Synthesis of 1D Bi2O3 nanostructures from hybrid electrospun fibrous mats and their morphology, structure, optical and electrical properties

Abstract

The aim of this study was to produce Bi2O3 nanowires using a combination of sol–gel process and electrospinning methods and a solution based on a 13% solution of polyacrylonitrile (PAN) in N,N-dimethylformamide (DMF) containing 1.5 g of bismuth (III) nitrate pentahydrate (Bi(NO3)3·5H2O). The obtained fibrous composite mats were dried at room temperature for 24 h followed by the calcination process in air at two different temperatures of 400 °C and 600 °C. Analysis of the morphology of the fabricated Bi2O3 nanomaterials based on TEM images showed that the obtained ceramic structures could be classified as one-dimensional Bi2O3 nanostructures, with the sizes of the presented structures being 260 nm, 125 nm and 200 nm for diameter, and 5.5μm , 2 μm and 2.125 μm for length, respectively. Moreover, further analysis of the morphology of the obtained Bi2O3 nanostructures with the use of SEM showed that their diameters ranged from 150 to 500 nm when a calcination temperature of 400 °C was employed, while Bi2O3 nanowires with diameters ranging from 150 to 450 nm were obtained at 600 °C. To analyse the chemical composition and oscillatory transitions of atoms vibrating between the oscillatory levels in the molecules of the produced 1D nanostructures, and to determine the functional groups existing therein, EDX and FTIR were used. Transmission peaks in FTIR spectra recorded for wave numbers in the range of 400–4000 cm-1 were due to the presence of vibrations in Bi–O bonds, which correspond to the structure of Bi2O3. In addition, a detailed analysis of optical constants of one-dimensional Bi2O3 nanostructures fabricated using a combination of sol–gel process, electrospinning and calcination methods has been presented in this paper for the first time. Optical studies based on the recorded UV–Vis spectra showed that the obtained Bi2O3 nanowires were characterized by sharp absorption edges of radiation in the near-ultraviolet range, with sharp absorption edges falling at wavelengths of 400 nm, regardless of the applied temperature during the calcination process. The study of optical constants showed that the Bi2O3 nanostructures exhibited refractive indices of 2.62 and 2.53 at temperatures of 400 °C and 600 °C, respectively, while dielectric constants were 6.87 and 6.42, respectively. The final stage of the study was the determination of the width of energy gaps of the produced bismuth oxide nanostructures, which were found to be 3.19 and 2.97 eV, respectively. The presented results of morphology and optical properties of the obtained one-dimensional Bi2O3 semiconductor nanostructures indicate a potential possibility to apply this type of materials for the production of a new generation of dye-sensitized photovoltaic cells (DSSCs).