Phosphate-Functionalized Chitosan/Ag Nanocomposites: Synergistic Optical Tunability and Enhanced Antimicrobial Activity

Phosphate chitosan and silver-doped (0.0–0.5%) phosphate chitosan nanocomposites were successfully synthesized via a sol–gel and solution-casting route to explore their structural, optical, and antimicrobial properties for optoelectronic and biomedical applications. FTIR analysis confirmed successful phosphorylation of chitosan and the incorporation of Ag nanoparticles through characteristic shifts in functional group vibrations. XRD patterns revealed a predominantly amorphous structure with broad peaks at 2θ ≈ 10.7° and 21.9°, while the absence of distinct Ag reflections indicated uniform dispersion of nanosized silver within the polymer matrix. SEM images displayed homogeneous surface morphology, further verifying effective doping and interaction between phosphate groups and Ag nanoparticles. UV–Vis spectroscopy demonstrated strong absorption in the UV region, and the calculated optical band gap values decreased slightly with increasing Ag content, suggesting enhanced electronic transitions and potential photoactivity. Antimicrobial assessment showed significant improvement in bacterial inhibition with Ag incorporation, confirming the synergistic effect of phosphate functionality and silver nanoparticles. The results highlight that phosphate chitosan–Ag nanocomposites combine structural flexibility, optical tunability, and bioactivity, making them promising candidates for multifunctional materials in optoelectronic devices, coatings, and biomedical systems.