CuWO4 with CuO and Cu(OH)2 Native Surface Layers for H2S Detection under in-Field Conditions

Abstract

The paper presents the possibility of detecting low H2S concentrations using CuWO4. The applicative challenge was to obtain sensitivity, selectivity, short response time, and full recovery at a low operating temperature under in-field atmosphere, which means variable relative humidity (%RH). Three different chemical synthesis routes were used for obtaining the samples labeled as: CuW1, CuW2, and CuW3. The materials have been fully characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). While CuWO4 is the common main phase with triclinic symmetry, different native layers of CuO and Cu(OH)2 have been identified on top of the surfaces. The differences induced into their structural, morphological, and surface chemistry revealed different degrees of surface hydroxylation. Knowing the poisonous effect of H2S, the sensing properties evaluation allowed the CuW2 selection based on its specific surface recovery upon gas exposure. Simultaneous electrical resistance and work function measurements confirmed the weak influence of moisture over the sensing properties of CuW2, due to the pronounced Cu(OH)2 native surface layer, as shown by XPS investigations. Moreover, the experimental results obtained at 150 °C highlight the linear sensor signal for CuW2 in the range of 1 to 10 ppm H2S concentrations and a pronounced selectivity towards CO, CH4, NH3, SO2, and NO2. Therefore, the applicative potential deserves to be noted. The study has been completed by a theoretical approach aiming to link the experimental findings with the CuW2 intrinsic properties.

CuxO Nanostructure-Based Gas Sensors for H2S Detection: An Overview

“…H 2 S is readily oxidized by atmospheric oxygen when irradiated with sunlight and can form SO 2 and H 2 SO 4 in the atmosphere, leading to acid rains [8]. Moreover, because H 2 S is heavier than air, it remains in the atmosphere for up to 18 h; thus, it can easily accumulate in areas such as mine tunnels, sewers, and manure tanks [9,10]. As stated by the United States Occupational Safety and Health Administration (US-OSHA, Washington, DC, USA), the concentration limit for exposure to H 2 S within 8 h is approximately 20 ppm [11].…”

Special Issue “Advanced Materials for Gas Sensors”

“…Another study [2] focused on H 2 S detection under the presence of humidity using CuWO 4 -based gas sensors. A comprehensive study was conducted in order to explain the major role played by the native Cu(OH) 2 surface layers within the sensing mechanism.…”