Hydrothermal assisted-green synthesis of Fe/N co-doped TiO2 nanocomposites using Vernonia amygdalina leaf extract

Abstract

In this paper, pure TiO2 and Fe/N co-doped TiO2 nanocomposites were prepared via hydrothermal-assisted-green synthesis method using aqueous extract of bitter leaf, Vernonia amygdalina. The doping of pure TiO2 was by wet impregnation of titanium isopropoxide with NH4NO3 and FeCl3.6H2O such that the theoretical Fe/N doped Ti molar ratio was 4:1. The prepared nanocomposites were annealed at 450 oC and characterized by High resolution thermal electron microscopy (HRTEM), X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS) and Brunauer–Emmett–Teller (BET) measurements methods. The XRD patterns confirmed the formation of anatase for pure TiO2 and rutile phase for Fe/N co-doped TiO2 samples. The phase transformation from anatase to rutile was linked to electronic movement between 3d and 2p orbitals of Fe and N respectively. The increase in average crystallite size of 37.4 nm observed for Fe-N-TiO2 was attributed to complete phase change from anatase to rutile. The HRTEM images of the assynthesized Fe/N co-doped TiO2 shows an agglomeration of small spherical shape nanoparticles with sizes in good agreement with the sizes obtained from XRD measurements. The co-doping effect of Fe and N was responsible for the increased surface area from 10.37 m2/g for pure TiO2 to 25.48 m2/g for Fe/N co-doped TiO2 nanocomposites respectively. This study demonstrated that the microstructural, textural, phase types and oxidation states of TiO2 were influenced by Fe and N.