Impact of pH on structural, morphological, optical, and magnetic properties of zinc oxide nanopowders synthesized by co-precipitation method.

The co-precipitation approach was used to synthesize zinc oxide (ZnO) nanopowders with varying pH values of the starting solution. The structural, optical, and morphological features of ZnO nanopowders synthesized were investigated. The hexagonal structure is confirmed by X-ray diffraction (XRD) patterns, which show a minor shift in crystallite size and strain values with pH. Raman Spectra showed the characteristic peaks of wurtzite structure with strong E2 high vibrational mode. FTIR confirms the ZnO functional groups, and there is a change in the wave number position of groups, which is analyzed with the Zn–O bond length studies of XRD patterns. Field emission scanning electron microscopy studies confirm the change in morphological properties from nanoflakes to spherical and then mixed morphology with increased pH value. The band gap energy of all the samples is measured using the UV–Vis spectra, and it is around 3.20 eV; a very minute change in the band gap is observed with the pH value. Defects and rate of recombination of electron and hole pair were analyzed using photoluminescence spectra and the concentration of defects and recombination is explained using the deconvolution peak analysis. It slightly changes with the pH value. The room-temperature magnetic hysteresis loops confirm the ferromagnetic nature of the samples and with an increase of pH, the required magnetic field to saturate the loop is more. The change in the magnetic properties is explained based on the defects in the samples. The observed results confirmed that the pH value influences the structural, morphological, and magnetic properties, and there is not much difference in the optical properties. This implies that manipulating process parameters allows the preparation of pure ZnO with varied morphological nanostructures, potentially improving its optical and sensing capabilities. [ABSTRACT FROM AUTHOR]