Flexible and low power CO gas sensor with Au-functionalized 2D WS2 nanoflakes

https://doi.org/10.1016/j.snb.2020.128040Get rights and content

Highlights

  • Gas sensors based on pristine and Au-decorated WS2 nanoflakes were prepared on flexible substrate.

  • Au-decorated WS2 nanoflakes showed good selectivity to CO gas along with excellent flexibility.

  • Sensing mechanism was discussed.

Abstract

A flexible and selective CO gas sensor was fabricated from Au-functionalized two-dimensional (2D) WS2 nanoflakes on polyamide substrate. Au-functionalized 2D WS2 nanoflakes gas sensors fabricated on polyamide can be operated under self-heating mode (1-5 V) with good selectivity to CO gas. Gas sensors fabricated on polyamide not only showed flexibility, but also demonstrated good stability and repeatability. In particular, even after 1000 times tilting, the optimized gas sensor could detect low concentrations of CO gas. The underlying sensing mechanism is discussed in detail. The results indicated the feasibility of realization of low-energy consumption and flexible gas sensors using Au-functionalization on 2D WS2 nanoflakes.

Introduction

Air pollution consists of particulate matter (PM), CO, NO2 O3, and SO2 [1]. It has been reported that 92% of the world’s population live in areas with poor air quality, which are in risk of premature death due to air pollution [2]. In fact, pollution which is the world's largest cause of disease and premature death, is responsible for 16% of total deaths worldwide [3]. Accordingly, air pollution is an active area of sensing research nowadays.

Among different developed sensing devices for detection of pollutant gases, soft gas sensors which are flexible and stretchable are of importance, due to the fact that such sensors can be easily implemented in portable, wearable, and low-power consumption electronics [4,5]. Generally, development of flexible gas sensors is a difficult challenge, since they should have comparable sensing performance with respect to sensitivity, selectivity and fast dynamics with other sensors on rigid substrates at low working temperatures. Furthermore, it should have an excellent stability and repeatability under tilting or stretching conditions for several times [6].

Thus far, gas sensors with flexible substrates such as plastics [7], polymers [8] and paper [9] have been reported. In particular, plastic substrates such as polyamide are very popular for realization of flexible gas sensors. In addition to flexibility, they have low cost and availability [6]. However, the success of flexible gas sensors, greatly depends on low operating temperature conditions. High temperatures are needed for both fabrication and operation of traditional gas sensors [10], seriously limiting the possibility of their application to flexible gas sensors. Accordingly, development of low power consuming gas sensors using self-heating technique is vital for the realization of flexible gas sensors. Such gas sensors not only have great flexibility to be installed in different places, but also their energy consumption is extremely low, enabling them to be used in instruments and electronic devices with low power consumption.

Based on the literature, resistive-based gas sensor generally need high temperatures for gas sensing which increases their power consumption. Self-heating mode-operation can decrease the power consumption, where the applied voltage for measuring of electrical resistance will generate heat inside the sensing layer and will provide the energy needed for adsorption of target gas [11]. To realize self-heated gas sensors, one dimension and two-dimensional (2D) morphologies often are preferred since they offer good surface area, where electrons in their pathways can be scattered by different obstacles, resulting in high heat generation.

Earth-abundant, layered transition metal dichalcogenides (TMDs) with two-dimensional structures, can be synthesized with large surface-area, and owing to possibility of tuning the band gaps and high mobility of charge carriers, they are considered as good materials for sensing studies [[12], [13], [14], [15], [16]]. Tungsten disulfide (WS2) as a TMD, has some unique properties including excellent thermal stability, low cost and tunable band structure [17]. Weak van der Waals forces connect vertically-stacked layers, facilitating diffusion of the target gas among the layers [18]. Accordingly, WS2 can be used for low temperature gas sensors [[19], [20], [21]]. Nonetheless, pristine WS2 gas sensors show low sensitivity, selectivity and long recovery time, limiting their applications for practical usages [22,23]. Noble metal functionalization is a promising avenue to enhancing the sensing properties of WS2 owing to the catalytic effect of Au. These improvements ultimately enhance the response, and selectivity of a gas sensor [24,25].

As a highly toxic gas, carbon monoxide (CO) has no signs such as color, taste, and odor [26]. It can be produced by incomplete combustion of fuels: a burning wood or stove and even a candle in a closed space are potential sources for the release of CO gas. Despite seemingly benign sources, CO is an invisible, silent killer, and at high concentrations death is likely. Exposure to 0.5 % of CO for 10 min can cause death [27]. Currently, over 15,000 intentional CO poisoning occurs annually [28]. Many people are poisoned by CO the home, due gasoline-powered engines like cooking appliances [29]. Also, CO is a biomarker, where the CO concentration in the exhaled breath of the sick people is higher than those of normal people [30,31]. Therefore, selective sensing of CO in a flexible and low-power consumption sensing device is useful for many applications.

In this wok, we realized Au-functionalized WS2 gas sensors for low power consumption CO gas sensing studies. It was found that selective and low-power CO gas sensor with good flexibility can be easily realized using combination of Au and 2D WS2 nanoflakes. While the sensing application of 2D metal oxide nanoflakes was previously reported [32], there has been rare report on the 2D WS2 nanoflakes. We demonstrated the possibility of sensing enhancement in TMDs in a simple way, which can be extended to the similar TMDs for fabrication of reliable gas sensors.

Section snippets

Fabrication of pristine and Au-functionalized of WS2 NSs gas sensors

Fig. 1a,b schematically illustrates the process for fabrication of the gas sensors. Polyamide substrate, (width: 15 mm, thickness: 25 μm, length: 20 mm) equipped with a bi-layered (Ti/Pt) electrode was used. First, a 0.005 g WS2 powder (ACS Materials) was uniformly dispersed in 0.01 ml 2-propanol under magnetic stirring. Then, using a micropipette, 0.075 μl (three drops) of the solution was coated onto the polyamide substrates and it was dried at 60 °C for 10 min. To realize the preparation of

Morphological, compositional and structural studies

SEM image of pristine 2D WS2 nanoflakes on the polyamide substrate is revealed in Fig. S1a in the Supplementary Information and that for Au-functionalize WS2 is provided in Fig. S1b. The sensing layer has covered the substrate surface, creating the considerable contacts between the sensing layer and the electrodes. Au was functionalized on the surfaces of WS2 nanoflakes, and corresponding TEM micrographs are presented in Fig. 2a-h. With increasing the irradiation time during synthesis, Au

Conclusion

In a nutshell, Au-functionalized 2D WS2 nanoflakes were realized on flexible polyamide substrate. The gas sensing results of pristine WS2 nanoflakes in self-heating operation with an optimal applied voltage of 2 V showed the poor selectivity. On the other hand, optimized Au-functionalized 2D WS2 nanoflakes revealed improved sensitivity as well as selectivity to CO gas. In addition, the Au-functionalized gas sensor kept its properties even after many-times bending, demonstrating good flexibility

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

CRediT authorship contribution statement

Jae-Hun Kim: Data curation, Investigation, Visualization, Data curation, Writing-original draft. Ali Mirzaei: Methodology, Visualization, Validation, Writing-original draft, Writing-review & editing. Hyoun Woo Kim: Supervision, Conceptualization, Project administration, Writing-review & editing. Sang Sub Kim: Supervision, Conceptualization, Funding acquisition, Resources, Writing-review & editing.

Acknowledgments

This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (2016R1A6A1A03013422). This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIT) (2019R1A2C1006193).

Jae-Hun Kim received his B.S. degree from Gyeongsang National University, Republic of Korea in 2013. In February 2015, he received M.S. degree from Inha University, Republic of Korea. He is now working as a Ph.D. candidate at Inha University, Republic of Korea. He has been working on oxide nanowire gas sensors.

References (62)

  • W. Yan et al.

    Effects of ambient humidity and temperature on the NO2 sensing characteristics of WS2/graphene aerogel

    Appl. Surf. Sci.

    (2018)
  • X. Li et al.

    WS2 nanoflakes based selective ammonia sensors at room temperature

    Sens. Actuators, B

    (2017)
  • D.-H. Baek et al.

    MoS2 gas sensor functionalized by Pd for the detection of hydrogen

    Sens. Actuators B

    (2017)
  • A. Mirzaei et al.

    CO gas sensing properties of In4Sn3O12 and TeO2 composite nanoparticle sensors

    J. Hazard. Mater.

    (2016)
  • K. Sircar et al.

    Carbon monoxide poisoning deaths in the United States, 1999 to 2012

    Am. J. Emer. Med

    (2015)
  • J.-H. Kim et al.

    Extremely sensitive and selective sub-ppm co detection by the synergistic effect of au nanoparticles and core-shell nanowires

    Sens. Actuators B

    (2017)
  • A.P. Dral et al.

    2D metal oxide nanoflakes for sensing applications: review and perspective

    Sens. Actuators B

    (2018)
  • Y. Chen et al.

    Morphology-controlled porous α-Fe2O3/SnO2 nanorods with uniform surface heterostructures and their enhanced acetone gas-sensing properties

    Mater. Lett.

    (2018)
  • D. Gu et al.

    Light enhanced VOCs sensing of WS2 microflakes based chemiresistive sensors powered by triboelectronic nangenerators

    Sens. Actuators B

    (2018)
  • Z. Qin et al.

    2D WS2 nanosheets with TiO2 quantum dots decoration for high-performance ammonia gas sensing at room temperature

    Sens. Actuators B

    (2017)
  • Y. Shi et al.

    Localized surface plasmon resonance enhanced label-free photoelectrochemical immunoassay by Au-MoS2 nanohybrid

    Electrochim. Acta

    (2018)
  • M.W. Jung et al.

    highly transparent and flexible NO2 gas sensor film based on MoS2/rGO composites using soft lithographic patterning

    Appl. Surf. Sci.

    (2018)
  • T. Xu et al.

    The ultra-high NO2 response of ultra-thin WS2 nanosheets synthesized by hydrothermal and calcination processes

    Sens. Actuators B

    (2018)
  • S. Hussain et al.

    Highly reactive 0D ZnS nanospheres and nanoparticles for formaldehyde gas-sensing properties

    Sens. Actuators B

    (2017)
  • O. Monereo et al.

    Self-heating effects in large arrangements of randomly oriented carbon nanofibers: application to gas sensors

    Sens. Actuators B

    (2015)
  • L.H. Qian et al.

    CO sensor based on Au-decorated SnO2 nanobelt

    Mater. Chem. Phys.

    (2006)
  • J.H. Kim et al.

    Low power-consumption CO gas sensors based on Au-functionalized SnO2-ZnO core-shell nanowires

    Sens. Actuators B

    (2018)
  • H. Liu et al.

    Physically Flexible, Rapid‐Response Gas Sensor Based on Colloidal Quantum Dot Solids

    Adv. Mater.

    (2014)
  • R. Alrammouza et al.

    A review on flexible gas sensors: From materials to devices

    Sens. Actuators A

    (2018)
  • M.C. McAlpine et al.

    Highly ordered nanowire arrays on plastic substrates for ultrasensitive flexible chemical sensors

    Nat. Mater.

    (2007)
  • G. Yang et al.

    Flexible graphene-based chemical sensors on paper substrates

    Phys. Chem. Chem. Phys.

    (2013)
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    Jae-Hun Kim received his B.S. degree from Gyeongsang National University, Republic of Korea in 2013. In February 2015, he received M.S. degree from Inha University, Republic of Korea. He is now working as a Ph.D. candidate at Inha University, Republic of Korea. He has been working on oxide nanowire gas sensors.

    Ali Mirzaei received his Ph.D. degree in Materials Science and Engineering from Shiraz University in 2016. He was visiting student at Messina University, Italy in 2015. Since 2016 he is postdoctoral fellow at Hanyang University in Seoul. He is interested in the synthesis and characterization of nanocomposites for gas sensing applications.

    Hyoun Woo Kim joined the Division of Materials Science and Engineering atHanyang University as a full professor in 2011. He received his B.S. and M. S. degreesfrom Seoul National University and his Ph.D. degree from Massachusetts Instituteof Technology (MIT) in electronic materials in 1986, 1988, and 1994, respectively.He was a senior researcher in the Samsung Electronics Co., Ltd. from 1994 to 2000.He has been a professor of materials science and engineering at Inha Universityfrom 2000 to 2010. He was a visiting professor at the Department of Chemistryof the Michigan State University, in 2009. His research interests include the one-dimensional nanostructures, nanosheets, and gas sensors.

    Sang Sub Kim joined the Department of Materials Science and Engineering, Inha University, in 2007 as a full professor. He received his B.S. degree from Seoul National University and his M.S and Ph.D. degrees from Pohang University of Science and Technology (POSTECH) in Material Science and Engineering in 1987, 1990, and 1994, respectively. He was a visiting researcher at the National Research in Inorganic Materials (currently NIMS), Japan for 2 years each in 1995 and in 2000. In 2006, he was a visiting professor at Department of Chemistry, University of Alberta, Canada. In 2010, he also served as a cooperative professor at Nagaoka University of Technology, Japan. His research interests include the synthesis and applications of nanomaterials such as nanowires and nanofibers, functional thin films, and surface and interfacial characterizations.

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