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<p>In this study, an environmentally friendly approach was developed for synthesizing Fe(III)–polyphenol complexes using Camellia sinensis (black tea) extract, which served as both a chelating and stabilizing agent. The resulting Fe(III)–complexes were incorporated into methyl cellulose (MC) to produce flexible MC–Fe composite films by a simple casting method. FTIR spectra confirmed the coordination of Fe<sup>3</sup>⁺ ions with hydroxyl and carbonyl groups from both polyphenolic ligands and MC, as evidenced by red shifts of the O–H stretching band from 3452 to 3443&#xa0;cm<sup>−1</sup> and of the C=O stretching band from 1644 to 1600&#xa0;cm<sup>−1</sup>. UV–Vis spectroscopy revealed a strong redshift in absorption with increasing Fe–complex content, and the optical band gap decreased markedly from 6.15&#xa0;eV (pure MC) to 1.69&#xa0;eV (MCFe3). The refractive index rose from 1.17 to 1.41, and the high-frequency dielectric constant increased from 1.35 to 3.27, indicating enhanced electronic polarizability and density of localized states. These quantitative changes are consistent with Fe–ligand coordination and band-gap narrowing rather than simple physical mixing. The nonlinear optical susceptibility (χ<sup>3</sup>) and nonlinear refractive index (<i>n₂</i>) increased proportionally with Fe-complex concentration, confirming improved light–matter interaction. Overall, the results demonstrate that incorporating green-synthesized Fe(III)–polyphenol complexes effectively tunes the optical constants of MC, offering a sustainable route to biopolymer composites for potential low-energy band-gap device applications.</p>

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Sustainable synthesis of iron (III) complex for modulating the optical band gap of methyl cellulose biopolymer films

  • 期刊论文

  • 发表日期：

    2026年5月23日

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  • Dana S. Muhammad,
  • Dara M. Aziz,
  • Dana A. Shukur,
  • Fuad H. Radha,
  • Peshawa O. Hama,
  • Omed Gh. Abdullah,
  • Shujahadeen B. Aziz

摘要

In this study, an environmentally friendly approach was developed for synthesizing Fe(III)–polyphenol complexes using Camellia sinensis (black tea) extract, which served as both a chelating and stabilizing agent. The resulting Fe(III)–complexes were incorporated into methyl cellulose (MC) to produce flexible MC–Fe composite films by a simple casting method. FTIR spectra confirmed the coordination of Fe3⁺ ions with hydroxyl and carbonyl groups from both polyphenolic ligands and MC, as evidenced by red shifts of the O–H stretching band from 3452 to 3443 cm−1 and of the C=O stretching band from 1644 to 1600 cm−1. UV–Vis spectroscopy revealed a strong redshift in absorption with increasing Fe–complex content, and the optical band gap decreased markedly from 6.15 eV (pure MC) to 1.69 eV (MCFe3). The refractive index rose from 1.17 to 1.41, and the high-frequency dielectric constant increased from 1.35 to 3.27, indicating enhanced electronic polarizability and density of localized states. These quantitative changes are consistent with Fe–ligand coordination and band-gap narrowing rather than simple physical mixing. The nonlinear optical susceptibility (χ3) and nonlinear refractive index (n₂) increased proportionally with Fe-complex concentration, confirming improved light–matter interaction. Overall, the results demonstrate that incorporating green-synthesized Fe(III)–polyphenol complexes effectively tunes the optical constants of MC, offering a sustainable route to biopolymer composites for potential low-energy band-gap device applications.