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Inkjet printing synthesis of sandwiched structured ionic liquidcarbon nanotube-graphene film: towards disposable electrode for sensitive heavy metal detection in environmental water samples Shuang Dong, Zhengyun Wang, Muhammad Asif, Haitao Wang, Yang Yu, Yulong Hu, Hongfang Liu, and Fei Xiao Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.6b04251 • Publication Date (Web): 03 Feb 2017 Downloaded from http://pubs.acs.org on February 3, 2017

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Industrial & Engineering Chemistry Research

Inkjet Printing Synthesis of Sandwiched Structured Ionic Liquid-Carbon

Nanotube-Graphene

Film:

towards

Disposable Electrode for Sensitive Heavy Metal Detection in Environmental Water Samples Shuang Dong†, Zhengyun Wang†, Muhammad Asif †, Haitao Wang†, Yang Yu†, Yulong Hu‡, Hongfang Liu*,†, Fei Xiao*,† †

Department of Chemistry and Chemical Engineering, Hubei Key Laboratory of

Material Chemistry and Service Failure, Key Laboratory for Large-Format Battery Materials and System, Ministry of Education, Huazhong University of Science and Technology, Wuhan 430074, PR China ‡

College of Science, Naval University of Engineering, 717 Jiefang Avenue, Wuhan

430033, China KEYWORDS: nanohybrid graphene film，disposable electrode，heavy metal ions detection，inkjet printing ABSTRACT: In this work, we have developed a new type of sandwiched structured ionic liquid (IL)–carbon nanotube (CNT)–graphene film (GF) synthesized by a facile and effective inkjet printing method. Owing to the synergistic effects of different components in the nanohybrid material, IL–CNT–GF material demonstrates outstanding properties including large surface area, sufficient surface active sites and fast charge transferability. When used in electrochemical determination of cadmium ion (Cd2+) and lead ion (Pb2+), it exhibits good sensing performance of high sensitivity, a wide linear range up to 1 µM, a low detection limit down to 0.1 nM for Cd2+ and 0.2

ACS Paragon Plus Environment


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nM for Pb2+ (S/N=3), and good selectivity as well. These outstanding electrochemical sensing performances allow it to be used for heavy metal detection in environment water samples. INTRODUCTION The ever-increasingly serious environmental pollutions, including atmospheric problems, noise hazard and water contamination, have seriously affected the human being health and the ecological balance. Specially, heavy metal contaminations in water have caused serious damages to the human immune systems due to the bioaccumulation in environment ecosystems, which urgently require the effective control and management.1-4 This demand has aroused significant concern in the design and development of high-efficient portable analytical instruments for real-time detection of heavy metal in environment samples.5, 6 Nowadays, great efforts have been devoted to developing electrochemical analytical instruments for heavy metal detection due to their fast response, high sensitivity, easy operation, portability and affordability. As a key ingredient implemented in electrochemical analytical instruments, the electrode system demonstrates significant impact on the overall performance of the analytical instruments. Noticeably, the electrode materials based on flexible thin film have sparked tremendous research interest for their collective attributes such as high flexibility under high tensile strain or large deformation, light weight and ultrathin thickness, which enable them to be rolled up or incorporated into miniaturized analytical apparatus.7-9 More importantly, thin film electrode materials made up of


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low-cost and accessible electrode materials by facile and scalable synthesis method can be used as disposable electrode for the analysis of multiple environment samples, which can circumvent the common problems of conventional electrodes such as carry-over and surface fouling, and therefore give rise to an improved accuracy of the analytical results. Freestanding graphene film (GF) assembled from individual graphene nanosheets (GNs) have been characterized by a unique set of structural and mechanical properties, such as high electronic conductivity, outstanding mechanical flexibility, excellent thermal and chemical stability.10-14 These properties make GF fascinating disposable electrode

material in electrochemical biosensors.15-18

Technologies actively explored for the fabrication of GF mainly include Langmuir–Blodgett method, inkjet printing, vacuum filtration and chemical vapor deposition.18-22Among these approaches, inkjet printing has recently been the subject of intense interest because of its ease of operation, relative low cost, and scalable manufacturing.23 However, GF usually suffers from the aggregation and restacking of GNs because of their inter-sheet van der Waals attraction, which inevitably reduces its specific surface areas and limits the electron transport and ions diffusion, and therefore decreases their sensitivity in electrochemical sensing. In order to prevent the aggregation and restacking of GNs, several functional nanomaterials have been employed as the “spacer” in the construction of GF. It was reported that the incorporation of one-dimensional (1D) carbon nanotubes (CNTs) into GF can expand the basal space between graphene layers, and thus increase the specific surface area of



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the resultant GF.24, 25 Nevertheless, carbon-based nanomaterials are usually subjected to the relative few surface functional groups for sufficient binding of target of interest. To overcome this defect, several functional molecules have been used to modify the carbon nanomaterial in order to endow them with more functions and exploit their multiple applications in a wider range. In this work, we reported a well-controlled inkjet printing method to synthesize a new type of nanohybrid sandwiched structured ionic liquid (IL)–CNT–GF nanohybrid material, and explored its practical application as flexible and disposable electrode for electrochemical detection of heavy metal ions in environment samples, as shown in Figure 1. The homogeneous IL–CNT–GN ink was obtained by ball milling of hydrophobic rGO powder and CNT with hydrophilic [Bmim]BF4 molecules, followed by transferring them into water upon ultrasonically agitation. ILs have gained great attention in virtue of their particular characteristics such as wide potential windows, high ionic conductivity, low toxicity, favorable biocompatibility and fantastic solvation properties.26-29 The use of hydrophilic IL (i.e., 1-butyl-3-methylimidazolium tetrafluoroborate, [Bmim]BF4) as the dispersing agent to promote the dispersion of GNs and CNTs through their intrinsic cation-π and π-π interaction to form a uniform IL–CNT–GN ink, which provides the possibility for the preparation of freestanding IL–CNT–GF material by full inkjet printing process.30-32 Moreover, the sufficient functional groups on ILs, such as CH3–CH2, CH2–N and CH3–N in imidazolium ring, and B–F in BF4–, can provide sufficient binding sites for the accumulation of metal ions, which can eliminate the unfavorable effects of toxic organic linkers that usually


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used.33 Owing to the synergistic effects of different components in the nanohybrid material, the resultant IL–CNT–GF electrode demonstrates outstanding properties including large surface area, sufficient surface active sites and fast charge transferability. When used in electrochemical determination of cadmium ion (Cd2+) and lead ion (Pb2+), the as-obtained nanohybrid exhibits good electrochemical sensing performances, with a linear range up to 1 µM for Pb2+ and Cd2+, and a low detection limit of 0.2 nM for Pb2+ and 0.1 nM for Cd2+ (S/N=3). Considering the good sensing performances of the resultant freestanding IL–CNT–GF electrode, the IL–CNT–GF material has been successfully used for real-time trace heavy metal detection in environment samples. It can be envisioned that the nanohybrid GF can not only perform as high-performance material in environmental monitoring of trace pollutant, but also offers new possibilities for other potential promising applications such as portable consumer electronics as well as wearable and implantable medical device for in vitro and in vivo health monitoring.

Figure 1. Schematic diagram of the fabrication process for IL–CNT–graphene film.



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EXPERIMENTAL SECTION Chemicals Graphite power, hydrazine hydrate, [Bmim]BF4, Bi(NO3)3, Pb(NO3)2, Cd(NO3)2, CH3COONa and CH3COOH were obtained from Sinopharm Group Chemical Reagent Co., Ltd. (Shanghai, China). Multi-walled carbon nanotubes (diameter:10~20 nm, length: 10~30 µm, purity: >95%) were purchased from Shenzhen Nanotech Port Co. Ltd. (Shenzhen, China). Bi3+, Pb2+ and Cd2+ stock solutions were prepared by diluting Bi(NO3)3, Pb(NO3)2 and Cd(NO3)2 standard stock solutions in 1.0 wt% HNO3, respectively. Acetate buffer (pH 4.6) was prepared by mixing appropriate amounts of CH3COONa and CH3COOH. Chemical reagents employed in this work were all of analytical grade. Apparatus Cyclic voltammetry (CV), electrodeposition, electrochemical impedance spectroscopy (EIS) and differential pulse anodic stripping voltammetry (DPASV) were performed in a conventional three-electrode system with a CHI760E electrochemical workstation (CHI Instruments, Shanghai, China). The nanohybrid GF, saturated calomel electrode (SCE) and a platinum wire were used as the working electrode, reference electrode and auxiliary electrode, respectively. Inkjet printing of nanohybrid GF was performed with a commercial Dimatix Materials Printer (DMP 2800, Dimatix-Fujifilm Inc.). The scanning electron microscope (SEM) images were obtained using a Hitachi S-4800 Field scanning electron microscope (FSEM). X-ray photoelectron spectroscopy (XPS) was performed with a VG Multilab 2000 X-ray


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photoelectron spectrometer, and the peak positions were internally referenced to the C 1s peak at 284.6 eV. Fourier transform infrared (FT–IR) spectra were recorded with a Fourier Transform InfraRed spectrometer (EQUINOX 55). The Raman spectra were recorded with a micro-Raman spectrometer (Reinshaw Raman Scope RM3000) using an Ar-ion laser with a 514.5 nm laser excitation. Fabrication of thin film electrodes Graphene oxide (GO) was synthesized from graphite powder based on a modified Hummers method, and was reduced by hydrazine hydrate to produce reduced GO (rGO).34, 35 10 mg rGO powder, 5 mg CNT and 1 mL IL were firstly mixed and ground in an agate mortar to form a uniform black gel (IL–CNT–GN gel). Then proper amount of IL–CNT–GN gel was transferred into water, and allowed to proceed for 1 h under vigorous ultrasonically agitating to form homogeneous IL–CNT–GN ink. 2 mg mL-1 IL–CNT–GN ink (droplet size = 10 pL) was printed on commercial paper to form IL–CNT–GF, which was performed on a commercial Dimatix Materials Printer. Finally, IL–CNT–GF on commercial paper was immersed in 5 M HCl solution at room temperature, and then the hybrid film can be easily peeled off from commercial paper after several bubbles generated on the surface of the commercial paper.23 In comparison, CNT–GF and GF were prepared by the similar process. Heavy metal ion detection procedure In a DPASV measurement, the three-electrode system using paper-like film (1 cm × 0.5 cm) as the working electrode was immersed into 0.2 M acetate buffer (pH 4.6)



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solution,36 containing 200 µg L−1 Bi3+ and target heavy metal ions. For the electrochemical deposition of Bi and heavy metal ions on IL–CNT–GF, a deposition potential of -1.2 V and deposition time of 300 s are chosen. After that, the anodic stripping was performed by applying a positive-going potential scan from -1.0 to -0.4 V with amplitude of 50 mV, a step increment of 8 mV and pulse period of 0.2 s.

RESULTS AND DISCUSSION Morphological and structural characterization IL–CNT–GF is freestanding, bendable and tailorable (Figure 2a inset), which can meet various requirements for constructing compact electrochemical sensing system. The top view SEM image reveals that IL–CNT–GF displays uniform surface topography (Figure 2a), while the rough corrugated graphene nanosheets and uniformly distributed CNTs in IL–CNT–GF can be observed at a higher resolution (Figure 2b). Figure 2c and 2d show that IL–CNT–GF features a typical multilayered structure similar to GF,37 where the graphene layers are spaced by the embedded CNTs to form a unique sandwiched structure. The intercalation of CNTs between graphene nanosheets not only prevent the restacking and aggregation of graphene but also increase surface area and improve electrical conductivity, which makes IL–CNT–GF excellent electrode material for electrochemical applications.


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Figure 2. (a) Top-sectional view SEM images of IL–CNT–GF at low magnification Inset is the macroscopic photograph of as-prepared IL–CNT–GF. (b) Top-sectional view SEM images of IL–CNT–GF at higher magnification. (c, d) Cross-sectional view SEM images of IL–CNT–GF with different magnifications.

Figure 3a shows the FT-IR spectra of CNT–GF, IL and IL–CNT–GF composites. Inset is structural formula of [Bmim]BF4. The CNT–GF does not display any distinguishable peaks except a weak C–H rock peak at 1377 cm-1, verifying that the carbon nanomaterials are lack of functional groups. After being modified with hydrophilic IL molecules, a large amount of functional groups appears on the IL–CNT–GF sample. It exhibits the presence of CH2–N and CH3–N stretching vibrations appears at 2960 cm-1, 2870 cm-1, 1573 cm-1, 1466 cm-1 and 1170 cm-1, which are ascribed to the vibration and the imidazolium ring in plane asymmetric



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stretching of IL. In addition, a strong absorption band centered at 1060 cm-1 can be observed, which assigned to (B–F) in BF4– in accordance with IL sample. These results taken together demonstrate that the IL molecules can be successfully modified on the surface of graphene and CNT through the strong interaction between them, leading to IL–CNT–GF with sufficient binding sites for heavy metal accumulation. Raman spectra have been employed to better understand the structural features of IL–CNT–GF. As shown in Figure 3b, since graphene and CNT are two kinds of typical sp2 hybridized carbon materials, the spectrum of IL–CNT–GF exhibits two prominent D-band (1335.3 cm−1) and G-band (1567.4 cm−1) originated from both rGO and CNT. In comparison to that of CNT–GF, there is no obvious peak shift for IL–CNT–GF. And the imidazolium ring in-plane antisymmetric stretching (1432 cm-1) that can be observed at Raman spectrum of pure IL is not detectable in IL–CNT–GF, suggesting that the hybrid GF maintains the typical characteristics of carbon materials.

Figure 3. (a) FT-IR spectra of CNT–GF, IL–CNT–GF sample, and IL sample. (b) Raman spectra of CNT–GF, IL–CNT–GF sample, and IL sample.


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IL–CNT–GF sample was qualitatively examined by XPS, using CNT–GF as the control. The XPS wide-scan spectrum of CNT–GF sample shown in Figure 4a exhibits two characteristic peaks corresponding to C 1s and O 1s at 284.6 eV and 531.3 eV, respectively. while Figure 4b shows IL–CNT–GF sample exhibits two additional peaks assigned to F 1s (691.8 eV) and N 1s (405.0 eV), verifying the presence of F and N element in IL. The curve fit of C1s spectra of CNT–GF sample shown in Figure 4c reveals a main type of carbon bond assigned to C=C/C–C (284.6 eV) and three weak oxygen-containing carbon bonds assigned to C–O (hydroxyl and epoxy, 286.3 eV), C=O (carbonyl, 288.3 eV) and C (O) O (carboxyl, 289.2 eV), while the surface C/O atomic ratio (7.3/1) is much higher than that of the original GO (2/1) reported previously,19 indicative of effective reduction of GO by hydrazine hydrate. The curve fit of C 1s spectra of IL–CNT–GF sample shown in Figure 4d reveals an additional peak assigned to the C–N bond appears at 285.6 eV, which should be attributed to the strong interaction between IL molecules and carbon materials.



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Figure 4. (a) XPS survey spectra of CNT–GF sample. (b) XPS survey spectra of IL–CNT–GF sample. (c) C 1s spectra of CNT–GF sample. (d) C 1s spectra of IL–CNT–GF sample.

Electrochemical characterization To investigate the electrochemical behavior of different hybrid GF, the EIS and CV measurements have been performed in 0.10 M KCl solution containing 1.0 mM K3Fe(CN)6 and 1.0 mM K4Fe(CN)6. Figure 5a shows the EIS of IL–CNT–GF, CNT–GF and GF. Figure 5a inset depicts the equivalent circuit for the nanohybrid film electrodes, where Rs is the solution resistance, and Cdl is the double layer capacitance, W is the Warburg impedance and Rct is the charge-transfer resistance. It is found that these three nanohybrid GF electrodes possess low charge-transfer


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resistance due to the excellent electrical conductivity. The Rct value of CNT–GF is calculated to be 72 Ω which is lower than that (87 Ω) of GF, indicating the introduction of CNT to GF can improve the electrical connectivity between the GNs and CNTs and thus accelerate the electron transfer of [Fe(CN)6]3-/4-. Moreover, the Rct value of IL–CNT–GF further decreases to 60 Ω, indicating the modification of IL molecules endows carbon materials better dispersibility, and therefore facilitates the electron transfer. Figure 5b shows the CV behavior of IL–CNT–GF along with the control GF and CNT–GF. A pair of quasi-reversible one-electron redox peak is observed on all the electrodes, while the peak current of CNT–GF is much larger than that of GF, suggesting that increased specific surface area is attributed to the incorporation of CNT into graphene nanosheets. In addition, IL–CNT–GF displays increased peak current (ip) and decreased peak potential separation (∆Ep) compared with GF and CNT–GF, further confirming superior electrochemical activity of IL–CNT–GF due to the modification of IL on the surface of graphene and CNT promotes the electron tranfer between the electrode and the redox species.

Figure 5. (a) Nyquist plots of IL–CNT–GF (black line), CNT–GF (red line) and GF (blue line) electrodes in 1.0 mM K3Fe(CN)6 + 1.0 mM K4Fe(CN)6, frequency range:



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0.1–105 Hz. Inset is the equivalent circuit. (b) CV curves of IL–CNT–GF (black line), CNT–GF (red line) and GF (blue line) electrodes in 1.0 mM K3Fe(CN)6 + 1.0 mM K4Fe(CN)6, scan rate: 20 mV s-1.

Electrochemical detection of heavy metal ions. With the purpose of reaching maximum sensitivity for the target metal by using paper-like electrodes, the experimental parameters mainly including deposition potential, preconcentration time and the concentration of Bi3+ were optimized. All the DPASV experiments were carried out in acetate buffer solution contained 1 µM each of Pb2+ and Cd2+. The effect of deposition potential on the DPASV responses of IL–CNT–GF was investigated in Figure S1. When the deposition potential turned negative from −1.0 to −1.2 V, the anodic peak currents for Cd2+ and Pb2+ significantly increased. As the deposition potential further decreased to −1.6 V, the anodic peak currents decreased slightly. Therefore, the optimal deposition potential for target metal detection is -1.2 V.38 The influence of preconcentration time on current responses of hybrid paper was shown in Figure S2. The DPASV responses increased proportionally with the preconcentration time from 50 s to 300 s in both Cd2+ and Pb2+ curves, suggesting longer preconcentration time can efficiently promote the deposition of target metal on the surface of paper-like electrode. As preconcentration time further increased to 600 s, the current responses slightly increased and displayed some deviation from the linear relationship with preconcentration time, which was probably owing to saturation of


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the surface active sites.39 Herein, a preconcentration time of 300 s was chosen for the following DPASV experiments. Figure S3 shows the effect of the concentrations of Bi3+ on the peak currents of Cd2+ and Pb2+ in the range from 0 to 600 µg L−1. The stripping peak currents of Cd2+ and Pb2+ increased with the Bi3+ concentrations from 0 to 200 µg L−1 and decreased in the range from 200 to 600 µg L−1. Thicker bismuth films may probably hinder mass transfer between working electrode and target metals,40 resulting in the decrement of current response after the maximum being reached at Bi3+ concentration of 200 µg L−1. Thus, 200 µg L−1 was chosen as the optimum Bi3+ concentration. we have also investigated the effect of pH value of the measure solution on the peak currents of Cd2+ and Pb2+ in the range from 3.6 to 6, as shown in Figure S6. It can be observed that the stripping peak currents of Cd2+ and Pb2+ increased with the pH value from 3.6 to 4.6 and decreased in the range from 4.6 to 6. Therefore, the optimum pH was 4.6. When the pH is low (4.6), the low current response can be attributed to the hydrolysis of Pb2+ and Cd2+ in the solution. In order to further demonstrate the electrocatalytic activities of hybrid film electrodes, DPASV measurements were then performed under the optimal



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experimental conditions. Figure 6a illustrates the DPASV analytical characteristics of IL–CNT–GF, CNT-GF and GF. It was found that well-defined peaks of Pb2+ and Cd2+ were observed, with the peak currents of Pb2+ and Cd2+ at the potentials of approximately −0.55 and −0.79 V, respectively. Moreover, the peak currents of Pb2+ and Cd2+ on IL–CNT–GF are much higher than that on GF and CNT-GF, indicative of enhanced electroactivity towards Pb2+ and Cd2+ detection.

The improved

electrocatalytic performance of IL–CNT–GF may be attributed to the following factors: (i) The incorporation of CNT and IL into GF decreases the agglomeration and restacking of graphene nanosheets, and provides sufficient active surface area for metal ions adsorption. (ii) The incorporation of CNT into GF can improve the electrical conductivity and facilitate the mass transport during the electrochemical reaction which increases the electrocatalytic activity towards the heavy metal ions. (iii) The sufficient functional groups of IL can promote the accumulation of heavy metal, thus increasing the sensitivity of heavy metal detection. Figure 6b illustrates the DPASVs of different concentrations of Pb2+ and Cd2+ on IL–CNT–GF in 0.2 M acetate buffer (pH 4.6) solution. From bottom to top, the increasing concentrations of heavy metal ions are 0, 0.001, 0.08, 0.2, 0.3, 0.4, 0.55, 0.7, 0.8 and 1 µM in sequence. The current response is linear to target metal ions concentrations up to 1 µM, and the correlation equations were defined as y (Cd2+) = -0.34-0.88x, R2 = 0.995 and y (Pb2+) = -0.34-0.75x, R2 = 0.994, respectively (y: current/ mA cm-2, x: concentration/µM) (Figure 6c, 6d). As shown in Figure 6c and Figure 6d, the sensitivity for Cd2+ is 0.88 mA cm-2 µM-1, and the sensitivity for Pb2+ is


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0.75 mA cm-2 µM-1, respectively. Furthermore, the limit of detection (S/N=3) is calculated to be 0.2 nM for Pb2+ and 0.1 nM for Cd2+, respectively (Figure S4), which are lower than those of many previously reported results (Table S1), demonstrating the IL–CNT–GF possesses high performance for the simultaneous determination of Cd2+ and Pb2+.

Figure 6. (a) DPASV of 1 µM of Cd2+ and Pb2+ on different electrodes in 0.2 M acetate buffer (pH 4.6), respectively. From bottom to upper: GF, IL–GF, CNT–GF and IL–CNT–GF. (b) DPASV of simultaneous analysis of Pb2+ and Cd2+ on IL–CNT–GF in 0.2 M acetate buffer (pH 4.6) with different concentrations (from bottom to upper: 0, 0.001, 0.08, 0.2, 0.3, 0.4, 0.55, 0.7, 0.8, 1 µM). (c) The calibration curve of Cd2+. (d) The calibration curve of Pb2+.



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Interference study The sensitivity of IL–CNT–GF electrode was performed by adding various ions into standard solution containing 200 nM Cd2+ and 200 nM Pb2+. The results shows that Al3+, Mn2+, Ba2+, K+, Na+, Ca2+, Mg2+, NH4+, Cl−, NO3−, SO42−, PO43− (200 nM, respectively) do not cause any significant interference for the detection of Pb2+ and Cd2+. However, the addition of Cu2+ (the proportional between concentration of Cu2+ and Pb2+, Cd2+ is 1:1:1) in the mixed solution results in tremendous decrease of current responses of Pb2+ and Cd2+, that is, 84.3% for cadmium and 54.9% for lead (Figure S5), which was probably due to the fierce competition for active sites on the electrode surface among these electrochemical deposited metals as well as the tendency to form the intermetallic compound between copper and target metals.41, 42 Table 1. Determination 50 nM each of Pb2+ and Cd2+ in environmental water samples. Added concentration (nM)

Found concentration (nM)

Recoveries (%)

Cd2+

Cd2+

Cd2+

Pb2+

96.46

95.38

95.68

97.14

Water sample

East Lake water

Tap water

Pb2+

0

0

50

50

0

0

50

50

Not detected 48.23

Pb2+ Not detected 47.69

RSD=1.23%

RSD=3.98%

Not detected

Not detected

47.84 RSD=3.25%

48.57 RSD=1.59%

Determination in environmental water samples Table 1 displays the IL–CNT–GF was used for the detection of 50 nM each of


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Pb2+ and Cd2+ in different kinds of environmental water samples. The samples were collected from East Lake water and Tap water, respectively, and diluted with HAc-NaAc buffer solution before DPASV measurements. Prior to the detection, the samples were filtered through a 0.3 µm membrane. No target metals ions could be detected in the real samples, suggesting the metal ions contents were lower than the detection limits.43 Then the standard addition technique was adopted by adding 50 nM each of Pb2+ and Cd2+ in environmental water samples. The recovery rates of Pb2+ and Cd2+ were higher than 95% and the RSD were below 5%, demonstrating that the proposed paper-like electrode can be used for the simultaneous detection of Pb2+ and Cd2+ in real environmental water samples.44, 45 CONCLUSIONS

In summary, we have developed a new type of IL–CNT–GF by a facile inkjet printing method. The incorporation of CNT into graphene nanosheets can prevent their aggregations and thus gives rise to larger active surface area and improved electron transport. The hydrophilic anion of IL modified on the surface of carbon materials made them easy to disperse in water, which enables them to be suitable for inkjet printing on various substrates. Additionally, the abundant functional groups of IL endow the hybrids film with plenty of binding sites for heavy metal enrichment. Consequently, IL–CNT–GF exhibits high electrocatalytic activity for heavy metal detection, and can be used for rapid heavy metal detection in environmental water samples. Moreover, the thin film electrode with tailorable shapes and adjustable properties would provide opportunity for wide spectrum of electrochemical



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applications. ASSOCIATED CONTENT Supporting Information. Effect of the deposition potential on the stripping peak current; Effect of the preconcentration time on the stripping peak current; Effect of the concentration of Bi3+ on the stripping peak current; DPASV of IL–CNT–GF in the presence of 0.2 nM of Pb2+ and 0.1 nM of Cd2+ and absence of Pb2+ and Cd2+; DPASV of IL–CNT–GF in the presence of 200 nM each of Pb2+, Cd2+ and Cu2+; Comparison of different electrodes for the detection of metal ions in terms of detection limit. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Authors *

E-mail: [email protected] (H. Liu).

*

E-mail: [email protected] (F. Xiao).

Author Contributions The manuscript was written through contributions of all authors. All authors have given approval to the final version of the manuscript. Notes The authors declare no competing financial interest.

ACKNOWLEDGMENT This research was supported by the Innovation Foundation of Huazhong University of Science and Technology Innovation Institute (No.2015ZZGH010 and 2015TS150), the Foundation Key Laboratory for Large-Format Battery Materials and System,


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Inkjet Printing Synthesis of Sandwiched Structured ... - ACS Publications

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