Hydrothermal formation of bismuth-titanate nanoplatelets and nanowires: the role of metastable polymorphs

Abstract

Understanding the processes involved in the formation of nanoparticles is a prerequisite for the control of their morphology. In this investigation we reveal the processes leading to the formation of...

Adaptation of the Crystal Structure to the Confined Size of Mixed-oxide Nanoparticles

“…BIT can be successfully synthesized with the hydrothermal treatment of an aqueous suspension of precipitated Bi 3+ and Ti 4+ ions in mineralizer hydroxide (NaOH or KOH) with a moderate concentration. 27,28,[30][31][32][50][51][52][53] The synthesized BIT nanoparticles appear in a wide variety of different nano-morphologies, including 2-D platelet crystals, (i.e., rectangular nanoplatelets and nanosheets), 27,28,32,50,52,53 1-D crystals (e.g., nanowires, nanobelts, nanobundles, nanorods), 27,28,[51][52][53] and 3-D nanostructures assembled from 1-D or 2-D nanoparticles. 30,31,51 Our research showed that the morphologies of the product particles crucially depend on the concentration of the mineralizer hydroxide.…”

“…30,31,51 Our research showed that the morphologies of the product particles crucially depend on the concentration of the mineralizer hydroxide. 52 The nanowires (NWs) formed when the precipitated ions were hydrothermally treated in aqueous solutions of NaOH with lower concentrations, whereas the nanoplatelets (NPLs) were obtained at higher NaOH concentrations. For example, the hydrothermal treatment for 38 hours at 200 °C produced NWs (from 15 nm to 35 nm wide and from several hundreds of nm to several µm long) in 0.5 mol/L NaOH, whereas the rectangular NPLs (approximately 10 nm thick and from 50 nm to 200 nm wide) were synthesized in 2-mol/L NaOH (Figure 6 (a) and (b)).…”

“…At the higher NaOH concentrations, the nanowires dissolved, while the NPLs grew epitaxially on the surfaces of the aggregated perovskite nanocrystallites (Figure 6 (c)). 52…”

“…Indeed, the XRD of the BIT NWs suggested a new structure, entirely different to the Aurivillius structure characteristic for the BIT. 52 (As explained below, the NW structure does not contain any perovskite-like layers). EDXS analyses showed the same composition for the two BIT morphologies within the uncertainty of the method.…”

“…54 Moreover, we showed that the metastable polymorphs have an important role in the hydrothermal synthesis of BIT nanoparticles. 52 Advances in controlled synthesis enabling the synthesis of small nanoparticles of inorganic materials with a complex structure, on the one hand, and the advances in structural characterization based on advanced electron microscopy, on the other, will pave the way to further discoveries of nanoparticles with new and interesting crystal structures. And with new structures, new properties of the nanoparticles can be expected.…”