Polymer-embedded stannic oxide nanoparticles as humidity sensors

Abstract

Stannic oxide (SnO 2) nanoparticles have been suspended in polyvinyl alcohol (PVA) matrix in different PVA:SnO 2 molar ratios ranging from 1:1 to 1:5 using simple chemical route. This suspension was deposited on ceramic substrate and upon drying was carefully detached from the substrate. SnO 2-embedded self-standing, transparent and flexible thin films were hence synthesized. Transmission electron microscopy (TEM) and X-ray diffraction (XRD) techniques show the rutile tetragonal structure of SnO 2 with particle size ~ 5 nm. UV–Visible spectroscopy demonstrates the band gap of 3.9 eV, which does not alter when embedded in polymer. Fourier transform infrared spectroscopy (FTIR) reveals that the properties of SnO 2 do not modify due to incorporation in the PVA matrix. The structures work as excellent humidity sensors at room temperature. For a critical PVA:SnO 2 molar ratio of 1:3, the resistance changes to five times of magnitude in 92% humidity within fraction of second when compared with resistance at 11% humidity. The sample regains its original resistance almost instantaneously after being removed from humid chamber. Nanodimensions of SnO 2 particles and percolation mechanism related to transport through polymer matrix and water molecule as a carrier has been used to understand the mechanism.