Nanostructured Zinc Oxide Gas Sensors

Abstract

Metal oxide semiconductors are used as gas sensors in a variety of spaceflight applications to detect the presence of various gases. Here, we report the synthesis, characterization, and sensor development of nanostructured zinc oxide (ZnO) semiconductors for gas sensing of CO₂ and O₂. Using a general hydrothermal reaction between zinc precursor salts (zinc nitrate, sulfate, acetate, and chloride) and a base (hexamethylenetetramine) at concentrations between 0.05 and 1.0 M, we show that nanostructured zinc oxide crystals can be grown directly onto glass substrates. The nanostructures generated vary significantly in size, morphology, and surface area depending on reagent and concentrations used, including nanorods (zinc acetate), nano-honeycombs (zinc nitrate), and nanoplates (zinc sulfate). We also report improvements to the adhesion and film homogeneity via spray pyrolysis, wherein substrates are pre-treated with an aerosolized spray of zinc salt precursors at high temperature. Lastly, we present the development of ZnO-coated substrates as CO₂ sensors via preliminary resistance measurements in air and under CO₂.