Spiral Structure of 7 Å Halloysite: Mathematical Models

Abstract

Halloysite is used for targeted delivery of drugs and other biomolecules. Renewed interest in examination by X-ray diffraction (XRD) to predict the size of particles that can be loaded onto the nanotubes has resulted. Anhydrous halloysite consists of spiraled tubules the length and diameter of which can be determined by measurement using an electron microscope. In spite of ample evidence regarding the spiral structure of halloysite, current programs to evaluate the structure of halloysite nanotubes consider it to be a hollow tube or a cylinder which prevents accurate prediction of its structure and leads to misinformation about the sizes of materials that can be loaded onto the nanotubes. The overall objective of the current study was to derive equations to estimate the structure of halloysite nanotubes which take into consideration its spiral structure. The study of Fourier transform either by electron diffraction or XRD led to the measurement of the spiral thickness and the nature of the spiral. Calculations of the nanotube dimensions may determine the ability of these carriers to allow the mechanical delivery of certain drugs.Here the structure of hydrated halloysite (hollow cylindrical tubes with a doughnut-like cross-section) and anhydrous halloysite (spiraled or helical structure) are described as previously reported in the literature. The Fourier transform of the spiraled structure was selected based on three different kinds of spirals: the Archimedean spiral, the Power spiral, and the Logarithmic spiral. Programs used to define the crystal structure of materials and to calculate the Fourier transform need to take the spiral structure into consideration.

Properties and applications of halloysite nanotubes: recent research advances and future prospects

“…For example, Hal sourced from Kalgoorlie in Western Australia is thin-walled and highly uniform in length, diameter, and morphology; Hal sourced from Camel Lake in South Australia is thick-walled and has a relatively uniform morphology with good tubule quality; and Hal sourced from Northland in New Zealand has a low tubular quality, characteristic of high irregularity in diameter, wall thickness, and morphology (Yuan et al, 2008). Furthermore, tubular Hal with different wall-thicknesses also have different spiral structures, for example, the thick-walled Hal presented by a Power spiral and the thin-walled Hal presented a Logarithmic spiral (Mitra, 2013).…”

Probing the Dehydroxylation of Kaolinite and Halloysite by In Situ High Temperature X-ray Diffraction

“…Depending on the amount of water, the two types of halloysite are usually considered with the general formula Al 2 Si 2 O 5 (OH) 4 nH 2 O: halloysite-(7 Å) and halloysite-(10 Å), regarding the (001) d-spacing, where n = 0 and n = 2, respectively [7,8]. The particle morphology of halloysite were described as a tubular or cylindrical shape [9]. Conversely, the kaolinite particles were reported as platelet-like grains.…”

Dehydroxylation of Kaolinite and Halloysite-Rich Samples: An In Situ Study of the Texture and Structural Evolutions

“…In addition, some drawbacks are related to the occurrence of secondary phases in their main deposits, which lead to the requirement of different physical and chemical treatments in order to control the purity of their respective raw materials [3][4][5][6]. Both kaolinite and halloysite are TO dioctahedric phyllosilicate, but kaolinite is characterized by platelet-like particles while halloysite exhibits a tubular and/or cylindrical shape [7]. Halloysite has the same general chemical composition as kaolinite with additional water content.…”

“…In the case of ceramics, the shaping process can enhance the initial texture, and during the sintering, the clay minerals are significantly modified [10][11][12][13][14], thus leading to the evolution of final structure and properties. For kaolinite and halloysite, the literature indicates that upon heating [5][6][7][8][9][10][11][12][13][14], these clay minerals will undergo dehydration, dehydroxylation and recrystallization transformations. It has also been shown that these transformations are influenced by the initial crystallinity degree, the particle size and the number of local defects of the kaolinite and halloysite raw materials.…”