3.1.2. TEM Analysis

TEM analysis was done for a detailed investigation of morphological characters. TEM images of the magnetic nanoparticles (Figure 3) were used to confirm the size and the shape of the nanoparticles. One can see from Figure 3a,b, that all the nanoparticles are homogeneous in size and shape. The size calculated using the TEM images ranges from 24 to 27 nm, whereas the shape is almost round. No agglomeration appeared in the micrograph, which may attribute to the homogeneous depression of these nanoparticles. TEM image (Figure 3c) shows that the nanoparticles have a mesoporous structure, which helps to achieve better catalytic properties.

**Figure 3.** TEM images of the Fe3O4 nanoparticles at (**a**) 100 nm; (**b**) 100 nm and (**c**) 50 nm magnifications.

## 3.1.3. FTIR Analysis of Nanoparticles

A small amount of the product formed by the addition of dopamine in Fe3O4 suspension was taken out, washed with distilled water and dried using desiccator. The dried product was then subjected to Fourier transfer infrared spectroscopic analysis. FTIR confirms the attachment of dopamine on iron oxide nanoparticles by the presence of four peaks. Absorption band at 3209 cm<sup>−</sup><sup>1</sup> corresponds to the characteristic starching frequency of hydroxyl groups merged with a starching frequency band of N-H. This broad band was due to catechol groups of dopamine at the surface. Bending vibration peak of N-H was at 1628 cm<sup>−</sup>1. Sharp peak at 1290 cm<sup>−</sup><sup>1</sup> indicated the presence of C-O bond. While peak at 1472 cm<sup>−</sup><sup>1</sup> was attributed to the C=C ring starching band overlapped with –CH2 scissoring band (Figure 4). The results were depicted to be comparable to previous research [24].

**Figure 4.** Comparative FTIR of naked Fe3O4 and polydopamine coated Fe3O4 nanoparticles.
