Sensor for volatile organic compounds using an

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from poly(3,4-ethylenedioxythiophene)- poly(styrenesulfonate) and ultra-large graphene oxide. Amirhossein Hasani, Hamed Sharifi. Dehsari, Jaber Nasrollah ...
Sensor for volatile organic compounds using an interdigitated gold electrode modified with a nanocomposite made from poly(3,4-ethylenedioxythiophene)poly(styrenesulfonate) and ultra-large graphene oxide Amirhossein Hasani, Hamed Sharifi Dehsari, Jaber Nasrollah Gavgani, Elham Khodabakhshi Shalamzari, et al. Microchimica Acta Analytical Sciences Based on Micro- and Nanomaterials ISSN 0026-3672 Microchim Acta DOI 10.1007/s00604-015-1487-7

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Author's personal copy Microchim Acta DOI 10.1007/s00604-015-1487-7

ORIGINAL PAPER

Sensor for volatile organic compounds using an interdigitated gold electrode modified with a nanocomposite made from poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) and ultra-large graphene oxide Amirhossein Hasani 1 & Hamed Sharifi Dehsari 2 & Jaber Nasrollah Gavgani 2 & Elham Khodabakhshi Shalamzari 2 & Alireza Salehi 1 & Farmarz Afshar Taromi 2 & Mojtaba Mahyari 3

Received: 2 December 2014 / Accepted: 25 March 2015 # Springer-Verlag Wien 2015

Abstract A highly efficient gas sensor is described based on the use of a nanocomposite fabricated from poly(3,4ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOTPSS) and ultra-large graphene oxide (UL-GO). The nanocomposite was placed by drop casting in high uniformity on interdigitated gold electrodes over a large area of silicon substrate and investigated for its response to volatile organic compounds (VOCs) at room temperature. Monolayers of ULGOs were synthesized based on a novel solution-phase method involving pre-exfoliation of graphite flakes. The nanocomposite was optimized in terms of composition, and the resulting vapor sensor (containing 0.04 wt% of UL-GO) exhibits strong response to various VOC vapors. The improved gas-sensing performance is attributed to several effects, viz. (a) an enhanced transport of charge carriers, probably a result of the weakening of columbic attraction between PEDOT and

PSS by the functional groups on the UL-GO sheets; (b) the increase in the specific surface area on adding UL-GO sheets; and (c) enhanced interactions between the sensing film and VOC molecules via the network of π-electrons. The sensitivity, response and recovery times of the PEDOT-PSS/UL-GO nanocomposite gas sensor with 0.04 wt% of UL-GO are 11.3 %, 3.2 s, and 16 s, respectively. At a methanol vapor concentration as low as 35 ppm, this is an improvement by factors of 110, 10, and 6 respectively, compared to a PEDOTPSS reference gas sensor without UL-GO. Keywords Ultra large graphene oxide . Gas sensor . PEDOT polystyrenesulfonate nanocomposite . VOCs detection

Introduction Amirhossein Hasani, Hamed Sharifi Dehsari and Jaber Nasrollah Gavgani contributed equally to this work. Electronic supplementary material The online version of this article (doi:10.1007/s00604-015-1487-7) contains supplementary material, which is available to authorized users. * Farmarz Afshar Taromi [email protected] 1

Department of Electrical Engineering, K.N. Toosi University of Technology, P.O.Box 16315-1355, Tehran, Iran

2

Department of Polymer Engineering and Color Technology, Amirkabir University of Technology, P.O.Box 15875-4413, Tehran, Iran

3

Department of Chemistry, Shahid Beheshti University, G. C., P.O. Box 19396-4716, Tehran, Iran

The increased emission of harmful volatile organic compounds (VOCs) and other gases since the mid-20th century has been thought to one of the causes for the increase in allergies, asthma, cancer, and emphysema, a phenomenon known as health warming [1–3]. Efforts are being undertaken to mitigate the VOCs concentration by monitoring and subsequently reducing VOCs emission from the household products, industrial processes, and synthetic products such as fuel, wax, paint, and etc. [4–6]. Therefore, it is important to develop low-cost, sensitive, resettable sensors that can be used to monitor and control the VOCs concentration in industrial exhaust gases. An effective and practical approach to advanced VOCs sensing system is the combination of functional polymers or organic material and other functional inorganic nanomaterials by solution processing.

Author's personal copy A. Hasani et al.

Poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT-PSS) is a conjugated polymer widely used as the active material in flexible and electronic nose sensing systems because of its good electrical conductivity, high transparency, low redox potential, good processability, and excellent environmental stability [7]. However, its limited structural and chemical properties remain major obstacles that inhibit its use in various practical applications [8]. Its combination with novel carbon nanostructures may be a potential solution to the shortcomings. Graphene, a one-atom thick two-dimensional (2D) carbon nanosheet exhibiting outstanding properties, holds great focus for various application including ultrasensitive detection [9, 10]. In order to explore its full potential, many efforts has been made to graphene prepared via the micromechanical cleavage of graphite [11] or via the reduction of graphene oxide (GO) and get novel properties in dangerous gas detection [10]. These sensors exhibit high sensitivity to gases, involving NH3, NO2, and so on [6, 12, 13]. The mechanism for sensing appears to be similar to that of carbon nanotube-based gas sensors [14, 15]. Although some studies have reported the graphene based sensors towards VOCs sensing, due to long response time prevent its applications [10, 16, 17]. Moreover, fabrication of sensors based this nanomaterial to VOCs detection remains difficult. As an alternative candidate for graphene, GO presents considerable advantage for gas sensing applications, especially for VOCs detection. GO can be exploited to substantially produce graphene and producing continuous films from GO suspensions is fairly straightforward and this was mainly because GO is water dispersible, thereby enabling succeeding exfoliation into few-layer nanostructures to form GO [10, 18, 19]. The distributed chemical groups including oxygen on GO platelets, can increase the sensitivity of the sensors towards VOCs. However, many groups have used the composite of PEDOT-PSS with many carbon nanostructures to solve the problems associated with PEDOT:PSS with regard to low sensivity and high response time of VOCs sensor [20–22]. Therefore, developing a novel VOCs sensing material that has high and even sensitivity for the full range of VOCs remains a challenge. This study aimed to develop the VOC gas sensors with high sensitivity, fast response and recovery, and good reversibility. The nanocomposite made from PEDOT-PSS and ultralarge graphene oxide (UL-GO) was used as the sensing component of the VOC gas sensors fabricated on interdigitated gold electrode. Monolayer UL-GO nanosheets were synthesized based on a novel solution-phase method involving preexfoliation of graphite flakes. We find that PEDOT-PSS/ULGO based VOCs sensors exhibit high VOCs sensitivity, as well as short response and recovery times to methanol.

Experimental Fabrication of PEDOT-PSS/UL-GO nanocomposites Ultra-large graphene oxide (UL-GO) was synthesized based on the modified Hummers method using expanded graphite [23–25]. The obtained UL-GO particles were diluted using deionized water (~1 mg·mL−1) and mildly sonicated for 20 min in a bath sonicator, followed by mild-speed centrifugation at 5000 rpm for 5 min. The UL-GOs with a mean lateral size of more than 70 μm were obtained. The various contents of UL-GO dispersion was mixed with filtered poly (3, 4ethylenedioxythiophene)-poly (styrenesulfonate) (PEDOTPSS, Clevios PH1000, www.heraeus-clevios.com) and 6 wt% dimethyl sulfoxide (DMSO, Merck, www. merckgroup.com) and a homogeneous aqueous dispersion was obtained after 6 h stirring. Figure 1 summarizes the preparation steps of PEDOT-PSS/UL-GO nanocomposite film. Fabrication of PEDOT-PSS/UL-GO nanocomposite gas sensors For fabrication of PEDOT-PSS/UL-GO nanocomposite gas sensors, interdigitated gold electrodes with 100 nm thickness were deposited on a SiO2/Si substrate (10×4 mm) by physical vapor deposition method (see Fig. 2a-c). The prepared PEDOT-PSS/UL-GO nanocomposite solution was then drop casted over a interdigitated gold electrode (see Fig. 2d and e). The width and inter-spacing of the gold electrodes are about 200 and 400 μm, respectively. Then the sensors were backed for 1 h in furnace (Exciton, EX1200-4 L) at 80 °C in nitrogen atmosphere. The PEDOT-PSS gas sensor in the presence of 6 wt% DMSO was also fabricated and tested as a reference for comparison. The fabricated PEDOT-PSS/UL-GO nanocomposite gas sensor is displayed in Fig. 2e and f. Characterization methods The aqueous dispersions of UL-GO sheets were examined under an optical microscope (Olympus BH2-DMA). Freeze dried UL-GO samples were examined on a scanning electron microscope (SEM, JEOL-6390) to obtain high quality images. Transmission electron microscope (TEM) images were obtained using a JEM-2200 FS at 200 kV to observe the ULGO sheets. For characterization of the UL-GO, Raman spectra of the UL-GO were observed with a Nanofinder 30 (Tokyo Instruments Co., Osaka, Japan). Fourier-transformed infrared spectroscopy (FTIR) analysis was performed using a Bruker, IFS-66/S over the wavenumber range of 4000–400 cm−1. The X-ray diffraction (XRD) studies were performed using a powder XRD system (Philips1825) with Cu Kα radiation (λ= 0.154 nm), operating at 40 keV and with a cathode current of 20 mA, to characterize the interlayer spacing of the UL-

Author's personal copy Sensor for volatile organic compounds using an interdigitated, modified gold electrode

Oxidization

Sonication

GO

Graphite oxide sheets

Expanded Graphite

Mild-speed centrifugation at 5000 rpm for 5 min

PEDOT-PSS + 6 wt% DMSO

Drop Casting

Stirring for 6 h

PEDOT-PSS/UL-GO nanocomposites film

PEDOT-PSS/UL-GO

UL-GO

Fig. 1 Preparation steps of PEDOT-PSS/ UL-GO nanocomposites film

GO sample. The roughness and surface morphology of the PEDOT-PSS/UL-GO nanocomposite sensing film was analyzed by using an atomic force microscopy (AFM, Dualscope/ Rasterscope C26, DME, Mahar Fan Abzar Co, Iran) with the tapping mode. The sensing film conductivity was measured using a 4-point probe. The UV–visible

Fig. 2 Schematic steps of gas sensor fabrication process

spectrometry (Lambda 650, Perkin Elmer) was used to verify the π–π* transitions in UL-GO and PEDOT-PSS at ambient temperature. The sensor resistances were measured in a closed steel chamber (lab-made) with a LCR meter (Pintek-LCR900) and vapor gas flows were injected into the closed steel chamber by a mass flow meter (Alicat scientific, Tucson, USA).

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The response and selectivity of the gas sensors were then assessed by the standard flow-through method towards methanol, ethanol, acetone, toluene, water, chlorobenzene, and propanol with gas concentrations ranging from 35 to 1000 ppm at room temperature. A constant flux of nitrogen of about 50 cm3·min−1 was mixed with the target gas source at different flow rate ratios to desired concentrations using mass flow controllers. All experiments were performed at room temperature (25±2 °C) and the relative humidity of 10±2 %. The sensitivity defined by the following equation: Sensitivity ¼

ΔR  100 R0

ð1Þ

and ΔR ¼ Rgas −R0

ð2Þ

where R0 and Rgas are the resistances of the sensor in nitrogen and target gas, respectively.

Results and discussion Characterization of UL-GO sheets Figure 3a presents optical micrograph of the UL-GO sheets, confirming a lateral size of up to 70 μm. The corresponding SEM image is presented in Fig. 3b. The UL-GO sheets had a lateral size mainly on the order of 30–70 μm. Moreover, many of them are even larger than 100 μm and up to 300 μm. However, fragments of smaller UL-GO sheets on the order of 10– 30 μm, were also observed due to breakages during the exfoliation process. TEM micrograph presented in Fig. 3c further confirmed monolayer exfoliation of UL-GO sheets. Moreover, this observation indicates that the UL-GO sheets indeed consisted of single layers, in good agreement with the optical and SEM observations. Figure 4a shows the XRD pattern of UL-GO sample, indicating that the as-prepared UL-GO had a distinct peak at 2θ=10.6° corresponding to a d-spacing of 8.32 A° according to Bragg’s law: 2dsinθ=nλ, where n is an integer determined by the given order, and λ is the wavelength. The individual UL-GO sheets are interlinked by a non-uniform network of hydrogen bonds between oxygenated functional groups and water molecules. Therefore the interlayer spacing of UL-GO sheets is proportional to the degree of oxidation. The Raman spectrum of the nanographitic systems has two main peaks: the G-band at ~ 1575 cm−1 corresponds to the planar configuration of sp2-hybridized carbon-based materials, while the Dband (~1352 cm−1) is activated when the defects participate in the double resonance Raman scattering near the K point of the Brillouin zone. Raman spectra shown in

Fig. 3 a Optical micrograph, b SEM image, and c TEM micrograph of the as-prepared UL-GO sheets

Fig. 4b indicate the D to G band intensity ratio, ID/IG is 0.85 which correspondent to successful synthesize of ULGO sheets. Besides, the chemical structure of as-prepared UL-GO sheets was presented by FTIR, as shown in Fig. 4c. The vibration modes of UL-GO sample were assigned as has been reported previously [26]. The band in the range of 3200–3400 cm−1 is attributed to the O–H stretching vibrations arising from hydroxyl groups in ULGO and water adsorbed on the UL-GO sheets. The absorption band at 1726 cm−1 is the characteristic band of C=O groups in carbonyl and carboxyl moieties. The band

Author's personal copy Sensor for volatile organic compounds using an interdigitated, modified gold electrode

Gas sensing properties

Fig. 4 a XRD pattern, b Raman spectrum, and c FTIR spectrum of asproduced UL-GO sheets

at 1627 cm−1 are associated with the skeletal vibrations of unoxidized graphitic domains (C=C) or the contribution from the stretching deformation vibration of intercalated water. Moreover, the bands at 1387, 1227 and 1135 cm−1 are assigned to the C-O (carboxy), C–OH, and C–O (alkoxy) bonds, respectively.

Figure 5 shows the sensivity of the UL-GO, PEDOT-PSS and PEDOT-PSS/UL-GO nanocomposite gas sensors towards various concentration of methanol vapor at room temperature. It indicates that the PEDOT-PSS/UL-GO nanocomposite gas sensors exhibits good sensivity towards methanol vapors. The gas responses towards 700 ppm methanol of pristine UL-GO, PEDOT-PSS, and PEDOTPSS/UL-GO (with 0.04 wt% UL-GO) nanocomposite gas sensors are calculated to be 0.2, 9.4, and 146.6 %, respectively. It is seen that the sensivity of pristine UL-GO to methanol is much lower than that of PEDOT-PSS, but the sensivity is substantially enhanced after UL-GO inclusion. The sensitivity changing behaviors may be attributed to the adsorption and desorption of methanol molecules of the sensing films. This improvement may be resulted in the separation of PEDOT and PSS chains, mainly because the coulombic attraction between PEDOT and PSS was weakened by oxygenated functional groups on UL-GO sheets [23, 27]. These covalently bond between PEDOT chains and UL-GO sheets made the conductive network. It corresponds to a significant increase of charge carrier concentration due to UL-GO incorporation. As shown in Fig. 5, the sensitivity of the PEDOT-PSS/UL-GO nanocomposite gas sensors increases remarkably, and the highest value is obtained with 0.04 wt% UL-GO in all methanol vapor concentration. The PEDOT-PSS/UL-GO (0.04 wt%) with a high conductivity of 1467 S·m−1 may form conduction channels that substantially enhance the charge transport process (Fig. S1, Electronic Supplementary Material, ESM). However, the sensitivity drops when the amount of UL-GO is further increased. This result has to do with reduction of the oriented conductive network between PEDOT chains and higher UL-GO concentration (Fig. S2, ESM). Measurements of AFM topographies and phase images were performed to further investigate phase separation between PEDOT and PSS chains. As shown in Fig. 6, the bright and dark domains are observed in phase images, corresponding to PEDOT-rich grains and PSS-rich grains, respectively [23, 27]. The shape of PEDOT-rich grains transforms from a short curved domain to a long stretched network with increasing the amount of UL-GO to 0.04 wt% [27]. It means that depletion of insulating PSS and generation of larger contact areas between oriented PEDOT-rich grains by moderate ULGO can add more conductive pathways for carriers to improve sensitivity of PEDOT-PSS/UL-GO nanocomposite gas sensors. It seems that the addition of UL-GO up to 0.04 wt% cause the shape of PEDOT-rich grains to changes the short curved domain again. The excessive UL-GO sheets is probably to result in more serious phase separation of PEDOT-PSS and influence the formation of oriented PEDOT-rich grains. Moreover from AFM images, it can be seen that pristine

Author's personal copy A. Hasani et al. Fig. 5 Sensitivity of UL-GO, PEDOT-PSS, and PEDTO-PSS/ UL-GO nanocomposite gas sensors to various concentration of methanol vapor at room temperature

PEDOT-PSS sensing film surface is very smooth containing only few tiny defects over a scan area of 5 μm × 5 μm (Fig. 6a). With 0.04 wt% UL-GO addition, the sensing film surface becomes relatively rough (Fig. 6b). The average surface roughness of PEDOT-PSS and PEDOT-PSS/UL-GO (0.04 wt%) sensing film are estimated to be ~ 1.33 and ~ 10.56 nm, respectively. The much larger surface roughness of PEDOT-PSS/UL-GO (0.04 wt%) sensing film suggests that significant enhancement of the active surface area of UL-GO improves gas adsorption. The sensitivity enhancement of PEDOT-PSS/UL-GO nanocomposite films can chiefly be attributed to the separation of PEDOT and PSS chains, and conductive network was formed between separated PEDOT Fig. 6 AFM topographical images of a pristine PEDOT-PSS, b PEDOT-PSS/UL-GO (0.04 wt%) and phase images of c pristine PEDOT:PSS and d PEDOT-PSS/UL-GO (0.04 wt%) sensing films

chains and UL-GO sheets (Fig. S2). Therefore, the PEDOTPSS/UL-GO nanocomposite film with 0.04 wt% UL-GO was used as the optimal film to study the other systematic test as shown in blow. In order to investigate the sensivity and selectivity of P E D O T- P S S a n d op t i m i z e d P E D O T- PS S / U L - G O (0.04 wt%) nanocomposite gas sensors, they were exposed to a variety of VOCs including methanol, ethanol, acetone, toluene, water, chlorobenzene, and propanol at concentration 200 ppm at room temperature. Figure 7 demonstrates the selectivity of PEDOT-PSS and optimized PEDOT-PSS/UL-GO nanocomposite gas sensor with 0.04 wt% UL-GO to various VOCs vapors. It can be seen that the PEDOT-PSS reference

Author's personal copy Optimiized PEDO OT-PSS/UL-GO (0.044 wt%) 35

[34] [35]

PEDOT-PSS

This work [28] [29] [30] [31] [32] [33]

Reference

Sensor for volatile organic compounds using an interdigitated, modified gold electrode

102 ~300 5 2 1–200 ppm 2.5–1000 ppm Silver nanoparticle-graphene/PIL Fe3O4-RGO/PIL

3.4 for 100 ppm ~3 for 2.5 ppm

16 20–30 – ~400 ~30 ~360 149 3.2 3–5 – ~120 ~30 600 20 35–1000 ppm 1–5000 ppm 100–100,000 ppm 100,000–1,000,000 ppm 100,000–500,000 ppm 0–10,000 ppm 1–90 ppm Optimized PEDOT-PSS/UL-GO PEDOT/Carbon nano tube (CNT) Polydiacetylene/Graphene Poly(methyl methacrylate)/CNT PEDOT-PSS/Nanowire Chitosan/CNT Reducer graphene oxide (RGO)/ poly(ionic liquid) (PIL)-PEDOT

gas sensor shows low response (≤ 5 %) at room temperature. The sensivity of optimized PEDOT-PSS/UL-GO nanocomposite gas sensor to methanol, ethanol, acetone, toluene, water, chlorobenzene and propanol are 35, 12.2, 8.8, 2.14, 6.6, 4.5, and 2.6 %, respectively. With 0.04 wt% UL-GO addition, the sensivity and selectivity to methanol are substantially improved. The optimized PEDOT-PSS/UL-GO nanocomposite gas sensor exhibits a remarkably high response to methanol and is almost sensitive to other VOCs vapors. Moreover, the sensivity, response and recovery times of the optimized PEDOT-PSS/UL-GO nanocomposite gas sensor is 11.3 %, 3.2 s, and 16 s respectively which is 110, 32, and 6 times higher than that of PEDOT-PSS reference gas sensor even under low methanol vapor concentration of 35 ppm (Table S1, ESM). Figure S5a (ESM) shows the dependence of the optimized PEDOT-PSS/UL-GO nanocomposite gas sensor sensitivity on concentration for methanol, ethanol, and acetone at room temperature. At 1000 ppm concentration, the gas response of optimized PEDOT-PSS/UL-GO nanocomposite gas sensor to methanol, ethanol, and acetone are 189, 85, and 3 %, respectively. It can be seen that the optimized PEDOT-PSS/UL-GO nanocomposite gas sensor shows relatively high response to methanol compared with ethanol, and acetone at room temperature (Fig. S5b, ESM). The response time of the optimized PEDOT-PSS/UL-GO nanocomposite gas sensor towards 35 ppm methanol, ethanol, and acetone are estimated to be ~ 3.2 s, while the recovery time of the optimized PEDOT-PSS/ UL-GO nanocomposite gas sensor towards as mentioned before VOCs vapors are ~ 16, 13.8, and 10.2 s, respectively (Fig. S5c,d, ESM). Compared with the recent literatures (see Table 1) on methanol gas detection at room temperature [28–35], the as-prepared optimized PEDOT-PSS/UL-GO nanocomposite gas sensor in this work showed the best sensitivity and the fastest response. The enhanced methanol

Table 1

Gaseous species

Fig. 7 Selectivity of the PEDOT-PSS and optimized PEDOT-PSS/ULGO nanocomposite gas sensors to various VOCs vapors of 200 ppm

The methanol detection performance of the optimized PEDOT-PSS/UL-GO nanocomposite gas sensor in this work, compared with the literatures

0

11 for 35 ppm ~12 for 3000 ppm ~30 for 100,000 ppm ~18 for 100,000 ppm 3 for 200,000 ppm ~11 for 1000 ppm 3.45 for 30 ppm

Recovery time (s)

5

Response time (s)

10

Sensitivity (%)

15

Detection range

20

Sensing materials

25

ΔR/R0 (%)

30

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sensing properties of optimized PEDOT-PSS/UL-GO nanocomposite gas sensor may be attributed to (I) improvement the formation of the linear and extended-coil conformation of PEDOT and PSS chains and increase of the surface roughness as shown in Fig. 6, (II) intrinsic sensing properties of PEDOT-PSS and UL-GO and (III) π-electron interaction by UL-GO loading in PEDOT-PSS sensing film (Fig. S3, ESM). (I) The gas sensitivity is directly proportional with the surface roughness of sensing film due to provide a specific surface-tovolume ratio [36]. The much larger surface roughness of optimized PEDOT-PSS/UL-GO nanocomposite film and formation of long stretched conductive networks of PEDOT therefore enhances the active surface-area for gas adsorption. (II) It is well-known that PEDOT-PSS and UL-GO under ambient conditions behaves as π-type semiconductor that contains hole-like charge carriers [20, 37–40]. When PEDOT-PSS/ UL-GO nanocomposite gas sensors is exposed to an electron donating gas like methanol, depletion of holes from the valence band of PEDOT-PSS and UL-GO occurs resulting in a significant increase in resistance. Thus, the addition of ULGO in PEDOT-PSS leads to synergistic effect on the increment of methanol response. (III) Methanol molecules may interact with not only UL-GO and PEDOT-PSS but also π–π bonding between UL-GO and PEDOT-PSS [20, 40] (see Fig. S6, ESM). Under the exposure to polar molecules like methanol, the interaction can induce charge-transfer across delocalized π-electrons resulting in the improved sensing performances.

Conclusion The PEDOT-PSS/UL-GO nanocomposite gas sensors has been successfully fabricated and characterized for VOCs vapors sensing. Monolayer UL-GO sheets were prepared employing a modified chemical method that involved preexfoliation of graphite flakes. The use of exfoliated graphite instead of conventional graphite intercalation compounds was aimed at minimizing possible breakage of the UL-GO sheets during the chemical process. The incorporation of UL-GO in PEDOT-PSS leads to considerable enhancement of VOCs response, dynamic behavior and selectivity to methanol due possibly to the phase separation of PEDOT and PSS, enhancement of direct charge transfers, increase of the specific surface area, intrinsic sensing properties of PEDOT-PSS and UL-GO, and π–π interaction in optimized PEDOT-PSS/UL-GO nanocomposite sensing film. The optimized PEDOT-PSS/UL-GO nanocomposite gas sensor with 0.04 wt% UL-GO exhibits high sensing performance to methanol with concentrations ranging from 35 to 1000 ppm at room temperature. From the results, the as-prepared optimized PEDOT-PSS/UL-GO nanocomposite gas sensor offers several distinct advantages over some other sensors including high sensing performances, low

temperature processing, high productivity, simplicity and low cost. Moreover, it will be useful for development of future wearable electronic technology.

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