Band Gap Tuning in Calcium Hydroxide-Nitrate Nanocomposite Materials

This study reports the band gap engineering in calcium hydroxide-nitrate nanocomposite materials (CHNNCs). The CHNNCs are produced by the simple chemical precipitation technique from an aqueous Ca(NO3)2–NaOH system. The molarity of precipitator NaOH is deliberately varied from 0.5 M to 1.5 M by keeping the constant molarity (e.g., 1 M) of the precursor Ca(NO3)2.4H2O solution. After that, the produced CHNNCs are examined using XRD, FESEM, FTIR, and UV–Vis spectroscopic methods to investigate the structural, morphological, surface functional, and optical characteristics of the various synthesized CHNNCs. The XRD study suggests an increase in crystallite size from 53 to 99 nm. The increase in crystallite size with an increase in the molarity of precipitator NaOH (0.5–1.5 M) is discussed in terms of nucleation and growth due to the presence of sodium nitrate. The FESEM photomicrographs also exhibit the impact of sodium nitrate that acts as an oxidizing agent leading to the release of water through the hydroxylation process that results in the changes of the surface morphology of the various synthesized CHNNCs. The UV–Vis spectroscopy analysis unveils a significant red shift in the absorbance spectra, indicating a reduction in band gap from approximately 5.57 eV to around 5.53 eV with the augmentation in crystallite size. The regulated development and nucleation of the Ca(OH)2-nitrate nanocomposite shape opens up a wide range of potential applications.