Green-synthesized NiO-doped chitosan nanocomposite films with tunable optical and dielectric properties for sustainable energy and optoelectronic applications

This work reports a sustainable approach for developing flexible chitosan (CS)–nickel oxide (NiO) nanocomposite films for energy and optoelectronic applications. The novelty lies in the use of a plant-mediated green synthesis to produce phase-pure, faceted NiO nanoparticles and their controlled incorporation into a biodegradable chitosan matrix at low loadings (4, 8, and 12 wt%) via solution casting. Structural and spectroscopic techniques (XRD, FESEM–EDS, FTIR, and UV–visible spectroscopy) confirm strong interfacial interactions between NiO and CS functional groups (–OH, –NH₂, C–O), leading to disrupted polymer chain ordering and uniform nanoparticle dispersion without loss of film flexibility. Optically, NiO incorporation induces a pronounced red shift of the absorption edge, increased Urbach energy, and a systematic reduction in optical bandgap, accompanied by enhanced refractive index, dielectric constant, and optical conductivity, indicating improved charge transport and photon–electron coupling. From a societal perspective, the use of renewable biopolymers and environmentally benign synthesis routes addresses the demand for low-cost, non-toxic, and energy-efficient materials. These results demonstrate a scalable and eco-friendly platform for flexible optoelectronic devices, UV-shielding coatings, and solar energy harvesting systems.