or rutile, or their mixtures). Fluoride anions of starting reagents are adsorbed on the surface sites of oxygen. The resultant anion overlayer may contribute to stabilization of surface and creation of repulsive interaction among the freestanding nanospheres. On the basis of these findings, we demonstrate that Ostwald ripening can now be employed as a general hollowing approach to architect interior spaces for both simple and complex nanostructures.

Titanium Dioxide Nanomaterials: Basics and Design, Synthesis and Applications in Solar Energy Utilization Techniques

“…Meanwhile, during the process of the crystal growth, larger particles grow at the expense of the smaller ones owing to the energy difference between the larger particles and the smaller ones of a higher solubility based on the Gibbs-Thompson law. This refers to the "Ostwald ripening" process applied and confirmed in numbers of papers (Li et al, 2007). In methanol, as Table 2 shows, a higher dielectric constant ( = 32.35) invites a higher solubility of the solid metal oxide and a lower supersaturation degree in this system, which predicts less nuclei numbers, inadequate nutriments-supply and slower crystal-growth rates (Hua et al, 2006), thus lower crystallinity.…”

Synthetic versatility of nanoparticles: A new, rapid, one-pot, single-step synthetic approach to spherical mesoporous (metal) oxide nanoparticles using supercritical alcohols

“…Therefore the MARIMO TiO 2 nanoparticles become small and sparse while the pore size becomes large at high temperature. On the other hand, hollow thick-shelled MARIMO NPs are formed at a slow heating rate via the Ostwald ripening effect (Scheme 1, slow heating) [69][70][71][72][73][74][75][76]. Because amorphous MARIMO TiO 2 formation was confirmed at low reaction temperatures (200 °C) and slower heating rates increased the shell thickness of the NPs, it can be inferred that the amorphous TiO 2 initially generated at low temperatures becomes crystalline as the temperature rises, concomitant with enhancement of the Ostwald ripening effect.…”

Density functional theory studies of doping in titania

“…Both band gap narrowing [27] and the formation of localized mid-gap states [28] have been proposed for the red-shift of the optical absorption edge. In addition, Sn-doped TiO 2 has also attracted much attention, with Sn-doped rutile TiO 2 reported to lead to a red-shift of the optical absorption edge [29], while other results indicate blue-shifting in Sn-doped anatase [30]; these experimental observations have been confirmed by our previous theoretical studies [31]. Following this, we presented systemic geometrical and electronic properties comparison as well as photocatalytic activity of group-IV (Si, Ge, Sn, Pb) doped-TiO 2 using GGA method [32].…”