Sensors and Actuators B 208 (2015) 122–127 Contents lists available at ScienceDirect Sensors and Actuators B: Chemical jo u r nal homep age: www.elsevier.com/locate/snb Comparative gas sensor response of SnO 2 , SnO and Sn 3 O 4 nanobelts to NO 2 and potential interferents P.H. Suman a , A.A. Felix a,b , H.L. Tuller b , J.A. Varela a , M.O. Orlandi a,∗ a Department of Physical-Chemistry, São Paulo State University, Araraquara, SP 14800-060, Brazil b Department of Materials Science and Engineering, Massachusetts Institute of Technology, Cambridge, MA 02139, USA a r t i c l e i n f o Article history: Received 12 May 2014 Received in revised form 8 October 2014 Accepted 28 October 2014 Available online 3 November 2014 Keywords: Tin oxide SnO2 SnO Sn3O4 Nanobelts Gas sensor a b s t r a c t The gas sensor performance of single crystalline tin oxide nanobelts in different oxidation states (SnO 2 , SnO and Sn 3 O 4 ), synthesized by a carbothermal reduction method, is reported. The synthesized mate- rials were characterized by X-ray diffraction, electron microscopy and nitrogen adsorption/desorption experiments. Gas sensor measurements showed that the sensor based on Sn 3 O 4 nanobelts exhibits the highest sensor response to 50 ppm NO 2 at 200 ◦ C with an approximately 155-fold increase in electrical resistance. Moreover, at this operating temperature, Sn 3 O 4 nanobelts were found to display the highest selectivity to NO 2 relative to CO while SnO nanobelts exhibited the highest selectivity to NO 2 relative to H 2 and CH 4 . These results show that tin oxide semiconducting nanomaterials, with the unusual oxida- tion states of SnO and Sn 3 O 4 , show great promise as alternatives to SnO 2 for use in high performance gas sensor devices. © 2014 Elsevier B.V. All rights reserved. 1. Introduction The development of chemical sensors with improved sensitivity has been greatly accelerated in recent years with the introduction of semiconductor nanostructures with optimized morphologies [1]. Such devices show promise for detecting pollutant gases at ppm, and even ppb levels, with high sensitivity, selectivity and response speed [2], thereby potentially satisfying a wide range of require- ments in the safety, health, environment and energy conservation areas [3,4]. SnO 2 is a wide band gap n-type semiconductor [5,6], and among many metal oxides studied for gas sensors applica- tions [7–11], is one of most investigated materials [12]. Due to its excellent thermal and chemical stability at different atmospheres, engineered SnO 2 -based gas sensors have been used for the detec- tion of different gases [13–16] taking advantage of chemical and/or morphological modifications and optimization of operating condi- tions. While SnO 2 is the most studied and best known gas sensing material, the gas sensor properties of tin oxides with other oxy- gen stoichiometries (e.g., SnO and Sn 3 O 4 ) have very recently been reported [17–19]. This delay in examination of these other tin ∗ Corresponding author at: Department of Physical-Chemistry, São Paulo State University – UNESP, Rua Francisco Degni 55, Quitandinha, P.O. Box 355, Araraquara, SP CEP: 14800-060, Brazil. Tel.: +55 16 3301 9644; fax: +55 16 3322 0015. E-mail address: orlandi@iq.unesp.br (M.O. Orlandi). oxides is not surprising given the difficulty in synthesizing these phases and their thermal instability at high temperatures (above 400 ◦ C for SnO [20,21] and above 500 ◦ C for Sn 3 O 4 [22]). SnO is reported to exhibit p-type conductivity, an indirect band gap of approximately 0.7 eV and a direct band gap of 2.7 eV and is found to crystallize in orthorhombic or tetragonal structures [23,24]. The gas sensor properties of tetragonal single crystalline SnO micro-disks, synthesized by a carbothermal reduction method, were recently reported, for the first time, by the authors [17]. These materi- als were found to exhibit an approximately 1000-fold response to 100 ppm NO 2 . This so-called Giant Chemo-Resistance (GCR) response was attributed to the existence of a high density of active lone pair electrons on the exposed (0 0 1) planes of the SnO structure. Even less examined than SnO, Sn 3 O 4 is an inter- mediate tin-oxide phase lying between SnO and SnO 2 [25]. The authors also reported, for the first time, the gas sensor properties of single crystalline Sn 3 O 4 nanobelts, synthesized by a carbother- mal reduction method [18]. These nanostructures displayed n-type semiconductor behavior and good sensitivity to O 2 . Given the initial attractive sensor response reported for both SnO and Sn 3 O 4 , the gas sensor performance of these new alternative tin oxide based mate- rials merit closer examination, particularly in comparison to the response of the standard SnO 2 sensor material. In this work, a comparative study of the gas sensor properties of SnO 2 , SnO and Sn 3 O 4 nanobelts synthesized by carbothermal reduction is presented. As demonstrated below, both SnO and Sn 3 O 4 nanobelts exhibit higher sensitivity and selectivity relative http://dx.doi.org/10.1016/j.snb.2014.10.119 0925-4005/© 2014 Elsevier B.V. All rights reserved.