Hierarchical SnS 2/SnO 2 nanoheterojunctions with increased active-sites and charge transfer for ultrasensitive NO 2 detection

Author(s): Juanyuan Hao ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵ , Dan Zhang ⁶ ^, ² ^, ³ ^, ⁷ , Quan Sun ¹ ^, ² ^, ³ ^, ⁴ , Shengliang Zheng ¹ ^, ² ^, ³ ^, ⁴ , Jianyong Sun ¹ ^, ² ^, ³ ^, ⁴ , You Wang ¹ ^, ² ^, ³ ^, ⁴ ^, ⁵

Publication date (Electronic): 2018

Journal: Nanoscale

Publisher: Royal Society of Chemistry (RSC)

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Abstract

An ultrasensitive NO ₂ sensing material was fabricated using ultrafine SnO ₂ nanoparticle-modified hierarchical SnS ₂ nanoflowers.

Abstract

SnS ₂ nanosheets with unique properties are excellent candidate materials for fabricating high-performance NO ₂ gas sensors. However, serious restacking and aggregation during sensor fabrication have greatly impacted the sensing response. In this study, flower-like hierarchical SnS ₂ was prepared by a simple microwave method and partially thermally oxidized to form hierarchical SnS ₂/SnO ₂ nanocomposites to further improve the sensing performance at low operating temperature. The fabricated SnS ₂/SnO ₂ sensor exhibited ultrahigh response (resistance ratio = 51.1) toward 1 ppm NO ₂ at 100 °C, roughly 10.2 times higher than that of pure SnS ₂ nanoflowers. The excellent and enhanced NO ₂ sensing performances of hierarchical SnS ₂/SnO ₂ nanocomposites were attributed to the novel hierarchical structure of SnS ₂ and the nanoheterojunction between SnS ₂ and the ultrafine SnO ₂ nanoparticles. The SnS ₂/SnO ₂ sensors also exhibited excellent selectivity and reliable repeatability. The simple fabrication of high performance sensing materials may facilitate the large-scale production of NO ₂ gas sensors.

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The ultimate aim of any detection method is to achieve such a level of sensitivity that individual quanta of a measured entity can be resolved. In the case of chemical sensors, the quantum is one atom or molecule. Such resolution has so far been beyond the reach of any detection technique, including solid-state gas sensors hailed for their exceptional sensitivity. The fundamental reason limiting the resolution of such sensors is fluctuations due to thermal motion of charges and defects, which lead to intrinsic noise exceeding the sought-after signal from individual molecules, usually by many orders of magnitude. Here, we show that micrometre-size sensors made from graphene are capable of detecting individual events when a gas molecule attaches to or detaches from graphene's surface. The adsorbed molecules change the local carrier concentration in graphene one by one electron, which leads to step-like changes in resistance. The achieved sensitivity is due to the fact that graphene is an exceptionally low-noise material electronically, which makes it a promising candidate not only for chemical detectors but also for other applications where local probes sensitive to external charge, magnetic field or mechanical strain are required.

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