*3.1. UV-Visible Analysis of the Synthesized PPy and PPy/GA Composites*

Figure 3a shows the UV-visible spectra of pure PPy and PPy/GA composites. Two significant absorption peaks can be seen in the spectra. At 312–319 nm and 445–480 nm, the first and second absorption peaks were found, respectively. The transition of electrons from the lowest occupied molecular orbital (LOMO) to the highest unoccupied molecular orbital (HUMO), which corresponds to the π–π\* electronic transition of the aromatic ring in the polymer chain, is responsible for the first absorption band [25]. The sum of polarons and bipolarons is assigned to the second absorption band, which serves to determine that the PPy component of the composites is made up of free carriers (mainly polarons) [26], suggesting the CPs in their oxidized and conducting state [27]. The difference in peak intensities is related to the difference in composite concentration in the solvent, whereas the difference in peak position is due to the length of the polymer chain. There is a change in the absorption spectra when GA is added to the PPy matrix. The first absorption band exhibited a small rise as GA concentrations increased. Both intensity and peak shifting

were detected in the second absorption peak. The absorption peak for PPy/GA 1 shifts toward a longer wavelength (red shift). The shift of peaks towards lower wavelengths was noted in the PPy/GA 2 through PPy/GA 5 composites. The absorption shift is caused by the blocking of ions or free radicals or the active site of the PPy by GA.

**Figure 3.** (**a**) UV-visible spectra of neat polypyrrole and its composites with gum arabic. (**b**) FTIR spectra of neat polypyrrole and its composites with gum arabic.

#### *3.2. FTIR Analysis of the Synthesized PPy and PPy/GA Composites*

The FTIR analysis of PPy and PPy/GA composites was performed in the range of 500 to 4000 cm−<sup>1</sup> to investigate the atomic and molecular vibrations and the types of bonding states in the synthesized materials. The low-intensity peak in the PPy spectrum in the region of 2954–2851 cm−<sup>1</sup> is attributable to the C–H and S=O stretching modes, which clearly reveals the existence of the benzenoid ring of DBSA in the polymer matrix in Figure 3b [28]. Sulfonate anions, –SO3 <sup>−</sup>, have a stretching vibration of S=O at 1170 cm<sup>−</sup>1, which compensates for the cation in the polypyrrole chains. The DBSA displays the distinctive signal at 652 cm−<sup>1</sup> in the PPy sample [29]. The stretching vibration of C=C can be seen at 1548 cm<sup>−</sup>1, whereas the stretching vibration of C–N in the Py ring can be seen at 1454–1471 cm<sup>−</sup>1. The signal at 1703 cm<sup>−</sup><sup>1</sup> is due to the out-of-plane wagging of the carbonyl group. At 1035 cm<sup>−</sup>1, the stretching vibration of C–H of the Py ring can be noticed [30,31]. The peak at 1291 cm−<sup>1</sup> is connected to C–N in a plane.

All of the typical peaks of PPy are seen in the FTIR spectra of PPy/GA composites, as explained above and shown in Figure 3b. The stretching vibration of the O–H bond is responsible for the wide and low-intensity peak at 3209 cm<sup>−</sup>1. The stretching vibration of the C=O bond of the carboxylate group of the GA molecule is responsible for the high peak intensity at 1683 cm−<sup>1</sup> [32,33]. The asymmetric stretching causes the strongest band at 1602 cm<sup>−</sup>1, whereas the symmetric stretching vibration of the carboxylic acid salt – COO<sup>−</sup> [34] causes the weaker band at 1422 cm<sup>−</sup>1. Some of the GA peaks are superimposed over the PPy in the composites, indicating that the GA particles have been effectively incorporated into the PPy matrix.
