Effect of nAg concentration & reaction time on the performance of nAg/0.1%PVP composite based humidity sensor

Abstract

nAg/PVP composite is reported for the first time as humidity sensing material offering five orders of magnitude change in resistance. Other parameters are sensitivity of 0.066 (1/%RH), linear response (R2 = 0.99) over a wide humidity range [5–95 %relative humidity (%RH)] and fast response (8 s) and recovery (10 s) time. Three different proportions of silver salt (AgNO3) and reducing agent (Na3C6H5O7), keeping their ratio (0.05) same in 0.1% PVP (samples S1, S2 and S3) are used to study role of molar concentration on reaction time and metal nanocomposite formation. UV–Vis data reveals decrease in optical band gap and reaction time, and increase in full width at half maximum (FWHM) as a function of concentration. Increase in FWHM indicates polydispersity. Spherical nAg/PVP particles (5–20 nm for S1, 5–25 nm for S2) and spherical, triangular, hexagonal (10–35 nm for S3) are demonstrated by TEM. Coordination of nAg with C=O and tertiary nitrogen (i.e. [ ] Group) is shown by FTIR through decrease in intensities and shift in positions of corresponding peaks. When tested as resistive humidity sensors, S2 sample demonstrated best of the three. Humidity sensing mechanism is explained on the basis of complex impedance spectra at various values of RH and FTIR spectra in dry environment and high humidity environment.