Tin Dioxide Functionalized Single-Walled Carbon Nanotube (SnO₂/SWNT)-Based Ammonia Gas Sensors and Their Sensing Mechanism

Abstract

Tin oxide functionalized single-walled carbon nanotubes (SWNTs) were synthesized on prefabricated microelectrodes by an electrochemical process. The shape, morphology, valence state and crystal structure of tin oxide were controlled by varying the deposition potential (E), charge density (C), and subsequent calcining temperature (T) and their structure-related sensing performance toward ammonia (NH 3 ) gas was characterized at 25 • C. Optimal sensing performance was obtained under the conditions of E = −0.625 V, C = 0.125 C/cm 2 , T = 400 • C. The underlying NH 3 sensing mechanisms of the SnO 2 /SWNTs hybrid nanostructures were studied, indicating that the higher Sn 2+ dopants in SnO 2 (obtained at a higher applied potential of −0.625 V) in the oxides as well as the greater active surface area (obtained at the optimal charge density of 0.125 C/cm 2 ) and the lowest calcining temperature of 400 • C are the key factors in improving the sensing performance. Selectivity of the gas sensors was determined by exposing them to CO and NO 2 at room temperature.Chemical sensors based on various nanostructures has attracted enormous attention, where gas sensing is now widely held as one of the most promising areas which nanotechnology will have a significant impact. 1 Advancements in nanotechnology have prompted the utilization of one-dimensional (1-D) semiconducting nanostructures as novel transducer materials 2 in sensing devices due to their ultra-high surface area-to-volume ratio that enhances surface adsorptive capacity, tunable electrical properties via dopants, and the ability to form ultra-high density arrays in small dimensions. In particular, single walled carbon nanotubes (SWNTs) have become a promising 1-D nanomaterial to develop devices with miniaturized size, simplicity, reliability, and low cost. 3-5 Even though pristine SWNTs display poor sensitivity and selectivity as a gas sensing material, its unique electronic properties have motivated researchers to use SWNTs as mandrels and to enhance their sensing capabilities through decoration of other materials (e.g., metals, metal oxides, conducting polymers). Metal oxides have been reported as good sensing materials for various analytes. 6 In particular, semiconducting metal oxides such as ZnO, 7 SnO 2 , 8-10 MoO 3 , 11 and Ga 2 O 3 9,12 were reported as good candidates for sensing gases such as CO, NO 2 and NH 3 under elevated temperature. Such metal oxide/SWNTs hybrid based chemiresistors are exploited by their enhanced sensitivity and selectivity toward various gaseous analytes via charge interactions with the SWNT mandrel and by simple measurement set up.SnO 2 is a n-type semiconductor with a wide bandgap (E g = 3.6 eV), excellent chemical stability, and sensing capability which makes it a suitable transducer material in gas sensors. 9 However, due to its high electrical resistivity at ambient temperature as synthesized, SnO 2 as a transducer must be operated at an elevated temperature for optimal performance. 8,13 To overcome this obstacle, 1-D nanomaterials ...

Room temperature amine sensors enabled by sidewall functionalization of single-walled carbon nanotubes

“…18 However, good results were only obtained at high temperatures and/or high concentrations of analyte. 19 Notably, pristine carbon nanotubes (p-CNTs) change their conductivity upon the interaction with gas molecules, 7 but the sensitivity and selectivity towards gas analytes are poor. Covalent or non-covalent modification of CNTs is an accessible procedure to provide graphitic materials with modulated functionalities and potential sensor response.…”

Synthesis of Platinum and Tin Oxide Co‐functionalized Single‐walled Carbon Nanotubes (Pt/SnO2/SWNTs) and their Sensing Properties toward Carbon Monoxide

“…In our previous work , the optimization of SnO 2 /SWNTs toward CO sensing has been systematically studied. Here, we electrodeposited Pt nanoparticles on SnO 2 /SWNTs to enhance the CO sensing performance at room temperature while promoting less CO poisoning.…”

“…A commercial potentiostat/galvanostat (SP‐200, Potentiostat/Galvanostat/EIS, BioLogic Science Instruments, France) was used for electrochemical deposition, a Pt wire (99.99 %, Sigma Aldrich, MO, USA) as the counter electrode and a saturated Ag/AgCl electrode (CHI‐111, CH Instrument, Inc., Austin, TX, USA) as the reference electrode. The detail optimization process of the SnO 2 functionalized SWNTs hybrid had been done in previous report .…”

“…The sensing performance of the Pt/SnO 2 /SWNTs nanostructures was studied by installing the sensing chips in a customized sensing cell (maximum three chips in three separate cells at one time) with inlet and outlet ports for gas flow and then clipping the chips to a Keithley 236 source to obtain an electrical connection. The electrical resistance was continuously recorded under an applied voltage fixed at 1 V. During the sensing measurement, the total gas flow rate was fixed at 200 sccm with desired analyte diluted with dry air.…”

Metal Oxide Gas Sensors by Nanostructures

“…Graphene-ZnO 17.4 (100 ppm) 1.25 (10 ppm) 23.5 (1 ppm) [36][37][38] Graphene-SnO 2 2.45 (20 ppm) 1.9 (500 ppm) 9 (400 ppm) [39][40][41] Graphene-TiO 2 -1.7 (10 ppm) 6.5 (100 ppm) [42,43] MWCNT-ZnO 1.025 (10 ppm) 41 (10 ppm) - [44,45] MWCNT-SnO 2 2 (10 ppm) 1.06 (60 ppm) 0 (100 ppm) [39,46,47] MWCNT-TiO 2 -2 (100 ppm) 7 (50 ppm) [48,49] SWCNT-ZnO 6 (250 ppm) -0 (50 ppm) [50,51] SWCNT-SnO 2 11.1 (10 ppm) 50 (100 ppm) 1.29 (50 ppm) [52][53][54] SWCNT-TiO 2 ---- Table 1.…”