Enhancing NO2 gas sensing performances at room temperature based on reduced graphene oxide-ZnO nanoparticles hybrids
Introduction
Graphene, a rapidly rising star on the horizon of materials science, has fascinated the scientific community in recent years due to its remarkable electronic conductivity, superior mechanical properties, large surface area, and high thermal stability [1], [2], [3]. Particularly, the extremely high carrier mobility of graphene nanosheets at room temperature indicates that graphene is a promising candidate for gas sensing operating at room temperature [4]. Additionally, graphene also exhibits detectable change in its electrical resistance after adsorption of guest gases, which further ensures graphene as good candidate for gas sensing [5]. Up to now, graphene-based materials obtained by various methods have been used for detection of gases at low operating temperature, such as, reduced graphene oxide (rGO) obtained by chemical reduction of GO [6], [7] and thermal reduction of GO [8], [9], graphene prepared by chemical vapor deposition (CVD) [10], [11], etc. Particularly, rGO has been attracted much interest due to its great advantages of low cost and bulk quantity production [12]. However, the gas sensors based on pure rGO suffer from some disadvantages, such as low sensitivity, long response and recovery times, which limit their further applications.
Recent research has shown that the electrical properties of rGO can be tuned by doping with other atoms, modification by guest molecules via noncovalent or covalent methods, which provide a new route for preparation of high-performance rGO-based sensing materials [13], [14]. For example, rGO-conducting polymers hybrids [15], organic molecules modified rGO [16], nitrogen and silica-doped rGO [17], noble metal modified rGO [18], and rGO-metal oxide hybrids [19] have been successfully used for detection of gases at room temperature. Among them, development of gas sensors based on metal oxides-rGO hybrids has also been attracted considerable attention due to the high-performance for gas sensing by using metal oxides as sensing materials. Indeed, some typical metal oxides, such as SnO2 [20], [21], [22], ZnO [19], [23], Cu2O [24], [25], and WO3 [26], [27] have been successfully used for enhancing the sensing properties of rGO-based gas sensors. However, these sensors still suffer from several shortcomings, such as high operating temperature, long response and recovery times, low sensitivity and so on.
ZnO, a typical n-type semiconductor with a direct wide band-gap (3.37 eV) and large excitation binding energy (60 meV), has been widely studied in gas sensing application due to its good response to a variety of reducing or oxidizing gases, low cost, and being friendly to the environment [28], [29]. Additionally, recent research has shown that ZnO can be used for enhancing the sensing performance of rGO. For example, Singh et al. have reported that ZnO decorated luminescent graphene exhibits response toward CO, NH3 and NO at room temperature [19]; Huang et al. prepared ZnO quantum dots/graphene nanocomposites for formaldehyde detection with fast response and recovery [22]; Yi et al. synthesized vertically aligned ZnO nanorods and graphene hybrid architectures for flexible gas sensors to detection of ethanol at 300 °C [30]; Zou et al. prepared ZnO nanorods on rGO for detection of ethanol at 260 °C [31]. It is obviously seen that these efforts have been devoted to enhancing the sensing properties of graphene-based materials by introduction of ZnO materials. However, these sensors still have more or less disadvantages, such as low sensitivity, high operating temperature. Therefore, it is indeed necessary to develop high-performance gas sensors for detection of gas at mild conditions.
In this study, a new gas sensor was fabricated using ZnO-rGO hybrids as sensing materials for detection of NO2 operating at room temperature. ZnO-GO hybrids were prepared by in situ production of ZnO nanoparticles on the surface of GO, followed by reduction of such hybrids using hydrazine hydrate as reducing agent. Most importantly, the NO2 sensor based on ZnO-rGO hybrids exhibits higher sensitivity, shorter response time and recovery time than those of pure rGO, indicating enhancing sensing performance of pure rGO by introduction of ZnO nanoparticles.
Section snippets
Materials
Zn(OAc)2·2H2O, methanol, KMnO4, H2O2 (30 wt%), N,N-dimethylformamide (DMF), NaNO3, and H2SO4 (98%) were purchased from Beijing Chemical Corp (Beijing, China). Hydrazine hydrate and KOH were purchased from Shanghai Chemical Corp. (Shanghai, China). Graphite powder was purchased from Aladin Ltd. (Shanghai, China). All chemicals were used without any further purification. The water used throughout all experiments was purified through a Millipore system.
Preparation of sensing materials
GO was prepared from natural graphite powder
Results and discussion
In the present work, ZnO-rGO hybrids were prepared by an one-pot method using GO and Zn(OAc)2·2H2O as sources. Fig. 1a shows the XRD patterns of the samples thus obtained, GO and rGO, respectively. It is seen that GO exhibits a strong diffraction peak at 2θ of 10.92° attributed to (0 0 2) diffraction of GO, indicating the formation of GO by Hummers method from graphite. Note that this peak disappears in the rGO and final hybrids, indicating the reduction of GO into rGO in the presence of
Conclusions
In summary, room temperature NO2 sensor has been successfully constructed using ZnO-rGO hybrids as sensing materials, and the sensor thus obtained exhibits better sensing performances than those of rGO. Our present work provides a novel method for development of high performance gas sensors using graphene-based materials.
Acknowledgments
This research work was financially supported by the National Natural Science Foundation of China (Grant No. 51202085) and Program for Chang Jiang Scholars and Innovative Research Team in University (No. IRT3018).
Sen Liu received his B.S. degree in 2005 in Chemistry and PhD degree in 2010 in Inorganic Chemistry from Jilin University. During the period of 2010 to 2012, he worked in Prof. Xuping Sun's group as a postdoctoral research associate in State Key Lab of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. He joined in College of Electronic Science and Engineering at Jilin University in 2012. Now he is an associate professor in Jilin University and
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Sen Liu received his B.S. degree in 2005 in Chemistry and PhD degree in 2010 in Inorganic Chemistry from Jilin University. During the period of 2010 to 2012, he worked in Prof. Xuping Sun's group as a postdoctoral research associate in State Key Lab of Electroanalytical Chemistry, Changchun Institute of Applied Chemistry, Chinese Academy of Sciences. He joined in College of Electronic Science and Engineering at Jilin University in 2012. Now he is an associate professor in Jilin University and his current research is focused on the preparation of functional materials and their sensing applications.
Bo Yu received his BS degree from the College of Electronics Science and Engineering, Jilin University, China in 2012. As an MS student, his research interests include sensing functional materials and devices.
Teng Fei received his BS degree in 2005 in chemical engineering and technology and PhD degree in 2010 in polymer chemistry and physics from Jilin University, China. He is currently a lecturer in the College of Electronics Science and Engineering, Jilin University. His research interests include sensing functional materials and devices.
Tong Zhang completed her MS degree in semiconductor materials in 1992 and her PhD in the field of microelectronics and solid-state electronics in 2001 from Jilin University. She was appointed as a full-time professor in the College of Electronics Science and Engineering, Jilin University in 2001. Her research interests are sensing functional materials, gas sensors, and humidity sensors.