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

TiO 2 nanomaterial is a semiconductor material that exhibits promising photocatalysis activity. TiO 2 nanomaterials can be converted into several forms, including TiO 2 nanotubes, which have a larger surface area and more applications. In this study, TiO 2 nanotubes were synthesized hydrothermally using TiO 2 micro powder precursors. The synthesis involved two hydrothermal stages: the first to synthesize TiO 2 nanoparticles from TiO 2 micro powder precursors, and the second to synthesize TiO 2 nanotubes from TiO 2 nanoparticle precursors. TiO 2 micro powder was added to the synthesis of TiO 2 nanoparticles by hydrothermal at mole ratios of TiO 2 /NaOH of 0.01, 0.025, and 0.04, respectively. The TiO 2 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 TiO 2 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 TiO 2 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 m 2 /g.