Compared with carbon dioxide, fluorinated greenhouse gases (F-type gases), such as hydrofluorocarbons (HFCs), perfluorocarbons (PFCs) and sulfur hexafluoride (SF6), have a stronger greenhouse effect, and their global warming potential can reach thousands or even tens of thousands of times that of carbon dioxide. Thus, the rapid online accurate detection of fluorinated greenhouse gases is highly desired and it can provide a basis for the evaluation of the greenhouse effect and a yardstick for the formulation of emission reduction measures. Unfortunately, these highly noble chemical gas molecules, especially at trace concentration levels, are extremely difficult to detect with conventional rapid screening methods. The use of the most common gas sensing techniques, semiconducting metal oxides, in the detection of HFCs and PFCs has not appeared within the scope of our knowledge. Herein, we report a novel N-doped tin oxide semiconducting metal oxide prepared by using a facile hydrothermal method. The experimental characterization results showed that the as-prepared materials were uniform spherical nanoparticles. The doping ratio of N-doped tin oxide was further optimized, and gas-sensing tests using these materials were carefully conducted. The results showed that the sensor had good detection performance for F-type gases, represented by SF6, C2F6 and C2H2F4, including low working temperature (200 °C), high selectivity, good repeatability, relatively high response, and low limit of detection (LOD ∼7 ppb). To the best of our knowledge, this is the first report on an F-type gas sensor based on semiconductor metal oxide. The ultra-fine particle size and uniform morphology of spherical particles, high concentration of oxygen vacancy defects and N doping contribute to the excellent performance of the sensor.
The capture and recovery of perfluorinated greenhouse gases CF 4 and C 2 F 6 from industrial exaust can not only mitigate global warming but also produce value-added products. Adsorption technology based on porous materials is promising for such purpose, while adsorbents with high capacity and selectivity are still lacking due to the chemical inertness of CF 4 and C 2 F 6 . Herein, three ultra-microporous Al-MOFs with multiple electropositive binding sites in 1D channel were synthesized and evaluated for CF 4 /C 2 F 6 adsorption. Among the synthesized Al-MOFs, Al-Fum displayed the best adsorption performance due to its desirable pore environment. It has a record-breaking C 2 F 6 adsorption capacity (3.30 mmol/g at 1 bar and 298 K) and C 2 F 6 /N 2 (10/90, v/v) selectivity (299.6 at 1 bar). In addition, it also displays excellent CF 4 adsorption performance, exceeding most of the reported adsorbents. Theoretical simulations demonstrate the high CF 4 /C 2 F 6 affinity towards Al-Fum is resulted from the multiple interactions of F atoms with H atoms of fumarate linkers and corner hydroxyl groups in frameworks. Moreover, dynamic column breakthrough tests confirmed the excellent separation performance of CF 4 /N 2 and C 2 F 6 /N 2 on Al-Fum with outstanding regenerability. Due to the green and energy-efficient synthesis method and outstanding adsorption performance, Al-Fum is considered to be an ideal porous material for CF 4 /C 2 F 6 capture under practical conditions.
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