Green Synthesis, Biological Potential, and Semiconducting Properties of MnO:ZnO Bimetallic Nanocomposites

Abstract

This study reports the successful fabrication of manganese oxide: zinc oxide bimetallic nanocomposites, employing aqueous extract of Curcuma zedoaria. Biological potential and electrical properties of the composites have also been evaluated. The composites were fabricated using manganese and zinc salts in different ratios, i.e., 1:1, 1:2, and 2:1, referred to as MnO₁:ZnO₁, MnO₁:ZnO₂, and MnO₂:ZnO₁, respectively. X-ray diffraction studies revealed the crystalline nature of the composites, with crystallite sizes of 21 nm for both MnO₁:ZnO₁ and MnO₁:ZnO₂, and 23 nm for MnO₂:ZnO₁. Moreover, the composites were demonstrated to be quite stable at high temperature. The MnO₂:ZnO₁ composite exhibited the strongest anti-bacterial (zone of inhibition = 21 mm) and anti-fungal (zone of inhibition = 18 nm) activities, as compared to the other composites. On the other hand, the MnO₁:ZnO₂ composite inhibited the DPPH radical strongly. Strong anti-leishmanial activity was shown by all the composites with IC₅₀ values of 0.03 (MnO₁:ZnO₁), 0.14 (MnO₁:ZnO₂), and 4.3 (MnO₂:ZnO₁) µg/mL. The nanocomposites also displayed optimum energy storage and semiconducting abilities. The band gaps calculated for MnO₁:ZnO₁, MnO₁:ZnO₂, and MnO₂:ZnO₁ were found to be 3.18, 3.26, and 3.11 eV, respectively. Optimum value of dielectric constant (~ 0.95) and capacitance (~ 1.0 pF) were observed for MnO₂:ZnO₁, while the MnO₁:ZnO₂ composite exhibited the best AC conductivity (1.8 × 10^− 9 S/m). All the samples exhibited the inverse relationship between capacitance and AC conductivity. The work thus shows that the combination of Mn and Zn imparts special characteristics to the nanocomposite, making it biologically effective and at the same time a suitable candidate for use in semiconductors.