Optical humidity sensor based on in situ and ex situ synthesized nAg/0.1%PVP composite coated on self supported PVP substrate

An optical based humidity sensor having linear response (R² = 0.99) over a wide range (06–94%RH) and high sensitivity is reported using nAg/0.1%PVP nanocomposite. Nanocomposite is prepared using in-situ and ex-situ approaches by chemical reduction method with silver salt (AgNO₃) as precursor, tri sodium citrate as reducing agent and PVP as capping agent. The nanocomposite is dip coated on hydrophilic PVP substrate of 80 µm thickness. The material is characterized by using UV–Vis, TEM and FTIR techniques. UV–Vis and TEM analysis are complementary to each other for exhibiting dependence of particle size on preparation approach − 10 nm (in-situ) to 40 nm (ex-situ). Humidity sensing mechanism is explained on the basis of FTIR spectra. Co-ordination between tertiary nitrogen ( ) and C=O group with nAg particles during nanocomposite formation is evidenced from low humidity FTIR. Breaking of these bonds is evidenced from high humidity FTIR. In/PVP/6-PVP sensors offer higher sensitivity (~ 0.68 ± 0.04 (1/% RH)) as compared to Ex/PVP/4:5-PVP sensors [~ 0.31 ± 0.04 (1/% RH)].