Effect of amorphous silica from rice husk on the structure and optical properties of PVA

Combining amorphous silica (SiO2) particles into polyvinyl alcohol (PVA) results in a composite with unique optical characteristics. This study investigates the effects of SiO2 particles derived from rice husks on PVÁs structure and optical properties. Samples were prepared by blending PVA with SiO2 particles and casting the mixture into composite sheets. FTIR analysis exposed a reduction in hydroxyl groups (–OH) as the SiO2 content increased, designating stronger interactions among the –OH group and the particles through hydrogen bonds. XRD analysis showed increased molecular disorder and amorphousness with higher SiO2 concentrations. These structural changes altered optical properties, increasing the absorption spectrum as SiO2 concentration rose. The direct transition band gap reduced from 5.42 to 5.13 eV, and the indirect transition band gap dropped from 4.65 to 3.52 eV for pure PVA and the composite with 10% SiO2 content, respectively. Urbach energy enlarged from 0.52 to 1.41 eV, and the refractive index rose from 1.93 to 1.98.