­Two-Stage Hydrothermal Synthesis of TiO₂ Nanotubes with Variations of TiO₂/NaOH Molar Ratio

Abstract

TiO2 nanomaterial is a semiconductor material that exhibits promising photocatalysis activity. TiO2 nanomaterials can be converted into several forms, including TiO2 nanotubes, which have a larger surface area and more applications. In this study, TiO2 nanotubes were synthesized hydrothermally using TiO2 micro powder precursors. The synthesis involved two hydrothermal stages: the first to synthesize TiO2 nanoparticles from TiO2 micro powder precursors, and the second to synthesize TiO2 nanotubes from TiO2 nanoparticle precursors. TiO2 micro powder was added to the synthesis of TiO2 nanoparticles by hydrothermal at mole ratios of TiO2/NaOH of 0.01, 0.025, and 0.04, respectively. The TiO2 nanoparticles obtained exhibit a morphology in the form of short fibers, with particle sizes increasing as the mole ratios are added. Furthermore, they possess an anatase crystal structure at all mole ratios of TiO2/NaOH. Subsequently, the TiO2 nanoparticles are calcined at 450°C. The results of the TiO2 nanoparticle calcination show that the morphology is in the form of short fibers, which are smaller than those of the uncalcinated sample. The calcinated sample also has larger particle sizes and an anatase crystal structure, compared to the uncalcinated sample. The TiO2 nanotubes obtained exhibit an elongated tube morphology with outer diameters ranging from 3.93 to 11.44 nm, inner diameters ranging from 2.5 to 4.25 nm, and a wall thickness of 1.09 to 3.4 nm. The surface area of the TiO2 nanotubes is 256.744 m2/g.