Structural and Optical Properties of In-Situ Synthesis of PVA/CdS Nanocomposites via Chemical Precipitation-Casting Method

Abstract

Polyvinyl alcohol/cadmium sulfide (PVA/CdS) nanocomposite films were prepared through an in-situ ligand-exchange chemical precipitation-casting method to distinguish the effect of Cd2+ complexation from that of CdS nanoparticle formation on the structural and optical properties of PVA. Different volumes (0.25, 0.5, 1, and 2mL) of cadmium tetraammine complex solution were incorporated into PVA, followed by treatment with ammonium sulfide. The films were characterized using X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), and Ultraviolet-visible spectroscopy (UV-Vis). XRD patterns confirmed the formation of nanocrystalline CdS with a hexagonal wurtzite structure and an average crystallite size of approximately 53nm, while Cd2+ coordination reduced the semicrystalline order of PVA. FTIR spectra verified interaction between Cd2+ and the hydroxyl groups of PVA and revealed characteristic Cd-S vibration bands, confirming in situ CdS formation. Optical measurements showed that Cd2+ complexation produced only minor changes, whereas increasing CdS content markedly enhanced UV absorption and reduced transmittance to approximately 0.5% below 300 nm for the 2 mL sample. The absorption edge shifted from 5.1 to 3.8 eV, and the direct optical band gap decreased from 5.45 to 4.60 eV. These findings demonstrate that in situ CdS formation provides tunable optical and dielectric properties suitable for UV-shielding, photonic, and optoelectronic coating applications.