Investigation of Structural and Optical Properties of Zinc Chromate Nanocrystals Prepared by Hydrothermal and Combustion Methods

Abstract

In this work zinc chromate (ZnCr2O4) samples were produced by hydrothermal and combustion methods. Effect of different synthesis methods upon the structural and optical properties were investigated. X-rays diffraction (XRD) results confirm the formation of the cubic spinel structure with crystallite sizes of 13.8 nm and 23.1 nm for the samples prepared by hydrothermal and combustion methods, respectively. The lattice parameters were calculated using Bragg’s law and found to be 8.33 Å and 8.12 Å for the samples prepared by hydrothermal and combustion methods, respectively. The microstrain values were 0.004823 ± 0.00043054 and 0.00482 ± 0.0002738 for the sample prepared by hydrothermal and combustion methods, respectively. The existence of metal oxide bonds at both samples was confirmed using Fourier transform infrared (FT-IR) spectroscopy technique. The absorption peaks for the Cr2O4 and Zn-O bonds were observed at 545.074 and 489.3 cm-1, respectively for the samples prepared by the hydrothermal method. While in the sample prepared by combustion method the absorption peaks of Cr2O4 and Zn-O bonds were observed at 545.14 and 489.2 cm-1, respectively. The Brunauer–Emmet–Teller (BET) speafic surface area measurements of the sample prepared by the hydrothermal method showed a value of 20.3919 m2/g, while the sample prepared by the combustion method showed a value of 19.81860 m²/g. N2 adsorption-desorption measurements were used to investigate the textural and character of the pores for the synthesized ZnCr2O4 samples. The optical properties were studied using Ultra violate–visible (Uv-vis) absorption spectroscopic technique. The results show that ZnCr2O4 samples have a direct band gap of 4.038 eV and 3.98 eV for the samples prepared by hydrothermal and combustion methods, respectively. It observed that the band gap increases as crystallite sizes decrease. It can be concluded that various methods for synthesis ZnCr2O4 samples lead to different structural properties and significantly affect the optical properties.