Effect of Na doping on structure, morphology and properties of hydrothermally grown one dimensional TiO₂ nanorod structures

Na doped TiO₂ nanorod structures have been prepared by one-step hydrothermal method. Structural analysis of undoped and doped TiO₂ nanorod samples revealed the formation of single rutile phase structure. XRD plots confirms the effective substitution of Ti⁴⁺ with Na⁺ in the samples by exhibiting a slight shift towards the lower angle in the 2θ value of the diffraction peaks compared to undoped TiO₂ sample. The distribution of sodium in TiO₂ lattice is confirmed by morphological and EDS analysis. FESEM images of doped samples revealed the formation of structures in the form of nanorods for 2 and 4% of dopant and then to nanoflowers on increasing the amount of dopant to 6%. TEM analysis revealed the formation of nanorods with a diameter about 250 nm. Each nanorod was found to be formed of individual thin nanorods with approx diameter of 25 nm. The presence of sodium (atomic% = 7.60) in the nanorods was also substantiated by EDS studies. From optical studies, with increase in dopant concentration, the absorption edge is seen to be shifted towards the longer wavelength and bandgap tends to show red shift with values varying from 3.0 to 2.74 eV.