Synthesis of Cu-doped TiO₂ nanorods with various aspect ratios and dopant concentrations

Colloidal TiO₂ nanorods were synthesized with different aspect ratios and successfully doped with copper via a controlled hydrolysis method. Inductively coupled plasma (ICP) atomic emission spectroscopy analyses showed that the asprepared TiO₂ nanorods contained ̃1.7-3.2 at% Cu. X-ray diffraction (XRD) and high-resolution transmission electron microscopy (HRTEM) analyses revealed that the doped nanorods are in a highly crystalline anatase structure and their crystal growth orientation is preferably [001]. The real doping of Ti lattices with Cu ions was evidenced by the analyses of surface compositions and chemical states of the nanorods using X-ray photoelectron spectroscopy (XPS). Through magnetic investigation using vibration sample magnetometry (VSM), it was verified that the Ti₁ - _xCu_xO₂ nanorods maintain apparent ferromagnetic ordering at room temperature (300 K). The origin of the ferromagnetic property was explained based on the concentration of oxygen vacancies increased by Cu doping, which was also identified by the XPS analyses. The saturation magnetization showed strong dependency on the aspect ratio of nanorods as well as the Cu content in TiO₂ nanorods.