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This article presents an investigation of the sensing properties of chemiresistors based on Cu₂O/CuO core–shell nanowires containing p–p′ heterojunctions. The nanowires were synthesized by a conventional hydrothermal method and used for the detection of ethanol and nitrogen dioxide, reducing and oxidizing agents, respectively. To unravel the chemical processes connected with gas detection, an in situ approach was applied. This approach was based on near-ambient pressure X-ray photoelectron spectroscopy combined with simultaneous monitoring of sensor responses. The in situ measurements were performed during exposure to the analytes at a total pressure of 0.05–1.05 mbar and 450 K and were correlated with chemiresistor response measurements carried out at a standard pressure and under an ambient atmosphere. The study revealed that heterojunction treatment with ethanol vapors, accompanied by partial reduction of the nanowires, is the key step to obtaining chemiresistors with good sensing performance. While the untreated heterojunctions exhibited poor n-type sensing responses, the treated ones showed significantly improved p-type responses. The treated sensors were characterized by a stable baseline, high reversibility, detection limits estimated as 50 ppm for ethanol and 100 ppb for nitrogen dioxide, and with response times in tens of seconds. In all cases, we propose a band scheme of Cu₂O/CuO heterojunctions and a gas-sensing mechanism.
 

Nitrogen fixation in a simulated natural environment (i.e., near ambient pressure, room temperature, pure water and incident light) would provide a desirable approach to future nitrogen conversion. As N≡N triple bond has a thermodynamically high cleavage energy, nitrogen reduction under such mild conditions typically undergoes associative alternating or distal pathways rather than follows a dissociative mechanism. Here we report that surface plasmon can supply sufficient energy to activate N₂ through a dissociative mechanism in the presence of water and incident light, as evidenced by in-situ synchrotron radiation-based infrared spectroscopy and near ambient pressure X-ray photoelectron spectroscopy. Theoretical simulation indicates that the electric field enhanced by surface plasmon, together with plasmonic hot electrons and interfacial hybridization, may play a critical role in N≡N dissociation. Specifically, AuRu core-antenna nanostructures with broaden light adsorption cross section and active sites achieve an ammonia production rate of 101.4 μmol·g^-1·h^-1 without any sacrificial agent at room temperature and 2-atm pressure. This work highlights the significance of
surface plasmon to activation of inert molecules, serving as a promising platform for developing novel catalytic systems.

In this article, we present the results of an investigation into chemical processes which take place at the surface of SnO₂-based chemiresistor in various atmospheres (1 mbar of argon, 1 mbar of oxygen, 0.1 mbar of ethanol, 1 mbar of oxygen + 0.1 mbar of ethanol mixture) at common working temperatures (450 and 573 K). The key method for nanoscale analysis was the Near Ambient Pressure X-ray Photoelectron Spectroscopy. In parallel the resistance and DC-responses of SnO₂ layer were in-situ monitored providing information about macroscale processes during gas sensing. The change in the sensor resistance after exposure to the ethanol-containing atmospheres together with the disappearance of the band bending effect and observation of different carbonaceous groups including ethoxy groups and acetaldehyde molecules on the sensor surface in the XPS spectra supported the theory of chemical interaction of ethanol with the chemisorbed oxygen. The NAP-XPS spectra also showed that the nanostructured tin oxide is partially reduced even after being exposed to pure oxygen at 573 K. Exposing this surface to the mixture of O₂/EtOH did not significantly increase the surface reduction probably due to slow kinetics of the ethanol reduction process and fast kinetics of the oxygen re-oxidation process. However, it was demonstrated that the surface of sensor is slowly getting contaminated by carbon.