NO₂ Interactions with MoO₃ and CuO at Atmospherically Relevant Pressures

Abstract

NO x concentrations in some geographic regions are harmful to human health. Gas filters to trap NO x and other toxic chemicals contain metal oxides, including MoO 3 and CuO. These materials are also being investigated for NO x gas sensors. In a step to understand the fundamental adsorption mechanism in sensors and the effect on binding site availability in gas filters, ambient-pressure X-ray photoelectron spectroscopy (APXPS) was used to study the interaction of NO 2 with polycrystalline MoO 3 and CuO surfaces under pressures up to 0.01 Torr (14 parts per million volume (ppmv)). Density functional theory-based computational modeling was performed to reveal the mechanisms of NO 2 interactions with the MoO 3 (010) and CuO(111) surfaces to aid interpretation of the experimental results. With pressure dependence, NO 2 interacts with reduced Mo 5+ atoms generated by oxygen vacancies and abstracts hydrogen atoms from hydroxyl groups on MoO 3 without accumulating N-containing species on the surface; vacancy-induced electronic states in the band gap are also removed, hinting toward an increase in the resistivity of the material. N-containing species begin accumulating on the CuO surface at atmospherically relevant pressures of 140 ppbv. NO 2 only decomposes at oxygen vacancy sites of CuO. The nitrogen species leave the CuO surface upon evacuation, highlighting the importance of in situ surface characterization when studying gas sensing and adsorption mechanisms. These results imply that NO 2 removes hydroxyl and O vac binding sties on these materials when used in gas filtration and sensing applications. Furthermore, the results show the key role of O vac sites in the gas sensing mechanism of MoO 3 and highlight the potential of APXPS for further studies of gas sensors.

Microwave-Assisted Hydrothermal/Impregnation Synthesis of Cu2O-Decorated rGO/In2O3 Nanorices for Sensitive SO2 Gas Sensors

“…In the case of NO 2 , NO 2 usually had larger electronic affinity than that of SO 2 and could more easily adsorb as NO 2 – ions by taking electrons from sensing material at low temperatures (<150 °C) , but NO 2 – would desorb progressively at moderate and high temperatures (>150 °C), resulting in limited NO 2 response at 200 °C. Moreover, the addition of Cu 2 O would not enhance the adsorption of NO 2 – ions possibly due to the weak interaction between copper oxide and NO 2 , leading to low NO 2 response and good SO 2 selectivity against NO 2 .…”

Operando Investigation of WS2 Gas Sensors: Simultaneous Ambient Pressure X-ray Photoelectron Spectroscopy and Electrical Characterization in Unveiling Sensing Mechanisms during Toxic Gas Exposure

“…There are recent reports of ambient pressure X-ray photoelectron spectroscopy (APXPS) being used to study the sensing mechanism of metal oxide-based sensing devices, ,− while very few have used it to investigate TMDs. , However, most of these previous studies have encountered challenges in concurrently measuring the electrical response and electronic properties, thus limiting the potential of operando dynamic APXPS to in situ static measurements. We summarize the most significant reports in the following paragraphs.…”