Synthesis and characterization of silver–zinc oxide nanocomposites for humidity sensing

Abstract

This study synthesizes hybrid of silver (Ag) and zinc oxide (ZnO) from their bulk salt to form Ag–ZnO nanocomposites for application as a humidity sensor. The Ag and ZnO nanoparticles are synthesized using chemical reduction method, followed by co‐mixing and calcination to yield the nanocomposite. The synthesized nanoparticles are characterized using SEM, TEM, XRD, and EDX to establish their morphological, structural and elemental composition. Sensing measurements were performed in a controlled proton‐type humidity chamber using saturated solutions of KOH and K 2 SO 4 as dehumidifier and humidifier respectively. We sintered and subjected to direct current resistance (Ω) and sensitivity measurement as a function of relative humidity (RH). Crystallinity pattern showed reflections from face centered cubic Ag and ZnO nanoparticles. The XRD peaks of the Ag–ZnO were attributed to the heterostructure and it agrees with SEM images showing Ag–ZnO isotopic and Ag–ZnO anisotropic under varying conditions. The study finds that sensitivity increases with relative humidity at a 10%RH interval. Ag‐ZnO sensor exhibits a higher sensitivity of 687Hz/%RH in comparison to ZnO nanosensor which has a maximum sensitivity of 324Hz/%RH. The increase in sensitvity of Ag‐ZnO can be attributed to the high surface area of absorption present in porous ZnO shell and the electrical capability of Ag core in transducing the water vapour absorbed into electrical signals. The Ag‐ZnO and ZnO sensor exhibits a fast response and recovery time of 54s and 73s, low hysteresis of 3.76%RH and 5.2%RH respectively. The result of the variation in resistance against relative humidity (RH) reveals a greater significant factor (SF) of 5.25 for Ag‐ZnO and 1,88 for ZnO. The hybrid of Ag‐ZnO nanocomposites proves to be a better humidity sensor and can serve as replacement for many other materials for humidity sensor currently in circulation in the market.