Mechanism of Interfacial Molecular Interactions Reveals the Intrinsic Factors for the Highly Enhanced Sensing Performance of Ag-Loaded Co3O4.

The noble metal-loaded strategy can effectively improve the gas-sensing performances of metal oxide sensors. However, the gas-solid interfacial interactions between noble metal-loaded sensing materials and gaseous species remain unclear, posing a significant challenge in correlating the physical and chemical processes during gas sensing. In this study, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and in situ Raman spectroscopy were conducted to collaboratively investigate the interfacial interactions involved in the ethanol gas-sensing processes over Co3O4 and Ag-loaded Co3O4 sensors. In situ DRIFTS revealed differences in the compositions and quantities of sensing reaction products, as well as in the adsorption-desorption interactions of surface species, among Co3O4 and Ag-loaded Co3O4 materials. In parallel, in situ Raman spectroscopy demonstrated that the ethanol atmosphere can modulate the electron scattering of Ag-loaded Co3O4 materials but not of raw Co3O4. In situ experimental results revealed the intrinsic reason for the highly enhanced sensing performances of the Ag-loaded Co3O4 sensors toward ethanol gas, including a decreased optimal working temperature (from 250 to 150 °C), an improved gas response level (from 24 to 257), and accelerated gas recovery dynamics. This work provides an effective platform to investigate the interfacial interactions of sensing processes at the molecular level and further advances the development of high-performance gas sensors.

Chemical Discrimination of Benzene Series and Molecular Recognition of the Sensing Process over Ti-Doped Co3O4.

This work achieved the chemical discrimination of benzene series (toluene, xylene isomers, and ethylbenzene gases) based on the Ti-doped Co3O4 sensor. Benzene series gases presented different gas-response features due to the differences in redox rate on the surface of the Ti-doped Co3O4 sensor, which created an opportunity to discriminate benzene series via the algorithm analysis. Excellent groupings were obtained via the principal component analysis. High prediction accuracies were acquired via k-nearest neighbors, linear discrimination analysis (LDA), and support vector machine classifiers. With the confusion matrix for the data set using the LDA classifier, the benzene series have been well classified with 100% accuracy. Furthermore, in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and density functional theory calculations were conducted to investigate the molecular gas-solid interfacial sensing mechanism. Ti-doped Co3O4 showed strong Lewis acid sites and adsorption capability toward reaction species, which benefited the toluene gas-sensing reaction and resulted in the highly boosted gas-sensing performance. Our research proposed a facile distinction methodology to recognize similar gases and provided new insights into the recognition of gas-solid interfacial sensing mechanisms.

Lattice expansion and oxygen vacancy of α-Fe2O3 during gas sensing.

Identifying the nature of gas-sensing material under the real-time operating condition is very critical for the research and development of gas sensors. In this work, we implement in situ Raman and XRD to investigate the gas-sensing nature of α-Fe2O3 sensing material, which derived from Fe-based metal-organic gel (MOG). The active mode of α-Fe2O3 as gas-sensing material originate from the thermally induced lattice expansion and the changes of surface oxygen vacancy of α-Fe2O3 could be reflected from the further monitored Raman scattering signals during acetone gas sensing. Meanwhile, the prepared α-Fe2O3 gas sensor exhibits excellent gas-sensing performance with high response value (Ra/Rg = 27), rapid response/recovery time (1 s/80 s) for 100 ppm acetone gas, and broad response range (5 - 900 ppm) at 183 °C. Strategies described herein could provide a promising approach to obtain gas-sensing materials with excellent performance and unveil the gas-sensing nature for other metal-oxide-based chemiresistors.

Metal-Organic Gel-Derived Multimetal Oxides as Effective Electrocatalysts for the Oxygen Evolution Reaction.

Exploring efficient and durable catalysts derived from earth-abundant and cost-effective materials is a highly desirable route to overcome the sluggish anodic oxygen evolution reaction (OER). A series of multinary metal-organic gels (MOGs) with various and alterable metal element compositions are prepared by straightforward mixing of metal ions with ligand 4,4',4''-[(1,3,5-triazine-2,4,6-triyl)tris(azanediyl)]tribenzoic acid (H3 TATAB) in solution at room temperature. Spinel-type metal oxides with excellent electrocatalytic OER performance were then obtained through calcination of the as-synthesized MOGs. In electrochemical testing, the trimetallic oxide CoFeNi-O-1 (derived from the MOG with a Co/Fe/Ni molar ratio of 5:1:4) exhibits remarkable catalytic activity with a low overpotential of 244 mV at a current density of 10 mA cm-2 and a small Tafel slope of 55.4 mV dec-1 in alkaline electrolyte, outperforming most recently reported electrocatalysts. This work not only provides a promising OER catalyst and enriches the application of MOGs in the catalytic field, but also offers a facile new route to acquiring multicomponent metal oxides with high electrocatalytic activity.

Cascade Reaction of Morita-Baylis-Hillman Acetates with 1,1-Enediamines or Heterocyclic Ketene Aminals: Synthesis of Highly Functionalized 2-Aminopyrroles.

A new strategy for the construction of two kinds of fully substituted pyrroles, including 2-aminopyrroles and bicyclic pyrroles from Morita-Baylis-Hillman (MBH) acetates with 1,1-enediamines (EDAMs), or heterocyclic ketene aminals (HKAs) via base-promoted tandem Michael addition, elimination, and aromatization sequence has been developed, affording the expected products in moderate to excellent yields. This methodology is a highly efficient, concise way to access 2-aminopyrroles or bicyclic pyrroles with diversity in molecular structures from accessible building blocks under moderate reaction conditions.