Green Chemistry Approach to Decline the Optical Band Gap of MC Polymer Using Hollyhock Natural Dye

The current study is about the role of hollyhock (HH) Dye on the band gap decline of methylcellulose (MC) biopolymer. The FTIR results revealed that HH dye is enriched with NH/OH functional groups which are crucial for interaction with MC functional groups. To keep the flexibility of the films and avoid fracture behaviors of the films after solvent evaporation glycerol as an efficient plasticizer was added to the MC-HH dye samples. The UV–vis. results of pure MC and MC: glycerol indicate that glycerol plasticizer has a negligible effect on the absorption manner of MC polymer. The addition of various amounts of HH dye greatly affected the optical behavior of the MC polymer. The absorption coefficient of the dye-doped films shifted to the visible and near-infrared region of UV–vis. The transmittance coefficient of the doped films declined compared to pure MC host materials. The optical refractive index shows the dispersion manner vs wavelength for the films inserted with HH dye. The band gap that separated the VB from the CB was determined using two approaches which are optical dielectric loss and the Taucs model. The most predominant transition type associated with electrons was identified based on some assumptions based on theoretical backgrounds. The W-D model was employed to determine additional optical parameters of the films. The Urbach energy for the films was determined and found to be lower in the doped samples compared to pure film.