Synthesis of nanostructured pirochromite magnesium chromate with egg shell membrane template

In this work, we report on the use of fresh and boiled egg shell membrane as bio-templates in the co-precipitation of pirochromite. The structure evolution, microstructure and optical properties of the ESM templated MgCr₂O₄ nanomaterial were studied by X-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy, Energy dispersive X-ray spectroscopy, elemental mapping and UV–Vis–NIR spectrophotometry. The annealing of the untemplated and templated co-precipitated MgCr₂O₄ powders at 1000 °C for 4 h produced single phased nanostructured material with spinel cubic crystal structure. The FTIR results showed slight variations in the band positions ν₁ and ν₂ which are attributed to the change in the microstructure due to the introduction of ESM in the preparation of MgCr₂O₄. The morphologies and average crystallite size of the annealed MgCr₂O₄ nanocrystalline powders depended on the type of the template. 3D hierarchical flake-like and mesh like structures were observed. The annealed MgCr₂O₄ nanocrystalline powders have shown excitonic absorptions in the visible range 300–500 nm due to the transitions that took place from the O-2p level to the Cr-3d level. The optical band gap energies were found to be 3.68–3.71 eV for the direct band gap and 3.30–3.37 eV for the indirect band gap. This could make these MgCr₂O₄ nanocrystalline powders possible photocatalysts in the visible range 300–500 nm.