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 Cu2O and CuO using a hot-soap method, and applied them to H2S sensing. Cu2O 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 Cu2O NCs having approximately 5 nm in crystallite size and 12 nm in colloidal size. The conversion of the Cu2O NCs to CuO NCs was undertaken by straightforward air oxidation at room temperature, as confirmed by XRD and UV-vis analyses. A thin film Cu2O NC sensor fabricated by spin coating showed responses to H2S in dilute concentrations (1–8 ppm) at 50–150 °C, but the stability was poor because of the formation of metallic Cu2S in a H2S atmosphere. We found that Pd loading improved the stability of the sensor response. The Pd-loaded Cu2O NC sensor exhibited reproducible responses to H2S at 200 °C. Based on the gas sensing mechanism, it is suggested that Pd loading facilitates the reaction of adsorbed oxygen with H2S and suppresses the irreversible formation of Cu2S.
Highlights
Copper oxides (Cu2 O or CuO) are among the important oxide materials because of their versatile functionalities
To produce high quality copper oxide nanocrystals, we focused on a hot-soap method in which metal precursors are dissolved in a high-boiling-point organic solvent with surface coordinating ligands to produce metal-ligand complexes, which are decomposed at elevated temperature [33,34]
Cu2 O nanocrystals (NCs) were synthesized by a heating-up method using oleylamine as a high-boiling-point solvent, which works as a coordinating ligand that suppresses the crystal growth
Summary
Copper oxides (Cu2 O or CuO) are among the important oxide materials because of their versatile functionalities. Major applications of copper oxides in chemistry include catalysis [1], solar cells [2,3], batteries [4,5,6], and, gas sensors [7,8,9]. For such applications, copper oxide nanostructures such as nanoparticles, nanocrystals, nanorods, nanocubes, nanosheets, etc. It has been reported that the reduction of the crystal size of oxides into a nanosize regime drastically improves the gas sensing properties [11,12]. The use of oxide nanoparticles and nanocrystals is one of the most efficient ways to develop high-performance gas sensors [15,16]
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