Effect of Alkali Strength on the Hydrothermal Growth of Photoactive TiO2 Nanowires

Titanium dioxide nanowires have been prepared by the alkali hydrothermal treatment of TiO2 nanoparticles in presence of different hydroxides and characterized using transmission electron microscopy (TEM), scanning electron microscopy (SEM), energy dispersive x-ray (EDX), N2 adsorption-desorption measurements, powder x-ray diffraction (XRD) and UV-Vis spectroscopy. Interestingly, only the strong bases (NaOH and KOH) formed mainly anatase titanium dioxide nanowires with the evident collapse of definitive (110) rutile XRD peak. The KOH-based titanium oxide nanowires exhibited comparatively low diameter (∼5 nm), high surface area (228.34 m2/g), and low band gap energy (2.90 eV), and showed the most remarkable photocatalytic degradation (98.87 %). However, the NH4OH-based titanium dioxides were nanoparticles having insignificantly modified morphology and least photocatalytic efficiency. The effect of operating variables on the degradation of aqueous methylene blue (MB) over the obtained alkali hydrothermal TiO2 was studied using response surface methodology, based on a bivariate central composite design (CCD) and optimized numerically.