The stability of halloysite nanotubes in acidic and alkaline aqueous suspensions.

The long term stability of natural halloysite nanotubes was studied at room temperature (22 ± 2 °C) in pure water, acidic and basic aqueous suspensions. The structural and morphological transformations of nanotubes were studied by TEM, SEM, nitrogen adsorption, XRD Raman and FTIR spectroscopy accompanied by monitoring the concentration of dissolved Si(IV) and Al(III) in solution. It has been revealed that, in 1 mol dm(-3) H(2)SO(4) solution, the dissolution of halloysite is initiated on the inner surface of nanotubes, leading to the formation of amorphous spheroidal nanoparticles of SiO(2) whereas, in 1 mol dm(-3) NaOH solution, dissolution of the inner surface of nanotubes is accompanied by the formation of Al(OH)(3) nanosheets.