Accepted Manuscript Title: Amino-functionalized mesoporous silica modified glassy carbon electrode for ultra-trace Copper (II) determination Author: Xingxin Dai Fagui Qiu Xuan Zhou Yumei Long Weifeng Li Yifeng Tu PII: DOI: Reference:
S0003-2670(14)00949-0 http://dx.doi.org/doi:10.1016/j.aca.2014.08.002 ACA 233402
To appear in:
Analytica Chimica Acta
Received date: Revised date: Accepted date:
21-6-2014 31-7-2014 5-8-2014
Please cite this article as: Xingxin Dai, Fagui Qiu, Xuan Zhou, Yumei Long, Weifeng Li, Yifeng Tu, Amino-functionalized mesoporous silica modified glassy carbon electrode for ultra-trace Copper (II) determination, Analytica Chimica Acta http://dx.doi.org/10.1016/j.aca.2014.08.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Amino-functionalized mesoporous silica modified glassy carbon electrode for ultra-trace Copper (II) determination Xingxin Dai a, Fagui Qiu c, Xuan Zhou a, Yumei Long a,b, Weifeng Li a, Yifeng Tu a college of Chemistry, Chemical engineering and Materials Science, Soochow University, Suzhou,
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a
Jiangsu 215123, P.R. China The Key Lab of Health Chemistry and Molecular Diagnosis of Suzhou
c
Department of Quartermaster Engineering, Jilin University, No, 5333, Xi’an Road, Changchun
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City 130062, P.R. China
Corresponding author. Tel.: +86 512 65880089; fax: +86 512 65880089
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b
Graphical abstract
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E-mail addresses: [email protected] (Y. Long), [email protected] (W. Li)
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NH2-MCM-41 modified glassy carbon electrode was prepared and it exhibited enhanced anodic stripping response towards Cu (II), which could result from the large surface area of MCM-41 and the good chelating ability of amine-group. The as-constructed electrochemeical sensor showed excellent analytical properties in the determination of Cu2+ and was successfully used for real sample assays. Highlights
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We report a facile method to selectively detect Cu2+ based on NH2-MCM-41 as sensing platform.
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NH2-MCM-41 has good affinity toward Cu2+. Detection limit of 0.9 ng/L and linear concentration range of 5-1000 ng/L are achieved.
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The method is successfully applied to detect Cu2+ in real samples.
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Abstract
This paper described a facile and direct electrochemical method for the determination of ultra-trace Cu2+ by employing amino-functionalized mesoporous
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silica (NH2-MCM-41) as enhanced sensing platform. NH2-MCM-41 was prepared by using a post-grafting process and characterized by X-ray diffraction (XRD),
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transmission electron microscopy (TEM) and fourier transform infrared (FTIR)
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spectroscopy. NH2-MCM-41 modified glassy carbon (GC) electrode showed higher sensitivity for anodic stripping voltammetric (ASV) detection of Cu2+ than that of
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MCM-41 modified one. The high sensitivity was attributed to synergistic effect
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between MCM-41 and amino-group, in which the high surface area and special mesoporous morphology of MCM-41 can cause strong physical absorption, and
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amino-groups are able to chelate copper ions. Some important parameters influencing
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the sensor response were optimized. Under optimum experimental conditions the sensor linearly responded to Cu2+ concentration in the range from 5 to 1000 ng/L with a detection limit of 0. 9 ng/L (S/N = 3). Moreover, the sensor possessed good stability and electrode renewability. In the end, the proposed sensor was applied for determining Cu2+ in real samples and the accuracy of the results were comparable to those obtained by inductively coupled plasma optical emission spectrometry (ICP-OES) method. Key words: Mesoporous silica; Amino-functionalized; Sensor; Anodic stripping voltammetry; Copper
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1. Introduction Copper (Cu2+) is an essential trace element and plays a crucial role in many biological systems [1-2]. It has been found in numerous enzymes and other proteins,
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and takes part in many intracellular redox reactions [3-4]. Both the deficiency and excess of copper in human body will be related to copper-transport diseases. For
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example, copper deficiency is found to cause Menkes disease, while copper excess
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could result in Wilson disease and several neurological disorders [5]. In addition, high level of Cu2+ will damage the biological retreatment systems in water and depresses
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the self-purification ability of natural waters [6]. Thus, it is of great significance to
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accurately determine Cu2+ in biological and environmental systems. Currently, a variety of techniques for Cu2+ detection have been developed,
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including atomic absorption spectroscopy[7-8], inductively coupled plasma
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spectroscopy[9], ion chromatography [10] and chemiluminescence [11]. However, many of these techniques are time consuming and are unsuitable for large scale monitoring because they commonly require expensive instruments, well-trained personnel and complicated sample pretreatments [12]. As a consequence, there is a growing interest to develop more efficient method for determining and monitoring levels of Cu2+. Electrochemical stripping analysis has been considered to be a very promising method for the determination of trace metals because of its advantages such as sensitivity, easy preparation, rapid analysis and low cost. This strategy is based on chemically-modified electrodes, which can selectively capture metal ions due to modifier and then stripping the electrodeposited metal [13]. One of the major
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challenges is to obtain a desirable material for electrode modification. Mesoporous silica, such as MCM-41 and SBA-16, are gaining increasing interest owing to their unique high pore volume, large surface area, tunable pore
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structures and biocompatibility [14]. The amorphous SiO2 pore wall approximates to a Langmuir surface, and can be easily manipulated to create specific adsorption sites for
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the target chemical species. In addition, the rich silanol groups (Si-OH) on their
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surfaces make them easily be modified with various functional groups, including -NH2, -SH, and -S-. Such functionalized Mesoporous silica materials can strongly
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interact with metal ions, and hence have been employed as adsorbents [15-18]. More
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importantly, MCM-41 grafted with -NH2 functional group is found to be more selective for Cu2+ at appropriate condition [16]. Therefore, amino-functionalized
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Cu2+ electrochemical sensor.
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MCM-41 is expected to be a favorable modification material in the development of
Building from these ideas, we have successfully prepared a novel Cu2+ sensor
based on NH2-MCM-41 modified glassy carbon electrode. The properties of the as-constructed Cu2+ sensor have been investigated and the proposed electrode shows great affinity towards Cu2+. The experimental conditions related to characteristic of the sensing system have also been studied and then the sensor is applied in real sample assay. 2. Experimental
2.1. Materials
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3-aminopropyltriethoxysilane (APS) was purchased from Sigma-Aldrich. Cetyltrimethylammonium bromide (CTAB), tetraethyl orthosilicate (TEOS), acetic acid, cupric acetate and sodium acetate were obtained from Sinopharm Chemical
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Reagent Co. Ltd. (China). All the chemicals were of analytical grade and used without further purification.
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All solutions were freshly prepared using doubly deionized water and acetic
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acid buffer solution (NaAc-HAc, 0.2M, pH 4.1) was chosen as the supporting
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electrolyte.
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2.2. Apparatus
The obtained products were characterized by XRD (PANalytical, X-Pert-Pro MPD
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with Cu-Kα radiation, λ=1.540598 Å), TEM (FEI Tecnai G20, an acceleration voltage of 200 kV), and FTIR spectroscopy (Prostar LC240). Element analysis was performed by ICP-OES on a Varian 710-ES system (USA). Electrochemical measurements were performed on a CHI611D electrochemical workstation (Chenhua Instruments Co., Shanghai, China). All electrochemical analysis was conducted in a conventional three-electrode system, in which a NH2-MCM-41-Nafion/GC, a platinum plate, and a saturated calomel electrode (SCE) served as working electrode, counter electrode and reference electrode, respectively. All the experiments were carried out in NaAc-HAc buffer solution (0.2 M, pH = 4.1) at room temperature.
2.3. Procedures
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MCM-41 was synthesized by sol-gel method modified from previous report [16]. Briefly, 0.3 g of cetyltrimethylammonium bromide (CTAB) was dissolved in 150 mL distilled water and stirred to form a homogeneous solution. Then, 1.5 mL of
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ammonia solution (28-30 W %) and 1.7 mL of tetraethyl orthosilicate (TEOS) were added in sequence to the solution under vigorous stirring. After about 12 h, the solid
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product was filtrated, washed with distilled water several times and dried in air at
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110 ℃ for 24 h. Finally, calcination was conducted in air at 550℃for 5 h to remove the template.
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Amino-functionalized MCM-41 was achieved by refluxing a dry toluene
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solution containing 0.5 g of the calcined MCM-41 and 2 mL of APS at 110 ℃. The modified MCM-41 was collected, rinsed with toluene via vacuum filtration, and dried.
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The resulting sample was denoted as NH2-MCM-41.
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Prior to modification, GCEs (diameter 3 mm) were carefully polished with 1.0
μm, 0.3 μm and 0.05μm alumina slurries in sequence and then rinsed ultrasonically with doubly distilled water. After sonicating in absolute ethanol and water, respectively, the cleaned GCEs were dried with nitrogen. The electrode was modified by a simple casting method. Firstly, an appropriate amount of the as-received NH2-MCM-41 was dispersed into ethanol (5 mg/mL) containing Nafion (1%) to form a homogeneous suspension with the aid of ultrasonication. Subsequently, 15 μL of the dispersion was spread onto the clean GCE surface and left it dry at room temperature (labeled as NH2-MCM-41-Nafion/GCE). For comparison, a MCM-41 modified electrode (labeled as MCM-41-Nafion/GCE) was also fabricated with the same
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procedure as described above. Tap water was taken from our research lab without pretreatment. Lake water was collected from Dushu Lake of Suzhou and the samples were purified using a filter
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paper to remove some of impurities. A rat serum sample was obtained from Medical College of Soochow University. For tea sample, 1.0 g of tea powder was weighed and
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placed into beaker. Then 10 mL mix acid (volume ratio: nitric acid/perchloric acid=5)
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was added and evaporated to near dryness. The obtained white sample was re-diffused into water and heated. Finally, the solution was cooled, filtered and quantitatively
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transferred into a 50 mL volumetric flask for further analysis. Prior to measurement,
method.
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all samples were diluted to meet the detecting concentration range of the proposed
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Electrochemical measurements were performed using linear sweep anodic
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stripping voltammetry (LSASV). The NH2-MCM-41-Nafion/GCE was immersed in 10 mL of NaAc-HAc buffer solution (0.2 M, pH=4.1), containing Cu2+ at different concentrations. The pre-concentration step was carried out in stirred solution at the potential of -0.6 V for 240 s and LSASV responses were recorded from -0.4 to 0.4 V with a scan rate of 0.1 Vs-1. After each measurement, the electrode was cleaned at potential of +0.5 V for 200 s to remove the residual metals.
3. Results and discussion 3.1 Characterization of the NH2-MCM-41 TEM images (Fig. 1A and B) confirm the formation of spherical MCM-41
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material with well-ordered, hexagonal pore structure. It should be noted that the conjugation of APS functional groups onto the MCM-41 did not affect its microstructure. Fig. 1C shows XRD patterns of order mesoporous material, MCM-41,
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and the NH2-functionalized sample, NH2-MCM-41. Three characteristic diffraction peaks of (100), (110) and (200) can be observed for both the samples, which suggest
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good crystallinity with the hexagonal structure of the pores and the modification
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process does not affect the framework integrity of the MCM-41.
The incorporation of amino groups into MCM-41 structure was verified by
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FTIR spectroscopy. Typical FTIR spectra of MCM-41 and NH2-MCM-41 samples are
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displayed in Fig. 1D. Both the samples have a strong absorption band around 1075 cm-1, which is attributed to the Si-O-Si asymmetric stretching vibration while the peak
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at about 800 cm-1 is due to the symmetric stretching vibration of Si-O-Si. After
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grafting APS, several new absorption bands can be found. The absorption bands around 1550 cm-1 and 685 cm-1 correspond to –NH2 symmetric bending vibration and N-H bending vibration, respectively [19]. C-H stretches result in absorption bands at 2930 cm-1 and 2858 cm-1. These results confirm the existence of APS functional group in the modified MCM-41 sample.
3.2. Electrochemical behaviors of the modified electrodes Fig. 2 shows the LSASV characteristics of bare (curve a), Nafion (curve b), MCM-41-Nafion (curve c) and NH2-MCM-41-Nafion (curve d) modified GC electrodes in 0.2 M NaAc-HAc buffer solution (pH 4.1) containing 1000 ng/L of Cu2+.
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As can be seen, there was no appreciable electrochemical features for bare GC and Nafion-modified electrodes. In the case of MCM-41-NafionGC electrode, a well-defined stripping peak at about -0.028 V was clearly observed, which
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corresponds to the re-oxidation of copper ions and the peak position is close to the equilibrium potential for Cu2+/Cu (-0.026 V) couple calculated using the Nernst
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equation. Strikingly, the stripping response was found to be significantly enhanced
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when the NH2-MCM-41-Nafion/GC electrode was employed. This affirms that the Cu2+ ion adsorption ability of electrode surface is greatly enhanced by NH2-MCM-41
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modification. The high affinity of NH2-MCM-41 could be related to the synergistic
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effect between mesoporous silica and amino-group, in which the high surface area and special mesoporous morphology of MCM-41 can cause strong physical absorption,
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and amino-groups are able to chelate copper ions.
3.3. Optimization of experimental parameters The influence of pH on the anodic stripping voltammetric responses of the
NH2-MCM-41-Nafion/GC electrode was investigated using NaAc-HAc buffer solution over the range from 3.6 to 5.6. As Fig. 3 shows, the anodic stripping peak current increases with increasing solution pH up to 4.1 at first and then decreases at higher pH values. At the pH lower than 4.1, the lone pair of electrons present on the nitrogen atom of the modifier functionalities may get protonated, which makes the surface of the modified electrode positive and inhibits pre-concentration of Cu2+.
On
the other hand, the decrease in the anodic stripping peak currents at higher pH values
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is due to the hydrolysis of Cu2+. Thereby, a NaAc-HAc buffer solution with pH of 4.1 was selected for all the subsequent experiments. Pre-concentration potential is very important for electrode accumulation and
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reduction in the stripping voltammetry analysis method. The influence of the deposition potential on anodic stripping peak currents after 240 s accumulation was
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investigated in the range from -1.0 to 0 V. As shown in Fig. 4A, the anodic stripping
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peak current for copper increases as the deposition potential increases from 0 to -0.6 V, and then decreases at potential more negative -0.6 V. The observed phenomena might
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be explained by the hydrogen evolution in the buffer solution (pH 4.1). It is well
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known that the larger the negative value of a deposition potential, the closer the hydrogen evolution is. When the applied deposition potential is more negative than
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-0.6 V, the hydrogen evolution near the electrode surface might disturb the deposition
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of metal on the electrode surface and make the stripping current response weak [20]. Therefore, a deposition potential of -0.6 V was chosen in all the subsequent work. Fig. 4B illustrates the dependence of the anodic stripping peak current on
deposition time under the applied deposition potential of -0.6 V. The anodic stripping peak current of 1000 ng/L Cu2+ increases linearly with pre-concentration time up to 240 s. For longer pre-concentration time, anodic stripping peak current was found to level off due to the saturation loading of active sites at the electrode surface. Consequently, the deposition time of 240 s was chosen for the balance between good sensitivity and short analysis time.
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3.4. Analytical performances Under the optimized conditions discussed above, LSASVs for the oxidation of different concentrations of copper were carried out on the NH2-MCM-41-Nafion/GC
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electrode. The results are shown in Fig. 5. The anodic stripping peak currents linearly increase as copper concentrations increases from 5 ng/L to 1000 ng/L (inset of Fig. 5).
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The linear regression equations is ip = 2.262C + 2.199 (ip: µA, C: µg L−1, R=0.996).
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The detection limit of 0.9 ng/L was calculated using the formula of 3s/N, in which s is the standard deviation of the blank signal and N is the slope of the calibration plot.
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Table 1 gives a comparison between the proposed method with the previously
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reported modified electrodes, which indicates that the electrode developed here is better than most reported analogues for electrochemical stripping determination of
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Cu2+.
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After each measurement, a renewed NH2-MCM-41-Nafion/GC electrode surface
was realized by in situ electrochemical cleaning process at +0.5 V for 200 s. As illustrated in Fig. 6, a fresh electrode exhibits a stripping current peak at -0.028 V in 1000 ng/L Cu2+ solution (curve a). After cleaning process, no current peak in blank solution is found any more (curve b), indicating the accumulated metals have been completely removed from the surface. The renewed electrode surface allows to eliminate the contamination of the surface and to minimize the memory effects. Furthermore, the regenerated electrode gives almost the same stripping current response in the 1000 ng/L Cu2+ solution, which suggests that the regenerated electrode can be used for Cu2+ detection in a reproducible manner. The stability of the
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NH2-MCM-41-Nafion/GC electrode stored at room temperature was studied. After one month the modified electrode still remained about 91.2% of its initial current response recorded in 1000 ng/L Cu2+ solution. The relative standard deviation was
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3.53% for eight consecutive measurements of 1000 ng/L Cu2+, indicating acceptable repeatability. In addition, five freshly prepared NH2-MCM-41-Nafion/GC electrodes
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were employed to measure 1000 ng/L Cu2+. All five electrodes exhibited similar
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current responses and a relative standard deviation of 2.63% was obtained.
3.5. Interference study
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The selectivity of the proposed method was also investigated since other metal ions might affect the detection of Cu2+ in real sample analysis. Fig. 7 shows the
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stripping peak current of 1000 ng/L Cu2+ in the presence of different concentrations of
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common metal ions under the optimized conditions. One can see that all the metal ions tested including 3105 ng/L Al3+, 3105 ng/L Fe3+, 3105 ng/L Co2+, 5105 ng/L Ni2+, 5105 ng/L Zn2+, 5105 ng/L Cd2+, 5105 ng/L Pb2+, 1106 ng/L Mg2+ and 1106 ng/L Bi3+ has little effect on the stripping peak current, indicating high selectivity of the NH2-MCM-41-Nafion/GC electrode for Cu2+ detection and its potential application for analysis in complex system. The high selectivity of the present electrochemical sensor should originate from the outstanding coordination ability of amine group toward Cu2+.
3.6. Applications
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To assess the practical application of the NH2-MCM-41-Nafion/GC electrode, the detection of Cu2+ in tap water, lake water, rat serum and tea water samples, was performed using the standard addition method. Before measurements with the
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proposed method, all real samples were diluted 10000-fold with 0.2 M NaAc-HAc (pH 4.1). Table 2 summarizes the results. The acceptable recovery in the range of
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97.5-107.5% was obtained, implying accuracy of the developed electrochemical
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sensor. We also evaluated the accuracy of the method by comparing the electrochemical results with those obtained by ICP-OES. The results are listed in
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Table 3. It can be seen that the results of the proposed sensor are in good agreement
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with the ICP-OES measurements, suggesting that the proposed method is reliable. Considering the environmental friend of mesoporous silica, functionalized
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methods.
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mesoporous silica materials make great promise for developing the electrochemical
4. Conclusions
In conclusion, the electrochemical performances of NH2-functionalized
MCM-41 and native MCM-41 have been investigated. It is found that the NH2-MCM-41 modified electrode exhibits higher sensitivity for Cu2+ monitoring than the MCM-41
modified one.
The excellent
electrochemical properties of
NH2-MCM-41 modified electrode might be ascribed to the large surface area and special mesoporous morphology of MCM-41, as well as the good chelating ability of amine-group. The sensor shows wide linear range, low detection limit and good
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renewability and was employed to determine Cu2+ in real samples with satisfactory results. It is expected that functionalized mesoporous materials could offer great
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potential for electrochemical sensor fabrication.
Acknowledgments
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This work was supported by the National Natural Science Foundation of China
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(21005053), the Priority Academic Program Development of Jiangsu Higher Education Institutions and The Project of Scientific and Technologic Infrastructure of
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M
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Suzhou (SZS201207).
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Figure captions:
Fig. 1: TEM images of MCM-41 (A) and NH2-MCM-41 (B); XRD patterns (C) and
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FTIR (D) of MCM-41 and NH2-MCM-41.
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Fig. 2: LSASV responses of Cu2+ on bare (a), Nafion (b), MCM-41/Nafion (c), and NH2-MCM-41/Nafion (d) modified GC electrodes.
Fig. 3: Effect of pH on the stripping voltammetric response in 0.2 M NaAc-HAc containing 1000 ng/L Cu2+ at NH2-MCM-41-Nafion/GC electrode (Conditions: pre-concentration potential and time are -0.6 V and 240 s, respectively).
Fig. 4: Effect of the deposition potential (A) and deposition time (B) on the stripping voltammetric responses of 1000 ng/L Cu2+ at NH2-MCM-41-Nafion/GC electrode in 0.2 M NaAc-HAc (pH = 4.1). Fig. 5: Linear sweep voltammograms after pre-concentration in 0.2 M pH 4.1 NaAc-HAc solution containing Cu2+ with different concentration. The inset shows
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the calibration curve. Conditions: pre-concentration potential and time are -0.6 V and 240 s, respectively. Refs
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[21] [22] [23] [24]
cr
Linear range (ng/L) 6.4×105-2.5×106 6.4×104-3.8×106 1×105-2×107 4.4×103-6.4×104 6.4×104-6.4×106 1.3×103-1.9×104 1×102 -5×103 3.2×103-6.4×108 3.2×102 -6.4×103 5×103 -1×105 5 to 1×103
2 6.4×102 1. 8 3.3×102 0.9
us
DNAzyme/ GCE C-Dot-TPEA/GCE CoO/EG MIP/CPE NIP/CPE GGH/OPPy-COOH MPS/NPG PPy/EBB/GCE AuNPs-GR/GCE CNTs/poly(1,2-DAB)/GCE NH2-MCM-41/GCE
Detection limit (ng/L) 4.1×105 6.4×103 9.4×104 1.5×103
an
Method
[25] [26] [27] [28] [29] This work
M
Fig. 6: LSASV responses of fresh NH2-MCM-41-Nafion/GC electrode in 1000 ng/L Cu2+ solution (a), regenerated electrode in blank solution (b) and the regenerated
d
electrode in 1000 ng/L Cu2+ solution (c).
Ac ce pt e
Fig. 7: Effects of various metal ions on the electrochemical stripping signals of Cu2+ at NH2-MCM-41-Nafion/GC electrode (1000 ng/L Cu2+ and 3105 ng/L each for Al3+, Fe3+, Co2+, 5105 ng/L each for Ni2+, Zn2+, Cd2+, Pb2+, 1106 ng/L each for Mg2+, Bi3+).
Table 1 A comparison of the analytical properties of the NH2-MCM-41/Nafion/GCE and other electrodes for Cu2+ determination AE-TPEA: N-(2-aminoethyl)-N,N’,N’-tris-(pyridine-2-yl-methyl)ethane-1,2-diamine MIP: molecular imprinted polymers; NIP: non-imprinted polymers; CPE: carbon paste electrode; GGH: Gly-Gly-His; OPPy : overoxidized polypyrrole; MPS :
Page 19 of 33
(3-mercaptopropyl)sulfonate;
NPG:
nanoporous
gold;
PPy:
polypyrrole;
EBB :Eriochrome Blue-black B; GR/GCE: electrochemical reduction of graphene
Ac ce pt e
d
M
an
us
cr
ip t
oxide on GCE electrode; CNTs : carbon nanotubes; 1,2-DAB : 1,2-Diaminobenzene;
Page 20 of 33
Table 2: Results of the recovery analysis of Cu2+ in different real samples (n=3)
Rat serum
116 6.1
100
214 7.3
98
100
311 8.0
97.5
200
546 10.1
0
119 9.4
100
222 14.5
100
316 9.0
200
524 8.2
0
296 6.9
100
103
98.5
101.3
102
503 19.5
103.5
691 12.6
98.8
385 7.3
492 18.0
107
100
593 9.8
104
200
691 17.6
98.5
d
100
Ac ce pt e
Tea
107.5
398 8.2
M
100
0
ip t
0
200
Recovery (%)
cr
Lake water
Found (ng/L)
us
Tap water
Added (ng/L)
an
Sample
Page 21 of 33
Table 3: Determination of Cu2+ in real samples using the proposed sensor and ICP-OES method. Proposed method (mg/L)
ICP-OES (mg/L)
Relative deviation
Tap water
1.16 0.06
1.22 0.04
-4.9%
Lake water
1.19 0.09
1.15 0.03
3.5%
Rat serum
2.96 0.07
2.83 0.08
4.6%
Tea
3.85 0.07
3.96 0.06
cr
ip t
Sample
Ac ce pt e
d
M
an
us
-3.1%
Page 22 of 33
ip t cr us an M d Ac ce pt e
Fig. 1A
Page 23 of 33
ip t cr us an M
Ac ce pt e
d
Fig .1B
Page 24 of 33
ip t cr us an
Ac ce pt e
d
M
Fig. 1C
Page 25 of 33
ip t cr us an
Ac ce pt e
d
M
Fig .1D
Page 26 of 33
ip t cr us an
2
Ac ce pt e
d
M
Fig.
Page 27 of 33
ip t cr us an
Ac ce pt e
d
M
Fig. 3-revised
Page 28 of 33
ip t cr us an
Ac ce pt e
d
M
Fig. 4A-revised
Page 29 of 33
ip t cr us an
Ac ce pt e
d
M
Fig .4B-revised
Page 30 of 33
ip t cr us an
Ac ce pt e
d
M
Fig. 5
Page 31 of 33
ip t cr us an
Ac ce pt e
d
M
Fig. 6-revised
Page 32 of 33
ip t cr us an
7
Ac ce pt e
d
M
Fig.
Page 33 of 33
S0003-2670(14)00949-0 http://dx.doi.org/doi:10.1016/j.aca.2014.08.002 ACA 233402
To appear in:
Analytica Chimica Acta
Received date: Revised date: Accepted date:
21-6-2014 31-7-2014 5-8-2014
Please cite this article as: Xingxin Dai, Fagui Qiu, Xuan Zhou, Yumei Long, Weifeng Li, Yifeng Tu, Amino-functionalized mesoporous silica modified glassy carbon electrode for ultra-trace Copper (II) determination, Analytica Chimica Acta http://dx.doi.org/10.1016/j.aca.2014.08.002 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Amino-functionalized mesoporous silica modified glassy carbon electrode for ultra-trace Copper (II) determination Xingxin Dai a, Fagui Qiu c, Xuan Zhou a, Yumei Long a,b, Weifeng Li a, Yifeng Tu a college of Chemistry, Chemical engineering and Materials Science, Soochow University, Suzhou,
ip t
a
Jiangsu 215123, P.R. China The Key Lab of Health Chemistry and Molecular Diagnosis of Suzhou
c
Department of Quartermaster Engineering, Jilin University, No, 5333, Xi’an Road, Changchun
us
City 130062, P.R. China
Corresponding author. Tel.: +86 512 65880089; fax: +86 512 65880089
an
cr
b
Graphical abstract
M
E-mail addresses: [email protected] (Y. Long), [email protected] (W. Li)
Ac ce pt e
d
NH2-MCM-41 modified glassy carbon electrode was prepared and it exhibited enhanced anodic stripping response towards Cu (II), which could result from the large surface area of MCM-41 and the good chelating ability of amine-group. The as-constructed electrochemeical sensor showed excellent analytical properties in the determination of Cu2+ and was successfully used for real sample assays. Highlights
►
We report a facile method to selectively detect Cu2+ based on NH2-MCM-41 as sensing platform.
► ►
NH2-MCM-41 has good affinity toward Cu2+. Detection limit of 0.9 ng/L and linear concentration range of 5-1000 ng/L are achieved.
►
The method is successfully applied to detect Cu2+ in real samples.
Page 1 of 33
Abstract
This paper described a facile and direct electrochemical method for the determination of ultra-trace Cu2+ by employing amino-functionalized mesoporous
ip t
silica (NH2-MCM-41) as enhanced sensing platform. NH2-MCM-41 was prepared by using a post-grafting process and characterized by X-ray diffraction (XRD),
cr
transmission electron microscopy (TEM) and fourier transform infrared (FTIR)
us
spectroscopy. NH2-MCM-41 modified glassy carbon (GC) electrode showed higher sensitivity for anodic stripping voltammetric (ASV) detection of Cu2+ than that of
an
MCM-41 modified one. The high sensitivity was attributed to synergistic effect
M
between MCM-41 and amino-group, in which the high surface area and special mesoporous morphology of MCM-41 can cause strong physical absorption, and
d
amino-groups are able to chelate copper ions. Some important parameters influencing
Ac ce pt e
the sensor response were optimized. Under optimum experimental conditions the sensor linearly responded to Cu2+ concentration in the range from 5 to 1000 ng/L with a detection limit of 0. 9 ng/L (S/N = 3). Moreover, the sensor possessed good stability and electrode renewability. In the end, the proposed sensor was applied for determining Cu2+ in real samples and the accuracy of the results were comparable to those obtained by inductively coupled plasma optical emission spectrometry (ICP-OES) method. Key words: Mesoporous silica; Amino-functionalized; Sensor; Anodic stripping voltammetry; Copper
Page 2 of 33
1. Introduction Copper (Cu2+) is an essential trace element and plays a crucial role in many biological systems [1-2]. It has been found in numerous enzymes and other proteins,
ip t
and takes part in many intracellular redox reactions [3-4]. Both the deficiency and excess of copper in human body will be related to copper-transport diseases. For
cr
example, copper deficiency is found to cause Menkes disease, while copper excess
us
could result in Wilson disease and several neurological disorders [5]. In addition, high level of Cu2+ will damage the biological retreatment systems in water and depresses
an
the self-purification ability of natural waters [6]. Thus, it is of great significance to
M
accurately determine Cu2+ in biological and environmental systems. Currently, a variety of techniques for Cu2+ detection have been developed,
d
including atomic absorption spectroscopy[7-8], inductively coupled plasma
Ac ce pt e
spectroscopy[9], ion chromatography [10] and chemiluminescence [11]. However, many of these techniques are time consuming and are unsuitable for large scale monitoring because they commonly require expensive instruments, well-trained personnel and complicated sample pretreatments [12]. As a consequence, there is a growing interest to develop more efficient method for determining and monitoring levels of Cu2+. Electrochemical stripping analysis has been considered to be a very promising method for the determination of trace metals because of its advantages such as sensitivity, easy preparation, rapid analysis and low cost. This strategy is based on chemically-modified electrodes, which can selectively capture metal ions due to modifier and then stripping the electrodeposited metal [13]. One of the major
Page 3 of 33
challenges is to obtain a desirable material for electrode modification. Mesoporous silica, such as MCM-41 and SBA-16, are gaining increasing interest owing to their unique high pore volume, large surface area, tunable pore
ip t
structures and biocompatibility [14]. The amorphous SiO2 pore wall approximates to a Langmuir surface, and can be easily manipulated to create specific adsorption sites for
cr
the target chemical species. In addition, the rich silanol groups (Si-OH) on their
us
surfaces make them easily be modified with various functional groups, including -NH2, -SH, and -S-. Such functionalized Mesoporous silica materials can strongly
an
interact with metal ions, and hence have been employed as adsorbents [15-18]. More
M
importantly, MCM-41 grafted with -NH2 functional group is found to be more selective for Cu2+ at appropriate condition [16]. Therefore, amino-functionalized
Ac ce pt e
Cu2+ electrochemical sensor.
d
MCM-41 is expected to be a favorable modification material in the development of
Building from these ideas, we have successfully prepared a novel Cu2+ sensor
based on NH2-MCM-41 modified glassy carbon electrode. The properties of the as-constructed Cu2+ sensor have been investigated and the proposed electrode shows great affinity towards Cu2+. The experimental conditions related to characteristic of the sensing system have also been studied and then the sensor is applied in real sample assay. 2. Experimental
2.1. Materials
Page 4 of 33
3-aminopropyltriethoxysilane (APS) was purchased from Sigma-Aldrich. Cetyltrimethylammonium bromide (CTAB), tetraethyl orthosilicate (TEOS), acetic acid, cupric acetate and sodium acetate were obtained from Sinopharm Chemical
ip t
Reagent Co. Ltd. (China). All the chemicals were of analytical grade and used without further purification.
cr
All solutions were freshly prepared using doubly deionized water and acetic
us
acid buffer solution (NaAc-HAc, 0.2M, pH 4.1) was chosen as the supporting
an
electrolyte.
M
2.2. Apparatus
The obtained products were characterized by XRD (PANalytical, X-Pert-Pro MPD
Ac ce pt e
d
with Cu-Kα radiation, λ=1.540598 Å), TEM (FEI Tecnai G20, an acceleration voltage of 200 kV), and FTIR spectroscopy (Prostar LC240). Element analysis was performed by ICP-OES on a Varian 710-ES system (USA). Electrochemical measurements were performed on a CHI611D electrochemical workstation (Chenhua Instruments Co., Shanghai, China). All electrochemical analysis was conducted in a conventional three-electrode system, in which a NH2-MCM-41-Nafion/GC, a platinum plate, and a saturated calomel electrode (SCE) served as working electrode, counter electrode and reference electrode, respectively. All the experiments were carried out in NaAc-HAc buffer solution (0.2 M, pH = 4.1) at room temperature.
2.3. Procedures
Page 5 of 33
MCM-41 was synthesized by sol-gel method modified from previous report [16]. Briefly, 0.3 g of cetyltrimethylammonium bromide (CTAB) was dissolved in 150 mL distilled water and stirred to form a homogeneous solution. Then, 1.5 mL of
ip t
ammonia solution (28-30 W %) and 1.7 mL of tetraethyl orthosilicate (TEOS) were added in sequence to the solution under vigorous stirring. After about 12 h, the solid
cr
product was filtrated, washed with distilled water several times and dried in air at
us
110 ℃ for 24 h. Finally, calcination was conducted in air at 550℃for 5 h to remove the template.
an
Amino-functionalized MCM-41 was achieved by refluxing a dry toluene
M
solution containing 0.5 g of the calcined MCM-41 and 2 mL of APS at 110 ℃. The modified MCM-41 was collected, rinsed with toluene via vacuum filtration, and dried.
d
The resulting sample was denoted as NH2-MCM-41.
Ac ce pt e
Prior to modification, GCEs (diameter 3 mm) were carefully polished with 1.0
μm, 0.3 μm and 0.05μm alumina slurries in sequence and then rinsed ultrasonically with doubly distilled water. After sonicating in absolute ethanol and water, respectively, the cleaned GCEs were dried with nitrogen. The electrode was modified by a simple casting method. Firstly, an appropriate amount of the as-received NH2-MCM-41 was dispersed into ethanol (5 mg/mL) containing Nafion (1%) to form a homogeneous suspension with the aid of ultrasonication. Subsequently, 15 μL of the dispersion was spread onto the clean GCE surface and left it dry at room temperature (labeled as NH2-MCM-41-Nafion/GCE). For comparison, a MCM-41 modified electrode (labeled as MCM-41-Nafion/GCE) was also fabricated with the same
Page 6 of 33
procedure as described above. Tap water was taken from our research lab without pretreatment. Lake water was collected from Dushu Lake of Suzhou and the samples were purified using a filter
ip t
paper to remove some of impurities. A rat serum sample was obtained from Medical College of Soochow University. For tea sample, 1.0 g of tea powder was weighed and
cr
placed into beaker. Then 10 mL mix acid (volume ratio: nitric acid/perchloric acid=5)
us
was added and evaporated to near dryness. The obtained white sample was re-diffused into water and heated. Finally, the solution was cooled, filtered and quantitatively
an
transferred into a 50 mL volumetric flask for further analysis. Prior to measurement,
method.
M
all samples were diluted to meet the detecting concentration range of the proposed
d
Electrochemical measurements were performed using linear sweep anodic
Ac ce pt e
stripping voltammetry (LSASV). The NH2-MCM-41-Nafion/GCE was immersed in 10 mL of NaAc-HAc buffer solution (0.2 M, pH=4.1), containing Cu2+ at different concentrations. The pre-concentration step was carried out in stirred solution at the potential of -0.6 V for 240 s and LSASV responses were recorded from -0.4 to 0.4 V with a scan rate of 0.1 Vs-1. After each measurement, the electrode was cleaned at potential of +0.5 V for 200 s to remove the residual metals.
3. Results and discussion 3.1 Characterization of the NH2-MCM-41 TEM images (Fig. 1A and B) confirm the formation of spherical MCM-41
Page 7 of 33
material with well-ordered, hexagonal pore structure. It should be noted that the conjugation of APS functional groups onto the MCM-41 did not affect its microstructure. Fig. 1C shows XRD patterns of order mesoporous material, MCM-41,
ip t
and the NH2-functionalized sample, NH2-MCM-41. Three characteristic diffraction peaks of (100), (110) and (200) can be observed for both the samples, which suggest
cr
good crystallinity with the hexagonal structure of the pores and the modification
us
process does not affect the framework integrity of the MCM-41.
The incorporation of amino groups into MCM-41 structure was verified by
an
FTIR spectroscopy. Typical FTIR spectra of MCM-41 and NH2-MCM-41 samples are
M
displayed in Fig. 1D. Both the samples have a strong absorption band around 1075 cm-1, which is attributed to the Si-O-Si asymmetric stretching vibration while the peak
d
at about 800 cm-1 is due to the symmetric stretching vibration of Si-O-Si. After
Ac ce pt e
grafting APS, several new absorption bands can be found. The absorption bands around 1550 cm-1 and 685 cm-1 correspond to –NH2 symmetric bending vibration and N-H bending vibration, respectively [19]. C-H stretches result in absorption bands at 2930 cm-1 and 2858 cm-1. These results confirm the existence of APS functional group in the modified MCM-41 sample.
3.2. Electrochemical behaviors of the modified electrodes Fig. 2 shows the LSASV characteristics of bare (curve a), Nafion (curve b), MCM-41-Nafion (curve c) and NH2-MCM-41-Nafion (curve d) modified GC electrodes in 0.2 M NaAc-HAc buffer solution (pH 4.1) containing 1000 ng/L of Cu2+.
Page 8 of 33
As can be seen, there was no appreciable electrochemical features for bare GC and Nafion-modified electrodes. In the case of MCM-41-NafionGC electrode, a well-defined stripping peak at about -0.028 V was clearly observed, which
ip t
corresponds to the re-oxidation of copper ions and the peak position is close to the equilibrium potential for Cu2+/Cu (-0.026 V) couple calculated using the Nernst
cr
equation. Strikingly, the stripping response was found to be significantly enhanced
us
when the NH2-MCM-41-Nafion/GC electrode was employed. This affirms that the Cu2+ ion adsorption ability of electrode surface is greatly enhanced by NH2-MCM-41
an
modification. The high affinity of NH2-MCM-41 could be related to the synergistic
M
effect between mesoporous silica and amino-group, in which the high surface area and special mesoporous morphology of MCM-41 can cause strong physical absorption,
Ac ce pt e
d
and amino-groups are able to chelate copper ions.
3.3. Optimization of experimental parameters The influence of pH on the anodic stripping voltammetric responses of the
NH2-MCM-41-Nafion/GC electrode was investigated using NaAc-HAc buffer solution over the range from 3.6 to 5.6. As Fig. 3 shows, the anodic stripping peak current increases with increasing solution pH up to 4.1 at first and then decreases at higher pH values. At the pH lower than 4.1, the lone pair of electrons present on the nitrogen atom of the modifier functionalities may get protonated, which makes the surface of the modified electrode positive and inhibits pre-concentration of Cu2+.
On
the other hand, the decrease in the anodic stripping peak currents at higher pH values
Page 9 of 33
is due to the hydrolysis of Cu2+. Thereby, a NaAc-HAc buffer solution with pH of 4.1 was selected for all the subsequent experiments. Pre-concentration potential is very important for electrode accumulation and
ip t
reduction in the stripping voltammetry analysis method. The influence of the deposition potential on anodic stripping peak currents after 240 s accumulation was
cr
investigated in the range from -1.0 to 0 V. As shown in Fig. 4A, the anodic stripping
us
peak current for copper increases as the deposition potential increases from 0 to -0.6 V, and then decreases at potential more negative -0.6 V. The observed phenomena might
an
be explained by the hydrogen evolution in the buffer solution (pH 4.1). It is well
M
known that the larger the negative value of a deposition potential, the closer the hydrogen evolution is. When the applied deposition potential is more negative than
d
-0.6 V, the hydrogen evolution near the electrode surface might disturb the deposition
Ac ce pt e
of metal on the electrode surface and make the stripping current response weak [20]. Therefore, a deposition potential of -0.6 V was chosen in all the subsequent work. Fig. 4B illustrates the dependence of the anodic stripping peak current on
deposition time under the applied deposition potential of -0.6 V. The anodic stripping peak current of 1000 ng/L Cu2+ increases linearly with pre-concentration time up to 240 s. For longer pre-concentration time, anodic stripping peak current was found to level off due to the saturation loading of active sites at the electrode surface. Consequently, the deposition time of 240 s was chosen for the balance between good sensitivity and short analysis time.
Page 10 of 33
3.4. Analytical performances Under the optimized conditions discussed above, LSASVs for the oxidation of different concentrations of copper were carried out on the NH2-MCM-41-Nafion/GC
ip t
electrode. The results are shown in Fig. 5. The anodic stripping peak currents linearly increase as copper concentrations increases from 5 ng/L to 1000 ng/L (inset of Fig. 5).
cr
The linear regression equations is ip = 2.262C + 2.199 (ip: µA, C: µg L−1, R=0.996).
us
The detection limit of 0.9 ng/L was calculated using the formula of 3s/N, in which s is the standard deviation of the blank signal and N is the slope of the calibration plot.
an
Table 1 gives a comparison between the proposed method with the previously
M
reported modified electrodes, which indicates that the electrode developed here is better than most reported analogues for electrochemical stripping determination of
d
Cu2+.
Ac ce pt e
After each measurement, a renewed NH2-MCM-41-Nafion/GC electrode surface
was realized by in situ electrochemical cleaning process at +0.5 V for 200 s. As illustrated in Fig. 6, a fresh electrode exhibits a stripping current peak at -0.028 V in 1000 ng/L Cu2+ solution (curve a). After cleaning process, no current peak in blank solution is found any more (curve b), indicating the accumulated metals have been completely removed from the surface. The renewed electrode surface allows to eliminate the contamination of the surface and to minimize the memory effects. Furthermore, the regenerated electrode gives almost the same stripping current response in the 1000 ng/L Cu2+ solution, which suggests that the regenerated electrode can be used for Cu2+ detection in a reproducible manner. The stability of the
Page 11 of 33
NH2-MCM-41-Nafion/GC electrode stored at room temperature was studied. After one month the modified electrode still remained about 91.2% of its initial current response recorded in 1000 ng/L Cu2+ solution. The relative standard deviation was
ip t
3.53% for eight consecutive measurements of 1000 ng/L Cu2+, indicating acceptable repeatability. In addition, five freshly prepared NH2-MCM-41-Nafion/GC electrodes
cr
were employed to measure 1000 ng/L Cu2+. All five electrodes exhibited similar
an
us
current responses and a relative standard deviation of 2.63% was obtained.
3.5. Interference study
M
The selectivity of the proposed method was also investigated since other metal ions might affect the detection of Cu2+ in real sample analysis. Fig. 7 shows the
d
stripping peak current of 1000 ng/L Cu2+ in the presence of different concentrations of
Ac ce pt e
common metal ions under the optimized conditions. One can see that all the metal ions tested including 3105 ng/L Al3+, 3105 ng/L Fe3+, 3105 ng/L Co2+, 5105 ng/L Ni2+, 5105 ng/L Zn2+, 5105 ng/L Cd2+, 5105 ng/L Pb2+, 1106 ng/L Mg2+ and 1106 ng/L Bi3+ has little effect on the stripping peak current, indicating high selectivity of the NH2-MCM-41-Nafion/GC electrode for Cu2+ detection and its potential application for analysis in complex system. The high selectivity of the present electrochemical sensor should originate from the outstanding coordination ability of amine group toward Cu2+.
3.6. Applications
Page 12 of 33
To assess the practical application of the NH2-MCM-41-Nafion/GC electrode, the detection of Cu2+ in tap water, lake water, rat serum and tea water samples, was performed using the standard addition method. Before measurements with the
ip t
proposed method, all real samples were diluted 10000-fold with 0.2 M NaAc-HAc (pH 4.1). Table 2 summarizes the results. The acceptable recovery in the range of
cr
97.5-107.5% was obtained, implying accuracy of the developed electrochemical
us
sensor. We also evaluated the accuracy of the method by comparing the electrochemical results with those obtained by ICP-OES. The results are listed in
an
Table 3. It can be seen that the results of the proposed sensor are in good agreement
M
with the ICP-OES measurements, suggesting that the proposed method is reliable. Considering the environmental friend of mesoporous silica, functionalized
Ac ce pt e
methods.
d
mesoporous silica materials make great promise for developing the electrochemical
4. Conclusions
In conclusion, the electrochemical performances of NH2-functionalized
MCM-41 and native MCM-41 have been investigated. It is found that the NH2-MCM-41 modified electrode exhibits higher sensitivity for Cu2+ monitoring than the MCM-41
modified one.
The excellent
electrochemical properties of
NH2-MCM-41 modified electrode might be ascribed to the large surface area and special mesoporous morphology of MCM-41, as well as the good chelating ability of amine-group. The sensor shows wide linear range, low detection limit and good
Page 13 of 33
renewability and was employed to determine Cu2+ in real samples with satisfactory results. It is expected that functionalized mesoporous materials could offer great
ip t
potential for electrochemical sensor fabrication.
Acknowledgments
cr
This work was supported by the National Natural Science Foundation of China
us
(21005053), the Priority Academic Program Development of Jiangsu Higher Education Institutions and The Project of Scientific and Technologic Infrastructure of
Ac ce pt e
d
M
an
Suzhou (SZS201207).
References
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cr
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[10] A. Błażewicz, W. Dolliver, S. Sivsammye, A. Deol, R. Randhawa, G. Orlicz-Szczęsna, R. Błażewicz, Determination of cadmium, cobalt, copper, iron, manganese, and zinc in thyroid glands of patients with diagnosed nodular goitre using ion chromatography, J. Chromatography B 878 (2010) 34-38. [11] H. Zamzow, K. H. Coale, K. S. Johnson, C. M. Sakamoto, Determination of
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ip t
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cr
[13] M. Heitzmann, L. Basaez, F. Brovelli, C. Bucher, D. Limosin, E. Pereira, J. C.
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Moutet, Voltammetric Sensing of Trace Metals at a Poly (pyrrol-malonic acid) Film Modified Carbon Electrode, Electroanalysis 17 (2005) 1970-1976.
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[14] Z. A. Alothman, A. W. Apblett, Preparation of mesoporous silica with grafted
M
chelating agents for uptake of metal ions, Chem. Eng. J. 155 (2009) 916-924. [15] M. Vasudevan, P. L. Sakaria, A. S. Bhatt, H. M. Mody, H. C. Bajaj, Effect of
d
Concentration of Aminopropyl Groups on the Surface of MCM-41 on Adsorption
Ac ce pt e
of Cu2+, Ind. Eng. Chem. Rs. 50 (2011) 11432-11439.
[16] K. F. Lam, K. L.Yeung, G. McKay, A rational approach in the design of selective mesoporous adsorbents, Langmuir 22 (2006) 9632-9641.
[17] T. Yokoi, H. Yoshitake, T. Tatsumi, Synthesis of amino-functionalized MCM-41 via direct co-condensation and post-synthesis grafting methods using mono-, diand tri-amino-organoalkoxysilanes, J. Mater. Chem. 14 (2004) 951-957.
[18] L. Bois, A. Bonhommé, A. Ribes, B. Pais, G. Raffin, F. Tessier, Functionalized silica for heavy metal ions adsorption, Colloids Surf. 221 (2003) 221-230. [19] K. M. Parida, D. Rath, Amine functionalized MCM-41: An active and reusable catalyst for Knoevenagel condensation reaction, J. Mol. Catal. A: Chem. 310
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(2009) 93-100. [20] R. Pauliukaitė, C. Brett, Characterization and Application of Bism-Film Modified Carbon Film Electrodes, Electroanalysis 17 (2005) 1354-1359.
ip t
[21] C. Ocaña, N. Malashikhina, M. delValle, V. Pavlov, Label-free selective impedimetric detection of Cu2+ ions using catalytic DNA, Analyst 138 (2013)
cr
1995-1999.
us
[22] X. Shao, H. Gu, Z. Wang, X. Chai, Y. Tian, G. Shi, Highly Selective Electrochemical Strategy for Monitoring of Cerebral Cu2+ Based on a Carbon
an
Dot-TPEA Hybridized Surface, Anal. Chem. 85 (2012) 418-425.
M
[23] T. Ndlovu, O. A. Arotiba, S. Sampath, R. W. Krause, B. B. Mamba, Electroanalysis of copper as a heavy metal pollutant in water using cobalt oxide
d
modified exfoliated graphite electrode, Phys. Chem. Earth 50 (2012) 127-131.
Ac ce pt e
[24] Z. H. Wang, X. L. Liu, J. M. Yang, Y. X. Qin, X. Q. Lu, Copper (II) determination by using carbon paste electrode modified with molecularly imprinted polymer, Electrochimica Acta 58 (2011) 750-756.
[25] M. Lin, M. Cho, W. S. Choe, J. B. Yoo, Y. Lee,. Polypyrrole nanowire modified with Gly-Gly-His tripeptide for electrochemical detection of copper ion, Biosens. Bioelectron. 26 (2010) 940-945.
[26] J. F. Huang, B. T. Lin, Application of a nanoporous gold electrode for the sensitive
detection
of
copper
via
mercury-free
anodic
stripping
voltammetry, Analyst 134 (2009) 2306-2313. [27] A. R. Zanganeh, M. K. Amini, Polypyrrole-modified electrodes with induced
Page 17 of 33
recognition sites for potentiometric and voltammetric detection of copper (II) ion, Sensors and Actuators B: Chemical 135 (2008) 358-365. [28] S. Wang, Y. Wang, L. H. Zhou, J. X. Li, S. L. Wang, H. L Liu, Fabrication of an
ip t
effective electrochemical platform based on grapheme and AuNPs for high sensitive detection of trace Cu2+, Electrochimica Acta 132 (2014) 7-14.
cr
[29] X. Gao, W. Wei, L.Yang, M. Guo, Carbon Nanotubes/Poly (1,2-diaminobenzene)
us
Nanoporous Composite Film Electrode Prepared by Multipulse Potentiostatic Electropolymerisation and Its Application to Determination of Trace Heavy
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Metal Ions, Electroanalysis 18 (2006) 485-492.
M
Figure captions:
Fig. 1: TEM images of MCM-41 (A) and NH2-MCM-41 (B); XRD patterns (C) and
d
FTIR (D) of MCM-41 and NH2-MCM-41.
Ac ce pt e
Fig. 2: LSASV responses of Cu2+ on bare (a), Nafion (b), MCM-41/Nafion (c), and NH2-MCM-41/Nafion (d) modified GC electrodes.
Fig. 3: Effect of pH on the stripping voltammetric response in 0.2 M NaAc-HAc containing 1000 ng/L Cu2+ at NH2-MCM-41-Nafion/GC electrode (Conditions: pre-concentration potential and time are -0.6 V and 240 s, respectively).
Fig. 4: Effect of the deposition potential (A) and deposition time (B) on the stripping voltammetric responses of 1000 ng/L Cu2+ at NH2-MCM-41-Nafion/GC electrode in 0.2 M NaAc-HAc (pH = 4.1). Fig. 5: Linear sweep voltammograms after pre-concentration in 0.2 M pH 4.1 NaAc-HAc solution containing Cu2+ with different concentration. The inset shows
Page 18 of 33
the calibration curve. Conditions: pre-concentration potential and time are -0.6 V and 240 s, respectively. Refs
ip t
[21] [22] [23] [24]
cr
Linear range (ng/L) 6.4×105-2.5×106 6.4×104-3.8×106 1×105-2×107 4.4×103-6.4×104 6.4×104-6.4×106 1.3×103-1.9×104 1×102 -5×103 3.2×103-6.4×108 3.2×102 -6.4×103 5×103 -1×105 5 to 1×103
2 6.4×102 1. 8 3.3×102 0.9
us
DNAzyme/ GCE C-Dot-TPEA/GCE CoO/EG MIP/CPE NIP/CPE GGH/OPPy-COOH MPS/NPG PPy/EBB/GCE AuNPs-GR/GCE CNTs/poly(1,2-DAB)/GCE NH2-MCM-41/GCE
Detection limit (ng/L) 4.1×105 6.4×103 9.4×104 1.5×103
an
Method
[25] [26] [27] [28] [29] This work
M
Fig. 6: LSASV responses of fresh NH2-MCM-41-Nafion/GC electrode in 1000 ng/L Cu2+ solution (a), regenerated electrode in blank solution (b) and the regenerated
d
electrode in 1000 ng/L Cu2+ solution (c).
Ac ce pt e
Fig. 7: Effects of various metal ions on the electrochemical stripping signals of Cu2+ at NH2-MCM-41-Nafion/GC electrode (1000 ng/L Cu2+ and 3105 ng/L each for Al3+, Fe3+, Co2+, 5105 ng/L each for Ni2+, Zn2+, Cd2+, Pb2+, 1106 ng/L each for Mg2+, Bi3+).
Table 1 A comparison of the analytical properties of the NH2-MCM-41/Nafion/GCE and other electrodes for Cu2+ determination AE-TPEA: N-(2-aminoethyl)-N,N’,N’-tris-(pyridine-2-yl-methyl)ethane-1,2-diamine MIP: molecular imprinted polymers; NIP: non-imprinted polymers; CPE: carbon paste electrode; GGH: Gly-Gly-His; OPPy : overoxidized polypyrrole; MPS :
Page 19 of 33
(3-mercaptopropyl)sulfonate;
NPG:
nanoporous
gold;
PPy:
polypyrrole;
EBB :Eriochrome Blue-black B; GR/GCE: electrochemical reduction of graphene
Ac ce pt e
d
M
an
us
cr
ip t
oxide on GCE electrode; CNTs : carbon nanotubes; 1,2-DAB : 1,2-Diaminobenzene;
Page 20 of 33
Table 2: Results of the recovery analysis of Cu2+ in different real samples (n=3)
Rat serum
116 6.1
100
214 7.3
98
100
311 8.0
97.5
200
546 10.1
0
119 9.4
100
222 14.5
100
316 9.0
200
524 8.2
0
296 6.9
100
103
98.5
101.3
102
503 19.5
103.5
691 12.6
98.8
385 7.3
492 18.0
107
100
593 9.8
104
200
691 17.6
98.5
d
100
Ac ce pt e
Tea
107.5
398 8.2
M
100
0
ip t
0
200
Recovery (%)
cr
Lake water
Found (ng/L)
us
Tap water
Added (ng/L)
an
Sample
Page 21 of 33
Table 3: Determination of Cu2+ in real samples using the proposed sensor and ICP-OES method. Proposed method (mg/L)
ICP-OES (mg/L)
Relative deviation
Tap water
1.16 0.06
1.22 0.04
-4.9%
Lake water
1.19 0.09
1.15 0.03
3.5%
Rat serum
2.96 0.07
2.83 0.08
4.6%
Tea
3.85 0.07
3.96 0.06
cr
ip t
Sample
Ac ce pt e
d
M
an
us
-3.1%
Page 22 of 33
ip t cr us an M d Ac ce pt e
Fig. 1A
Page 23 of 33
ip t cr us an M
Ac ce pt e
d
Fig .1B
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ip t cr us an
Ac ce pt e
d
M
Fig. 1C
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ip t cr us an
Ac ce pt e
d
M
Fig .1D
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ip t cr us an
2
Ac ce pt e
d
M
Fig.
Page 27 of 33
ip t cr us an
Ac ce pt e
d
M
Fig. 3-revised
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ip t cr us an
Ac ce pt e
d
M
Fig. 4A-revised
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ip t cr us an
Ac ce pt e
d
M
Fig .4B-revised
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ip t cr us an
Ac ce pt e
d
M
Fig. 5
Page 31 of 33
ip t cr us an
Ac ce pt e
d
M
Fig. 6-revised
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ip t cr us an
7
Ac ce pt e
d
M
Fig.
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