SnO2 nanocomposite: Electrochemical and gas sensing performance

Journal Pre-proof Sonochemical preparation and characterization of rGO/SnO2 nanocomposite: Electrochemical and gas sensing performance Aditya Chaudhari, Bharat A. Bhanvase, Virendra Kumar Saharan, Paresh H. Salame, Yuvraj Hunge PII:

S0272-8842(20)30160-7

DOI:

https://doi.org/10.1016/j.ceramint.2020.01.156

Reference:

CERI 24088

To appear in:

Ceramics International

Received Date: 26 September 2019 Revised Date:

14 January 2020

Accepted Date: 15 January 2020

Please cite this article as: A. Chaudhari, B.A. Bhanvase, V.K. Saharan, P.H. Salame, Y. Hunge, Sonochemical preparation and characterization of rGO/SnO2 nanocomposite: Electrochemical and gas sensing performance, Ceramics International (2020), doi: https://doi.org/10.1016/j.ceramint.2020.01.156. This is a PDF file of an article that has undergone enhancements after acceptance, such as the addition of a cover page and metadata, and formatting for readability, but it is not yet the definitive version of record. This version will undergo additional copyediting, typesetting and review before it is published in its final form, but we are providing this version to give early visibility of the article. Please note that, during the production process, errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain. © 2020 Published by Elsevier Ltd.

Sonochemical

Preparation

and

Characterization

of

rGO/SnO2

Nanocomposite: Electrochemical and Gas Sensing Performance

Aditya Chaudhari1, Bharat A. Bhanvase*,1, Virendra Kumar Saharan2, Paresh H. Salame3, Yuvraj Hunge4 1

Department of Chemical Engineering, Laxminarayan Institute of Technology, Rashtrasant

Tukadoji Maharaj Nagpur University, Nagpur 440033, MS, INDIA 2

Department of Chemical Engineering, Malaviya National Institute of Technology, Jaipur

302017, Rajasthan, INDIA 3

Department of Physics, Institute of Chemical Technology, Mumbai, MS, INDIA

4

Department of Physics, Savitribai Phule Pune University, Pune, MS, INDIA

* Corresponding author: E-mail address: (B. A. Bhanvase) [email protected], [email protected]

Declarations of interest: none

1

2

Abstract The present investigation deals with solution-based sonochemical production of graphene oxide (GO) and reduced graphene oxide-SnO2 (rGO/SnO2) nanocomposite. These rGO/SnO2 nanocomposites were analysed with XRD, TEM, FTIR and UV/visible techniques. While synthesizing rGO/SnO2 nanocomposites, use of the ultrasound generated cavitational events which has evidently improved the uniform deposition of SnO2 on graphene nanosheets. These rGO/SnO2 nanocomposites were explored for their potential electrochemical as well as gas sensing applications. The cyclic voltammetry (CV) studies revealed a good electrochemical performance of rGO/SnO2 nanocomposite with a specific capacitance of 35 F/g. Further, the influence of NO2 gas concentration was investigated on rGO/SnO2 nanocomposite based sensor at various temperatures. The nanocomposite displayed the highest response of 99.9% with a very short response time of 14 secs for 100 ppm concentration of NO2 gas at 150 oC. These sonochemically derived rGO/SnO2 nanocomposite based sensor showed excellent performance towards NO2 gas compared to other selected gases under the same conditions. --------------------------------------------------------------------------------------------------------------------Keywords: rGO/SnO2 nanocomposite; Cavitation effects; NO2 gas sensors; Response; Supercapacitors

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1. Introduction The burning of various fuels and motor vehicle exhaust contain many toxic and harmful gases, which primarily have NO2 gas. Prolong exposure of NO2 gas could result in several respiratory problems like cough, wheezing, reduced lung function and increased asthma attack etc., these problems could also recur at the lower concentration on NO2 [1] Therefore, its selective detection at low concentration is very much essential. Currently, there are several problems with sensing materials in terms of sensitivity, high-temperature operation, reversibility, poor selectivity, high material and fabrication costs [2–4]. Further, supercapacitors are finding interesting usage in portable electronic devices due to their significant features like high power density, extended cycle life and short charge-discharge time [5,6]. The active materials used for the preparation of electrodes of the supercapacitors are based on metal oxides [7,8]. For these applications, the transition metal oxides like SnO2 are less expensive alternative but suffer from its low electrical conductivity [7]. SnO2 is a distinctive n-type metal oxide and have been used in several applications in combination with various other nanostructures [9–11]. The performance of these metal oxides like SnO2 can be enhanced with its deposition on selected carbon nanostructure like graphene [12]. With the loading of SnO2 nanoparticles on graphene sheets, the problems mentioned above can be addressed successfully. This can be realised owing to the high surface area, more interfacial contacts present in the 2D structure of graphene, and also due to higher charge carrier mobility [13–15]. Further, reduced graphene oxide (rGO) showed better performance in term of conductivity as compared to graphene oxide (GO), which is attributed to reduced oxygen functionalities in the rGO compared to GO. The uniform deposition of SnO2 nanoparticles on rGO nanosheet is utmost important. Therefore, the application of ultrasound in the preparation of rGO/SnO2 nanocomposite promotes the uniform deposition of SnO2 nanoparticles on rGO nanosheets without any agglomeration [16,17]. Therefore, in the present work ultrasound-assisted production of rGO/SnO2 4

nanocomposite was accomplished, which substantially enhances the deposition of SnO2 nanoparticles on rGO nanosheets. During ultrasonic irradiation, ultrasound waves get passed through the reaction medium; due to this, the formation of several microbubbles takes places. These microbubbles collapse after its growth in a very short time, which results in the generation of the intense environment due to cavitational effects. These cavitational effects, in turn, result in the turbulence, liquid circulation and microjet formation, and this is accountable for the reduction in the particle size and uniform nanomaterials deposition [16–18]. Formation of nanoparticles is also attributed to enhanced nucleation rate and solute transfer in the aqueous medium, which is due to powerful micromixing and turbulence [19]. In view of this, the present work deals with sonochemical preparation of rGO/SnO2 nanocomposite in aqueous solution. The successful formation of rGO/SnO2 nanocomposite was confirmed with the help of XRD, TEM, FTIR and UV/vis characterization techniques. The prepared rGO/SnO2 nanocomposites were explored for its potential electrochemical as well as gas sensing applications. 2. Experimental 2.1 Materials Sonochemical production of rGO/SnO2 nanocomposite was accomplished with the use of various precursors like graphite powder, NaNO3, KMnO4 and 30% H2O2 purchased from Loba Chemie Pvt. Ltd. Mumbai, 98% H2SO4 and 37% HCl taken from SD Fine-Chem Limited Mumbai and stannous chloride obtained from Thermo Fisher Scientific India Pvt. Ltd. India. All essential solutions were prepared in distilled water using these chemicals without further purification. 2.2 Production of rGO/SnO2 nanocomposite with the aid of ultrasound Initially, the preparation of GO was accomplished using a modified hummers method with the aid of ultrasound [16,20,21]. The preparation of an aqueous solution of as-prepared GO (0.1 g) in

5

200 ml distilled water was accomplished, to this mixture, 8.5 ml of 37% HCl was added later. The resultant blend was sonicated for 30 minutes. After this, 0.15 g of stannous chloride (SnCl4.2H2O) was added to the sonicated solution, and further sonication was performed for 30 minutes. The as-synthesized rGO/SnO2 nanocomposite was separated with the help of centrifugation (5000 rpm for 10 min). The obtained product was then washed with water and again centrifuged at 5000 rpm for 10 min to get the desired final product. This final product was then dried in an oven at 100

for 2h and was used for further characterizations.

2.3 Characterization UV/Vis spectrum of rGO/SnO2 nanocomposite produced by the sonochemical method was recorded using UV/VIS Spectrophotometer (LABINDIA Analytical, Model: UV3200). XRD analysis of rGO/SnO2 nanocomposite performed using powder X-ray diffractometer (Rigaku Mini-Flex). Raman analysis of rGO/SnO2 nanocomposite was carried by using Confocal Micro Raman Spectrometer (STR-500, AIRIX Corporation), while, FTIR analysis of rGO/TiO2 nanocomposite was carried out on Fourier Transform Infrared Spectrophotometer (Shimadzu-IR Affinity-1, Japan). The TEM images of rGO/TiO2 nanocomposite were taken using Transmission Electron Microscope (Hitachi, Japan, Model: H-7500). Elemental Map images and EDAX analysis of rGO/TiO2 nanocomposite were obtained using Transmission Electron Microscopy (Tecnai G2 20, FEI Company). XPS analysis was undertaken using the Omicron ESCA instrument, Germany. 2.4 Electrochemical and gas sensing study using rGO/SnO2 nanocomposite based sensor The Electrochemical performance over these rGO/SnO2 nanocomposites was measured using standard three-electrode cell configuration on Metrohm Autolab (PGSTAT 128N). In order to measure the galvanostatic charge-discharge (GCD) of the prepared nanocomposite, 0.28 gm of nanocomposite along with 0.03 gm of activated carbon and 0.04 gm of PVDF was dispersed in

6

10 ml of N, N-dimethylformamide (DMF). Then, this solution was sonicated using probe sonicator for 30 min. The solution’ viscosity was suitably adjusted so that it could be tape-casted over conducting stainless steel mesh using Doctor’s blade, for three-cell electrochemical measurement by keeping it in the oven. The gas sensing measurements of rGO/SnO2 nanocomposite pellets were accomplished using the computer-controlled static gas sensing system. This system was made with the use of sealed stainless steel test chamber which has gas inlet-outlet arrangement. The temperature of the sensor was controlled with a system having a flat heating plate with a temperature controller. A sensor having a dimension of 1 cm × 1cm size was prepared, over which electrical contacts of silver were made. The rGO/SnO2 nanocomposite pellets were placed on the heating plate, in the test chamber. The test chamber was preheated at a required temperature with the use of a temperature controller. For successful measurement, first, the sensor was heated till its base resistance is stabilized. Thereafter, the fabricated sensor was exposed to the selected gas at the estimated (from 1 to 100 ppm) gas concentrations in the chamber and then variation in the resistance as a function of time was recorded with Keithley 6514 electrometer, connected to the film sensor. The selected gases for the study were NO2, Acetone, LPG, NH3, and SO2. The recovery of the gas sensor was accomplished by venting it with the fresh air through the system outlet once measurements were recorded. The gas-sensing performance was estimated with the following relation (1);  R − Rair Response (%) =  gas  R gas 

  × 100 

(1)

where, Rair and Rgas are the resistances in air and test gas, respectively.

3. Results and Discussion 3.1 Structural Characterizations of rGO/SnO2 nanocomposite

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UV-visible absorption spectra, shown in Figure 1 (a), exhibited a peak at around 235 nm, which is a characteristic peak of graphene oxide prepared by the sonochemical method, thus confirming the formation of graphene oxide using a modified Hummers method assisted by ultrasound. The observed characteristic peaks at 230 and 300 nm confirms the π-π* transition (aromatic C=C bonds) and the presence of n→π* transition (due to C=O bonds), respectively [22]. Also, UV-vis spectra over the sample revealed a peak around 335nm, which can be accredited to the formation of graphene-attached SnO2 nanocomposite. Additionally, sonochemically prepared rGO/SnO2 nanocomposite depicts a broad absorption peak from 250 nm to 300 nm, which confirms the deposition of SnO2 on rGO nanosheets. Figure 1 (b) depicts the XRD pattern of ultrasonically produced rGO/SnO2 nanocomposite. The observed characteristics peaks at 26.9°, 32.9°, 51.1° and 62.6° analogous to the (hkl) planes at (110), (101), (211) and (112), respectively are because of the deposition of nanosized SnO2 particles on the rGO nanosheets. The characteristics peaks of SnO2 loaded on rGO was compared and matched to JCPDS file no. 00-041-1445. The peaks of the prepared sample matched well with the standard data, thus confirming the phase formation of the desired compound. The broad diffraction peak at 26.9o is due to the reduction of GO to rGO during the preparation of rGO/SnO2 nanocomposite. The sonochemical formation of rGO/SnO2 nanocomposite was also established with Raman analysis (Figure 1 (c)). The presence of the noticeable characteristic peaks at around 1328 and 1574 cm-1 in the recorded spectrum of sonochemically prepared rGO/SnO2 nanocomposite represents the D-band (disordered band), and G-band (graphitic band), which are due to the defects in the carbon structure and sp2 in-plane vibrations attributed to bonded carbon atoms, respectively. The estimated value of the ratio of ID/IG for the sonochemically prepared rGO/SnO2 nanocomposite was found to be 1.11, and this is attributed to the existence of the enormous extent of defects and porosity of the rGO matrix. Further, the peaks at 495 and 653 cm-1 endorses

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the existence Eg and A1g vibrations of SnO2 nanoparticle deposited on rGO nanosheets to form rGO/SnO2 nanocomposite with ultrasound. The FTIR analysis of ultrasonically produced rGO/SnO2 nanocomposite is represented in Figure 1 (d). In the recorded spectrum, wide peak around 3350 cm−1 represents the O-H stretching vibration. The presence of C=O stretching of the carbonyl functional group was confirmed due to the presence of a characteristic peak at 1719 cm−1 [23]. The appearance of the peak at 1582 cm-1 endorsed to the skeletal vibration of rGO [24]. Also, the existence of the characteristic peaks at 1395 and 1230 cm-1 signifies the O–H deformation and C–OH stretching vibration, respectively [23]. The absorption band at 1165 cm-1 is credited to C–O arising from epoxy or alkoxy functional group. The absorption band at 1035 cm-1 is assigned to the C-O stretching [25], and less intense peak at 864 cm-1 is due to O-C=O groups [26]. These obtained results describe the partial reduction of GO to rGO. Further, the absorption band positioned at 670 cm-1 is allocated to the Eu mode of SnO2 (anti-symmetric O–Sn–O stretching) [27]. The existence of the Eu mode in rGO/SnO2 designates the deposition of SnO2 nanoparticles on the rGO nanosheets. Also, the characteristic peak at 560 cm-1 can be attributed to the Sn-OH vibrations [27]. TEM images at higher magnification reveal the lattice fringes in the nanocomposites which correspond to (200) and (101) planes, and are in match with the dhkl spacing of those obtained by the powder XRD results, thus confirming the formation of the desired phase, i.e. SnO2 by ultrasound-assisted method (Figure 2 (A)). From TEM, uniform distribution of smaller sized SnO2 nanoparticles (3 to 5 nm) on rGO nanosheets is revealed. This can be ascribed to the cavitational effects of ultrasound, which generates extreme shearing action, micromixing and turbulence due to physical effects produced by the transient collapse of cavities formed due to ultrasound [16,17]. Also, the elemental mapping over the sample reveals a uniform distribution of Sn, O, C elements, thereby confirming homogenous mixing and the desired composite

9

formation of the material (Figure 2 (B)). Furthermore, the semi-quantitative analysis over these sample executed by energy dispersive x-ray analysis (EDAX) reveals the presence of desired elements viz. C, Sn, O in the sample (Figure 2 (C)). Figure 3 shows the XPS spectra of rGO/SnO2 nanocomposite. In C 1s XPS spectrum, peaks at 284.2, 286.24, 287.8, and 288.8 eV are corresponding to sp2 carbon, C-O, C=O (carbonyl) and O-C=O groups, respectively [28]. Further, the intensity of the peaks corresponding to C-O, C=O (carbonyl) and O-C=O groups is found to be drastically decreased in the spectrum, which represents a significant reduction of GO in rGO during rGO/SnO2 nanocomposite formation in the presence of ultrasound [27–29]. The presence of prominent peaks 495.2 eV and 486.3 eV, confirms the mixed-valence state of Sn in the composite [30], which in turn could be responsible for the pseudo-capacitive behaviour of the nanocomposite. No impurity peaks were observed for the sample from the spectrum, thus indicating the high purity of compound synthesised by the ultrasound-assisted method.

3.2 Cyclic Voltammetry (CV) and Galvanostatic Charge/Discharge (GCD) Studies On the Electrode Made from rGO/SnO2 Nanocomposite Cyclic voltammetry (CV) is an ideal tool for an investigation of capacitive behaviour of electrode materials. The electrochemical testing over fabricated electrode was accomplished with the use of a conventional three-electrode cell. The fabrication of the working electrode was done by casting the blend of as prepared rGO/SnO2 nanocomposite, carbon black and PVDF (80:8:12 wt.%). The representative electrochemical experiments were performed with the use of electrochemical workstation containing 1M KOH as electrolyte solution at room temperature. The fabricated electrode was used as a working electrode, while platinum foil and Ag/AgCl electrode were used as a counter and the reference electrode, respectively. The CV tests were performed between 0.0V and 0.5V potential in 1 M KOH aqueous electrolyte solution. Figure 4 (A) shows the rectangular-like shape, and there are no apparent redox peaks in the CV curves, 10

indicating an ideal capacitive response from the nanocomposite. This could arise from combined electric double layer capacitance (EDLC) formation at the interfaces as well as possible metal oxide redox reactions. The near rectangular shapes were observed in the case of lower scan rates, whereas the behaviours show deviation at higher scan rate for these samples. These types of limitations at higher load indicates that the usual metal oxide pseudo-capacitive reactions are involved. Also, at high scan rates, the current density for the sample can be seen increasing, thus confirming the ideal capacitive behaviour. Figure 4 (B) shows galvanostatic charge/discharge (GCD) measurement of rGO/SnO2 nanocomposite, asymmetric shape of the curve is displayed at 1 mA, indicating a pseudocapacitive behaviour of the sample. From the GCD curve, a usual initial potential drop, as a result of losses due to internal resistance can be seen. The GCD curve also exhibited nearly similar charge-discharge time, indicating high reversibility. Here the voltage range used was 0.4V to 0.6V. The specific capacitance of GO/SnO2 was found to be 35 F/g.

3.3 Gas sensing properties of gas sensor prepared with rGO/SnO2 nanocomposite The rGO/SnO2 nanocomposite based gas sensor was fabricated, in order to establish its application towards NO2 gas sensing. Figure 5 depicts the response curves of ultrasonically prepared rGO/SnO2 nanocomposite based gas sensor for selected NO2 gas concentrations, which were in the wide range of 1 ppm to 100 ppm at 150 °C temperature. It has been observed that with an increase in the NO2 gas concentration from 1 ppm to 100 ppm at 150 °C, the response time gets drastically reduced from 29.9 sec to 14.17 sec, respectively. However, the recovery time was found to be increased from 182 to 509 sec, with an increase in the NO2 gas concentration from 40 ppm to 100 ppm. Further, this rGO/SnO2 nanocomposite based sensor established the fast response times, which is attributed to the quick change in the resistance and recovery when it is exposed to the NO2 gas. Also, it has been observed that this sensor showed noticeable response even at low NO2 concentration (0.5 ppm), which is attributed to the 11

reduction in the resistance of the rGO/SnO2 nanocomposite based sensor with exposure to NO2 gas. This reduction in the resistance is because of higher adsorption of NO2 gas on the ultrasonically prepared rGO/SnO2 nanocomposite. The use ultrasonic irradiations enhance the dispersion of SnO2 nanoparticles on rGO nanosheets and also the surface area of rGO/SnO2 nanocomposite, which is responsible for adsorption of a larger number of NO2 gas molecules that drastically reduces the resistance of the fabricated sensor. Figure 6 depicts the response (%) and response time (sec) at different concentration (ppm) of NO2 gas for rGO/SnO2 nanocomposite based sensor at an operating temperature of 150 °C. It is observed that the percentage response gets increased from 2.16 to 97.24% with an increasing concentration of NO2 gas from 1 ppm to 100 ppm; also the response time gets reduced 29.9 sec to 14.17 with increasing NO2 gas concentration. Further, the percentage response gets increased drastically with an increase in the concentration of NO2 gas from 1 ppm to 40 ppm, which is 90.17% at 40 ppm NO2 gas concentration. The percentage response was found to be increased gradually after 40 ppm NO2 gas concentration and reaches to 97.24% for 100 ppm NO2 gas concentration. This is attributed to attainment of saturation due to adsorption of NO2 after 40 ppm NO2 gas concentration [4,31]. Further, in the present investigation, the selectivity of rGO/SnO2 nanocomposite based sensor at an operating temperature of 150 °C was studied by considering various target gases like NO2, acetone, LPG, NH3 and SO2. This parameter is very much essential for real-time practical application of rGO/SnO2 nanocomposite based sensor. The NO2 gas is reported to have adverse effects on a human being with a concentration higher than 5 ppm, and it can also cause respiratory problems at very less concentration (0.1 ppm) [31]. Figure 7 depicts the percentage response of ultrasonically prepared rGO/SnO2 nanocomposite based sensor towards selected gases at 100 ppm concertation and 150oC. From this, it can be said that the NO2 gas can display better response compared to other selected gases for a given concentration. These results present

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the applicability of ultrasonically prepared rGO/SnO2 nanocomposite material for the detection of NO2 gas. Further, higher percentage response in case of NO2 gas compared to other selected gases confirmed the greater reaction rate between rGO/SnO2 nanocomposite material surface and NO2 gas molecules [31].

4. Conclusions In present work, using ultrasound-assisted synthesis method, rGO/SnO2 nanocomposite was successfully prepared. The ultrasound-assisted method resulted in the uniform deposition of SnO2 nanoparticles having particle size 3 to 5 nm on rGO nanosheets. The use of ultrasound and reduction of GO are the responsible parameters for uniform deposition of SnO2 nanoparticles on rGO. These nanocomposites were tested for gas sensing as well as electrochemical energy storage applications. For gas sensing, the observed percentage response was seen increased from 2.16 to 97.24% with an increased concentration of NO2 gas from 1 to 100 ppm; also the response time was found to reduce from 29.9 sec to 14.17 sec. Further, the prepared rGO/SnO2 nanocomposite based sensor showed the highest selectivity towards NO2 gas (with a lower detection limit of 1 ppm) compared other gases. CV results displayed a

specific

capacitance of 35 F/g. The results obtained show the suitability of ultrasonically prepared rGO/SnO2 nanocomposite for NO2 gas sensing and supercapacitor applications.

References [1]

C. Boulart, M.C. Mowlem, D.P. Connelly, J.-P. Dutasta, C.R. German, A novel, low-cost, high performance dissolved methane sensor for aqueous environments, Opt. Express. 16 (2008) 12607. doi:10.1364/OE.16.012607.

[2]

J.Z. Ou, W. Ge, B. Carey, T. Daeneke, A. Rotbart, W. Shan, Y. Wang, Z. Fu, A.F. Chrimes, W. Wlodarski, S.P. Russo, Y.X. Li, K. Kalantar-zadeh, Physisorption-Based Charge Transfer in Two-Dimensional SnS 2 for Selective and Reversible NO 2 Gas

13

Sensing, ACS Nano. 9 (2015) 10313–10323. doi:10.1021/acsnano.5b04343. [3]

N. BARSAN, D. KOZIEJ, U. WEIMAR, Metal oxide-based gas sensor research: How to?, Sensors Actuators B Chem. 121 (2007) 18–35. doi:10.1016/j.snb.2006.09.047.

[4]

H. Zhang, J. Feng, T. Fei, S. Liu, T. Zhang, SnO2 nanoparticles-reduced graphene oxide nanocomposites for NO2 sensing at low operating temperature, Sensors Actuators B Chem. 190 (2014) 472–478. doi:10.1016/j.snb.2013.08.067.

[5]

X. Peng, L. Peng, C. Wu, Y. Xie, Two dimensional nanomaterials for flexible supercapacitors, Chem. Soc. Rev. 43 (2014) 3303. doi:10.1039/c3cs60407a.

[6]

Y. Liang, Z. Wang, J. Huang, H. Cheng, F. Zhao, Y. Hu, L. Jiang, L. Qu, Series of in-fiber graphene supercapacitors for flexible wearable devices, J. Mater. Chem. A. 3 (2015) 2547–2551. doi:10.1039/C4TA06574C.

[7]

P. Simon, Y. Gogotsi, Materials for electrochemical capacitors, Nat. Mater. 7 (2008) 845– 854. doi:10.1038/nmat2297.

[8]

P. Rambabu, S.K. Srivastava, P. Das, G.R. Turpu, rGO- SnO 2 Composites for Supercapacitor Applications, IOP Conf. Ser. Mater. Sci. Eng. 149 (2016) 012169. doi:10.1088/1757-899X/149/1/012169.

[9]

Y. Liu, Y. Jiao, Z. Zhang, F. Qu, A. Umar, X. Wu, Hierarchical SnO 2 Nanostructures Made of Intermingled Ultrathin Nanosheets for Environmental Remediation, Smart Gas Sensor, and Supercapacitor Applications, ACS Appl. Mater. Interfaces. 6 (2014) 2174– 2184. doi:10.1021/am405301v.

[10]

H. Wang, Y. Qu, H. Chen, Z. Lin, K. Dai, Highly selective n-butanol gas sensor based on mesoporous SnO2 prepared with hydrothermal treatment, Sensors Actuators B Chem. 201 (2014) 153–159. doi:10.1016/j.snb.2014.04.049.

14

[11]

S. Wang, J. Yang, H. Zhang, Y. Wang, X. Gao, L. Wang, Z. Zhu, One-pot synthesis of 3D hierarchical SnO2 nanostructures and their application for gas sensor, Sensors Actuators B Chem. 207 (2015) 83–89. doi:10.1016/j.snb.2014.10.032.

[12]

X. Zhu, Y. Guo, H. Ren, C. Gao, Y. Zhou, Enhancing the NO2 gas sensing properties of rGO/SnO2 nanocomposite films by using microporous substrates, Sensors Actuators B Chem. 248 (2017) 560–570. doi:10.1016/j.snb.2017.04.030.

[13]

F. Mendoza, D.M. Hernández, V. Makarov, E. Febus, B.R. Weiner, G. Morell, Room temperature gas sensor based on tin dioxide-carbon nanotubes composite films, Sensors Actuators B Chem. 190 (2014) 227–233. doi:10.1016/j.snb.2013.08.050.

[14]

H.Y. Jeong, D.-S. Lee, H.K. Choi, D.H. Lee, J.-E. Kim, J.Y. Lee, W.J. Lee, S.O. Kim, S.Y. Choi, Flexible room-temperature NO2 gas sensors based on carbon nanotubes/reduced graphene hybrid films, Appl. Phys. Lett. 96 (2010) 213105. doi:10.1063/1.3432446.

[15]

N. Van Hieu, L.T.B. Thuy, N.D. Chien, Highly sensitive thin film NH3 gas sensor operating at room temperature based on SnO2/MWCNTs composite, Sensors Actuators B Chem. 129 (2008) 888–895. doi:10.1016/j.snb.2007.09.088.

[16]

M.P. Deosarkar, S.M. Pawar, S.H. Sonawane, B.A. Bhanvase, Process intensification of uniform loading of SnO2 nanoparticles on graphene oxide nanosheets using a novel ultrasound assisted in situ chemical precipitation method, Chem. Eng. Process. Process Intensif. 70 (2013) 48–54. doi:10.1016/j.cep.2013.05.008.

[17]

M.P. Deosarkar, S.M. Pawar, B.A. Bhanvase, In situ sonochemical synthesis of Fe3O4– graphene nanocomposite for lithium rechargeable batteries, Chem. Eng. Process. Process Intensif. 83 (2014) 49–55. doi:10.1016/j.cep.2014.07.004.

[18]

T.P. Shende, B.A. Bhanvase, A.P. Rathod, D.V. Pinjari, S.H. Sonawane, Sonochemical synthesis of Graphene-Ce-TiO2 and Graphene-Fe-TiO2 ternary hybrid photocatalyst

15

nanocomposite and its application in degradation of crystal violet dye, Ultrason. Sonochem. 41 (2018) 582–589. doi:10.1016/j.ultsonch.2017.10.024. [19]

S.R. Shirsath, B.A. Bhanvase, S.H. Sonawane, P.R. Gogate, A.B. Pandit, A novel approach for continuous synthesis of calcium carbonate using sequential operation of two sonochemical

reactors,

Ultrason.

Sonochem.

35

(2017)

124–133.

doi:10.1016/j.ultsonch.2016.09.009. [20]

D.P. Barai, B.A. Bhanvase, V.K. Saharan, Reduced Graphene Oxide-Fe 3 O 4 Nanocomposite Based Nanofluids: Study on Ultrasonic Assisted Synthesis, Thermal Conductivity, Rheology, and Convective Heat Transfer, Ind. Eng. Chem. Res. 58 (2019) 8349–8369. doi:10.1021/acs.iecr.8b05733.

[21]

W.S. Hummers, R.E. Offeman, Preparation of Graphitic Oxide, J. Am. Chem. Soc. 80 (1958) 1339–1339. doi:10.1021/ja01539a017.

[22]

V. Babaahmadi, M. Montazer, Reduced graphene oxide/SnO2 nanocomposite on PET surface: Synthesis, characterization and application as an electro-conductive and ultraviolet blocking textile, Colloids Surfaces A Physicochem. Eng. Asp. 506 (2016) 507– 513. doi:10.1016/j.colsurfa.2016.07.025.

[23]

L. Tang, V.H. Nguyen, Y.R. Lee, J. Kim, J.-J. Shim, Photocatalytic activity of reduced graphene oxide/SnO2 nanocomposites prepared in ionic liquid, Synth. Met. 201 (2015) 54–60. doi:10.1016/j.synthmet.2015.01.018.

[24]

C. Hou, Q. Zhang, M. Zhu, Y. Li, H. Wang, One-step synthesis of magneticallyfunctionalized reduced graphite sheets and their use in hydrogels, Carbon N. Y. 49 (2011) 47–53. doi:10.1016/j.carbon.2010.08.040.

[25]

G. Xie, J. Cheng, Y. Li, P. Xi, F. Chen, H. Liu, F. Hou, Y. Shi, L. Huang, Z. Xu, D. Bai, Z. Zeng, Fluorescent graphene oxide composites synthesis and its biocompatibility study,

16

J. Mater. Chem. 22 (2012) 9308. doi:10.1039/c2jm16678j. [26]

S. Baek, S.-H. Yu, S.-K. Park, A. Pucci, C. Marichy, D.-C. Lee, Y.-E. Sung, Y. Piao, N. Pinna, A one-pot microwave-assisted non-aqueous sol–gel approach to metal oxide/graphene nanocomposites for Li-ion batteries, RSC Adv. 1 (2011) 1687. doi:10.1039/c1ra00797a.

[27]

S.-K. Park, S.-H. Yu, N. Pinna, S. Woo, B. Jang, Y.-H. Chung, Y.-H. Cho, Y.-E. Sung, Y. Piao, A facile hydrazine-assisted hydrothermal method for the deposition of monodisperse SnO 2 nanoparticles onto graphene for lithium ion batteries, J. Mater. Chem. 22 (2012) 2520–2525. doi:10.1039/C1JM14199F.

[28]

S. Stankovich, D.A. Dikin, R.D. Piner, K.A. Kohlhaas, A. Kleinhammes, Y. Jia, Y. Wu, S.T. Nguyen, R.S. Ruoff, Synthesis of graphene-based nanosheets via chemical reduction of

exfoliated

graphite

oxide,

Carbon

N.

Y.

45

(2007)

1558–1565.

doi:10.1016/j.carbon.2007.02.034. [29]

J. Yan, T. Wei, W. Qiao, B. Shao, Q. Zhao, L. Zhang, Z. Fan, Rapid microwave-assisted synthesis of graphene nanosheet/Co3O4 composite for supercapacitors, Electrochim. Acta. 55 (2010) 6973–6978. doi:10.1016/j.electacta.2010.06.081.

[30]

S.

Das,

D.-Y.

Kim,

C.-M.

Choi,

Y.-B.

Hahn,

Influence

of

aqueous

hexamethylenetetramine on the morphology of self-assembled SnO2 nanocrystals, Mater. Res. Bull. 46 (2011) 609–614. doi:10.1016/j.materresbull.2010.12.034. [31]

D.N. Oosthuizen, D.E. Motaung, H.C. Swart, In depth study on the notable roomtemperature NO2 gas sensor based on CuO nanoplatelets prepared by sonochemical method: Comparison of various bases, Sensors Actuators B Chem. 266 (2018) 761–772. doi:10.1016/j.snb.2018.03.106.

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List of Figures Figure 1. (a) UV-visible absorption spectrum of graphene oxide and rGO/SnO2 nanocomposite, (b) XRD pattern, (c) Raman spectrum and (d) FTIR spectrum of rGO/SnO2 nanocomposite prepared by ultrasound-assisted method.

Figure 2. (A) TEM Image, (B) Elemental Map images for C, Sn, and O and (C) EDS of rGO/SnO2 nanocomposite prepared by ultrasound assisted method.

Figure 3. XPS survey spectrum of ultrasonically prepared rGO/SnO2 nanocomposite and resolved fitting signal of C 1s, Sn 3d and O 1s.

Figure 4. (A) Cyclic voltammetry (CV), and (B) Galvanostatic charge-discharge (GCD) profile for rGO/SnO2 nanocomposites prepared by ultrasound assisted method.

Figure 5. The response curves to different concentration (ppm) NO2 of the sensor based on rGO/SnO2 nanocomposite prepared by ultrasound assisted method at operating temperature of 150 °C.

Figure 6. The response (%) and response time (sec) at different concentration (ppm) of NO2 for rGO/SnO2 nanocomposite based sensor at operating temperature of 150 °C.

Figure 7. The response curves of different gases on the sensor based on rGO/SnO2 nanocomposite prepared by ultrasound assisted method at operating temperature of 150 °C and 100 ppm concentration.

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Figure 1. (a) UV-visible absorption spectrum of graphene oxide and rGO/SnO2 nanocomposite, (b) XRD pattern, (c) Raman spectrum and (d) FTIR spectrum of rGO/SnO2 nanocomposite prepared by ultrasound-assisted method.

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Figure 2. (A) TEM Image, (B) Elemental Map images for C, Sn, and O and (C) EDS of rGO/SnO2 nanocomposite prepared by ultrasound assisted method.

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Figure 3. XPS survey spectrum of ultrasonically prepared rGO/SnO2 nanocomposite and resolved fitting signal of C 1s, Sn 3d and O 1s.

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0.003

10mV/s 20mV/s 30mV/s 50mV/s

0.002

(A)

Current (A)

0.001 0.000 -0.001 -0.002 -0.003 -0.004

0.0

0.1

0.2

0.3

0.4

0.5

Potential (V)

0.6

(B)

Potential (V)

0.4

1mA

0.2 0.0

-0.2 -0.4 0

20

40

60

80

100

Time (sec) Figure 4. (A) Cyclic voltammetry (CV), and (B) Galvanostatic charge-discharge (GCD) profile for rGO/SnO2 nanocomposites prepared by ultrasound assisted method.

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Gas off

100

Response (%)

80

Gas in

Gas off

Gas in Gas in

60 40 40 ppm 60 ppm 80 ppm 100 ppm

20 Gas in

0 200

400

600

800

1000

Time (sec) 80 70 60 Response (%)

Gas off

1 ppm 5 ppm 10 ppm 20 ppm

50 40

Gas off

30

Gas in

20 10 Gas in

0 0

100

Gas off

200

300 400 Time (sec)

500

600

Figure 5. The response curves to different concentration (ppm) NO2 of the sensor based on rGO/SnO2 nanocomposite prepared by ultrasound assisted method at operating temperature of 150 °C.

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32 100

30 28

Response (%)

26 24

60

22 40

20 18

20

16 Response (%) Response Time (sec)

0

Response Time (sec)

80

14 12

0

20

40

60

80

Concentration (ppm)

100

Figure 6. The response (%) and response time (sec) at different concentration (ppm) of NO2 for rGO/SnO2 nanocomposite based sensor at operating temperature of 150 °C.

25

100

Response (%)

80

60 NO2 Acetone LPG NH3

40

20

SO2

0 0

200

400

600

Time (sec) Figure 7. The response curves of different gases on the sensor based on rGO/SnO2 nanocomposite prepared by ultrasound assisted method at operating temperature of 150 °C and 100 ppm concentration.

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Declaration of Interest Statement Authors declares that there is no known conflict of interest.

Dr. Bharat A. Bhanvase and All Authors Professor Chemical Engineering Department Laxminarayan Institute of Technology, Nagpur (India)