nafion electrode

Journal Pre-proofs Simultaneous detection of trace Cd(II) and Pb(II) by differential pulse anodic stripping voltammetry using a bismuth oxycarbide /nafion electrode Yaxiao Zhang, Chao Li, Yingchun Su, Wei Mu, Xiaojun Han PII: DOI: Reference:

S1387-7003(19)30738-5 https://doi.org/10.1016/j.inoche.2019.107672 INOCHE 107672

To appear in:

Inorganic Chemistry Communications

Received Date: Revised Date: Accepted Date:

21 July 2019 29 October 2019 6 November 2019

Please cite this article as: Y. Zhang, C. Li, Y. Su, W. Mu, X. Han, Simultaneous detection of trace Cd(II) and Pb(II) by differential pulse anodic stripping voltammetry using a bismuth oxycarbide /nafion electrode, Inorganic Chemistry Communications (2019), doi: https://doi.org/10.1016/j.inoche.2019.107672

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Simultaneous detection of trace Cd(ϩ) and Pb(ϩ) by differential pulse anodic stripping voltammetry using a bismuth oxycarbide /nafion electrode Yaxiao Zhang,a Chao Li, a Yingchun Su, a Wei Mu*a and Xiaojun Han*a Heavy metal pollution causes serious health threat to humanbeings. Herein we fabricated a novel bismuth oxycarbide (BOC) modified glassy carbon electrode (GCE) for the simultaneous detection of cadmium and lead ions using differential pulse anodic stripping voltammetry (DPASV). The main factors influencing the detection performance, such as solution pH, deposition voltage and deposition time were optimized to be 4.5, -1.3v, and 700s, respectively. The detection limits for lead ions and cadmium ions were 4.30 μg/L and 3.97 μg/L, respectively. These detection limits are both lower than 5 μg/L for cadmium ions and 10 μg/L for lead ions national standards. The BOC modified GCE exhibits good applicability, selectivity and reliability for the detection of lead ions and cadmium ions. BOC/GCE may find great potential for heavy metal ions detection in real water sample.

back to the solution during the dissolution process, where the working electrode acts as anode. The anode peak current is proportional to metal concentration. Due to the toxicity of the mercury electrode, the bismuth film electrode was developed as a potential alternative in heavy metal ions detection.[18] As a “green” electrode, the bismuth electrode has been extensively studied, and many literatures have reported that adding a certain concentration of bismuth ions to the solution can improve the sensitivity of the sensor by co-deposition with heavy metal ions in many literatures.[19-21] Bismuth-based materials can be a source of bismuth ions to form a “fused alloy” with heavy metals[22]. The non-toxic bismuth-based material can avoid releasing free bismuth ions in electrolyte during the operating the detection process. It can be used as a green material to get lower detection limits for in-situ detection and practical applications. Only few papers were reported for electrochemical detection using simple bismuth compound modified electrodes.[23-25] It is still a challenge to develop new bismuth based materials for heavy metal ion detection.

1. Introduction Heavy metal pollution is one of the most harmful pollutions throughout the world. It is mainly caused by mining, exhaust emissions, sewage irrigation and the use of over-standard heavy metal products.[1, 2] Due to their non-degradable property, heavy metals can accumulate in ecosystem.[3-7] They inactivate proteins, denature various enzymes and ultimately threating human health. Cadmium mainly damage to the renal tubules/glomeruli and cause kidney poisoning, leading to proteinuria, amino aciduria and diabetes.[8] At the same time, cadmium ions can replace calcium ions in the bone to influence the normal calcium deposition. It also hinders the normal solidification and maturation of collagen, leading to rickets.[9] The most common symptoms after lead poisoning are neurasthenia, gastrointestinal dyspepsia, paralysis and toxic encephalopathy.[10] High concentrations of lead can cause severe abdominal cramps and toxic hepatitis even exposed for a short period of time. The national standard stipulates that the maximum concentration of cadmium and lead ions in drinking water should not exceed 5 μg/L and 10 μg/L, respectively.

In this work, a bismuth oxycarbide (BOC) was synthesized to modify the glass carbon electrode, which showed sensitive cadmium and lead ion detection using differential pulse anodic stripping voltammetry. The bismuth oxycarbide modified glassy carbon electrode exhibited great potential for the simultaneous detection of heavy metal ions.

Many methods have been developed to detect heavy metal ions in water bodies, such as ultraviolet spectrophotometry (UV)[11], atomic absorption (AAS), atomic fluorescence (AFS)[12], inductively coupled plasma (ICP)[13], X-ray fluorescence (XRF)[14], and inductively coupled plasma mass spectrometry (ICP-MS)[15]. But these methods have some common defects of requiring large equipments, complicated operation processes, long detection time and well-trained analysts. Compared with these strategies, electrochemical method possesses the advantages of fast response, low cost and convenient operation. And it has the possibility to be applied for in-situ detection.[16] In numerous electrochemical methods, anodic stripping voltammetry has been considered as an efficient and popular technique for the detection of trace heavy metals.[17] During the preconcentration process, the metal ions in solution are reduced and enriched on the surface of the working electrode (cathode). Then the metal is rapidly oxidized a. State

2. Experimental 2.1 Materials Bi(NO3)3·5H2O, trimesic acid (H3BTC) and nafion (5 wt%) were purchased from Aladdin (China) without further purification. Sodium acetate (AR) was purchased from Xilong Chemicals (China). Methanol and N,N-Dimethylformamide were purchased from Fuyu Chemicals (China). CdCl 2 and Pb(NO3)2 were purchased from Tianjin Kermel Chemicals

Key Laboratory of Urban Water Resource and Environment School of Chemistry and Chemical Engineering, Harbin Institute o f Technology, Harbin, China, 150001

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(China). The working supporting electrolyte comprised of 0.1 mol/L acetate buffer (pH 4.5). 2.2 Preparation of bismuth oxycarbide The process of preparing bismuth oxycarbide was derived from the previous reports.[26, 27] In briefly, 0.46 mmol Bi(NO3)3·5H2O and 0.69 mmol trimesic acid were added to the 50 mL Teflon-lined stainless-steel autoclave. Then, 15 mL of methanol was added to the mixture drop by drop. The autoclave was sealed and left over-night for about 10 h. The autoclave was heated to 120 Ԩ for 12 h and then cooled down to room temperature. The light yellow powder was filtered and washed by methanol for 3 times. The product was then dried in air at 60 Ԩ. 2.3 Fabrication of modified electrode

Fig.1. SEM image (a) XRD pattern of the as-prepared sample (b), and the EDX mapping (c) of BOC.

The working electrode was obtained by pipetting 10 μL of bismuth oxycarbide suspension (1 mg/L) onto the surface of a clean glassy carbon electrode under infrared irradiation for 1015 minutes. Then 5 μL of a 0.5 wt% nafion solution was added forming a nafion film under infrared irradiation for about 20 minutes.

The characteristic peaks were consistent with the crystallinity of the Bi 2O2CO3 according to JCPDS NO. 411488.[28] EDX mapping analysis of BOC indicated the homogeneous dispersion and coexistence of Bi, O, and C elements (Fig. 1c). The X-ray photoelectron spectroscopy was employed for further analysis (Fig. 2). The survey scan in Fig. 2a reveals that the as-prepared sample was mainly composed of three elements: Bi, O and C. Fig. 2b showed two strong peaks at 159.6 eV and 164.9 eV corresponding to Bi 4f 5/2and Bi 4f7/2, which was assigned to Bi 3+ in BOC. Fig. 2c showed the C 1s peak at 284.8 eV and 288.6 eV which were caused by the adventitious carbon species and CO 32- in BOC. The O 1s peak (Fig. 2d) centers at 531.8 eV could be ascribed to the Bi-O bonds in BOC.[29, 30]

2.4 Electrochemical measurements The bismuth oxycarbide (BOC) /glassy carbon electrode (GCE), saturated calomel electrode (SCE), and Pt wire electrodes were immersed in a beaker containing 0.1 mol/L acetate buffer (pH 4.5) and a certain amount of target heavy metal ions. The working electrode was held at −1.3 V for 700 s, before the differential pulse voltammetry was applied from -1.3 to -0.4 V with amplitude of 25 mV, a pulse width of 50 ms, and a potential step of 5 mV.

3.2 Electrochemical behaviors of different electrodes

2.5 Characterizations

As shown in Fig. 3, differential pulse anodic stripping voltammetry (DPASV) was used to investigate the electrochemical behaviors of a bare glass carbon electrode and the GCE modified with BOC in acetate buffer (pH=4.5) containing 50 μg/L Cadmium(ϩ) or 50 μg/L lead(ϩ), respectively. The potential ranges were from -1.3 V to -0.4 V. When a GCE was introduced to detect 50 μg/L lead ions, the DPV curve showed almost no dissolution peaks. While for the GCE modified with bismuth oxycarbide, the dissolution profile showed a distinct peak shape (Fig. 3a). The bismuth ions in the BOC were reduced by cathode current, which promoted the codeposition of heavy metal ions on the electrode surface. In addition, the BOC compound increased the surface area of the electrode and promoted electrons transfer. Similarly, the obvious peak of lead ions was observed on BOC modified GCE electrode, whist no peak was found using pure GCE electrode (Fig. 4b). These results confirmed the validity of BOC for metal ion detection.

All electrochemical measurements were performed on an electrochemical workstation (AUT84528, Switzerland). The surface morphology and valence state of the material were determined by Scanning Electron Microscopy (SEM, FEI Quanta 200 FEG, 20 kV) and X-ray photoelectron spectra (XPS, 20 eV pass energy), respectively.

3. Results and discussion, 3.1 Characterization of the bismuth oxycarbide The SEM image showed the morphology of bismuth oxycarbide (BOC). The bismuth based materials in a particle aggregated by sheets with the thickness of about 189 nm (Fig. 1a). The crystal structure of as-prepared BOC was characterized by XRD (Fig. 1b).

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The deposition potential played a very important role in the DPASV analysis. The deposition time and pH value were set to be 500 s and 4.5, respectively. Fig. 4b showed the effect of different deposition potentials on the stripping peaks. Low deposition potential (> -1.3 V) could not reduce enough metal ions. In high voltage (< -1.3 V), hydrogen could be generated, which will interfere with the detection of heavy metal ions by competing for active sites on the electrode surface.[33] -1.3 V was the suitable deposition voltage for the detection of both lead and cadmium ions. Another important factor was the deposition time. Fig. 4c showed the effect of deposition time on the DPASV peak values. As time increased, the current value increased gradually. At 700s, the current reached the maximum value. When deposition time was applied more than 700 s, the value of current peak decreased as time increasing. Short deposition time could not adsorb enough heavy metal ions on the surface of the electrode. While a very long deposition time could lead to excessive deposition of metal ions on the electrode.[34, 35] It resulted in reducing the sensitivity and detection limit by fouling and blocking the active sites, as well as a waste of energy. Therefore, 700s was selected as the optimal deposition time. The optimized electrolyte pHs of 4.5, deposition potential of -1.3 V and deposition time of 700 s were used in follow-up detection process.

Fig.2. XPS spectra of as-prepared BOC sample: (a) survey scan, (b) Bi4f, (c) C1s, and (d) O1s elements

Fig.3. DPV curves of 50 μg/L Cd(ϩ) (a) and Pb(ϩ) (b) in acetate buffer detected by bare GCE and BOC modified GCE, respectively. Fig.4. Effect of (a) pH, (b) deposition potential, and (c) deposition time on the electrochemical behavior of the BOC/GCE in acetate buffer containing 50 μg/L Cd(ϩ) or 50 μg/L Pb(ϩ).

3.3 Optimization of experimental conditions In order to obtain a clear relationship between peak current and heavy metal ions concentration, a series of ion concentrations were detected using this method. Three main influencing factors (the pH of the electrolyte, deposition potential and deposition time) were investigated to optimize experimental conditions. Optimization of these experimental parameters was carried out in an electrolyte containing 50 μg/L lead ions or 50 μg/L cadmium ions.

3.4 Electrochemical detection of Cd(ϩ) and Pb(ϩ) DPASV was used to detect different concentrations of cadmium/lead ions individually in acetate buffer under optimized experimental conditions using BOC/GCE. The simultaneously detection for cadmium and lead ions were also conducted. As shown in Fig. 5a, a series of DPASV curves for different concentrations of Cd(ϩ) were obtained. The stripping peak current of cadmium ions increased with metal ions concentration from 0 μg/L to 50 μg/L. The corresponding calibration curve (Fig. 5b) was represented as I (μA) = 0.00557C (μg/L)-0.03467 with a correlation coefficient (R 2) of 0.976. The limit of detection (LOD) was calculated to be 3.76 μg/L for Cd(ϩ) at a signal-to-noise ratio (S/N) of 3. Similarly, the DPASV curve (Fig. 5c) showed the relationship between peak current and lead ion concentration. The concentration of lead ions also exhibited a positive correlation linear relationship with the stripping peak current value in the range of 0-50 μg/L. Linear

The effect of solution pH on the stripping peak current was carried out in acetate buffer at pH from 3.0 to 5.5 (Fig. 4a). Deposition potential and deposition time were set to be -1.3V and 500s, respectively. The peak current value for both ions increased gradually from pH 3.0 to 4.5 and decreased afterwards. The hydrolysis of lead ions and cadmium ions were occurred, which is reflected by the decrease of peak current.[31] When the pH value of the electrolyte was low, the solution contained more hydrogen ions, which could compete with the heavy metal ions for the active site to reduce on the surface of the electrode.[32] The optimal pH is 4.5.

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fitting formula is I (μA) = 0.01087C (μg/L)-0.0297 (R2 = 0.984). LOD was obtained to be 3.58 μg/L for Pb(ϩ) at a signal-to-noise ratio (S/N) of 3.[36] Corresponding linear relationship curves set in Fig. 5d.

Fig.6. DPASV curves of BOC/GCE for the simultaneous detection of Cd(ϩ) and Pb(ϩ) at concentration range of 0 μg/L, 10 μg/L, 20 μg/L, 30 μg/L, 40 μg/L and 50 μg/L(a). The calibration curve of Cd(ϩ) (b) and Pb(ϩ) (c) Table 1 The Bismuth oxycarbide /GCE compared with the other previous papers Detection limit (µg/L)

Linear range (µg/L)

Electrode

Fig.5. DPASV curves of BOC/GCE for the individual detection of Cd(ϩ) (a) and Pb(ϩ) (c) at a concentration of 0 μg/L, 5 μg/L, 10 μg/L, 20 μg/L, 30 μg/L, 40 μg/L, and 50 μg/L. Calibration curves corresponding to peak current towards Cd(ϩ) (b) and Pb(ϩ) (d). Acetate buffer (pH 4.5) was used as supporting electrolyte with amplitude of 25 mV, a deposition potential of -1.3 V, a deposition time of 700 s and a step potential of 5 mV. Simultaneous detection of lead ions and cadmium ions was more meaningful for practical applications. Thus the experiment was carried out with two target heavy metal ions in the acetate buffer. DPASV curves were obtained under the optimal experimental conditions with different concentrations of cadmium and lead ions from 10 μg/L to 50 μg/L (Fig. 6a). Two individual and well-defined peaks appeared at potential approximately -0.81 V and -0.56 V corresponding to cadmium and lead ions, respectively, which revealed that the BOC/GCE sensor can detect two target metal ions simultaneously. Both peak currents assigned to cadmium and lead ions increased as metals ion concentrations increasing. The linearization equations were I (μA) = 0.0209C (μg/L)-0.1313 for Cd(II) (R2=0.990) and I (μA) = 0.0203C (μg/L)-0.0961 (R2=0.995) for Pb(II) ions, respectively. The LOD were obtained to be 4.30 μg/L and 3.97 μg/L corresponding to Cd(II) and Pb(II) ions (Fig. 6b and c). The data obtained from the BOC modified electrodes showed relative lower detection limits and easier preparation process than previous methods listed in Table 1.

Ref. Cd(ϩ)

Pb(ϩ)

Cd(ϩ)

Pb(ϩ)

CB-15-crown-5/GCE

4.7

3.3

16-190

11-186

[37]

BiF4/CPE

1.2

9.8

20-100

20-100

[38]

PPh3/MWCNT/IL/CPE

8.32

12.43

0.01-16

0.02-31

[39]

Bi/Cu/SPE

60

172

111-1348

270-2693

[40]

Bi2O3/SPE

8

16

20-300

20-300

[25]

BiFE

1.4

9.6

10-100

10-100

[41]

Bi oxycarbide /GCE

4.24

3.97

10-50

10-50

This work

3.5 Stability, reproducibility and selectivity of BOC/GCE The BOC/GCE was kept in a refrigerator at 4Ԩ for two months to study its stability. The DPASV response still remained 98.69% and 95.94% of the original peak values for cadmium and lead ions, respectively, indicating excellent stability of the modified electrode. Four electrodes were tested with DPASV as parallel experiments with 50 μg/L Cd(ϩ) and 50 μg/L Pb(ϩ) in the electrolyte to study the reproducibility of modified electrodes. The relative standard deviations (RSDs) were 2.07 % for Cd(ϩ) and 4.16 % for Pb(ϩ), respectively. The selectivity of modified electrode was performed in acetate buffer containing 50 μg/L Cd(ϩ) and 50 μg/L Pb(ϩ) with 5000 μg/L of ions including K+, Na+, Ca2+, Mg2+, Al3+, Fe3+, Mn2+, Cu2+, Zn2+, Cl-, SO42-, and NO3-. The change of peak currents less than 5 % indicates good selectivity of the modified electrode for the target metal ions detection in the real water sample. 3.6 Determination of Cd(ϩ) and Pb(ϩ) in real samples In order to further study the reliability for the practical application, BOC/GCE were used for the detection of cadmium and lead ions in deionized water and tap water. The experimental

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results were shown in Table 2. For both cadmium and lead ions, the recovery rate in each case is greater than 89 % and less than 102 %, which indicated that the detection methods for the two target heavy metal ions have potential in actual water sample detections.

[1] M.S. Islam, M.K. Ahmed, M. Raknuzzaman, M. Habibullah-AlMamun, M.K. Islam, Heavy metal pollution in surface water and sediment: A preliminary assessment of an urban river in a developing country, Ecological Indicators. 48 (2015) 282-291. [2] H. Wang, Y. Su, H. Kim, D. Yong, L. Wang, X. Han, A highly efficient ZrO2 nanoparticle based electrochemical sensor for the detection of organophosphorus pesticides, Chinese Journal of Chemistry. 33 (2015) 1135-1139. [3] X. Zhao, Y. Su, S. Li, Y. Bi, X. Han, A green method to synthesize flowerlike Fe(OH)3 microspheres for enhanced adsorption performance toward organic and heavy metal pollutants, Journal of Environmental Sciences. 73 (2018) 47-57. [4] Y. Xu, Y. Hou, Y. Wang, Y. Wang, T. Li, C. Song, N. Wei, Q. Wang, Sensitive and selective detection of Cu 2+ ions based on fluorescent Ag nanoparticles synthesized by R-phycoerythrin from marine algae Porphyra yezoensis, Ecotoxicology and Environmental Safety. 168 (2019) 356-362 [5] H. Ma, D. Yong, H. Kim, Z. Zhang, S. Ma, X. Han, A Ferricyanide-mediated Activated Sludge Bioassay for Determination of the Toxicity of Water, Electroanalysis. 28 (2016) 580-587. [6] Y. Su, S. Ma, K. Jiang, X. Han, CdTe-paper-based Visual Sensor for Detecting Methyl Viologen, Chinese Journal of Chemistry. 33 (2015) 446-450. [7] D. Liu, X. Pan, W. Mu, C. Li, X. Han, Detection of tetracycline in water using glutathione-protected fluorescent gold nanoclusters, Analytical Sciences.35 (2019) 367-370. [8] C. Li, X. Zhao, X. Han, Simultaneous determination of trace Cd 2+ and Pb 2+ using GR/l-cysteine/Bi modified screen-printed electrodes, Analytical Methods. 10 (2018) 4945-4950. [9] A. Chatta, M. Khan, Z. Mirza, A. Ali, Heavy metal (cadmium, lead, and chromium) contamination infarmed fish: a potential risk for consumers' health, Turkish Journal of Zoology. 40 (2016) 248-256. [10] B.P. Lanphear, S. Rauch, P. Auinger, R.W. Allen, R.W. Hornung, Low-level lead exposure and mortality in US adults: a population-based cohort study, The Lancet Public Health. 3 (2018) e177-e184. [11] J. Peng, J. Li, W. Xu, L. Wang, D. Su, C.L. Teoh, Y.-T. Chang, Silica nanoparticle-enhanced fluorescent sensor array for heavy metal ions detection in colloid solution, Analytical Chemistry. 90 (2018) 1628-1634. [12] L. Xu, L.C. Zhang, X.D. Hou, K.L. Xu, Adsorption of heavy metal ions on two types of manganese oxides analyzed by AAS and AFS, Xu L , Zhang L C , Hou X D , et al. Adsorption of Heavy Metal Ions on Two Types of Manganese Oxides Analyzed by AAS and AFS[J]. Spectroscopy and Spectral Analysis, 2012, 32(10):28422846. [13] P. Liang, Y. Qin, B. Hu, C. Li, T. Peng, Z. Jiang, Study of the adsorption behavior of heavy metal ions on nanometer-size titanium dioxide with ICP-AES, Fresenius Journal of Analytical Chemistry. 368 (2000) 638-640. [14] Y.Z. Peng, Y.M. Huang, D.X. Yuan, L.I. Yan, Z.B. Gong, Rapid Analysis of Heavy Metals in Coastal Seawater Using Preconcentration with Precipitation/Co-precipitation on Membrane and Detection with X-Ray Fluorescence, Chinese Journal of Analytical Chemistry. 40 (2012) 877-882. [15] S.X. Liang, W. Xin, W.U. Hong, Determination of 9 Heavy Metal Elements in Sediment by ICP-MS Using Microwave Digestion for Sample Preparation, Spectroscopy & Spectral Analysis, 32 (2012) 809. [16] S.K. Pandey, P. Singh, J. Singh, S. Sachan, S. Srivastava, S.K. Singh, Nanocarbon-based electrochemical detection of heavy metals, Electroanalysis. 28 (2016) 2472-2488. [17] E.D. Abd, A.K. Youssef, Hyphenation of ionic liquid albumin glassy carbon biosensor or protein label-free sensor with differential pulse stripping voltammetry for interaction studies of human serum

Table 2 Recoveries of Cd(ϩ) and Pb(ϩ) in real water samples Sample

Deionized water

Tap water

Metal

Cd(ϩ)

Pb(ϩ)

Cd(ϩ)

Pb(ϩ)

Detected (µg/L)

0

0

0

0

Added (µg/L)

50.0

50.0

50.0

50.0

Found (µg/L)

48.7±1.5

51±1,4

44.9±1.2

45.0±1.9

Recovery (%)

97.4

101.9

89.8

90.1

4. Conclusions In this paper, the BOC modified electrode was fabricated for the detection of Cd(ϩ) and Pb(ϩ). The experimental conditions were optimized. Under the optimal experimental conditions (pH: 4.5, deposition voltage: -1.3v, and deposition time: 700s), the calibration curve of Cd(ϩ) and Pb(ϩ) was obtained in the individual and simultaneous detections. The detection of actual water samples by BOC modified electrode was also investigated. The results showed that the BOC modified electrode hold great potential for the detection of actual water samples.

Conflicts of interest There are no conflicts of interest.

Acknowledgements This work was supported by the National Key R&D Program of China (2016YFC0401104). HIT Environment and Ecology Innovation Special Funds (HSCJ201617), the National Natural Science Foundation of China (Grant No.21773050), the Harbin Distinguished Young Scholars Fund (No. 2017RAYXJ024), and State Key Laboratory of Urban Water Resource and Environment (Harbin Institute of Technology) (No. 2017DX05).

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Highlights

A novel electrochemical sensor was fabricated using bismuth oxycarbide to modify glassy carbon electrode to detect cadmium and lead ions. The bismuth oxycarbide was synthesized through a solvothermal method. There is no direct use of bismuth-containing compound modified electrodes for heavy metal ion detection. Another major advantage of this method is that no bismuth ions are added to the solution.

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Graphical abstract

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