Synthesis of single-phase zinc chromite nano-spinel embedded in polyvinyl alcohol films and its effects on energy band gap

Polymer nanocomposite films based on polyvinyl alcohol (PVA) and synthesis spinel zinc chromite (ZnCr₂O₄) nanoparticle films were obtained using the in situ chemical reduction method and solution casting technique, for different concentration of ZnCr₂O₄ nanoparticles. The characterization of the polymer nanocomposite films was carried out using XRD, SEM, and UV–visible Spectroscopy. The XRD analyses confirmed the cubic nanocrystalline ZnCr₂O₄ phase formation and an average crystallite size of approximately (23.35–25.36) nm. The UV–visible measurement of nanocomposite film shows two broad absorption peaks with a maximum at 410 and 570 nm, which correspond to the characteristics of the ZnCr₂O₄ nanoparticles. The effect of various concentration of ZnCr₂O₄ nanoparticle on the optical energy gap of nanocomposite films has been studied to comprehend the optimum conditions for the synthesis process. The significant decreasing of the direct allowed energy band gap of the PVA was observed upon increasing the ZnCr₂O₄ concentration, from (6.13 eV) for pure PVA to (4.76 eV) for 0.04 M ZnCr₂O₄ concentration. The decrease in the optical energy gap can be correlated to the formation of charge-transfer complexes within the base polymer network on embedding ZnCr₂O₄ nanoparticles.