Thermal behavior study of pristine and modified halloysite nanotubes

Abstract

Pristine halloysite nanotubes (HNTs) were studied by thermogravimetry (TG) up to 800°C. Etching of alumina from inside the tube (causing a significant increase in tube lumen) was realized by treating the material with an acidic H 2 SO 4 solution at 50°C. Both materials were characterized by TG-FTIR techniques and their thermal behaviors were compared with that of kaolinite. The coupling of TG with FTIR enables to detect the gases evolved during the TG experiments, thus confirming that only pristine HNTs undergo dehydration with the loss of interlayer water molecules at around 245°C, while dehydroxylation occurs in all these materials in close temperature ranges around 500°C. TG runs at five different heating rates (2, 5, 10, 15 and 20°C min -1 ), was carried out in the same experimental conditions used for the thermal analysis study with the aim to investigate dehydration and dehydroxylation kinetics using some isoconversional methods recommended by the ICTAC kinetic committee, and thermogravimetric data under a modulated rising temperature program. Finally, the results of the kinetic analysis were discussed and explained in terms of the strengths of the hydrogen bonds broken during these processes.

Effect of the Biopolymer Charge and the Nanoclay Morphology on Nanocomposite Materials

“…These peaks are attributed to the dehydroxylation of alumina groups of the HNT lumen. 45 On the contrary, the DTG curve of alginate/HNT does not show the dehydroxylation process, in agreement with the specific interaction between the polymer and HNT inner surface. Namely, the ionic exchange involving alginate COOgroups and Al-OH groups generate significant structural changes that cancels out the weight loss at 700-800 °C due to dehydroxylation of alumina groups.…”

“…7,44 Moreover, the TG method was reported for investigating dehydration and dehydroxilation of nanoclays. 45 MD 120 values (Table 1) evidenced that the water content of methylcellulose (non ionic) is much lower with respect to those of alginate (anionic) and chitosan (cationic). Filling polymers with clay nanoparticles (HNT and Kao) shaped the thermal behavior of bioplastics.…”

Thermal behavior and dehydration kinetic study of SiO2/PEG hybrid gel glasses

“…Additional information can be drawn by carrying out a kinetic analysis of dehydration, which received increasing attention in the recent years for the ability of this approach to provide important information on possible relation between the removal of water molecules and the structural properties (composition of the counterbalancing cations, charge of the silica units, etc. ) of different kinds of hydrated materials.…”

Conformational analysis of bovine serum albumin adsorbed on halloysite nanotubes and kaolinite: a Fourier transform infrared spectroscopy study

“…1,2 Clay minerals generally have permanent negative and variable surface charges, thus charged protein molecules can be adsorbed via electrostatic interactions, which depend on the negatively and positively charged states of protein molecules in the medium investigated. In addition to cation exchange and electrostatic forces, the hydrophobic (the tetrahedral surface) and hydrophilic' regions (the octahedral surface) on the clay mineral surface are also responsible for both the position and mobility of the water molecules in the halloysite interlayers and on the kaolinite surfaces 3,4 as well as for the adsorption of the hydrophobic protein patches. 1 Hydrophobic interactions are, on the other hand, one of the main forces in the structural stability of proteins in solution.…”