Effect of pH on Structural and Optical Properties of Magnesium Chromates Nanocrystals Synthesized by Combustion Method

Abstract

In this work magnesium chromate (MgCr2O4) samples were produced by combustion method. Sample 1 was prepared without adding ammonia hydroxide (pH = 0.96) during synthesis steps whilst sample 2 was prepared with ammonia hydroxide (pH = 8.62). Sample 1 was obtained in 2:10 h whilst sample 2 was produced in 45 min. Effect of pH upon structural properties were investigated by X-rays diffraction (XRD) technique. The results confirm the formation of the cubic spinel structure with average crystallite sizes of 13.0 nm and 8.0 nm for sample 1 and sample 2,

respectively. The lattice parameters were calculated using Bragg’s law and found to be 8.30 Å and 8.33 Å for sample 1 and sample 2, respectively. The X-rays densities values were 2.227× 106 g/cm3 and 2.206× 106 g/cm3 for the sample 1 and sample 2, respectively. The obtained microstrain values were 0.007148 and 0.015206 for sample 1 and sample 2, respectively. The optical properties were studied using Ultra violate - Visible (Uv-Vis) absorption technique. The results show that MgCr2O4 samples have a direct band gap of 3.007 eV and 3.057 eV for the sample 1 and sample 2, respectively. It observed that the band gap of sample 2 was slightly greater compared to sample 1. This associated with crystallite sizes of the samples. It can be concluded that control of pH can significantly reduce the duration of combustion synthesis method.