Influence of Pb+2-Thiourea complex concentration on the structural, optical, thermal and electrical properties of PbS/PVP-PVA nanocomposite films

Deposition of nanocomposite films of lead sulphide (PbS) nanoparticles in blend (1: 1) of polyvinyl pyrrolidone (PVP) and Polyvinyl alcohol (PVA) by dip-coating from a precursor aqua-methanolic solution containing of Pb+2-TU complex (LTUC) is reported. To obtain nanocomposite films, solid precursor films are heated at about 110 degrees C in air for 10 mins to convert the LTUC in to PbS nanoparticles in PVP-PVA by in-situ thermolysis. PbS/PVP-PVA films with different loading of PbS was prepared by varying the concentration of LTUC in precursor solutions. The effect of LTUC on themicrostructural, optical, thermal and electrical properties of the films was investigated. The X-ray diffraction of films confirms the presence of PbS nanoparticles in PVP-PVA matrix. The band gaps of PbS/PVP-PVA films varied from 1.8 to 0.8 eVas the concentration of LTUC varied from 0.0125 to 0.1M due to formation of PbS nanoparticles. Transmission electron microscopy (TEM) shows that PbS nanoparticles are spherical with maximum diameter of 18 to 22 nm. The Fourier transformed infrared (FTIR) spectroscopy and X-Ray photoelectron spectroscopy (XPS) indicate the formation of hydrogen bond between -O-H group of PVA and -C = O group of PVP. However, PbS nanoparticles does not interact with either of the polymers. Thermogravimetric analysis (TGA) reveals that there was an improvement in thermal stability of PbS/PVP-PVA nanocomposites as compared to PVP-PVA blend. The dc conductivities of PVP-PVA and PbS/ PVP-PVA(0.1 M) NC were found to be 3.2 x 10(-6) S cm(-1) and 14.2 x 10(-6) S cm(-1), respectively.