Spontaneous scrolling of Al2Si2O5(OH)4 nanosheets into halloysite nanotubes stimulated by structural doping with GeO2

Al
₂
Si
₂
O
₅
(OH)
₄
(halloysite) multiwalled nanotubes (MWNTs) were synthesized for the first time using a simple hydrothermal preparation technique involving the reaction SiO
₂
+ Al(OH)
₃
in the presence of 0.1-0.2 mole fraction GeO
₂
substituted for SiO2. The inclusion of small amounts of Ge(IV) into the Al
₂
Si
₂
O
₅
(OH)
₄
structure together with the creation of Si(IV) vacancies stimulates curving of layered nanosheets, such that they scroll to form spheroids, and finally tubes. At 0.5 GeO
₂
substitution, small single-walled imogolite-type nanotubes (SWNTs) with the Al
₂
Si
_x
Ge
_1-x
O
₃
(OH)
₄
structure are formed instead alongside x-ray amorphous particles. Thus the substitution of GeO
₂
for SiO
₂
provides a direct method to control the morphology of nanostructured aluminosilicates.