Obtenção de α-Fe2O3 e α-Fe2O3/MWCNTs nanoestruturados e avaliação das suas propriedades eletroquímicas

Abstract

In the present work, nanostructures of the iron oxide (α-Fe2O3) were synthesized by the microwave hydrothermal method, varying the synthesis conditions such as the pH of the precursor solution and the time of synthesis. The samples were structurally characterized by X-ray diffraction (XRD) and Raman spectroscopy from which it was possible to evaluate the influence of the experimental parameters on the long and short range structural order of the synthesized samples. The XRD results showed the formation of the rhombohedral structure for α-Fe2O3 samples. The Raman active vibrational modes that characterize the α-Fe2O3 phase were observed for all the samples. UV-vis spectra showed the absorption bands expected for the iron oxide and allowed the obtention of band gap values for the samples. Scanning electron microscopy (SEM) images showed that the size and morphology of the formed particles are influenced by the time of synthesis and pH value of the solution. Nanocomposite films between α-Fe2O3 and multi-walled carbon nanotubes (MWCNTs) as well as pure films of these materials were prepared by the interfacial method. The α-Fe2O3/MWCNTs sample showed the characteristic diffraction peaks of hematite and MWCNTs. By the Raman spectroscopy technique it was possible to observe the vibrational modes of α-Fe2O3 and the MWNCNTs characteristic bands in the nanocomposite film. SEM images confirm the interaction between MWCNTs and α-Fe2O3 nanoparticles. The electrochemical performance of α-Fe2O3/MWCNTs film was evaluated for supercapacitors application. Cyclic voltammetry and galvanostatic charge and discharge results showed a superior performance of the nanocomposite film compared to pure α-Fe2O3 and MWCNTs films suggesting a synergistic contribution between the materials. The nanocomposite film exhibited a high specific capacitance of 110.34 F g-1 at current density of 0.75 A g-1 and retention capacity of 86% after 500 cycles and also showed a correlation between energy density and power density within the range established for supercapacitor devices.