Optical and Structural Modification of Polyvinyl Alcohol Induced by MoS₂ and WS₂ Nanomaterial Incorporation

Abstract

As a semi-crystalline polymer, polyvinyl alcohol (PVA) has been extensively used in optical/opto-electronic applications owing to its excellent transparency, chemical stability, and processability.1–3 However, the large optical band gap of PVA limits efficient light absorption in the visible region. The optical, structural, and morphological properties of PVA thin films have been systematically tuned by embedding semiconductor MoS2/WS2 and its hybrid forms via solution casting to obtain uniform ≈ 150 nm-thick films. X-ray diffraction studies indicated that the hexagonal crystalline nature of MoS2 and WS2 was retained in the PVA matrix and that the hybrid nanocomposite exhibited improved ordering. Field-emission scanning microscopy revealed that well-dispersed GNPs and MWCNTs are induced by strong interactions with the nanomaterials, as evidenced by rough surfaces and larger grain sizes on the PVA film with increasing amounts of nanomaterial, especially dual-filler. Optical studies using UV-Vis spectroscopy showed a substantial increase in absorption and the absorption coefficient, and a decrease in transmittance of the nanocomposite films. The optical band gap as calculated from Tauc plots corresponding to direct transitions went down monotonically from 4.1 eV for neat PVA to 3.8 eV for PVA/MoS2, 3.68 eV for PVA/WS2, and finally 3.5 eV for the PVA/MoS2/WS2 hybrid, reflecting the emergence of localized electronic states and synergy between the two nano-materials.