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Near-Infrared Tunable Laser Absorption Spectroscopic Acetylene Sensor System Using a Novel Three Mirror-Based, Dense Pattern Gas Cell
摘要： By contrast with the widely reported traditional two mirror‐based Herriott cell, a three mirror‐based dense pattern gas cell was proposed, of which the modeling and design were proven to be effective through a comparison between the simulated spot pattern and effective path length and those of the experimental results. A mechanical structure was designed to adjust the position/angle of the three mirrors for aligning the optical path. The experimentally measured reflection number was 60, resulting in an optical path length of ~11 m, which agrees well with the theoretical value of 10.95 m. Combined with a near‐infrared laser with a center wavenumber located at an acetylene (C2H2) absorption line of 6521.2 cm?1, a C2H2 sensor system was established to verify the feasibility of the three mirror‐based gas cell. Assisted by a data acquisition (DAQ) card, a LabVIEW platform was developed to generate the drive signal of the laser and acquire the second harmonic (2f) signal from the output of the detector. Through Allan variance analysis, the limit of detection (LoD) of the sensor system is 4.36 ppm at an average time of 0.5 s; as the average time exceeds 10 s, the LoD is <1 ppm. The proposed model and design of the three mirror‐based gas cell can be used to realize similar gas cells with different absorption path lengths for gas detection based on infrared absorption spectroscopy.
关键词： laser absorption spectroscopy,multipass gas cell,acetylene detection,wavelength modulation spectroscopy
更新于2025-09-16 10:30:52
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Dumbbell to Core–Shell Structure Transformation of Ni–Au Nanoparticle Driven by External Stimuli
摘要： Conversion of CO2 gas to CO fuels is one of the most promising solutions for the increasing threat of global warming and energy crisis. The efficient catalyst Ni–Au dumbbell converting CO2 into CO at elevated temperatures has high CO product selectivity; however, the accompanied atomic diffusion and subsequent surface reconstruction affect the catalytic efficiency of chemical reaction. Atomic scale characterization of structural evolution of the catalyst, which is essential to correlate the functional mechanism to active catalyst surfaces, is yet to be studied. Here, in situ transmission electron microscopy experiments and atomistic simulations are performed to characterize the structural evolution of Ni–Au dumbbell nanoparticles under two different external stimuli. In the condition of high temperature and vacuum, the Ni–Au nanostructure reveals a clear shape reconstruction from the initial dumbbell to core–shell-like, which is induced by capillary force to minimize free surface energy of the system. The shape transformation involves two stages of processes, initial fast Au diffusion followed by slow source-controlled diffusion. At ambient temperature, the combination of CO2 and electron flux surprisingly induces analogous structural transformation of Ni–Au nanostructure, where the associated chemical reaction and CO absorption stimulate the Au migration on Ni surface. Such surface reconstruction can be widely present in catalytic reactions in different environmental conditions, and the results herein demonstrate the detailed processes of Ni–Au structure evolution, which provide important insights for understanding the catalyst performance.
关键词： core–shell,in situ TEM,catalyst,Ni–Au,gas cell
更新于2025-09-04 15:30:14