Optical characterization of chitosan/poly(vinyl alcohol) hybrid hydrogels and the effect of genipin crosslinking and multiwalled carbon nanotube fillers

This study investigates the optical properties of chitosan/poly(vinyl alcohol) (CS/PVA) hybrid hydrogels, focusing on the effects of genipin (GEN) crosslinking and multiwalled carbon nanotubes (MWCNTs) incorporation. CS/PVA hydrogels, CS/PVA/MWCNTs nanocomposites, and their genipin-crosslinked versions (CS/PVA/GEN and CS/PVA/MWCNTs/GEN) were prepared via solution casting, alongside pure CS and PVA hydrogel membranes as controls. The hydrogels were characterized using UV–Vis–NIR spectroscopy, FT-IR spectroscopy, AFM, and XRD to evaluate their refractive index, optical behavior, molecular structure, surface properties, and crystallinity. Adding a small amount of MWCNTs (0.01% w/v) significantly reduced light transmittance across the UV–Vis–NIR range, while GEN crosslinking nearly eliminated UV transmission. Furthermore, GEN induced localized states within the bandgap energy, reducing the edge band ( E e ), optical bandgap ( E g ) and Urbach energy ( E U ), while enhancing optical conductivity ( σ o p t ) and dielectric properties ( ɛ ′ , ɛ ′ ′ ). These findings demonstrate that GEN and MWCNTs effectively enhance the optical and dielectric properties of CS/PVA hydrogels, making them promising candidates for photonics, optical sensing, and optoelectronic applications. • CS/PVA hydrogels with genipin and MWCNTs show tunable optical behavior for photonic applications. • MWCNTs increase crystallinity, while genipin reduces it by limiting chain folding. • CS/PVA hydrogels crosslinked with genipin achieve nearly 0% UV transmission. • Genipin crosslinking reduces bandgap energy by increasing localized states. • MWCNTs improve dielectric storage ( ɛ ′ ), while genipin enhance dielectric loss ( ɛ ′ ′ ).