Synthesis of Cu2O/CuO Nanocrystals and Their Application to H2S 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 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.

Visible light active heterostructured photocatalyst system based on CuO plate‐like particles and SnO2 nanofibers

“…where α is the absorption coefficient, hν is the photon energy, A is a constant, E g is the optical band gap of the material, and n = 2 for direct transitions. The (αhν) 2 ‐hν relation of CuO particles is shown as inset in Figure A, from which the direct band gap is found to be 1.8 eV, in close agreement with the literature …”

H2S Sensing Properties of a Diode-Type Device Using ZnO Nanorods Coupled with CuO Nanocrystals

“…The current in the forward and reverse directions significantly reduced after exposure to H2S. We have recently confirmed that CuO NCs-based sensors respond to H2S by an increase in electrical resistance due to reaction of adsorbed oxygen with H2S, representing a typical behavior of p-type semiconductors [3]. Thus, the observed increase in resistance for the present device is possibly due to surface reaction of adsorbed oxygen with H2S and the resulting annihilation of holes.…”

Nanostructured Cu2O Synthesized via Bipolar Electrochemistry

“…Both crystallite size and lattice constants are presented in Table 1. The particle size was calculated using Scherrer's equation [35] (Equation (2)), where D is the crystallite size in nm, λ is the Cu Kα radiation wavelength (1.5046 Å), K is the shape factor (0.9), β hkl is the full width at half maximum (FWHM) in radians, and θ is the scattering angle in radians. As seen in Table 1, crystallite size decreased as the applied potential in the BPE synthesis increased, with a minimum (14.5 nm) occurring at the maximum applied potential of 8.0 V. Similarly, by extending the reaction time from 1 to 3 h (sample synthesized at 4.5 V, red and blue patterns in Figure 1), crystallite size increased from 21.7 to 27.1 nm.…”