Structural, Electronic, and Mechanical Properties of Single-Walled Halloysite Nanotube Models

Abstract

Halloysite is a clay mineral with stoichiometry Al 2 Si 2 O 5 (OH) 4 • nH 2 O that can grow into long tubules and is chemically similar to kaolinite. In this work we present a systematic study on the stability, electronic, and mechanical properties of zigzag and armchair single-walled halloysite nanotubes by means of the self-consistent charge density-functional tight-binding method (SCC-DFTB). The detailed analysis is focused on structural properties, strain energy, and band gap as a function of tube radii and Mulliken charge distribution. The strain energy of halloysite nanotubes does not have a monotonic character and the most stable structures should be observed in the region of radii above 24 Å, in agreement with experimental data. Analysis of the electronic density of states shows that all tubes are insulators. Our calculations predict that single-walled halloysite nanotubes have Young modulus in the same order of imogolite and inorganic nanotubes, but smaller than that of carbon nanotubes. Even though most of the properties are adequately described by simpler halloysite models, further studies on multiwalled and larger diameter tubes are in progress.

Surface Improvement of Halloysite Nanotubes

“…A view of a single HNT crystal with clear representation of the crystal axes is included as the insert in Figure 1 [32]. Reflections of S0 were detected at 2θ = 11.…”

Clay Mineral Nanotubes: Stability, Structure and Properties

“…Halloysite is a clay mineral normally described as a gibbsite octahedral sheet (Al(OH) 3 ), which is modified by siloxane groups at the outer surface (figure 6), and has a 1:1 Al:Si ratio and stoichiometry Al 2 Si 2 O 5 (OH) 4 .nH 2 O (Guimaraes et al, 2010). Halloysite exhibits a range of morphologies, and according to Joussein et al (2005) the structure will depend on crystallization conditions and geological occurrences.…”

“…Halloysite is a clay mineral with stoichiometry Al 2 Si 2 O 5 (OH) 4 .nH 2 O that can grow into long tubules and is chemically similar to kaolinite (Giese & Datta, 1973;White et al, 2009). It consists of a gibbsite octahedral sheet (Al(OH) 3 ), which is modified by siloxane groups at the outer surface (Guimaraes et al, 2010). The chrysotile structure is composed of brucite (Mg(OH) 2 ) and tridymite (silicon dioxide, SiO 2 ) layers.…”

“…This method has been successfully applied to inorganic and carbon NTs (Enyashin & Seifert, 2005;Ivanovskaya et al, 2006;Stefanov et al, 2008;Enyashin et al, 2009;Kuc & Heine, 2009;Rasche et al, 2010). In our laboratory, we have applied successfully the SCC-DFTB method to investigate the stability, electronic and mechanical properties of the nanostructured aluminosilicates (Guimaraes et al, 2007;Kuc & Heine, 2009;Guimaraes et al, 2010).…”

Structural reinforcement of microvascular networks using electrostatic layer-by-layer assembly with halloysite nanotubes

“…This value is significantly lower than bulk values for alumina or silica, and more than an order of magnitude lower than theoretically modeled values for single halloysite nanotubes, which are in the range of 234-339 GPa. 47 The reduced modulus is likely due to two factors. The first is weak bonding between the halloysite and the PDADMAC within the multilayer, which is ionic rather than covalent.…”