), the indexing of the significant peaks is a little complex. The SEM/EDX analysis, i.e., micrographs (Fig. , i-iii, inset), and colourmaps (Fig. a-j) of the various regions of all the five iron oxide NPs samples represented the nearly uniform distribution of metals with varying degree of impurity in respective samples. The samples from analytical grade commercial capping agents like CTAB and MC, along with the case of simple base hydrolysis (FeBH), have shown the least impurity (Table ) level (generally the sulfur from the precursor side), i.e., in the range of (0.5-7%) w/w. As expected, the FePM sample showed the largest impurity due to the waste extract (PM). However, in some places, the However, other than these two cases without capping ligands, i.e., (FeAH) and (FeBH), the peak distortion in other samples having ligands indicates the shape anisotropy and defects in the electronic environment around the F +2 /Fe +3 center. The zeta potential (ζ) measurement shows the negative surface charge (Fig. & Table ) in the range of (-4.03 -28.07 mV) in ethanol dispersion. Ethanol, a lower dielectric solvent than water, minimizes the effect of pH on (ζ); thus, the measured (ζ) fairly reflects the charge on the surface. From a low and negative, in the case of no capping ligands (FeBH -4.03 mV), the zeta potential rises to a high negative in the case of capping ligands (FePM -28.7 mV). However, the negative (ζ) in all cases demonstrates the effect of anionic capping ligands modifying the surface charges of the nanoparticles. Nonetheless, along with the residual presence of surface ligand, such a large variation of (ζ) may also be due to the polymorphic and anisotropic variation of nanoparticles. Noticeably, this (ζ) also shows a correlation with the observed potential of zero charge discussed later. The diffuse reflectance UV-vis absorption spectra with the absorption edge at 565 nm to 515 nm (Fig. ) along with Tauc analysis (Fig. ) equation (5) shows that the Eg of the samples lies in the range of 0.4 to 2.1 eV. These iron oxide samples slightly shift to a higher band gap due to quantum confinement. Moreover, due to the impurity of different polymorphic forms and anisotropy in the sample, there is a noise in the spectrum. 32