Synthesis of very-fine PbS nanoparticles dispersed homogeneously in MC matrix: effect of concentration on the structural and optical properties of host polymer

Abstract

Well-dispersed polymer nanocomposite films based on methylcellulose (MC) and lead sulfide (PbS) were prepared by two-step methods; the fine-PbS nanoparticles are first synthesized by in situ chemical reduction method while the films are made by solution casting technique. The effect of different concentration of PbS nanoparticles on the structural, optical properties, surface morphology, and chemical composition of the host polymer matrix were studied by x-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, UV–vis absorption spectroscopy, Scanning electron microscope (SEM), and Energy-dispersive x-ray spectroscopy (EDS) techniques. XRD studies reveal that the synthesized PbS nanoparticles are in cubic nanocrystalline phase with the very-fine grain size distribution between 2.23 to 4.46 nm. The homogeneous distribution of PbS in MC matrix was supported by both UV–vis spectra analysis and SEM images. The UV–vis measurement of nanocomposite films shows high absorption in the visible range, which correlate to the characteristics of the PbS nanoparticles. The effect of various concentration of PbS nanoparticle on the energy band gap of nanocomposite films has been analysed to understand the optimum conditions for the synthesis process. Significant reduction of the direct allowed energy band gap of the MC is observed upon increasing the PbS concentration, from 6.25 eV for pure MC to 1.92 eV for 0.3 M PbS concentration. A linear correlation in the refractive index at infinite frequency with PbS concentration revealed a well-distribution of the dopant throughout the host MC. The analysis of the refractive index was correlated with the results of SEM measurement.