Design of NiCo2O4 porous nanosheets/α-MoO3 nanorods heterostructures for ppb-level ethanol detection

Facet-specific NiCo2O4/Fe2O3 p-n heterojunction with promising triethylamine sensing properties

Semiconductor gas sensing materials with specific crystal facets exposure have attracted researchers' attention recently. However, related research mainly focuses on single metal oxide semiconductor. The research on crystal facets designing of semiconductor p-n heterojunction is still highly challenging. Herein, based on NiCo2O4 octahedral nanocrystals with high-energy {111} crystal facets as substrate, Fe2O3 nanorods with {001} crystal facets were decorated to obtain a facet-specific NiCo2O4/Fe2O3 p-n heterojunction. The p-n heterojunction showed promising triethylamine sensing properties with a high response of 70 (Ra/Rg, 100 ppm) at 300 °C, which was about 57 and 10 times higher than that of pristine NiCo2O4 and Fe2O3, respectively. Theoretical calculation suggested that the electronic coupling effect formed by d-orbitals of Co-Fe in heterojunction strengthened the influence on the orbitals of N site in triethylamine, which improved the triethylamine adsorption and interface charge transfer. The results indicate that crystal facets designing of NiCo2O4 and Fe2O3 can achieve synergistic optimization of surface/interface characteristics of p-n heterojunction, thereby achieving a comprehensive improvement in gas sensing performance. This study not only provides a high performance triethylamine sensing material, but also greatly enriches the gas sensing mechanism of p-n heterojunction at the atomic and electronic levels.

Designing a TiO2-MoO3-BMIMBr nanocomposite by a solvohydrothermal method using an ionic liquid aqueous mixture: an ultra high sensitive acetaminophen sensor

This study shows a simplistic, efficient procedure to synthesize TiO₂-MoO₃-BMIMBr nanocomposites. Powder X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoelectron spectroscopy have all been used to completely analyse the materials. The detection of acetaminophen (AC) has been examined at a modified glassy carbon electrode with TiO₂-MoO₃-BMIMBr nanocomposites. Moreover, the electrochemical behavior of the nanocomposite modified electrode has been studied by cyclic voltammetry (CV), differential pulse voltammetry (DPV), chronoamperometry and electrochemical impedance spectroscopy (EIS). The linear response of AC was observed in the range 8.26-124.03 nM. The sensitivity and detection limits (S/N = 3) were found to be 1.16 μA L mol^-1 cm^-2 and 11.54 nM by CV and 24 μA L mol^-1 cm^-2 and 8.16 nM by DPV respectively.

Advanced Strategies to Improve Performances of Molybdenum-Based Gas Sensors

Molybdenum-based materials have been intensively investigated for high-performance gas sensor applications. Particularly, molybdenum oxides and dichalcogenides nanostructures have been widely examined due to their tunable structural and physicochemical properties that meet sensor requirements. These materials have good durability, are naturally abundant, low cost, and have facile preparation, allowing scalable fabrication to fulfill the growing demand of susceptible sensor devices. Significant advances have been made in recent decades to design and fabricate various molybdenum oxides- and dichalcogenides-based sensing materials, though it is still challenging to achieve high performances. Therefore, many experimental and theoretical investigations have been devoted to exploring suitable approaches which can significantly enhance their gas sensing properties. This review comprehensively examines recent advanced strategies to improve the nanostructured molybdenum-based material performance for detecting harmful pollutants, dangerous gases, or even exhaled breath monitoring. The summary and future challenges to advance their gas sensing performances will also be presented.

Volatile Organic Compounds Gas Sensors Based on Molybdenum Oxides: A Mini Review

As a typical n-type semiconductor, MoO₃ has been widely applied in the gas-detection field due to its competitive physicochemical properties and ecofriendly characteristics. Volatile organic compounds (VOCs) are harmful to the atmospheric environment and human life, so it is necessary to quickly identify the presence of VOCs in the air. This review briefly introduced the application progress of an MoO₃-based sensor in VOCs detection. We mainly emphasized the optimization strategies of a high performance MoO₃, which consists of morphology-controlled synthesis and electronic properties functional modification. Besides the general synthesis methods, its gas-sensing properties and mechanism were briefly discussed. In conclusion, the application status of MoO₃ in gas-sensing and the challenges still to be solved were summarized.

Sr-Doped Cubic In2O3/Rhombohedral In2O3 Homojunction Nanowires for Highly Sensitive and Selective Breath Ethanol Sensing: Experiment and DFT Simulation Studies

In recent years, it is urgent and challenging to fabricate highly sensitive and selective gas sensors for breath analyses. In this work, Sr-doped cubic In₂O₃/rhombohedral In₂O₃ homojunction nanowires (NWs) are synthesized by one-step electrospun technology. The Sr doping alters the cubic phase of pure In₂O₃ into the rhombohedral phase, which is verified by the high-resolution transmittance electron microscopy, X-ray diffraction, and Raman spectroscopy, and is attributable to the low cohesive energy as calculated by the density functional theory (DFT). As a proof-of-concept of fatty liver biomarker sensing, ethanol sensors are fabricated using the electrospun In₂O₃ NWs. The results show that 8 wt % Sr-doped In₂O₃ shows the highest ethanol sensing performance with a high response of 21-1 ppm, a high selectivity over other interfering gases such as methanol, acetone, formaldehyde, toluene, xylene, and benzene, a high stability measured in 6 weeks, and also a high resistance to high humidity of 80%. The outstanding ethanol sensing performance is attributable to the enhanced ethanol adsorption by Sr doping as calculated by DFT, the stable rhombohedral phase and the preferred (104) facet exposure, and the formed homojunctions favoring the electron transfer. All these results show the effective structural modification of In₂O₃ by Sr doping, and also the great potency of the homojunction Sr-doped In₂O₃ NWs for highly sensitive, selective, and stable breath ethanol sensing.