Effect of adding methyl orange/silver (MO-Ag) nanoparticles on the optical and structural properties of polyvinyl alcohol (PVA)

This study analyses the effect of adding an equal amount of methyl orange/silver nanoparticles (MO-Ag) on the optical and structural properties of polyvinyl alcohol (PVA). The X-ray diffraction reveals nearly the same behavior of all spectra with a main broad peak centered at 2 theta = 23.43 degrees, which is due to the semi-crystalline nature of the PVA/(MO-Ag) nanocomposite samples related to the (110) plane. FT-IR spectroscopy showed increased intensity of some bands, indicating a strong interaction between the functional groups in PVA, MO, and Ag nanoparticles. Raman spectroscopy provides information about the molecular structure and vibrations, which is important for understanding properties of the samples. UV-visible absorption spectra showed that the MO-Ag doped PVA films had higher absorbance and a red-shift in absorption edge, indicating a decreased optical band gap. The Tauc relation was used to estimate the direct and indirect band gaps, which decreased with increasing MO-Ag content, showing the band gap was reduced upon doping. As Ag content increased, optical conductivity also increased due to charge transfer between PVA and MO-Ag molecules. The real and imaginary parts of the optical dielectric function showed a sharp absorption band that red-shifted and increased in intensity with higher MO-Ag content. UV-Vis further showed molecular structure changes leading to increased refractive index n with increasing MO-Ag doping. Moreover, doping PVA films with MO-Ag decreased the optical band gap and increased absorbance, optical conductivity, and refractive index, modifying the optical and structural properties.