Optimization of the Alkaline Hydrothermal Route to Titanate Nanotubes by a Doehlert Matrix Experience Design

Abstract

In spite of the controversy about the chemical structure and formation mechanism of hydrogenotitanates nanotubes (HNTs) through a basic hydrothermal treatment of TiO 2, HNTs are still the subject of intense research owing to their unique features including large specific surface area, photocatalytic potential, and ion-exchangeable ability. The properties of nanotubes depend mostly on three critical parameters: (1) NaOH concentration, (2) reaction time, and (3) the hydrothermal temperature. However, these parameters are not well controlled in the literature, leading most of the time to different titanates with controversial assignment of their nanostructures. In order to optimize the elaboration route of titanates nanotubes, we report here for the first time an experience design using a Doehlert matrix with N experiences ( N = K 2 + K + 1; K is equal to the parameters numbers). By solving Doehlert matrix, we obtained the optimum conditions ( T = 144 °C, C NaOH = 11.88 mol·L −1, and hydrothermal reacting time of 14.6 h). High yields of titanates nanotubes are therefore obtained that are identified by DRX as H 2 Ti 2 O 5 ·H 2 O.