- Email: [email protected]
A freestanding all-solid-state polymeric membrane Cu2+-selective electrode based on three-dimensional graphene sponge
Analytica Chimica Acta xxx (xxxx) xxx
Contents lists available at ScienceDirect
Analytica Chimica Acta journal homepage: www.elsevier.com/locate/aca
A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge Jinghui Li a, c, Wei Qin a, b, * a
Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research (YIC), Chinese Academy of Sciences (CAS), Shandong Provincial Key Laboratory of Coastal Environmental Processes, YICCAS, Yantai, Shandong, 264003, PR China b Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266200, PR China c University of the Chinese Academy of Sciences, Beijing, 100049, PR China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
A freestanding all-solid-state polymeric membrane Cu2þ-ISE based on three-dimensional graphene sponge (3D GS) is developed. The 3D GS can be used as both electrode substrate and solid contact for construction of Cu2þ-ISE. The electrode shows a stable potential response with a LOD of 2.5 109 M.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 26 February 2019 Received in revised form 1 April 2019 Accepted 4 April 2019 Available online xxx
A novel freestanding all-solid-state polymeric membrane Cu2þ-selective electrode (Cu2þ-ISE) is proposed based on three-dimensional graphene sponge (3D GS). The 3D GS electrode has been characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and contact angle measurements. Experiments show that 3D GS possesses a large electrical double layer capacitance, good conductivity, and high hydrophobicity. Based on these superior properties, 3D GS has been applied as both electrode substrate and solid contact for construction of a freestanding all-solid-state polymeric membrane Cu2þ-ISE. The 3D GS-based Cu2þ-ISE shows a good Nernstian response ranging from 1.0 108 to 7.9 104 M with a low detection limit of 2.5 109 M. Moreover, the proposed Cu2þ-ISE exhibits a stable potential response with a reduced water layer at the sensing membrane/3D GS interface and is not affected by interferences from light, O2 and CO2. © 2019 Elsevier B.V. All rights reserved.
Keywords: Three-dimensional graphene sponge Freestanding electrode Solid contact All-solid-state ion-selective electrode Copper
1. Introduction
* Corresponding author. Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research (YIC), Chinese Academy of Sciences (CAS), Shandong Provincial Key Laboratory of Coastal Environmental Processes, YICCAS, Yantai, Shandong, 264003, PR China. E-mail address: [email protected] (W. Qin).
Ion selective electrodes (ISEs) have been widely employed in numerous fields, such as clinical analysis, environmental monitoring, and process control, due to their cost-effectiveness, high reliability, and simple operation [1e3]. All-solid-state ion-selective electrodes (ASS-ISEs) are considered to be the new generation of ISEs, which can be attributed to their excellent properties, including
https://doi.org/10.1016/j.aca.2019.04.003 0003-2670/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: J. Li, W. Qin, A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.04.003
2
J. Li, W. Qin / Analytica Chimica Acta xxx (xxxx) xxx
convenient storage and maintenance, easy miniaturization, and high durability [3]. However, the existence of the “block” interface between the underlying metal and ion-selective membrane (ISM) can lead to signal noises and drifts, which restricts the wide applications of ASS-ISEs [4]. To enhance the potential stabilities of ASS-ISEs, various transducing materials possessing ionic to electronic conductivities have been introduced as solid contacts, which are applied between the underlying electrodes and ISMs [1,5e8]. It should be noted that the fabrication of most of these solid-contact ASS-ISEs requires two steps: an intermediate layer is first formed on electron conducting substrate by drop-coating or electrodeposition, and then an ISM is drop-casted on the surface of the intermediate layer. Such procedures could make it complicated to fabricate a solid-contact ASS-ISE. A new type of ASS-ISEs so called single-piece ASS-ISEs, which are prepared by directly incorporating conducting polymers (CPs) into membrane cocktail, was initially proposed by Bobacka et al. [9,10]. Unfortunately, most CPs are sensitive to gas, light and redox interferences [1,11,12]. The arisen single-piece ASS-ISEs with improved sensing properties have been developed by adding carbon nanotubes (CNTs) into ISMs [13e15]. Some challenges still remain since the low dispensability of CNTs in organic solvents and poor compatibilities with polymer materials. The dispensabilities of CNTs in organic solvents can be further improved by modifying CNTs with lipophilic groups [16,17] or using moderate lipophilic ionic additive [18], whereas the electrical conductivity of CNTs could be affected and unnecessary interferences may be introduced into the sensing membrane, resulting in the deterioration of potentiometric performance [19]. Recently, a simple, low-cost and paper-like freestanding ASS-ISE has been developed [20]. In this ASS-ISE, CNTs conductive paper was used as both electric conductor and solid contact by directly drop-casting the sensing membrane cocktail on the paper.
Analytical performance of the paper-based potentiometric sensor was comparable with that of conventional ASS-ISEs. However, it is time-consuming to remove the excess of surfactants through rinsing of CNTs paper. Graphene paper, prepared by the vacuum infiltration method, has also been used to construct freestanding ASS-ISEs [21]. Nevertheless, the accessible surface area of the twodimensional self-assembling layer-by-layer graphene paper can be reduced due to the irreversible restacking and agglomeration of individual graphene nanosheets caused by van der Waals forces [22,23]. Three-dimensional monothlic graphene sponge (3D GS) can prevent the agglomeration of graphene sheets, resulting in a welldefined and cross-linked 3D interconnected porous structure, and thus enlarge the specific surface area. Because of its large specific surface area, high electric conductivity and good mechanical strength, 3D GS has been widely used in practical applications, such as environmental remediation [24,25], energy storage and conversion [26,27], and sensors [28,29]. Depending on different application requirements, the pore size and shape of 3D GS can be controlled by regulating parameters during the fabrication of GS [30]. In addition, the 3D porous interconnected structure of GS could provide more sites for ion adsorption and diffusion, and facilitate ion to electron transfer [25,31]. These outstanding properties of 3D GS prompt us to study the possibility of taking advantage of GS to develop a novel freestanding ASS-ISE. Herein, we propose a freestanding Cu2þ-selective electrode (Cu2þ-ISE) based on 3D GS. The mesopore and micropore structures of 3D GS contribute to a large specific surface area as well as a high double layer capacitance. The 3D GS material also exhibits an excellent hydrophobicity and good electric conductivity. It will be shown that 3D GS can be used as both electrode substrate and solid contact for construction of a novel freestanding Cu2þ-ISE.
Fig. 1. Schematic illustration of the transduction mechanism of the GS-based all-solid-state ISE.
Please cite this article as: J. Li, W. Qin, A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.04.003
J. Li, W. Qin / Analytica Chimica Acta xxx (xxxx) xxx
2. Experimental 2.1. Reagents and materials o-Xylylene bis(diisobuty1dithiocarba-mate) (copper ionophore II, o-XBDiBDTC), sodium tetrakis[3,5-bis(trifluoro-methyl)phenyl] borate (NaTFPB), poly(vinyl chloride) (PVC), and 2-nitrophenyl octyl ether (o-NPOE) were purchased from Sigma-Aldrich. Graphene sponge was purchased from Nanjing JCNANO Technology Co., Ltd., and tetrahydrofuran (THF), copper chloride (Cu(Cl)2) and other materials with analytical-reagent grade were obtained from Sinopharm Chemical Reagent Co., Ltd. Deionized water was obtained from a Pall Cascada system. 2.2. Characterization The morphology of 3D GS was analyzed by a field-emission scanning electron microscopy (FESEM, FEI, Nova NanoSEM 450). Contact angle measurements were carried out by a contact angle apparatus (JY-PHb, Chengde JINHE instrument). N2 adsorption and desorption isotherms were measured by a surface area and porosity analyzer (Micromeritics, ASAP 2020). The specific surface area was determined by the BrunauerEmmettTeller (BET) method, and the pore size distribution was calculated from adsorption branches using the BarrettJoynerHalenda (BJH) method. 2.3. Fabrication of the 3D GS-based all-solid-state Cu2þ-ISE The 3D GS (6 cm 6 mm) electrode was wrapped by an insulation polymer (polydimethylsiloxane, PDMS), except for the bottom region. A copper wire was inserted in the middle of 3D GS acting as an electrical lead. The ISM for the 3D GS-based Cu2þ-ISE was composed of 1.00 wt% copper ionophore, 0.86 wt% NaTFPB, 32.71 wt% PVC, and 65.43 wt% o-NPOE. The membrane components (625 mg) were dissolved in 5 ml THF to form a membrane cocktail solution. The cocktail solution was then casted into a glass ring (50 mm diameter) fixed on a glass plate. After drying overnight, the ISM with a thickness of ~200 mM was punched by a disk with 8 mm
3
diameter and glued to a plasticized PVC tube (~3 mm long, 6 mm i.d. and 8 mm o.d.). The PVC tube was subsequently mechanically fixed outside of 3D GS. The effective distance of 3D GS between the copper wire and the ISM membrane was ~3 cm. For comparison, the fabrication of the coated-wire Cu2þ-ISE was the same as GS/Cu2þISE, except that the conductive substrate was a gold (Au) electrode (Au/Cu2þ-ISE). Before measurements, the GS/Cu2þ-ISEs were conditioned in 1.0 103 M Cu(Cl)2 for 1 day and in 1.0 109 M Cu(Cl)2 for 2 days. 2.4. Potentiometric measurements Potentiometric measurements were performed in magnetically stirred Cu(Cl)2 solutions in the activity range from 1.0 1010 to 7.9 104 M using a digital ion analyzer (PXSJ-216, Shanghai Leici Instruments, China). The reference electrode was a double-junction Hg/Hg2Cl2 (saturated KCl) electrode containing a salt bridge solution of 0.1 M LiOAc. The liquid junction potentials and the activity coefficients were corrected with the Henderson and Debye-Hückel equations, respectively. 2.5. Electrochemical measurements Electrochemical measurements, such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronopotentiometry, were carried out using an electrochemical workstation (CHI 660C, Shanghai Chenhua, China) with a threeelectrode system. The GS or GS/Cu2þ-ISE, Ag/AgCl (3 M KCl) and platinum wire were used as working electrode, reference electrode and counter electrode, respectively. 3. Results and discussion 3.1. Transduction mechanism of the 3D GS-based freestanding ASSISEs The transduction mechanism of the carbon nanomaterial-based solid contact is related to the presence of an electrical double layer
Fig. 2. (a) Photograph of the GS freestanding electrodes. The inset shows the GS/Cu2þ-ISE. (b) Low and (c) high magnification SEM images of GS. (d) Contact angle of GS.
Please cite this article as: J. Li, W. Qin, A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.04.003
4
J. Li, W. Qin / Analytica Chimica Acta xxx (xxxx) xxx
formed at the ISM/solid contact interface [32]. This interface can act as an asymmetric capacitor and the capacitive mechanism has further been confirmed by the synchrotron radiation X-ray photoelectron spectroscopy and synchrotron radiation valence band spectroscopy, indicating that the adsorption of a lipophilic anion in ISM onto the carbon nanomaterials can result in the formation of electrical double layer [33]. The ion-to-electron transduction mechanism of 3D GS in the ASS-ISE is schematically shown in Fig. 1. At the GS/ISM interface, the large surface area of 3D GS provides more sites for the adsorption of TFPB and then 3D GS can convert the ionic signal to an electrical signal [33]. Moreover, the considerable adsorption of TFPB contributes to a high electrical double layer capacitance, which can buffer and stabilize the potential stability of the 3D GS-based freestanding ASS-ISE. Thus, 3D GS is competent for an effective ion-to-electron transducer. 3D GS transports the electrical signal to the reading instrument due to its good electrical conductivity. Therefore, 3D GS is a promising candidate to act as both solid contact and electrode substrate for construction of a simple and novel freestanding ASS-ISE.
based Cu2þ-ISE shows a stable potential response (Fig. 5a). The Nernstian response with a slope of 28.6 ± 0.7 mV/decade (n ¼6, R2 ¼ 0.9969) can be obtained in the range of 1.0 108 to 7.9 104 M (Fig. 5b). The detection limit of the GS/Cu2þ-ISE is 2.5 109 M, which was calculated as the intersection of the two slope lines.
3.2. Characterization of 3D GS 3D GS was prepared by reducing graphene oxide with L-ascorbic acid and the bulk electrical conductivity of 3D GS was close to ~100 S m1, which indicates that 3D GS can be used as freestanding electrodes [34]. The photograph of the 3D GS electrodes is shown in Fig. 2a. The inset shows the prepared GS/Cu2þ-ISE. Fig. 2b and c shows the microscopic structures of 3D GS. The interconnected 3D graphene framework, formed by the self-assembly of plentiful flexible graphene sheets with each other, can provide more sites for TFPB adsorption [33]. It is known that a high hydrophobicity of a solid contact is crucial for preventing the formation of an undesirable water layer between the solid contact and ISM. The contact angle of the GS was measured. As shown in Fig. 2d, the GS material has a high hydrophobicity with a contact angle of 120 , and thus can be used as an effective solid contact for ASS-ISEs. To investigate the specific surface area and porosity of 3D GS, the N2 adsorption/desorption experiments were carried out. In Fig. 3a, the isotherms of 3D GS show the hybrid type I/IV, indicating the characteristics of micropore and mesopore structures [35]. The existence of the mesopore and micropore structures can further be verified by the pore size distributions (centered at 2.5 and 0.5 nm) shown in Fig. 3b and c. The mesopore and micropore structures of GS contribute to the large specific surface area, which was determined to be 388 m2/g. 3.3. Electrochemical characterization of the 3D GS electrode Electrochemical performances of the GS electrode were evaluated by CV and EIS, respectively. As illustrated in Fig. 4a, the GS electrode shows a much larger capacitance compared with the bare Au electrode, which is due to the large interfacial contact area of 3D GS [3]. Fig. 4b exhibits the impedance plot for the GS electrode in which the capacitive line with the absence of a high-frequency semicircle is approximate 90 , indicating fast charge transfers across the GS/solution interface as well as good conductivity of the GS electrode. 3.4. Potentiometric performance of the GS-based freestanding allsolid-state Cu2þ-ISE Fig. 5a shows the potentiometric responses of the GS/Cu2þ-ISE measured in Cu(Cl)2 in the activity range of 7.9 104 1.0 1010 M at different concentrations. As can be seen, the GS-
Fig. 3. (a) Nitrogen adsorption/desorption isotherms of GS. (b) Mesopore and (c) micropore size distributions of GS.
Please cite this article as: J. Li, W. Qin, A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.04.003
J. Li, W. Qin / Analytica Chimica Acta xxx (xxxx) xxx
Fig. 4. (a) Cyclic voltammograms of the GS and Au electrodes in 0.1 M KCl at a scan rate of 100 mV s1. (b) Impedance spectrum of the GS electrode in 0.1 M KCl at the opencircuit potential. Initial potential, 0.2 V; excitation amplitude, 10 mV; frequency range, 0.3 Hz to 10 kHz.
3.5. Potential stability Current-reversed chronopotentiometry was used to evaluate the short-term potential stability of the GS/Cu2þ-ISE. Fig. 6 shows the typical chronopotentiograms for the GS/Cu2þ-ISE and Au/Cu2þISE recorded in 1.0 105 M Cu(Cl)2. According to the equation DE/ Dt ¼ I/C [11], the potential drift (DE/Dt) is correlated with the electrode low-frequency capacitance (C) and the implemented current (I), therefore, an electrode with a large capacitance could have a high potential stability. Indeed, the potential drift of the GS/ Cu2þ-ISE was found to be 2 mVs1, which is much lower than that obtained from the Au/Cu2þ-ISE (415 mVs1). The low-frequency capacitances for the GS/Cu2þ-ISE and Au/Cu2þ-ISE were 500 mF and 2.4 mF, respectively. These results indicate that the freestanding GS electrode with a higher low-frequency capacitance can effectively improve the potential stability of the all-solid-state Cu2þ-ISE. 3.6. Impedance of the freestanding all-solid-state Cu2þ-ISE The impedance spectra of GS/Cu2þ-ISE and Au/Cu2þ-ISE were tested in 1.0 105 M Cu(Cl)2. As shown in Fig. 7, each electrode exhibits a high-frequency semicircle, representing the bulk resistance including sensing membrane resistance and the contact resistance at the ISM/GS or Au interface. The values for the highfrequency resistance of the GS/Cu2þ-ISE and Au/Cu2þ-ISE were 0.12 and 0.19 MU, respectively. The results indicate that the GS
5
Fig. 5. (a) Time-dependent responses of the GS/Cu2þ-ISE to Cu2þ in the activity range of 7.9 104 - 1.0 1010 M. (b) Calibration curve for the GS/Cu2þ-ISE.
electrode shows a low charge-transfer resistance at the sensing membrane/GS interface as compared to the Au electrode [6]. Furthermore, in the low-frequency part, the Au/Cu2þ-ISE shows a large semicircle while the GS/Cu2þ-ISE exhibits a negligible lowfrequency semicircle, indicating the presence of a low charge transfer resistance in parallel with the high double layer capacitance between the ISM and GS electrode. 3.7. Effects of O2, CO2 and light The interferences of light, O2, and CO2 on the potential response of the GS/Cu2þ-ISE were investigated (Fig. 8). The proposed GS/ Cu2þ-ISE was immersed in 1.0 105 M Cu(Cl)2 with the ambient light on/off to test the effect of light on the potential stability. The potential responses were also recorded by immersing the GS-based electrode in 1.0 105 M Cu(Cl)2 and by sequentially bubbling O2 and N2, or CO2 and N2 for 30 min. As illustrated in Fig. 8, no obvious potential drifts are observed when the electrode is under the O2, CO2 and light exposures, demonstrating that the response of the GS-based Cu2þ-ISE could not be affected by O2, CO2, and light. These results are in good agreement with those of other carbon-material based ASS-ISEs [5,36,37]. 3.8. Water layer test The water layer test was used to investigate the influence of the
Please cite this article as: J. Li, W. Qin, A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.04.003
6
J. Li, W. Qin / Analytica Chimica Acta xxx (xxxx) xxx
Fig. 6. Chronopotentiograms of the GS/Cu2þ-ISE and Au/Cu2þ-ISE at the applied currents of ±1 nA for 60 s.
Fig. 9. Water layer test for the GS/Cu2þ-ISE.
water layer at the ISM/GS interface on the potential stability of ASSISEs [3]. The GS/Cu2þ-ISE was exposed to 1.0 105 M Cu(Cl)2, 0.1 M NaCl, and then back to 1.0 105 M Cu(Cl)2 sequentially. As shown in Fig. 9, the GS/Cu2þ-ISE exhibits a stable response, and no evident positive or negative potential drift is found during the water layer test, suggesting a dramatically reduced water layer at the ISM/GS interface. These results can be ascribed to the highly hydrophobic characteristic of 3D GS. 4. Conclusions
Fig. 7. Impedance plots of the GS/Cu2þ-ISE and Au/Cu2þ-ISE. Initial potential, 0.2 V; excitation amplitude, 100 mV; frequency range, 0.01e100 kHz. The magnification of the impedance spectra is shown in the inset.
In summary, a novel and simple freestanding Cu2þ-ISE has been fabricated by using 3D GS as both electrode substrate and solid contact. The 3D interconnected network of GS can offer a large specific surface area for ion adsorption and facilitate ion to electron transfer. The GS-based Cu2þ-ISE shows a stable Nernstian response with a low detection limit and good robustness to light, O2, and CO2 interferences. Due to the high hydrophobic characteristic of GS, no notable water layer is formed at the sensing membrane/GS interface. In addition, the GS freestanding electrode can be tailored for other shapes or sizes, which offers potential promise for low-cost mass manufacture and miniaturization. Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (21677172), the National Key Research and Development Program of China (2016YFC1400700), and the Taishan Scholar Program of Shandong Province (TSPD20181215). References
Fig. 8. Effects of light, O2 and CO2 interferences on the potential stability of the GS/ Cu2þ-ISE in 1.0 105 M CuCl2.
[1] J. Bobacka, A. Ivaska, A. Lewenstam, Potentiometric ion sensors, Chem. Rev. 108 (2008) 329e351. [2] A. Lewenstam, Routines and challenges in clinical application of electrochemical ion-sensors, Electroanalysis 26 (2014) 1171e1181. [3] J. Hu, A. Stein, P. Bühlmann, Rational design of all-solid-state ion-selective electrodes and reference electrodes, TrAC Trends Anal. Chem. 76 (2016) 102e114.
Please cite this article as: J. Li, W. Qin, A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.04.003
J. Li, W. Qin / Analytica Chimica Acta xxx (xxxx) xxx [4] J. Bobacka, A. Lewenstam, A. Ivaska, Equilibrium potential of potentiometric ion sensors under steady-state current by using current-reversal chronopotentiometry, J. Electroanal. Chem. 509 (2001) 27e30. [5] J. Hu, X.U. Zou, A. Stein, P. Bühlmann, Ion-selective electrodes with colloidimprinted mesoporous carbon as solid contact, Anal. Chem. 86 (2014) 7111e7118. [6] B. Paczosa-Bator, Ion-selective electrodes with superhydrophobic polymer/ carbon nanocomposites as solid contact, Carbon 95 (2015) 879e887. [7] D. Yuan, A.H.C. Anthis, M. Ghahraman Afshar, N. Pankratova, M. Cuartero, G.A. Crespo, et al., All-solid-state potentiometric sensors with a multiwalled carbon nanotube inner transducing layer for anion detection in environmental samples, Anal. Chem. 87 (2015) 8640e8645. [8] J. Li, T. Yin, W. Qin, An effective solid contact for an all-solid-state polymeric membrane Cd2þ-selective electrode: three-dimensional porous graphenemesoporous platinum nanoparticle composite, Sensor. Actuator. B Chem. 239 (2017) 438e446. [9] J. Bobacka, T. Lindfors, M. McCarrick, A. Ivaska, A. Lewenstam, Single-piece allsolid-state ion-selective electrode, Anal. Chem. 67 (1995) 3819e3823. €berg, J. Bobacka, A. Lewenstam, A. Ivaska, Characterization of [10] T. Lindfors, P. Sjo a single-piece all-solid-state lithium-selective electrode based on soluble conducting polyaniline, Anal. Chim. Acta 385 (1999) 163e173. [11] J. Bobacka, Potential stability of all-solid-state ion-selective electrodes using conducting polymers as ion-to-electron transducers, Anal. Chem. 71 (1999) 4932e4937. [12] T. Lindfors, Light sensitivity and potential stability of electrically conducting polymers commonly used in solid contact ion-selective electrodes, J. Solid State Electrochem. 13 (2009) 77e89. [13] J. Zhu, Y. Qin, Y. Zhang, Preparation of all solid-state potentiometric ion sensors with polymer-CNT composites, Electrochem. Commun. 11 (2009) 1684e1687. [14] J. Zhu, X. Li, Y. Qin, Y. Zhang, Single-piece solid-contact ion-selective electrodes with polymerecarbon nanotube composites, Sensor. Actuator. B Chem. 148 (2010) 166e172. [15] Y. Liu, T. Yuan, J. Zhu, Y. Qin, D. Jiang, Polymeremultiwall carbon nantubes composites for durable all solid-contact H2PO 4 -selective electrodes, Sensor. Actuator. B Chem. 219 (2015) 100e104. [16] J. Chen, M.A. Hamon, H. Hu, Y. Chen, A.M. Rao, P.C. Eklund, et al., Solution properties of single-walled carbon nanotubes, Science 282 (1998) 95e98. [17] F.X. Rius-Ruiz, D. Bejarano-Nosas, P. Blondeau, J. Riu, F.X. Rius, Disposable planar reference electrode based on carbon nanotubes and polyacrylate membrane, Anal. Chem. 83 (2011) 5783e5788. [18] C. Wardak, Solid contact cadmium ion-selective electrode based on ionic liquid and carbon nanotubes, Sensor. Actuator. B Chem. 209 (2015) 131e137. [19] E. Jaworska, W. Lewandowski, J. Mieczkowski, K. Maksymiuk, A. Michalska, Simple and disposable potentiometric sensors based on graphene or multiwalled carbon nanotubes e carboneplastic potentiometric sensors, Analyst 138 (2013) 2363e2371. [20] M. Novell, M. Parrilla, G.A. Crespo, F.X. Rius, F.J. Andrade, Paper-based ion-
7
selective potentiometric sensors, Anal. Chem. 84 (2012) 4695e4702. [21] J. Ping, Y. Wang, K. Fan, W. Tang, J. Wu, Y. Ying, High-performance flexible potentiometric sensing devices using free-standing graphene paper, J. Mater. Chem. B 1 (2013) 4781e4791. [22] L. Jiang, Z. Fan, Design of advanced porous graphene materials: from graphene nanomesh to 3D architectures, Nanoscale 6 (2014) 1922e1945. [23] S. Mao, G. Lu, J. Chen, Three-dimensional graphene-based composites for energy applications, Nanoscale 7 (2015) 6924e6943. [24] H. Bi, X. Xie, K. Yin, Y. Zhou, S. Wan, L. He, et al., Spongy graphene as a highly efficient and recyclable sorbent for oils and organic solvents, Adv. Funct. Mater. 22 (2012) 4421e4425. [25] X. Xu, L. Pan, Y. Liu, T. Lu, Z. Sun, D.H.C. Chua, Facile synthesis of novel graphene sponge for high performance capacitive deionization, Sci. Rep. 5 (2015) 8458. [26] C. Lin, C. Niu, X. Xu, K. Li, Z. Cai, Y. Zhang, et al., A facile synthesis of three dimensional graphene sponge composited with sulfur nanoparticles for flexible LieS cathodes, Phys. Chem. Chem. Phys. 18 (2016) 22146e22153. [27] W. Zhang, Y. Li, S. Peng, Facile synthesis of graphene sponge from graphene oxide for efficient dye-sensitized H2 evolution, ACS Appl. Mater. Interfaces 8 (2016) 15187e15195. [28] S. Chun, A. Hong, Y. Choi, C. Ha, W. Park, A tactile sensor using a conductive graphene-sponge composite, Nanoscale 8 (2016) 9185e9192. [29] J. Huang, J. Wang, Z. Yang, S. Yang, High-performance graphene sponges reinforced with polyimide for room-temperature piezoresistive sensing, ACS Appl. Mater. Interfaces 10 (2018) 8180e8189. [30] X. Xie, Y. Zhou, H. Bi, K. Yin, S. Wan, L. Sun, Large-range control of the microstructures and properties of three-dimensional porous graphene, Sci. Rep. 3 (2013) 2117. [31] X. Xu, Z. Sun, D.H.C. Chua, L. Pan, Novel nitrogen doped graphene sponge with ultrahigh capacitive deionization performance, Sci. Rep. 5 (2015) 11225. [32] G.A. Crespo, S. Macho, J. Bobacka, F.X. Rius, Transduction mechanism of carbon nanotubes in solid-contact ion-selective electrodes, Anal. Chem. 81 (2009) 676e681. [33] M. Cuartero, J. Bishop, R. Walker, R.G. Acres, E. Bakker, R. De Marco, et al., Evidence of double layer/capacitive charging in carbon nanomaterial-based solid contact polymeric ion-selective electrodes, Chem. Commun. 52 (2016) 9703e9706. [34] X. Zhang, Z. Sui, B. Xu, S. Yue, Y. Luo, W. Zhan, et al., Mechanically strong and highly conductive graphene aerogel and its use as electrodes for electrochemical power sources, J. Mater. Chem. 21 (2011) 6494e6497. [35] Z.A. Alothman, A review: fundamental aspects of silicate mesoporous materials, Materials 5 (2012) 2874e2902. [36] J. Ye, F. Li, S. Gan, Y. Jiang, Q. An, Q. Zhang, et al., Using sp2-C dominant porous carbon sub-micrometer spheres as solid transducers in ion-selective electrodes, Electrochem. Commun. 50 (2015) 60e63. [37] J. Li, T. Yin, W. Qin, An all-solid-state polymeric membrane Pb2þ-selective electrode with bimodal pore C60 as solid contact, Anal. Chim. Acta 876 (2015) 49e54.
Please cite this article as: J. Li, W. Qin, A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.04.003
Contents lists available at ScienceDirect
Analytica Chimica Acta journal homepage: www.elsevier.com/locate/aca
A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge Jinghui Li a, c, Wei Qin a, b, * a
Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research (YIC), Chinese Academy of Sciences (CAS), Shandong Provincial Key Laboratory of Coastal Environmental Processes, YICCAS, Yantai, Shandong, 264003, PR China b Laboratory for Marine Biology and Biotechnology, Qingdao National Laboratory for Marine Science and Technology, Qingdao, 266200, PR China c University of the Chinese Academy of Sciences, Beijing, 100049, PR China
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
A freestanding all-solid-state polymeric membrane Cu2þ-ISE based on three-dimensional graphene sponge (3D GS) is developed. The 3D GS can be used as both electrode substrate and solid contact for construction of Cu2þ-ISE. The electrode shows a stable potential response with a LOD of 2.5 109 M.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 26 February 2019 Received in revised form 1 April 2019 Accepted 4 April 2019 Available online xxx
A novel freestanding all-solid-state polymeric membrane Cu2þ-selective electrode (Cu2þ-ISE) is proposed based on three-dimensional graphene sponge (3D GS). The 3D GS electrode has been characterized by cyclic voltammetry, electrochemical impedance spectroscopy, and contact angle measurements. Experiments show that 3D GS possesses a large electrical double layer capacitance, good conductivity, and high hydrophobicity. Based on these superior properties, 3D GS has been applied as both electrode substrate and solid contact for construction of a freestanding all-solid-state polymeric membrane Cu2þ-ISE. The 3D GS-based Cu2þ-ISE shows a good Nernstian response ranging from 1.0 108 to 7.9 104 M with a low detection limit of 2.5 109 M. Moreover, the proposed Cu2þ-ISE exhibits a stable potential response with a reduced water layer at the sensing membrane/3D GS interface and is not affected by interferences from light, O2 and CO2. © 2019 Elsevier B.V. All rights reserved.
Keywords: Three-dimensional graphene sponge Freestanding electrode Solid contact All-solid-state ion-selective electrode Copper
1. Introduction
* Corresponding author. Key Laboratory of Coastal Environmental Processes and Ecological Remediation, Yantai Institute of Coastal Zone Research (YIC), Chinese Academy of Sciences (CAS), Shandong Provincial Key Laboratory of Coastal Environmental Processes, YICCAS, Yantai, Shandong, 264003, PR China. E-mail address: [email protected] (W. Qin).
Ion selective electrodes (ISEs) have been widely employed in numerous fields, such as clinical analysis, environmental monitoring, and process control, due to their cost-effectiveness, high reliability, and simple operation [1e3]. All-solid-state ion-selective electrodes (ASS-ISEs) are considered to be the new generation of ISEs, which can be attributed to their excellent properties, including
https://doi.org/10.1016/j.aca.2019.04.003 0003-2670/© 2019 Elsevier B.V. All rights reserved.
Please cite this article as: J. Li, W. Qin, A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.04.003
2
J. Li, W. Qin / Analytica Chimica Acta xxx (xxxx) xxx
convenient storage and maintenance, easy miniaturization, and high durability [3]. However, the existence of the “block” interface between the underlying metal and ion-selective membrane (ISM) can lead to signal noises and drifts, which restricts the wide applications of ASS-ISEs [4]. To enhance the potential stabilities of ASS-ISEs, various transducing materials possessing ionic to electronic conductivities have been introduced as solid contacts, which are applied between the underlying electrodes and ISMs [1,5e8]. It should be noted that the fabrication of most of these solid-contact ASS-ISEs requires two steps: an intermediate layer is first formed on electron conducting substrate by drop-coating or electrodeposition, and then an ISM is drop-casted on the surface of the intermediate layer. Such procedures could make it complicated to fabricate a solid-contact ASS-ISE. A new type of ASS-ISEs so called single-piece ASS-ISEs, which are prepared by directly incorporating conducting polymers (CPs) into membrane cocktail, was initially proposed by Bobacka et al. [9,10]. Unfortunately, most CPs are sensitive to gas, light and redox interferences [1,11,12]. The arisen single-piece ASS-ISEs with improved sensing properties have been developed by adding carbon nanotubes (CNTs) into ISMs [13e15]. Some challenges still remain since the low dispensability of CNTs in organic solvents and poor compatibilities with polymer materials. The dispensabilities of CNTs in organic solvents can be further improved by modifying CNTs with lipophilic groups [16,17] or using moderate lipophilic ionic additive [18], whereas the electrical conductivity of CNTs could be affected and unnecessary interferences may be introduced into the sensing membrane, resulting in the deterioration of potentiometric performance [19]. Recently, a simple, low-cost and paper-like freestanding ASS-ISE has been developed [20]. In this ASS-ISE, CNTs conductive paper was used as both electric conductor and solid contact by directly drop-casting the sensing membrane cocktail on the paper.
Analytical performance of the paper-based potentiometric sensor was comparable with that of conventional ASS-ISEs. However, it is time-consuming to remove the excess of surfactants through rinsing of CNTs paper. Graphene paper, prepared by the vacuum infiltration method, has also been used to construct freestanding ASS-ISEs [21]. Nevertheless, the accessible surface area of the twodimensional self-assembling layer-by-layer graphene paper can be reduced due to the irreversible restacking and agglomeration of individual graphene nanosheets caused by van der Waals forces [22,23]. Three-dimensional monothlic graphene sponge (3D GS) can prevent the agglomeration of graphene sheets, resulting in a welldefined and cross-linked 3D interconnected porous structure, and thus enlarge the specific surface area. Because of its large specific surface area, high electric conductivity and good mechanical strength, 3D GS has been widely used in practical applications, such as environmental remediation [24,25], energy storage and conversion [26,27], and sensors [28,29]. Depending on different application requirements, the pore size and shape of 3D GS can be controlled by regulating parameters during the fabrication of GS [30]. In addition, the 3D porous interconnected structure of GS could provide more sites for ion adsorption and diffusion, and facilitate ion to electron transfer [25,31]. These outstanding properties of 3D GS prompt us to study the possibility of taking advantage of GS to develop a novel freestanding ASS-ISE. Herein, we propose a freestanding Cu2þ-selective electrode (Cu2þ-ISE) based on 3D GS. The mesopore and micropore structures of 3D GS contribute to a large specific surface area as well as a high double layer capacitance. The 3D GS material also exhibits an excellent hydrophobicity and good electric conductivity. It will be shown that 3D GS can be used as both electrode substrate and solid contact for construction of a novel freestanding Cu2þ-ISE.
Fig. 1. Schematic illustration of the transduction mechanism of the GS-based all-solid-state ISE.
Please cite this article as: J. Li, W. Qin, A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.04.003
J. Li, W. Qin / Analytica Chimica Acta xxx (xxxx) xxx
2. Experimental 2.1. Reagents and materials o-Xylylene bis(diisobuty1dithiocarba-mate) (copper ionophore II, o-XBDiBDTC), sodium tetrakis[3,5-bis(trifluoro-methyl)phenyl] borate (NaTFPB), poly(vinyl chloride) (PVC), and 2-nitrophenyl octyl ether (o-NPOE) were purchased from Sigma-Aldrich. Graphene sponge was purchased from Nanjing JCNANO Technology Co., Ltd., and tetrahydrofuran (THF), copper chloride (Cu(Cl)2) and other materials with analytical-reagent grade were obtained from Sinopharm Chemical Reagent Co., Ltd. Deionized water was obtained from a Pall Cascada system. 2.2. Characterization The morphology of 3D GS was analyzed by a field-emission scanning electron microscopy (FESEM, FEI, Nova NanoSEM 450). Contact angle measurements were carried out by a contact angle apparatus (JY-PHb, Chengde JINHE instrument). N2 adsorption and desorption isotherms were measured by a surface area and porosity analyzer (Micromeritics, ASAP 2020). The specific surface area was determined by the BrunauerEmmettTeller (BET) method, and the pore size distribution was calculated from adsorption branches using the BarrettJoynerHalenda (BJH) method. 2.3. Fabrication of the 3D GS-based all-solid-state Cu2þ-ISE The 3D GS (6 cm 6 mm) electrode was wrapped by an insulation polymer (polydimethylsiloxane, PDMS), except for the bottom region. A copper wire was inserted in the middle of 3D GS acting as an electrical lead. The ISM for the 3D GS-based Cu2þ-ISE was composed of 1.00 wt% copper ionophore, 0.86 wt% NaTFPB, 32.71 wt% PVC, and 65.43 wt% o-NPOE. The membrane components (625 mg) were dissolved in 5 ml THF to form a membrane cocktail solution. The cocktail solution was then casted into a glass ring (50 mm diameter) fixed on a glass plate. After drying overnight, the ISM with a thickness of ~200 mM was punched by a disk with 8 mm
3
diameter and glued to a plasticized PVC tube (~3 mm long, 6 mm i.d. and 8 mm o.d.). The PVC tube was subsequently mechanically fixed outside of 3D GS. The effective distance of 3D GS between the copper wire and the ISM membrane was ~3 cm. For comparison, the fabrication of the coated-wire Cu2þ-ISE was the same as GS/Cu2þISE, except that the conductive substrate was a gold (Au) electrode (Au/Cu2þ-ISE). Before measurements, the GS/Cu2þ-ISEs were conditioned in 1.0 103 M Cu(Cl)2 for 1 day and in 1.0 109 M Cu(Cl)2 for 2 days. 2.4. Potentiometric measurements Potentiometric measurements were performed in magnetically stirred Cu(Cl)2 solutions in the activity range from 1.0 1010 to 7.9 104 M using a digital ion analyzer (PXSJ-216, Shanghai Leici Instruments, China). The reference electrode was a double-junction Hg/Hg2Cl2 (saturated KCl) electrode containing a salt bridge solution of 0.1 M LiOAc. The liquid junction potentials and the activity coefficients were corrected with the Henderson and Debye-Hückel equations, respectively. 2.5. Electrochemical measurements Electrochemical measurements, such as cyclic voltammetry (CV), electrochemical impedance spectroscopy (EIS) and chronopotentiometry, were carried out using an electrochemical workstation (CHI 660C, Shanghai Chenhua, China) with a threeelectrode system. The GS or GS/Cu2þ-ISE, Ag/AgCl (3 M KCl) and platinum wire were used as working electrode, reference electrode and counter electrode, respectively. 3. Results and discussion 3.1. Transduction mechanism of the 3D GS-based freestanding ASSISEs The transduction mechanism of the carbon nanomaterial-based solid contact is related to the presence of an electrical double layer
Fig. 2. (a) Photograph of the GS freestanding electrodes. The inset shows the GS/Cu2þ-ISE. (b) Low and (c) high magnification SEM images of GS. (d) Contact angle of GS.
Please cite this article as: J. Li, W. Qin, A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.04.003
4
J. Li, W. Qin / Analytica Chimica Acta xxx (xxxx) xxx
formed at the ISM/solid contact interface [32]. This interface can act as an asymmetric capacitor and the capacitive mechanism has further been confirmed by the synchrotron radiation X-ray photoelectron spectroscopy and synchrotron radiation valence band spectroscopy, indicating that the adsorption of a lipophilic anion in ISM onto the carbon nanomaterials can result in the formation of electrical double layer [33]. The ion-to-electron transduction mechanism of 3D GS in the ASS-ISE is schematically shown in Fig. 1. At the GS/ISM interface, the large surface area of 3D GS provides more sites for the adsorption of TFPB and then 3D GS can convert the ionic signal to an electrical signal [33]. Moreover, the considerable adsorption of TFPB contributes to a high electrical double layer capacitance, which can buffer and stabilize the potential stability of the 3D GS-based freestanding ASS-ISE. Thus, 3D GS is competent for an effective ion-to-electron transducer. 3D GS transports the electrical signal to the reading instrument due to its good electrical conductivity. Therefore, 3D GS is a promising candidate to act as both solid contact and electrode substrate for construction of a simple and novel freestanding ASS-ISE.
based Cu2þ-ISE shows a stable potential response (Fig. 5a). The Nernstian response with a slope of 28.6 ± 0.7 mV/decade (n ¼6, R2 ¼ 0.9969) can be obtained in the range of 1.0 108 to 7.9 104 M (Fig. 5b). The detection limit of the GS/Cu2þ-ISE is 2.5 109 M, which was calculated as the intersection of the two slope lines.
3.2. Characterization of 3D GS 3D GS was prepared by reducing graphene oxide with L-ascorbic acid and the bulk electrical conductivity of 3D GS was close to ~100 S m1, which indicates that 3D GS can be used as freestanding electrodes [34]. The photograph of the 3D GS electrodes is shown in Fig. 2a. The inset shows the prepared GS/Cu2þ-ISE. Fig. 2b and c shows the microscopic structures of 3D GS. The interconnected 3D graphene framework, formed by the self-assembly of plentiful flexible graphene sheets with each other, can provide more sites for TFPB adsorption [33]. It is known that a high hydrophobicity of a solid contact is crucial for preventing the formation of an undesirable water layer between the solid contact and ISM. The contact angle of the GS was measured. As shown in Fig. 2d, the GS material has a high hydrophobicity with a contact angle of 120 , and thus can be used as an effective solid contact for ASS-ISEs. To investigate the specific surface area and porosity of 3D GS, the N2 adsorption/desorption experiments were carried out. In Fig. 3a, the isotherms of 3D GS show the hybrid type I/IV, indicating the characteristics of micropore and mesopore structures [35]. The existence of the mesopore and micropore structures can further be verified by the pore size distributions (centered at 2.5 and 0.5 nm) shown in Fig. 3b and c. The mesopore and micropore structures of GS contribute to the large specific surface area, which was determined to be 388 m2/g. 3.3. Electrochemical characterization of the 3D GS electrode Electrochemical performances of the GS electrode were evaluated by CV and EIS, respectively. As illustrated in Fig. 4a, the GS electrode shows a much larger capacitance compared with the bare Au electrode, which is due to the large interfacial contact area of 3D GS [3]. Fig. 4b exhibits the impedance plot for the GS electrode in which the capacitive line with the absence of a high-frequency semicircle is approximate 90 , indicating fast charge transfers across the GS/solution interface as well as good conductivity of the GS electrode. 3.4. Potentiometric performance of the GS-based freestanding allsolid-state Cu2þ-ISE Fig. 5a shows the potentiometric responses of the GS/Cu2þ-ISE measured in Cu(Cl)2 in the activity range of 7.9 104 1.0 1010 M at different concentrations. As can be seen, the GS-
Fig. 3. (a) Nitrogen adsorption/desorption isotherms of GS. (b) Mesopore and (c) micropore size distributions of GS.
Please cite this article as: J. Li, W. Qin, A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.04.003
J. Li, W. Qin / Analytica Chimica Acta xxx (xxxx) xxx
Fig. 4. (a) Cyclic voltammograms of the GS and Au electrodes in 0.1 M KCl at a scan rate of 100 mV s1. (b) Impedance spectrum of the GS electrode in 0.1 M KCl at the opencircuit potential. Initial potential, 0.2 V; excitation amplitude, 10 mV; frequency range, 0.3 Hz to 10 kHz.
3.5. Potential stability Current-reversed chronopotentiometry was used to evaluate the short-term potential stability of the GS/Cu2þ-ISE. Fig. 6 shows the typical chronopotentiograms for the GS/Cu2þ-ISE and Au/Cu2þISE recorded in 1.0 105 M Cu(Cl)2. According to the equation DE/ Dt ¼ I/C [11], the potential drift (DE/Dt) is correlated with the electrode low-frequency capacitance (C) and the implemented current (I), therefore, an electrode with a large capacitance could have a high potential stability. Indeed, the potential drift of the GS/ Cu2þ-ISE was found to be 2 mVs1, which is much lower than that obtained from the Au/Cu2þ-ISE (415 mVs1). The low-frequency capacitances for the GS/Cu2þ-ISE and Au/Cu2þ-ISE were 500 mF and 2.4 mF, respectively. These results indicate that the freestanding GS electrode with a higher low-frequency capacitance can effectively improve the potential stability of the all-solid-state Cu2þ-ISE. 3.6. Impedance of the freestanding all-solid-state Cu2þ-ISE The impedance spectra of GS/Cu2þ-ISE and Au/Cu2þ-ISE were tested in 1.0 105 M Cu(Cl)2. As shown in Fig. 7, each electrode exhibits a high-frequency semicircle, representing the bulk resistance including sensing membrane resistance and the contact resistance at the ISM/GS or Au interface. The values for the highfrequency resistance of the GS/Cu2þ-ISE and Au/Cu2þ-ISE were 0.12 and 0.19 MU, respectively. The results indicate that the GS
5
Fig. 5. (a) Time-dependent responses of the GS/Cu2þ-ISE to Cu2þ in the activity range of 7.9 104 - 1.0 1010 M. (b) Calibration curve for the GS/Cu2þ-ISE.
electrode shows a low charge-transfer resistance at the sensing membrane/GS interface as compared to the Au electrode [6]. Furthermore, in the low-frequency part, the Au/Cu2þ-ISE shows a large semicircle while the GS/Cu2þ-ISE exhibits a negligible lowfrequency semicircle, indicating the presence of a low charge transfer resistance in parallel with the high double layer capacitance between the ISM and GS electrode. 3.7. Effects of O2, CO2 and light The interferences of light, O2, and CO2 on the potential response of the GS/Cu2þ-ISE were investigated (Fig. 8). The proposed GS/ Cu2þ-ISE was immersed in 1.0 105 M Cu(Cl)2 with the ambient light on/off to test the effect of light on the potential stability. The potential responses were also recorded by immersing the GS-based electrode in 1.0 105 M Cu(Cl)2 and by sequentially bubbling O2 and N2, or CO2 and N2 for 30 min. As illustrated in Fig. 8, no obvious potential drifts are observed when the electrode is under the O2, CO2 and light exposures, demonstrating that the response of the GS-based Cu2þ-ISE could not be affected by O2, CO2, and light. These results are in good agreement with those of other carbon-material based ASS-ISEs [5,36,37]. 3.8. Water layer test The water layer test was used to investigate the influence of the
Please cite this article as: J. Li, W. Qin, A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.04.003
6
J. Li, W. Qin / Analytica Chimica Acta xxx (xxxx) xxx
Fig. 6. Chronopotentiograms of the GS/Cu2þ-ISE and Au/Cu2þ-ISE at the applied currents of ±1 nA for 60 s.
Fig. 9. Water layer test for the GS/Cu2þ-ISE.
water layer at the ISM/GS interface on the potential stability of ASSISEs [3]. The GS/Cu2þ-ISE was exposed to 1.0 105 M Cu(Cl)2, 0.1 M NaCl, and then back to 1.0 105 M Cu(Cl)2 sequentially. As shown in Fig. 9, the GS/Cu2þ-ISE exhibits a stable response, and no evident positive or negative potential drift is found during the water layer test, suggesting a dramatically reduced water layer at the ISM/GS interface. These results can be ascribed to the highly hydrophobic characteristic of 3D GS. 4. Conclusions
Fig. 7. Impedance plots of the GS/Cu2þ-ISE and Au/Cu2þ-ISE. Initial potential, 0.2 V; excitation amplitude, 100 mV; frequency range, 0.01e100 kHz. The magnification of the impedance spectra is shown in the inset.
In summary, a novel and simple freestanding Cu2þ-ISE has been fabricated by using 3D GS as both electrode substrate and solid contact. The 3D interconnected network of GS can offer a large specific surface area for ion adsorption and facilitate ion to electron transfer. The GS-based Cu2þ-ISE shows a stable Nernstian response with a low detection limit and good robustness to light, O2, and CO2 interferences. Due to the high hydrophobic characteristic of GS, no notable water layer is formed at the sensing membrane/GS interface. In addition, the GS freestanding electrode can be tailored for other shapes or sizes, which offers potential promise for low-cost mass manufacture and miniaturization. Declaration of interests The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgements This work was financially supported by the National Natural Science Foundation of China (21677172), the National Key Research and Development Program of China (2016YFC1400700), and the Taishan Scholar Program of Shandong Province (TSPD20181215). References
Fig. 8. Effects of light, O2 and CO2 interferences on the potential stability of the GS/ Cu2þ-ISE in 1.0 105 M CuCl2.
[1] J. Bobacka, A. Ivaska, A. Lewenstam, Potentiometric ion sensors, Chem. Rev. 108 (2008) 329e351. [2] A. Lewenstam, Routines and challenges in clinical application of electrochemical ion-sensors, Electroanalysis 26 (2014) 1171e1181. [3] J. Hu, A. Stein, P. Bühlmann, Rational design of all-solid-state ion-selective electrodes and reference electrodes, TrAC Trends Anal. Chem. 76 (2016) 102e114.
Please cite this article as: J. Li, W. Qin, A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.04.003
J. Li, W. Qin / Analytica Chimica Acta xxx (xxxx) xxx [4] J. Bobacka, A. Lewenstam, A. Ivaska, Equilibrium potential of potentiometric ion sensors under steady-state current by using current-reversal chronopotentiometry, J. Electroanal. Chem. 509 (2001) 27e30. [5] J. Hu, X.U. Zou, A. Stein, P. Bühlmann, Ion-selective electrodes with colloidimprinted mesoporous carbon as solid contact, Anal. Chem. 86 (2014) 7111e7118. [6] B. Paczosa-Bator, Ion-selective electrodes with superhydrophobic polymer/ carbon nanocomposites as solid contact, Carbon 95 (2015) 879e887. [7] D. Yuan, A.H.C. Anthis, M. Ghahraman Afshar, N. Pankratova, M. Cuartero, G.A. Crespo, et al., All-solid-state potentiometric sensors with a multiwalled carbon nanotube inner transducing layer for anion detection in environmental samples, Anal. Chem. 87 (2015) 8640e8645. [8] J. Li, T. Yin, W. Qin, An effective solid contact for an all-solid-state polymeric membrane Cd2þ-selective electrode: three-dimensional porous graphenemesoporous platinum nanoparticle composite, Sensor. Actuator. B Chem. 239 (2017) 438e446. [9] J. Bobacka, T. Lindfors, M. McCarrick, A. Ivaska, A. Lewenstam, Single-piece allsolid-state ion-selective electrode, Anal. Chem. 67 (1995) 3819e3823. €berg, J. Bobacka, A. Lewenstam, A. Ivaska, Characterization of [10] T. Lindfors, P. Sjo a single-piece all-solid-state lithium-selective electrode based on soluble conducting polyaniline, Anal. Chim. Acta 385 (1999) 163e173. [11] J. Bobacka, Potential stability of all-solid-state ion-selective electrodes using conducting polymers as ion-to-electron transducers, Anal. Chem. 71 (1999) 4932e4937. [12] T. Lindfors, Light sensitivity and potential stability of electrically conducting polymers commonly used in solid contact ion-selective electrodes, J. Solid State Electrochem. 13 (2009) 77e89. [13] J. Zhu, Y. Qin, Y. Zhang, Preparation of all solid-state potentiometric ion sensors with polymer-CNT composites, Electrochem. Commun. 11 (2009) 1684e1687. [14] J. Zhu, X. Li, Y. Qin, Y. Zhang, Single-piece solid-contact ion-selective electrodes with polymerecarbon nanotube composites, Sensor. Actuator. B Chem. 148 (2010) 166e172. [15] Y. Liu, T. Yuan, J. Zhu, Y. Qin, D. Jiang, Polymeremultiwall carbon nantubes composites for durable all solid-contact H2PO 4 -selective electrodes, Sensor. Actuator. B Chem. 219 (2015) 100e104. [16] J. Chen, M.A. Hamon, H. Hu, Y. Chen, A.M. Rao, P.C. Eklund, et al., Solution properties of single-walled carbon nanotubes, Science 282 (1998) 95e98. [17] F.X. Rius-Ruiz, D. Bejarano-Nosas, P. Blondeau, J. Riu, F.X. Rius, Disposable planar reference electrode based on carbon nanotubes and polyacrylate membrane, Anal. Chem. 83 (2011) 5783e5788. [18] C. Wardak, Solid contact cadmium ion-selective electrode based on ionic liquid and carbon nanotubes, Sensor. Actuator. B Chem. 209 (2015) 131e137. [19] E. Jaworska, W. Lewandowski, J. Mieczkowski, K. Maksymiuk, A. Michalska, Simple and disposable potentiometric sensors based on graphene or multiwalled carbon nanotubes e carboneplastic potentiometric sensors, Analyst 138 (2013) 2363e2371. [20] M. Novell, M. Parrilla, G.A. Crespo, F.X. Rius, F.J. Andrade, Paper-based ion-
7
selective potentiometric sensors, Anal. Chem. 84 (2012) 4695e4702. [21] J. Ping, Y. Wang, K. Fan, W. Tang, J. Wu, Y. Ying, High-performance flexible potentiometric sensing devices using free-standing graphene paper, J. Mater. Chem. B 1 (2013) 4781e4791. [22] L. Jiang, Z. Fan, Design of advanced porous graphene materials: from graphene nanomesh to 3D architectures, Nanoscale 6 (2014) 1922e1945. [23] S. Mao, G. Lu, J. Chen, Three-dimensional graphene-based composites for energy applications, Nanoscale 7 (2015) 6924e6943. [24] H. Bi, X. Xie, K. Yin, Y. Zhou, S. Wan, L. He, et al., Spongy graphene as a highly efficient and recyclable sorbent for oils and organic solvents, Adv. Funct. Mater. 22 (2012) 4421e4425. [25] X. Xu, L. Pan, Y. Liu, T. Lu, Z. Sun, D.H.C. Chua, Facile synthesis of novel graphene sponge for high performance capacitive deionization, Sci. Rep. 5 (2015) 8458. [26] C. Lin, C. Niu, X. Xu, K. Li, Z. Cai, Y. Zhang, et al., A facile synthesis of three dimensional graphene sponge composited with sulfur nanoparticles for flexible LieS cathodes, Phys. Chem. Chem. Phys. 18 (2016) 22146e22153. [27] W. Zhang, Y. Li, S. Peng, Facile synthesis of graphene sponge from graphene oxide for efficient dye-sensitized H2 evolution, ACS Appl. Mater. Interfaces 8 (2016) 15187e15195. [28] S. Chun, A. Hong, Y. Choi, C. Ha, W. Park, A tactile sensor using a conductive graphene-sponge composite, Nanoscale 8 (2016) 9185e9192. [29] J. Huang, J. Wang, Z. Yang, S. Yang, High-performance graphene sponges reinforced with polyimide for room-temperature piezoresistive sensing, ACS Appl. Mater. Interfaces 10 (2018) 8180e8189. [30] X. Xie, Y. Zhou, H. Bi, K. Yin, S. Wan, L. Sun, Large-range control of the microstructures and properties of three-dimensional porous graphene, Sci. Rep. 3 (2013) 2117. [31] X. Xu, Z. Sun, D.H.C. Chua, L. Pan, Novel nitrogen doped graphene sponge with ultrahigh capacitive deionization performance, Sci. Rep. 5 (2015) 11225. [32] G.A. Crespo, S. Macho, J. Bobacka, F.X. Rius, Transduction mechanism of carbon nanotubes in solid-contact ion-selective electrodes, Anal. Chem. 81 (2009) 676e681. [33] M. Cuartero, J. Bishop, R. Walker, R.G. Acres, E. Bakker, R. De Marco, et al., Evidence of double layer/capacitive charging in carbon nanomaterial-based solid contact polymeric ion-selective electrodes, Chem. Commun. 52 (2016) 9703e9706. [34] X. Zhang, Z. Sui, B. Xu, S. Yue, Y. Luo, W. Zhan, et al., Mechanically strong and highly conductive graphene aerogel and its use as electrodes for electrochemical power sources, J. Mater. Chem. 21 (2011) 6494e6497. [35] Z.A. Alothman, A review: fundamental aspects of silicate mesoporous materials, Materials 5 (2012) 2874e2902. [36] J. Ye, F. Li, S. Gan, Y. Jiang, Q. An, Q. Zhang, et al., Using sp2-C dominant porous carbon sub-micrometer spheres as solid transducers in ion-selective electrodes, Electrochem. Commun. 50 (2015) 60e63. [37] J. Li, T. Yin, W. Qin, An all-solid-state polymeric membrane Pb2þ-selective electrode with bimodal pore C60 as solid contact, Anal. Chim. Acta 876 (2015) 49e54.
Please cite this article as: J. Li, W. Qin, A freestanding all-solid-state polymeric membrane Cu2þ-selective electrode based on three-dimensional graphene sponge, Analytica Chimica Acta, https://doi.org/10.1016/j.aca.2019.04.003