*3.2. UV-Visible Spectroscopy*

The POA/BaSO4 nanocomposite was characterized to understand the absorption behavior of the POA/BaSO4 nanocomposite. To analyze the absorption behavior of composite materials, the materials were scanned in the wavelength range of 200–800 nm at the rate of 400 nm/min under a UV-visible spectrophotometer. The spectrophotometer was furnished with UV Winlab programming to record and analyze the information. A blank reference was used to conduct baseline correction on the spectrophotometer. The absorption spectra of the pure POA and POA/BaSO4 nanocomposites are shown in Figure 3. The significant absorption peak appeared at 273 nm, related to π-π\* aromatic C=C band transitions and n-π\* aromatic C=N band transitions. The *o*-anisidine monomer-to-monomer attachment was responsible for conjugation and polarity. The interaction of the BaSO4 nanofiller and POA matrix resulted in a change in the absorption behavior of the composites. The absorption behavior of the composites was significantly different than that of the pure polymer, as shown in Figure 3a. There was a notable shifting of the absorption peak towards higher wavelengths, resulting in the marvel of the red shift at ~520 nm. Moreover, the absorption intensity of the composites was much higher than that of the pure polymer, indicating the role of barium-sulfate filler in improving the absorption properties of the POA/BaSO4 composites. The other composites also showed similar absorption behaviors, as depicted in Figure 3b–f. The absorption intensity was enhanced with the increase in the barium-sulfate-load percentage in the composites [17].
