The structure evolution of halloysite nanotubes during the acid leaching process: A molecular dynamics study

Abstract

For the acid-leaching process of halloysite nanotubes (HNTs), the structure and energetic evolution is crucial for the basic understanding and further modification of HNTs. The specific surface area, pore volume, and bond distribution of HNTs at different Al leaching percentages were studied by molecular dynamics simulation. With the increase of the Al leaching percentage, the inner diameter of the halloysite nanotubes is gradually enlarged, forming some nanoporous (1–20 nm) interlayer spaces inside the tube wall of HNTs due to the strong bondings between the adjacent layers, and the specific surface area and pore volume of HNTs increased in a complex way at each transition stages. For the transition structures, the interlayer nanopores greatly increase the specific surface area and pore volume of HNTs, which is more obvious after 50% Al leaching. The free water molecules inside lumen structure of HNTs would have an impact on the thermodynamics and the structure evolution of HNTs. Although the transition structures with extremely large loading capacity may not be naturally most stable, they might be stabilized or achieved by some fast transient regulation methods.