Transferring the wide band gap chitosan: POZ-based polymer blends to small optical energy band gap polymer composites through the inclusion of green synthesized Zn2+-PPL metal complex

Abstract

In this study, the solution of black tea leaves (BTL) was extracted and used as a green coordination approach to synthesize Zinc metal ions (Zn2+)- polyphenol (PPL) complexes (Zn2+-PPL complexes) with increased UV–vis absorption. The FTIR of the BTL and Zn2+-PPL complex confirms the formation of the Zn2+-PPL complex through the wide variation in the intensity of FTIR bands. XRD shows that the interaction between Zn2+ ions and PPL produced an amorphous Zn2+-PPL complex. The prepared Zn2+-PPL complex with chitosan: Poly(2-ethyl-2-oxazoline) (CS: POZ) polymer blends exhibit enhanced optical properties. The polymer composite (PC) films are synthesized using the solution casting process. FTIR, XRD, and UV–vis spectroscopy techniques approve the synthesis of PCs films with handled optical properties. The structural properties of CS: POZ: Zn2+-PPL complex composite films confirm the amorphous phase dominant. The optical properties of CS: POZ blend and CS: POZ: Zn2+-PPL complex films are determined using UV–Visible spectroscopy, including refractive index (n), absorption edge, dielectric loss (εi), dielectric constant (εr), and bandgap energy (Eg). The Eg is measured by examining the εi optical parameter, whereas the types of electronic transition in the films are detected using Tauc's technique. Significant optical parameters such as localized charge density (N/m*), high-frequency dielectric constant (ε∞), relaxation time (τ), optical mobility (μopt), optical resistivity (ρopt), and plasma angular frequency (ωp) of electrons are measured. The N/m* values are increased from 7.3 × 1055m3/kg to 35.3 × 1055m3/kg by adding Zn2+-complex concentration, resulting in a significant reduction (4.8 eV to 1.6 eV) in the Eg. The Wemple–DiDomenico single oscillator model was used to measure the oscillator dispersion energy (Ed) and average oscillator energy (Eo) property.