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Ultratrace detection of toxic heavy metal ions found in water bodies using

hydroxyapatite supported nanocrystalline ZSM-5 modified electrodes

Balwinder Kaura, Rajendra Srivastava*a, Biswarup Satpatib

Supporting Information

Electronic Supplementary Material (ESI) for New Journal of Chemistry.This journal is © The Royal Society of Chemistry and the Centre National de la Recherche Scientifique 2015

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Synthesis of Materials In a typical synthesis of Nano-ZSM-5, 0.48 g sodium aluminate (53 wt.% Al2O3, 43 wt.% Na2O)

was dissolved in 25 mL distilled water (Solution A). 2.13 g PrTES was mixed with 25 mL

TPAOH (Solution B). Solution A and solution B were mixed, and the resultant solution was

stirred for 15 minutes at room temperature, until it became a clear solution. 19.13 g TEOS was

added into the resultant solution and stirring was continued for 6 h. The molar composition of the

gel mixture was 90 TEOS/10 PrTES/2.5 Al2O3/3.3 Na2O/25 TPAOH/2500 H2O. This mixture

was transferred to a Teflon-lined autoclave, and hydrothermally treated at 443 K for 3 days under

static conditions. The final product was filtered, washed with distilled water, and dried at 373 K.

Material was calcined at 823 K for 6 h under flowing air. For comparison, conventional ZSM-5

was synthesized at 443 K using the same synthesis composition as mentioned above for Nano-

ZSM-5, but without PrTES additive.

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Fig. S1. XRD patterns of ZSM-5, Nano-ZSM-5, and Ag-ZSM-5 materials after immersion in

SBF solution for 20 days.

10 20 30 40 50 60

HAP/Nano-ZSM-5

10 20 30 40 50 60

10 20 30 40 50 60

Inte

nsity

(a.u

.)

HAP/ZSM-5

HAP/Ag-ZSM-5

4

Fig. S2. EDX elemental maps of representative elements in (a) Ag-Nano-ZSM-5 and (b) Ag-

ZSM-5 materials after immersion period of 20 days.

(a)

(b)

5

Fig. S3. CV at HAP/Ag-Nano-ZSM-5/GCE in the presence of As3+ (50 ppb) in 0.1 M PBS (pH

7) at a scan rate of 20 mV/s. The CV shows a reduction peak (i) at 0.08 V which corresponds to

the reduction of As3+ to As0 and an oxidation peak (ii) at 0.150 which corresponds to the

oxidation of As3+ to As0.

-0.2 0.0 0.2 0.4 0.6 0.8

-10

-5

0

5

10

15

(ii)

(i)

Potential (V)

Cur

rent

(A

)

6

Fig. S4. Optimization of experimental conditions: Influence of (a) pH of supporting electrolyte,

(b) deposition potential, and (c) deposition time on the stripping peak current response of

HAP/Ag-Nano-ZSM-5/GCE in the presence of 50 ppb of each heavy metal ions (Cd2+, Pb2+,

As3+, and Hg2+) individually. SWSV parameters were selected as: Step potential 4 mV; square

wave amplitude 25 mV; and square wave frequency 15 Hz.

4 5 6 7 80

4

8

12

16

20(a)

Cur

rent

(A

)

pH

Cd2+

Pb2+

As3+

Hg2+

-1.2 -0.8 -0.4 0.0

4

8

12

16

20

Potential (V)

(b)

Cur

rent

(A

)

Cd2+

Pb2+

As3+

Hg2+

0 20 40 60 80 1000

4

8

12

16

20

(c)

Cd2+

Pb2+

As3+

Hg2+

Cur

rent

(A

)

Time (s)

7

Fig. S5. Comparison of SWSV of 50 ppb each of (a) Cd2+, Pb2+ in 0.1 M PBS (pH 5) at a

deposition potential of -1 V and (b) As3+, Hg2+ in 0.1 M PBS (pH 7) at a deposition potential of -

0.5 V at different modified electrodes (HAP/Ag-Nano-ZSM-5/GCE, Ag-Nano-ZSM-5/GCE,

HAP/Ag-ZSM-5/GCE ) and bare GCE. SWSV parameters were selected as: Step potential 4 mV;

square wave amplitude 25 mV; square wave frequency 15 Hz and deposition time 100 s.

-1.0 -0.8 -0.6 -0.4 -0.2 0.0

0

4

8

12

16

20

Pb2+

Cd2+

(a)

Cur

rent

(A

)

HAP/Ag-Nano-ZSM/GCE Ag-Nano-ZSM-5/GCE HAP/Ag-ZSM/GCE Bare GCE

0.0 0.2 0.4 0.6 0.8 1.00

2

4

6

8

10

12

Cur

rent

(A

)

(b)Hg2+As3+

Potential (V)

HAP/Ag-Nano-ZSM/GCE Ag-Nano-ZSM-5/GCE HAP/Ag-ZSM/GCE Bare GCE

8

Fig. S6. Comparison of SWSV of 50 ppb each of (i) Cd2+, Pb2+ in 0.1 M PBS (pH 5) at a

deposition potential of -1 V and (ii) As3+, Hg2+ in 0.1 M PBS (pH 7) at a deposition potential of -

0.5 V at (a) HAP/Ag-Nano-ZSM-5/GCE and (b) physically mixed conventional HAP and Ag-

Nano-ZSM-5 modified GCE. SWSV parameters were selected as: Step potential 4 mV; square

wave amplitude 25 mV; square wave frequency 15 Hz and deposition time 100 s.

-0.8 -0.6 -0.4 -0.2 0.00

3

6

9

12

15

18(i) Pb2+

Cd2+

(a) (b)

Cur

rent

(A

)

0.0 0.2 0.4 0.6 0.8 1.00

3

6

9

12

Cur

rent

(A

)

Potential (V)

Hg2+As3+(ii)

(a) (b)

9

Fig. S7. Interference study: SWSV at HAP/Ag-Nano-ZSM-5/GCE by varying the concentration

of one metal ion whereas that of second was kept constant under the optimized conditions.

SWSV parameters were selected as: Step potential 4 mV; square wave amplitude 25 mV; square

wave frequency 15 Hz and deposition time 100 s.

-1.0 -0.8 -0.6 -0.4 -0.2 0.00

30

60

90

120 (a)

Pb2+

Cd2+

Cur

rent

(A

)

-0.8 -0.6 -0.4 -0.2 0.0

0

20

40

60

80

100

120(b) Pb2+

Cd2+

0.0 0.3 0.6 0.9 1.20

15

30

45

60

75

90 Hg2+

As3+

Potential (V)

(d)

0.0 0.3 0.6 0.9 1.20

10

20

30

40

Hg2+

As3+ (c)

Cur

rent

(A

)

Potential (V)

10

Fig. S8. SWSV response at HAP/Ag-Nano-ZSM-5/GCE for (a) individual analysis of Zn2+ with

different concentrations (from inner to outer of curves 50, 200, 500, 800, 1000 ppb); and (b)

interference study with varying concentrations of Zn2+ (from inner to outer of curves 50, 150,

200, 500, 800 ppb) in the presence of a fixed concentration (10 ppb) of Cd2+, Pb2+ in 0.1 M PBS

(pH 5). SWSV parameters were selected as: Step potential 4 mV; square wave amplitude 25 mV;

square wave frequency 15 Hz and deposition time 100 s.

-1.4 -1.2 -1.0 -0.8 -0.6 -0.40

3

6

9

12

15

Cur

rent

(A

)

(a)Zn2+

-1.5 -1.2 -0.9 -0.6 -0.3 0.00

3

6

9

12

15

Potential (V)

Cur

rent

(A

)

Zn2+

(b)Pb2+

Cd2+

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Fig. S9. SWSV response at HAP/Ag-Nano-ZSM-5/GCE for (a) individual analysis of Cu2+ with

different concentrations (from inner to outer of curves 30, 50, 500, 1000, 1500 ppb); and (b)

interference study with varying concentrations of Cu2+ (from inner to outer of curves 10, 30, 50,

100, 200 ppb) in the presence of a fixed concentration (10 ppb) of Cd2+, Pb2+ in 0.1 M PBS (pH

5). SWSV parameters were selected as: Step potential 4 mV; square wave amplitude 25 mV;

square wave frequency 15 Hz and deposition time 100 s.

-0.6 -0.3 0.0 0.3 0.6 0.90

10

20

30

40

50

60Cu2+ (a)

Cur

rent

(A

)

-0.9 -0.6 -0.3 0.0 0.3 0.6 0.90

3

6

9

12

15

18

Cur

rent

(A

)

(b)

Potential (V)

Cu2+

Pb2+

Cd2+

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Fig. S10. SWSV response at HAP/Ag-Nano-ZSM-5/GCE for the interference study with varying

concentrations of Hg2+ (from inner to outer of curves 2, 10, 50, 100 ppb) in the presence of a

fixed concentration (10 ppb) of Cd2+, Pb2+ in 0.1 M PBS (pH 5). SWSV parameters were

selected as: Step potential 4 mV; square wave amplitude 25 mV; square wave frequency 15 Hz

and deposition time 100 s.

-1.0 -0.5 0.0 0.5 1.00

7

14

21

28

Potential (V)

Cur

rent

(A

)

Hg2+Cd2+

Pb2+

13

Fig. S11. SWSV response at HAP/Ag-Nano-ZSM-5/GCE in 0.1 M PBS (pH 7) for the

interference study (a) with varying concentrations of Cu2+ (from inner to outer of curves 50, 100,

200, 500 ppb) in the presence of a fixed concentration (10 ppb) of As3+ and (b) with varying

concentrations of Cu2+ (from inner to outer of curves 30, 50, 100, 150 ppb) in the presence of a

fixed concentration (10 ppb) of Hg2+. SWSV parameters were selected as: Step potential 4 mV;

square wave amplitude 25 mV; square wave frequency 15 Hz and deposition time 100 s.

-0.5 0.0 0.5 1.00

3

6

9

12

15

18(a)

As3+

Cur

rent

(A

)

Cu2+

-0.5 0.0 0.5 1.00

4

8

12

16

Hg2+

Cu2+

(b)

Cur

rent

(A

)

Potential (V)

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Fig. S12. The stability response for 20 times repetitive SWSV measurements in the presence of

50 ppb Cd2+. Inset shows corresponding SWSV response at HAP/Ag-Nano-ZSM-5/GCE in the

presence of 50 ppb Cd2+ in 0.1 M PBS (pH 5). SWSV parameters were selected as: Step

potential 4 mV; square wave amplitude 25 mV; square wave frequency 15 Hz and deposition

time 100 s.

0 5 10 15 200

5

10

15

20

-1.0 -0.8 -0.6 -0.4 -0.2 0.00

5

10

15

20

25

Cur

rent

(A

)

Potential (V)

Cur

rent

(A

)

Stripping Number

15

Fig. S13. The current response at different HAP/Ag-Nano-ZSM-5/GCEs (n=10) in the presence

of 50 ppb Cd2+. Inset shows corresponding SWSV response at 10 different HAP/Ag-Nano-ZSM-

5/GCEs in the presence of 50 ppb Cd2+ in 0.1 M PBS (pH 5). SWSV parameters were selected

as: Step potential 4 mV; square wave amplitude 25 mV; square wave frequency 15 Hz and

deposition time 100 s.

0 2 4 6 8 100

5

10

15

20C

urre

nt (

A)

Electrode Number

-1.0 -0.8 -0.6 -0.4 -0.2 0.00

5

10

15

20

25

Cur

rent

(A

)

Potential (V)

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Table S1. Ionic compositions (mM) of SBF.

Ion Na+ K+ Mg2+ Ca2+ Cl- HCO3- HPO42- SO4

2-

SBF 142.0 5.0 1.5 2.5 147.8 4.2 1.0 0.5

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Table S2. Comparison of HAP/Ag-Nano-ZSM-5/GCE with other electrodes reported in the

literature for heavy metal ion detection.

S.No. Modified electrode Analyte Linear range Detection

limit

Reference

1. AuNP–SWCNT film

electrode

Pb2+

3.31 ppb - 22.29 ppb 0.546 ppb [1]

2. GC/NHAP/ionophore/Naf

ion electrode

Pb2+ 1.04 ppb - 166 ppb 0.2 ppb [2]

3. AuNPs/GC electrode Cd2+

Pb2+

Hg2+

-

-

-

3.4 ppm

6.2 ppm

6.0 ppm

[3]

4. SNACs/GCE Cd2+

Pb2+

Hg2+

10 ppb – 539.6 ppb

18.6 ppb – 1.2 ppm

18.0 ppb -198.6 ppm

2.7 ppb

1.2 ppb

4.9 ppb

[4]

5. carbon nanoparticle-based

SPEs

Cd2+

Pb2+

Hg2+

5 ppb - 100 ppb

5 ppb - 100 ppb

1 ppb - 10 ppb

-

3 ppb

-

[5]

6. γ-AlOOH@SiO2/ Fe3O4

electrode

Cd2+

Pb2+

Hg2+

1.1 ppb – 15.7 ppb

0.4 ppb – 99.5 ppb

4 ppb – 56.2 ppb

-

-

-

[6]

7. HAP/Ag-Nano-ZSM-

5/GCE

Cd2+

Pb2+

As3+

Hg2+

0.5 ppb - 1600 ppb

0.6 ppb - 1600 ppb

0.9 ppb - 1800 ppb

0.8 ppb - 1800 ppb

0.1 ppb

0.1 ppb

0.2 ppb

0.2 ppb

This work

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References

1. M.-P. Ngoc Bui, C. A. Li, K. N. Han, X.-H. Pham and G. H. Seong, Analyst, 2012, 137,

1888-1894.

2. D. Pan, Y. Wang, Z. Chen, T. Lou and W. Qin, Anal. Chem., 2009, 81, 5088-5094.

3. X. Xu, G. Duan, Y. Li, G. Liu, J. Wang, H. Zhang, Z. Dai and W. Cai, ACS Appl. Mater.

Interfaces, 2013, 6, 65-71.

4. R. Madhu, K. V. Sankar, S.-M. Chen and R. K. Selvan, RSC Adv., 2014, 4, 1225-1233.

5. G. Aragay, J. Pons and A. Merkoci, J. Mater. Chem., 2011, 21, 4326-4331.

6. Y. Wei, R. Yang, Y.-X. Zhang, L. Wang, J.-H. Liu and X.-J. Huang, Chem. Commun.,

2011, 47, 11062-11064.