In this work, the band gap energies of magnesium oxide (MgO) were investigated to see if calcination time affects the band gap energies of the MgO. MgO nanomaterials have been prepared by a sol-gel method. MgO precursors produced were calcined at a temperature of 600 °C for 24 hours and 48 hours. The structural characterization of samples is achieved using X-Ray Diffraction (XRD) and the morphology as well as particle size of MgO were examined by Field Emission Scanning Electron Microscopy (FESEM). UV-Vis NIR spectroscopy was used to determine the band gap energies of the materials. From the results, the band gap energy of the MgO with a longer heating time exhibited a higher value.

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Ultra-thin MgO nanosheets obtained by a sol-gel method were found to have cubic crystal structure with a space group of Fm-3m. The thickness of the sheets for the 600°C and 5 h annealing condition sample is 2 nm. Although the MgO sheets are two-dimensional and ultra-thin, unlike graphene, they are polycrystalline. Their bandgap energies are dependent on the thermal annealing conditions (which affect the thickness of the MgO nanosheets). It is found that there was bandgap narrowing of the MgO nanosheets with respect to the bulk values. UV-visible spectroscopy and X-Ray Photoelectron spectroscopy (XPS) enables us to identify the shifts of the valence and conduction bands causing the bandgap narrowing.

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