Characterization studies of heat-treated halloysite nanotubes
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ORIGINAL PAPER
Characterization studies of heat‑treated halloysite nanotubes M. Türkay Aytekin1 · Halit L. Hoşgün2 Received: 25 November 2019 / Accepted: 22 June 2020 © Institute of Chemistry, Slovak Academy of Sciences 2020
Abstract The halloysite nanotubes (HNTs), subjected to different temperatures in the range 250–1000 °C, were investigated at room temperature. The materials have been prepared in various times (2, 4, 6 h) at different temperatures (250, 450, 600, and 1000 °C) and heating rates (5, 10, 20 °C/min). Morphology, structural and physical properties of raw, and thermally treated HNTs were systematically analyzed by X-ray diffraction (XRD), field-emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), the nitrogen adsorption–desorption isotherm (BET), as well as Fourier transform infrared (FT-IR) spectroscopy. The XRD patterns indicate that the crystal structure of halloysite is stable up to 450 °C. The scanning electron micrograph images of the Halloysite nanotubes showed that the unheated and heated halloysite nanotubes possessed typical tubular shapes. Tubular shapes were observed even at 1000 °C. Fourier transform infrared spectroscopy was also used to examine the variations of chemical structures. The Fourier transform infrared spectra of unheated and thermally treated halloysite nanotubes showed the presence of hydroxyl stretching and bending vibration frequencies in the samples. In this study, the structural properties of natural halloysite nanotubes are comprehensively reviewed in terms of given temperature, heating rate, and time. It is thought that the obtained results will guide the design and preparation of halloysite-based new structural and functional materials which can be applicable in various fields. Keywords Halloysite · Nanotube · Heat treatment · Infrared · Characterization
Introduction Halloysite is a naturally occurring two-layered aluminosilicate clay mineral. The name of Halloysite was derived from Omalius d’Halloy and was first used by Berthier as a dioctahedral 1:1 clay mineral of the kaolin group. It has a similar structure and chemical composition as kaolinite. Crystal structure of halloysite is consisting of (Si–O) tetrahedral layer and (Al−O) octahedral layer (Liu et al. 2014; Yuan et al. 2015), and it is available in abundance in many countries such as China, America, Brazil, France, Belgium, New Zealand, Turkey, and others (Joussein et al. 2005; Liu et al. 2013; Zhou et al. 2014; Yuan et al. 2015; Zhang et al. 2016). Halloysite possesses a tubular morphology in contrast to a stacked plate-like structure of kaolinite. This morphological difference can lead to * M. Türkay Aytekin [email protected] 1
Department of Physics, Science Faculty, Eskişehir Techinical University, 26470 Eskişehir, Turkey
Department of Chemical Engineering, Bursa Technical University, Bursa, Turkey
2
significant differences in textural properties such as specific surface area and porosity on calcination of halloysite nanotube. The most important fe
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