Effect of post treatments on the structure and thermal stability of titanate nanotubes

Abstract

TiO2 sol was prepared hydrothermally in an autoclave from aqueousTiOCl2 solutions as a starting precursor. Titanate nanotubes were obtained when the sol–gel-derivedTiO2 sol was treated chemically with a 10 M NaOH solution and subsequently heated in the autoclave at150 °C for 48 h. The samples were characterized using XRD, TEM, SEM, EDX, Ramanspectroscopy, and a BET surface area analyser. The effect of post treatments, suchas washing with and without hydrochloric acid and calcination, on the phasestructure, shape and morphology, pore structures, and BET surface area of thetitanate nanotubes was investigated. When a sample containing 7.08 wt% Na (afterwashing only with water) was calcined at different temperatures from 300 to900 °C, it showed the formation of a mixture of sodium trititanates and sodium hexatitanatesand was found to preserve the tubular morphology at higher temperatures.However, a sample containing 0.06 wt% Na obtained after prolonged washingwith hydrochloric acid followed by heat treatment showed the formation ofTiO2 anataseinvolving TiO2 (B) as an intermediate at lower temperatures and anatase was further transformed to the rutilephase when the temperature was raised. On the basis of different observations, a general formulaNaxH2−xTi3O7·nH2O has been proposed for the trititanate nanotubes.