Synthesis of Cu 2 O/CuO nanocrystals and their application to H 2 S sensing

Abstract

Semiconducting metal oxide nanocrystals are an important class of materials that have versatile applications because of their useful properties and high stability. Here, we developed a simple route to synthesize nanocrystals (NCs) of copper oxides such as Cu 2 O and CuO using a hot-soap method, and applied them to H 2 S sensing. Cu 2 O NCs were synthesized by simply heating a copper precursor in oleylamine in the presence of diol at 160 ◦ C under an Ar flow. X-ray diffractometry (XRD), dynamic light scattering (DLS), and transmission electron microscopy (TEM) results indicated the formation of monodispersed Cu 2 O NCs having approximately 5 nm in crystallite size and 12 nm in colloidal size. The conversion of the Cu 2 O NCs to CuO NCs was undertaken by straightforward air oxidation at room temperature, as confirmed by XRD and UV-vis analyses. A thin film Cu 2 O NC sensor fabricated by spin coating showed responses to H 2 S in dilute concentrations (1–8 ppm) at 50–150 ◦ C, but the stability was poor because of the formation of metallic Cu 2 S in a H 2 S atmosphere. We found that Pd loading improved the stability of the sensor response. The Pd-loaded Cu 2 O NC sensor exhibited reproducible responses to H 2 S at 200 ◦ C. Based on the gas sensing mechanism, it is suggested that Pd loading facilitates the reaction of adsorbed oxygen with H 2 S and suppresses the irreversible formation of Cu 2 S.