2.4.5. Antibacterial Activity

The antibacterial capability of the poly(o-anisidine)/BaSO4 nanocomposites was assessed using the disc-diffusion technique. Antibacterial testing was carried out by using the disc-diffusion method. Bacterial growth was carried out by using the nutrient-growth agar method. Only Gram-negative bacteria (*Pseudomonas aeruginosa*) were used in the MacConkey agar. *Pseudomonas aeruginosa* can grow on MacConkey but *Staphylococcus aureus* cannot grow on MacConkey. The media were autoclaved, chilled, and deposited in petri plates for 41 min. Forty-one minutes later, hardened agar plates were covered with a fresh inoculum (20 mL) of bacteria cultures. The UVAS diagnostic lab provided bacterial cultures. Every plate contained sterile paper discs dipped in various suspensions of the POA/BaSO4 nanocomposites. For 24 h, the agar plates were incubated at 37 ◦C (310 K). The zones of inhibition were studied following a 24-hour incubation period. The magnitude of the presence or absence of growth inhibition zones was used to determine the sensitivity and resistance of bacteria in sensitivity tests.

#### **3. Results and Discussion**

The synthesized poly(*o*-anisidine)/BaSO4 nanocomposites were characterized by various techniques, as mentioned above. Six samples were prepared, in which one was the pure polymer and other five were nanocomposites with BaSO4 nanoparticles (1%, 3%, 5%, 7%, and 10%). The barium-sulfate nanoparticles were characterized by powder XRD and the average particle size was 25.26 nm, as reported by Ahmad et al. [44]. The composites were further analyzed by using the following analytical techniques.

### *3.1. FTIR Spectroscopic Studies*

The FTIR analysis of the poly(*o*-anisidine)/BaSO4 nanocomposites was carried out to determine the structural changes in the material. The C=C stretching mode of the quinoid ring appeared at 1591 cm<sup>−</sup>1, which was attributed to the stretching vibration of the o-methoxy group. The poly(2-methoxy aniline) signal appeared at 3379 cm<sup>−</sup>1, which was attributed to the N-H stretching mode. The C=C stretching modes of the benzenoid ring appeared at 1469, 1206, and 1032 cm<sup>−</sup>1, which were attributed to the stretching vibration of the o-methoxy group. The methoxy band clearly indicated the existence of poly(*o*-methoxy aniline) in the spectra. The spectrum in Figure 2b shows the addition of 1% of the BaSO4 nanoparticles in the poly(*o*-anisidine) matrix at 2837 cm<sup>−</sup>1, demonstrating the interaction of the poly(*o*-anisidine) with the BaSO4 that appeared as the peak was deeper and wider.

**Figure 2.** FTIR spectra of (**a**) pure POA, (**b**) 1% of POA/BaSO4, (**c**) 3% of POA/BaSO4, (**d**) 5% of POA/BaSO4, (**e**) 7% of POA/BaSO4, and (**f**) 10% of POA/BaSO4.

The peak that appeared at 2837 cm−<sup>1</sup> with the addition of 3 percent of the BaSO4 nanoparticles in the poly(*o*-anisidine) matrix was practically the same as in the 1 percent, indicating that the 3 percent addition of the BaSO4 nanoparticles improved the properties of the polymer. The peak at 2116 cm−<sup>1</sup> indicated the interaction of the BaSO4 nanoparticles with the polymer matrix when 3 percent of the BaSO4 nanoparticles was added to the polymer matrix. The peak at 1568 cm−<sup>1</sup> was linked to the quinoid ring's (C=C) stretching modes.

The characteristic peak was observed at 1266 cm−<sup>1</sup> after the addition of 5% of the BaSO4 nanoparticles in the polymer matrix, as shown in Figure 2d, indicating that the 5 percent addition of the BaSO4 nanoparticles increased the features of the polymer. The peak at 1628 cm−<sup>1</sup> indicated the interaction of the BaSO4 nanoparticles with the polymer matrix when 5 percent of the BaSO4 nanoparticles was added to the polymer matrix. The peak at 1568 cm−<sup>1</sup> was linked to the quinoid ring's (C=C) stretching modes.

The peak at 3511 cm−<sup>1</sup> was, again, found by adding 7% of the BaSO4 nanoparticles to the polymer matrix, as shown in Figure 2e, which was deep but not as wide as in the prior cases, indicating that the 7% addition of the BaSO4 nanoparticles improved the polymer properties. Furthermore, the spectrum revealed that when 7% of the BaSO4 nanoparticles are added to the polymer matrix, a peak at 1628 cm−<sup>1</sup> indicates that the BaSO4 nanoparticles are bound to the polymer matrix. The quinoid ring's (C=C) stretching modes were attributed to the peak at 1589 cm<sup>−</sup>1.

Figure 2f shows the spectra of 10% of the BaSO4 nanoparticles. It can be seen that due to the addition of 10% of the BaSO4 nanoparticles in the poly(*o*-anisidine), a sharp and comparatively deep peak appeared at 3511 cm<sup>−</sup>1, which showed the addition of 10% of BaSO4 NPs, which increased the features of the poly(*o*-anisidine) differently. The peak that formed at 1626 cm−<sup>1</sup> after the addition of 10% of the BaSO4 nanoparticles to the poly(*o*anisidine) matrix illustrated the binding of BaSO4 nanoparticles to the polymer matrix. The quinoid-ring stretching modes (C=C) were exhibited at 1589 cm−<sup>1</sup> [30].
