Looking into how nickel doping affects the structure, morphology, and optical properties of TiO2 nanofibers

Abstract

In this paper, we have systematically studied the structural, morphological, and optical properties of Ni-doped TiO<inf>2</inf>, synthesized via a simple, cost-effective electrospinning method followed by calcination at 500 °C. The nanofibers with a core-shell structure were relatively homogeneous, smooth and randomly oriented, and there were no significant differences in fiber diameters due to Ni²⁺ content. Core loss mapping using electron energy loss spectroscopy confirmed an even distribution of titanium and relatively uniform nickel in the fibers. It was found that doping with 0.5 mol.% Ni²⁺ decreased the rutile content, while doping with 1 mol.% Ni²⁺resulted in a pure anatase phase with a significantly increased specific surface area (36.6 m²/g). Further increase in Ni²⁺ content (3–10 mol.%) not only prolonged the response of TiO<inf>2</inf> nanofibers to visible light, but also increased the specific surface area (49.5 m²/g), decreased crystallite size (7 nm), and increased rutile content in TiO<inf>2</inf> (33 wt.%). Photoluminescence analysis revealed that doping TiO<inf>2</inf> with different amounts of Ni²⁺ leads to a gradual decrease of emission spectra intensity and red shift in the maxima positions. The XPS results confirmed that as the Ni²⁺ content enlarged, the Ti²⁺ and Ti³⁺ content increased significantly, effectively promoting the formation of oxygen vacancies. Raman analysis showed that an increase in nickel content (3–5 mol.%) led to a decrease and shift in peak intensity due to Ti³⁺ formation and also the possible presence of NiTiO<inf>3</inf> phases. HRTEM analysis showed that Ni was doped into the substitution sites of both the anatase and rutile TiO<inf>2</inf> lattice but had a stronger influence on the distortion of the anatase phase. The photocatalytic activity of Ni-doped TiO<inf>2</inf> nanofibers was explored by analyzing the degradation of an antibiotic, oxytetracycline, monitored in laboratory conditions under visible light irradiation. After 60 min of irradiation, the degradation of OTC with 1Ni-TiO<inf>2</inf> reached 76.4 % and with 10Ni-TiO<inf>2</inf> 70.5 %.