Synthesis of titanate nanotubes and the mechanism of their formation

Nanotubes of H2Ti2O5·H2O and Na2Ti2O4(OH)2 have been synthesized by a solvothermal method using tetrabutyl orthotitanate as titanium source with the pH being adjusted by addition of sodium hydroxide or hydrochloric acid solution,without any post-treatment with hydrochloric acid or water being required.The composition,morphology and structure of the samples were determined by XRD,HRTEM,TEM and EDS.When pH values of 8-9 were employed,H2Ti2O5·H2O was obtained whereas at pH 12-13,Na2Ti2O4(OH)2 was formed.It is proposed that the process involves initial formation of a sheet-like structure,which curls into a tube-like structure under the high temperatures and pressures in the solvothermal system,resulting in the final nanotube structures.