3.4.5. Fourier Transform Infrared (FT-IR) Spectroscopy

The bioactive compounds present in biomass filtrate of *R. oryaze* strain E3, which is responsible for the reduction of metal precursors to form MgO-NPs, are identified by FT-IR analysis which recorded a wavenumber between 400 to 4000 cm–1, as shown in Figure 6. The peak observed at 3700 cm–1 signifies to –OH stretching band [69]. The broadness peak at 3431 cm–1 is corresponding to the O–H stretching vibration mode of the hydroxyl groups overlapped with the NH stretching mode of amines [62]. The medium observed peaks at 1650 cm–1 are signified to the bending mode of primary amine (N–H) overlapped with either amide and carboxylate salt (see XPS analysis). The medium peak at 1435 cm–1 corresponds to the C=O stretching of carboxylate salt as well as the adsorption of CO<sup>3</sup> 2– and CO<sup>2</sup> at the surface of MgO-NPs [70,71]. The adsorption of such functional groups on the surface of MgO-NPs has a critical role in catalytic reactions [72]. whereas the peak at 1030 cm–1 matched the Mg–OH stretching [73] with C-H out-of-plane bend. The peak located at 930 cm–1 corresponds to C-O stretching, *trans*-C-H out-of-plane bend, and P–O which refers to phosphate-containing molecules [74]. The successful fabrication of Mg-O was confirmed by peaks observed at a wavenumber between 400 to 700 cm–1, as reported in various published studies [69,75,76]. The peaks observed in FT-IR spectra reflect the role of metabolites involved in biomass filtration of *R. oryaze* strain E3 for reducing and stabilizing of MgO-NPs.

**Figure 6.** The FT-IR spectrum of myco-synthesized MgO-NPs fabricated by metabolites of *R. oryaze* strain E3.
