| In the chemical industrial production processes,a tiny leak of toxic gas may lead to catastrophic events and even casualties.The monitoring of NH3,one of the most widely used chemicals,has been a focal point due to its high toxicity.Exposure to trace amounts of NH3 can lead to irritation of the oral mucosa,burns on the skin and much more.The existing commercial NH3 gas sensors still have some problems such as low sensitivity and poor selectivity,so it is urgent to develop NH3 gas sensors with high sensitivity and fast-detecting.As a typical two-dimensional transition metal dichalcogenides(TMDs)nanomaterial,SnSe2 is of great interest for gas sensing applications owing to its distinctive semiconductor characteristics,a large number of active sites and high specific surface area.In this paper,the gas sensing performance of SnSe2 has been gradually improved through the combination of morphology modulation,heterojunction construction and noble metal modifications.The specific works are as follows:(1)Morphology modulation.SnSe2 was prepared by the conventional solvothermal method.The unique hollow rod and typical nanoflower three-dimensional hierarchical structure were obtained by adjusting the parameters such as the concentration of surfactant and the reaction time.The morphology evolution mechanism was analyzed by scanning electron microscopy(SEM)and X-ray diffraction(XRD)in detail.During the gas sensing detection,compared to SnSe2 nanoflower,the hollow rod hierarchical structure which is consist of super-thin layers with a thickness of 4 nm shows higher response in NH3(50 ppm)with a sensitivity of 3.65 and response/recovery time of 20/36 s,which could be attributed to its higher specific surface area and more active sites.(2)Heterojunction construction.SnSe2/SnO2 heterostructures were constructed by in situ thermal oxidation of SnSe2 materials in air with varying temperatures and times.High-resolution transmission electron microscopy(HRTEM)combined with X-ray photoelectron spectroscopy(XPS)confirmed the formation of the heterojunction.After being oxidized at 400? for 1 h,SnSe2/SnO2 possesses the highest sensitivity to NH3(50 ppm)of 10.38,which is 3 and 7 times higher than pure SnSe2 and SnO2,respectively,and a shorter response/recovery time of 15/17 s.The working temperature reduces from 140? to 100 ?.The reason for the improved gas sensing performance may be attributed to the enhanced surface chemisorbed oxygen and new electron transport channels with the formation of SnSe2/SnO2 heterojunction.(3)Gold nanoparticle modifications.Different contents of gold nanoparticles were used to modify the surface of SnSe2/SnO2 composite by ion sputtering.The SEM and element mapping prove the uniform dispersion of gold nanoparticles on SnSe2/SnO2 surface.When the sputtering time is 30 s,the Au-SnSe2/SnO2 gas sensor presents a sensitivity of 17.30 to 50 ppm NH3 and the selectivity is approximately 8-17 times higher than that of other gases.Additionally,the working temperature is further reduced to 80?.The significant improvement might come from the synergistic effect of the catalytic property of Au nanoparticles and the formation of SnSe2/SnO2 heterojunctions,Au/SnSe2 and Au/SnO2 Schottky junctions.The improved sensing performance demonstrates the great potential of Au-SnSe2/SnO2 for practical applications in NH3 gas sensors.In conclusion,the SnSe2 hollow rod structure composed of only 4 nm thick nanosheets was obtained by the solvothermal method for the first time,and the gas sensing performance was better than that of conventional nanoflowers.The gas sensing properties of SnSe2-based two-dimensional materials could be improved step by step through the construction of heterojunction and noble metal modification.The main innovation of this work lies in the acquisition of the unique hollow rod structure,and the effective modification through facile measures. |
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