synthesisandvoltammetricdeterminationofpb(ii)using azif-8 … · 2019. 7. 30. · researcharticle...

Research ArticleSynthesis and Voltammetric Determination of Pb(II) Usinga ZIF-8-Based Electrode

Dinh Quang Khieu 1 Mai Thi Thanh12 Tran Vinh Thien3 Nguyen Hai Phong1

Duc Hoang Van4 Pham Dinh Du5 and Nguyen Phi Hung6

1University of Sciences Hue University Hue 530000 Vietnam2Faculty of Physics-Chemistry-Biology Quang Nam University Tam Ky 560000 Vietnam3Faculty of Natural Science Phu Yen University Phu Yen 620000 Vietnam4University of Education Hue University Hue 530000 Vietnam5Faculty of Natural Sciences u Dau Mot University u Dau Mot 820000 Vietnam6Department of Chemistry Quy Nhon University Quy Nhon 590000 Vietnam

Correspondence should be addressed to Dinh Quang Khieu dqkhieuhueunieduvn

Received 24 October 2017 Accepted 12 April 2018 Published 10 May 2018

Academic Editor Fateme Razeai

Copyright copy 2018 Dinh Quang Khieu et al +is is an open access article distributed under the Creative Commons AttributionLicense which permits unrestricted use distribution and reproduction in any medium provided the original work is properly cited

Zeolite imidazole framework-8 (ZIF-8) was prepared by the hydrothermal process +e obtained ZIF-8 was a characteristic ofX-ray-diffraction (XRD) transmission electron microscope (TEM) thermal gravity-differential thermal analysis (TG-DTA) anddynamic light scattering (DLS) +e obtained ZIF-8 possessed large specific area and was highly dispersed Its morphologyconsisted of nanospherical particles with 30ndash50 nm in diameter Chemical stability of ZIF-8 in different conditions was studied+e ZIF-8 was used as an electrode modifier for the determination of trace levels of lead +e parameters including solvents andsolution pH were investigated +e repeatability reproducibility accuracy linear range limit of detection and limit ofquantitation were also addressed +e results showed that ZIF-8 is a potential electrode modifier for differential pulse anodicstripping method to determine Pb(II) in aqueous solution

1 Introduction

Metal-organic frameworks (MOFs) are gaining significant at-tention for their potential applications in gas separation andstorage sensors and catalysis [1ndash3] during the last years Zeoliteimidazole frameworks ZIF-8 being a kind of MOFs consist ofZn atoms linked through nitrogen atoms by 2methyl-imidazole(denoted as Im) links to create neutral frameworks and toprovide tunable nanosized pores formed by four- six- eight-and twelve-membered ring ZnN4 [4] ZIF-8 has appeared asa novel kind of highly porous materials combining desirableproperties fromboth zeolites and conventionalMOFs includinghigh surface areas crystallinity thermal and chemical stability[4ndash7] ZIF-8 is a promising class of nanoporous materials forgas separating membrane [5 8] gas adsorption storage ofhydrogen [9 10] and catalysts [11ndash13]

Heavy metals (Hg(II) Pb(II) Cd(II) Ni(II) and so on)are considered to be one of the main sources of pollution in

the environment Lead is one of the most dangerous envi-ronmental pollutants as it has toxic chemical influence even atvery small concentration [14 15] So it is urgently needed tofind a very sensitive method for the determination of leadtrace in the environment Several analytical techniques suchas spectroscopic methods especially graphite furnace atomicadsorption spectroscopy (GF-AAS) [16] inductively coupledplasma mass spectroscopy (ICP-MS) [17] and X-ray fluo-rescence [18] are employed currently for trace analysis oflead +ese methods have excellent sensitivities and goodselectivity but several disadvantages such as time-consumingand high cost of instrument limit their applications

Electrochemical methods including anodic strippingvoltammetric techniques (ASV) have been recognized asrobust tools for trace analysis because of different advantagessuch as faster analysis higher selectivity and sensitivity lowcost easy operation and possibility to perform analysis insitu [19 20] Differential pulse anodic stripping voltammetry

HindawiJournal of ChemistryVolume 2018 Article ID 5395106 12 pageshttpsdoiorg10115520185395106

(DP-ASV) as one kind of the ASVmethod has been appliedfor the determination of trace heavy metal ions because ofits remarkably high sensitivity Glassy carbon electrodeschemically modified with porous materials such as modifiedmesoporous materials [21] clay-mesoporous silica composite[22] multiwall carbon nanotubes [14] reduced grapheneoxidechitosan [23] pretreated graphite pencil [24] graphenefilms [25] and polyaniline and polypyrrole film [26] havereceived considerable attention for ASV because they exhibitsignificant improvements in terms of fast response highselectivity low detection limit and renewability

Due to high surface areas highly order structure andhigh reactive site density the usage of MOFs-based com-posite for the electrochemical field is becoming increasingMao et al [27] reported the usage of copper (II)-22prime-bipyridine-benzene-135-tricarboxylate (Cu(II) basedMOF-199) as selective electrocatalysts for the reduction ofO2 and CO2 MOF modified by Au-SH-SiO2 nanoparticleswas utilized to determinate hydrazine and L-cysteine byelectrochemistry analysis [28] +e amino-functionalizedMOF-199 material could provide an excellent modifier fordeveloping a sensitive electrode for the determination of leadtrace [29] Ag-loaded ZIF-8 nanocrystals were used as anelectrode modifier to detect hydrazine AgZIF-8CPE(carbon paste electrode) performed a good catalytic per-formance toward hydrazine oxidation [30] Xiao et al [20]reported the nitrogen-doped microporous carbon preparedfrom pyrolysis of ZIF-8 as an excellent electrode modifier todetermine Pb(II) and Cd(II) in aqueous solution

In the previous paper [31] we demonstrated the using ofZIF-8-modified electrode to determine Pb(II) in aqueoussolution In the present work we continue to refine the studyon the use of ZIF-8 as an electrode modifier for the de-termination of Pb(II) by the voltammetric technique +estability of ZIF-8 over time in several solvents and in dif-ferent pH solutions was studied ZIF-8 has been used tomodify the glassy carbon electrode (GCE) for Pb(II) de-termination using DP-ASV methods Several parametersrelated to the electrode performance were studied and op-timized for using in the analysis To our knowledge this isthe first report on using modified electrode-based ZIF-8material for the determination of lead by the DP-ASV

2 Experimental

21 Materials Zinc nitrate hexahydrate (Zn(NO3)2middot6H2ODaejung Korea) methanol (CH3OH Merck Germany)and 2-methylimidazole (C4H6N2 Aldrich USA) were utilizedin the synthesis of ZIF-8 For electrochemistry performancebismuth(III) nitrate pentahydrate (Bi(NO3)3middot5H2O Sigma-Aldrich USA) was used to prepare the bismuth film Nafionsolution was prepared from stock solution (5d 0874 gmiddotmLminus1 Aldrich USA) and ethanol (96 MerckGermany) with a volume ratio VnafionVethanol 14BrittonndashRobinson buffer solution (B-R BS) of pH 47was prepared from 004M H3BO3 004M H3PO4 and004M CH3COOH (Merck Germany) pH of the B-R BSwas adjusted by the addition of 10M sodium hydroxidesolutions into the B-R BS and then checked by the pH

meter +e working solution of Pb(II) was prepared dailyfrom stock solution (1000 ppm Merck Germany)

22 Synthesis of ZIF-8 ZIF-8 was synthesized according to[32ndash34] Briefly zinc nitrate (28mmol) was dissolved inmethanol (14mL) 2-Methylimidazole (644mmol) wasdissolved in methanol (14mL) and this solution was addedto the zinc solution under sonication condition for 30minutes and then vigorously stirred for 24 h at roomtemperature Finally this solution was centrifuged at300 rpm and washed thoroughly with methanol +iswashing procedure was repeated 5 times +e resultingcrystals were dried overnight at 120degC

23 Voltammetric Procedure

231 Preparation of Working Electrode-Modified Electrodes+e preparation procedure was carried out as in [28] Inbrief glassy carbon electrode (GCE) was first polished with005 μm Al2O3 slurry on a polishing cloth and then rinsedultrasonically with 2MHNO3 absolute ethanol and double-distilled water Subsequently the GCE was electrochemicallycleaned by a cyclic potential scan between minus11 V and +03Vin 05M acetate buffer solution pH 45 with the scan rate of010Vmiddotsminus1 After that the electrode was rinsed with double-distilled water +e nafionZIF-8 composite was prepared bydispersing 25mg ZIF-8 into 10mL nafion (01 wt) andsonicated+eGCEwas coated with 5 μL of the nafionZIF-8composite and dried under the room temperature (sim25degC)(denoted as NafZIF-8GCE) For the same procedure theGCE modified by nafion was denoted as NafGCE Bis-muth film (BiF) was formed simultaneously with Pb(II)preconcentration +e bismuth deposition was conductedat minus12 V potential under stirring for 120 s +e GCENafGCE and NafZIF-8GCE modified by BiF weredenoted as BiFGCE NafBiFGCE and NafBiFZIF-8GCE respectively

232 Voltammetric Procedure Solution under study (finalvolume of 10mL) containing 004M B-R BS (pH 47) and200 ppb Pb(II) was transferred into the electrochemical cellwith the 3 electrodes +en voltammetric measurement wasconducted as follows

(i) For surveying voltammetric characteristics of Pb(II)on the modified GCE Pb(II) was accumulated on thesurface of the modified electrode at a potential ofminus12V (Eacc) for an accumulated time of 120 s (tacc)During this step the electrode was rotated ata constant rate of 1000 rpm After that the electroderotation was off and then cyclic voltammograms(CVs) were recorded from ndash11V to +03V (forwardpotential scan) and then from +03V to minus11 V(reverse potential scan) at a scan rate of 01 Vmiddotsminus1

(ii) For differential pulse anodic stripping voltammetric(DP-ASV) determination of Pb(II) on modifiedGCE during the DP-ASV procedure Pb(II) wasaccumulated on the surface of the rotating modified

2 Journal of Chemistry

electrode as done for the above procedure After thatthe electrode rotation was off for 10 s and then DP-ASV voltammograms were recorded from minus11V to+03V at a scan rate of 002Vmiddotsminus1 DP-ASV vol-tammograms of blank solution (without Pb(II) andprepared from double-distilled water) were similarlyrecorded before each measurement

24 Apparatus XRD was performed by powder X-ray dif-fraction (XRD) recorded on 8D Advance Bucker Germanywith CuKα radiation +ermal behavior of ZIF-8 was ana-lyzed by thermal analysis (TG-DTA) using Labsys TGSetaram (France) under air atmosphere Morphology wasobserved by scanning electron microscopy using Jeol Jem-2100F TEM (Japan) Particle sizes were analyzed by DLSwith Nanobrook 90plus PALS A CPA-HH5 ComputerizedPolarography Analyzer (Vietnam) was used for voltammetryexperiments All measurements were done in the cell withthree electrodes a GCE with a diameter of 28plusmn 01mm usedfor formatting the modified electrode as a working electrodea AgAgCl3M KCl as a reference electrode and a platinumwire as an auxiliary electrode All measurements werecarried out at room temperature

3 Results and Discussion

31 Synthesis of ZIF-8

311 Characterization of ZIF-8 +e XRD pattern of ZIF-8is shown in Figure 1 +e XRD pattern of ZIF-8 was agreedwell with patterns from [34ndash36] and no obvious peaks ofimpurities can be detected in the XRD patterns +ere arewell-defined diffractions (011) (022) (112) (022) (013)(224) (114) (233) (134) and (334) at two theta of 72 101127 149 161 221 249 255 and 265 degree respectivelyin the XRD pattern of ZIF-8 indicating that the crystallinityof ZIF-8 in this work was relatively high

TEM observation of ZIF-8 is presented in Figure 2(a)+e morphology of ZIF-8 consisted of nanospherical par-ticles around 30ndash40 nm in diameter +e crystallite size wasevaluated by Sherrerrsquos equation from the peak (011) +ecrystallite size of ZIF-8 was 494 nm +e particle size wasalso analyzed by DLS as shown in Figure 2(b) +e distri-bution curve exhibited the symmetric bell-shape indicatingthat the particle size had normal distributions +e ag-glomerate mean size of ZIF-8 estimated by DLS was 707 nm+e size calculated by DLS is the agglomerate size (grainsize) which is formed from single particles +e singleparticles observed by the TEM consisted of crystallites +ecrystallite size was calculated by XRD+e fact the mean sizecalculated by XRD is similar to that calculated by TEMindicates that the single phase of ZIF-8 with high crystal-linity was obtained Since the agglomerate sizes are onlyapproximately 15ndash2 times the size of particle or crystallitesize the agglomerates observed by the TEM are loosen andhighly dispersible

+e nitrogen sorption study for the ZIF-8 reveals a re-versible type I isotherm a characteristic of microporousmaterials (not shown here) +e sample of ZIF-8 possessed

the high specific surface area of 1484 m2middotgminus1 and the totalvolume of 116 cm3middotgminus1 which was similar or higher withthat in the previous literatures [35ndash37]

312 Stability of ZIF-8 +e stability of ZIF-8 in differentconditions is important for its application in catalyst as wellas an electrode modifier In present paper the effects of timesolvents and pH on the ZIF-8 structure were investigated

Figure 3(a) shows XRD patterns of ZIF-8 exposed toambient atmosphere for 1ndash12 months +e characteristicdiffractions of ZIF-8 were unchangeable indicating that ZIF-8 was stable in ambient condition for a year +e chemicalstability of ZIF-8 was investigated in refluxing C2H5OHH2O and C6H6 at boiling temperature as shown in Figure 3(b)XRD patterns showed that ZIF-8 maintained full crystallinityfor 8 hours at boiling conditions

XRD patterns of ZIF-8 submerged in water at roomtemperature for 1ndash14 days are shown in Figure 4(a) XRDpatterns collected at designated intervals showed that ZIF-8was stable in water for at least 14 days ZIF-8 was soaked inwater with pH ranging from 2 to 12 for 24 hours XRDanalyses (Figure 4(b)) showed that characteristic peaks ofZIF-8 submerged in pH 2 solution were not observed im-plying that ZIF-8 was unstable in this condition However itwas stable in the pH ranging from 27 to 12

32 Electrochemical Performance of ZIF-8-BasedModified Electrodes

321 Selection of Experimental Conditions In order toverify the electrochemical activity of ZIF-8 in the modifiedGCE for detection of Pb(II) the electrochemical experi-ments in GCE modified with and without ZIF-8 wereperformed by DP-ASVs As can be seen in Figure 5(a) thestripping voltammetry peak varied from minus0624 to minus0586Vindicating that Ep of Pb(II) depended on the kind of workingelectrodes +e nafion was added because nafion membranecan be used as a coating to limit the interference of surface-active compounds as well as a stabilizer to improve themechanical stability of the bismuth film electrode [38] +e

0 10 20 30 40 50 60

334

134

01302

211

200

201

1

233

222

114

500

Cps

Inte

nsity

(au

)

2θ (degree)

Figure 1 XRD pattern of ZIF-8

Journal of Chemistry 3

current response on the NafGCE (curve c) and the bareGCE (curve e) exhibited the broad peaks especially onNafGCE was almost not detectable By the addition of ZIF-8

the current response at NafZIF-8GGE provided a well-defined peak as that at BiFGCE which is widely used inDP-ASV for the determination of Pb(II) It is worth noting that

100 nm

(a)

1500

00100 1000

Diameter (nm)1000

00

1000

Und

ersiz

e

q (

)

(b)

Figure 2 TEM observation (a) and size distribution curve (b) of ZIF-8

ZIF-8 (3 months)ZIF-8 (6 months)ZIF-8 (8 months)ZIF-8 (12 months)

ZIF-8 (1 months)

ZIF-8

500

Cps

Inte

nsity

(arb

)

2θ (degree)5 10 15 20 25 30 35

(a)

5 10 15 20 25 30

ZIF-8 (H2O)ZIF-8 (C2H5OH)

ZIF-8 (C6H6)

ZIF-8

500

Cps

Inte

nsity

(arb

)

2θ (degree)

(b)

Figure 3 XRD patterns of ZIF-8 in ambient atmosphere (a) ZIF-8 in refluxing some boiling solvents for 10 hours (b)

ZIF-8 (3 days)ZIF-8 (7 days)

ZIF-8

ZIF-8 (14 days)

500

Cps

Inte

nsity

(arb

)

2θ (degree)5 10 15 20 25 30

(a)

5 10 15 20 25 30 35

ZIF-8 (pH = 20)ZIF-8 (pH = 27)ZIF-8 (pH = 60)ZIF-8 (pH = 100)

1000

Cps

ZIF-8ZIF-8 (pH = 120)

Inte

nsity

(arb

)

2θ (degree)

(b)

Figure 4 XRD patterns of ZIF-8 submerged in water at room temperature (a) and water with different pHs (b)


adding ZIF-8 and incorporating the bismuth film exhibitedthe well-defined stripping signal with highest intensity +eintensity of Ip (peak current) at BiFNafZIF-8GCE was182-fold when compared with that at BiFGCE as well asNafZIF-8GCE

+e favorable signal-promoting effect of the ZIF-8 in-dicated that it could accelerate the rate of electron transfer ofPb(II) and had good electrocatalytic activity for the redoxreaction of Pb(II) +e porous structure of ZIF-8 with thebinding properties of the nitrogen group provides a highnumber of reactive sites that are ready for accessing thetarget analyte (Pb(II)) +is synergistic combination of theseeffects leads to a greater amount of lead accumulation on thesurface of BiFNafZIF-8GCE greatly improving its strip-ping peak current +e solvent for dispersing ZIF-8 ofteneffects significantly on the current peak (Ip) +ree solvents(eg dimethylformamide (DMF) water and ethanol) wereused to disperse ZIF-8 +e signals Ip were presented at

Figure 5(b) +e results showed that water was favorable fordispersing ZIF-8 because it provided highest Ip with lowest(relative standard deviation) RSDip 09+erefore water wasselected as a dispersion solvent for further studies +econcentration of Bi(III) in analytical solution may influencethe properties of the in situ bismuth film onGCE and effect onthe accumulation efficiency and DP-ASV method As seenfrom Figure 5(c) the stripping peak currents increased withthe Bi(III) concentration from 0 to 300 ppb and decreased inthe range 300 to 600 ppb with the peak at 300 ppb +e de-creasing of the stripping peak currents after peak beingreached was due to hindering mass transfer caused by toothick bismuth film+erefore the optimized concentration ofbismuth was chosen as 300 ppb of Bi(III) for further study

+e effect of pH on the response of Pb(II) has beenconducted in the pH ranging from 26 to 56 as shown inFigure 6(a) It was noted that the anodic peak current in-creases with increasing pH from 26 to 33 A further increase

10

15

20

25

30

35

40

I (microA

)

E (V)ndash08 ndash07 ndash06 ndash05 ndash04

(A) BiFNafminusZIF-8G(B) BiFNafGCE(C) NafGCE

(D) NafminusZIF-8GCE(E) GCE(F) BiFGCE

(a)

10

15

20

25

30

35

40 RSDIp ()Solvent

DMF 093H2O 091C2H5OH 135

I (microA

)


(b)

10 100 300 500 700 10000

10

20

30

40

I pP

b (microA

)

[BiIII] (ppb)

(c)

Figure 5 (a) DP-ASVs of Pb(II) (50 ppb) in acetate buffer solution (pH 47) at BiFNafZIF-8GCE (A) BiFNafGCE (B) NafGCE (C)NafZIF-8GCE (D) bare GCE (E) and BiFGCE (F) (b) Anodic stripping current (Ip) of Pb(II) for DMF H2O and C2H5OH solvent (c) Ipof Pb(II) versus Bi(III) concentration for preparing the BiF film on the electrode Pb(II) 50 ppb acetate buffer (pH 47) VZIF-8 5 μL(25mg of ZIF-81mL DMF)


in the pH leads to a decline of the current +ese obser-vations might be explained as follows at low pH the signalintensity of lead was low which was due to the protonatedamino groups repulsing with the cations via electrostaticrepulsion With the increase of pH the protonated aminogroups decrease and electrostatic attraction results ina higher stripping current of lead +e best signal intensitywith low RSDEp (44) is reached at pH 33 +e pH 33was chosen for the optimal pH+e relationship between pHand anodic peak potential Ep is shown in Figure 6(b) Ascan be seen anodic peak potential shifts negatively withincreasing pH from 27 to 56 suggesting that protons in-volved directly to lead oxidation or the oxidation washindered at low concentrations of protons +e linear re-gression equation can be expressed as follows

Ep(mV) (minus0031 plusmn 0010)pHminus(minus0428 plusmn 0041)

(R minus09651 ple 0001)(1)

where Ep is the anodic peak potential and R is the relationcoefficient

+e linear relation between Ep and pH is significant (R

minus09651 ple 0001) (Figure 6(c)) +e slope of regression is

close to the theoretical value of 12 times 00599 (25degC) It ispossible that the electrochemical process has the involve-ment of a proton and two electrons

322 Effects of Scan Rate Important information about theelectrochemical mechanism can usually be obtained from therelationship between peak current and scan rate +ereforethe effect of scan rate on Ep and Ip was investigated by CV asshown in Figure 7 If the electrooxidation reaction is irre-versible then Ep is dependent on v As can be seen fromFigure 7(a) peak potential shifts to higher potential as scanrate increases and then it is concluded that electron transferin Pb(II) electrooxidation is irreversible Peak current in-creases with an increase in the scan rate from 20ndash500mVmiddotsminus1(Figure 7(b)) suggesting that the electron transfer reactioninvolved with a surface-confined process [39]

In order to determine if the electrooxidation reaction isadsorption or diffusion controlled the plots of peak current(Ip) against square root of the scan rate (v12) and ln Ipagainst ln v are performed in Figure 8 If a plot of Ip versusv12 is linear and intercepting the origin this process iscontrolled by diffusion [40] In the range 20 to 500mVmiddotsminus1

ndash30

ndash20

ndash10

0

10

20

30

I (microA

)

E (V)

pH = 27pH = 32pH = 36pH = 41

pH = 46pH = 49pH = 56

ndash12 ndash08 ndash04 0 04

(a)

0

5

10

15

20

25

I p (micro

A)

pH27 32 36 41 4649 56

(b)

2 3 4 5 6

ndash060

ndash055

ndash050

E p (V

)

pH

(c)

Figure 6 (a) Anodic stripping current (Ip) of Pb(II) at different pHs and condition [Pb(II)] 500 ppb [Bi(III)] 300 ppb (Ip was the meanvalue for successive measurements for four times) (b) effect of pH on Ip of anodic peak (c) linear regression of Ep versus pH


Ip of lead electrooxidation varied lineally on v12 and wasexpressed by the following

Ip (0048 plusmn 0001)v12

+(minus0641 plusmn 0004) (2)

Even the plot of Ip on v12 as shown in Figure 8(a) waslinear (R 0999 ple 0001) the intercept does not crossthe origin because 95 confidence interval ((minus0645) to(minus0637)) for intercept does not contain zero It means thatthe electrode process of lead electrooxidation was notcontrolled by the diffusion process

On the other hand the slope of linear regression line forln Ip and ln v can provide information about the diffusion- oradsorption-controlled process A slope close to 1 is expected forthe adsorption-controlled electrode process while close to 05for the diffusion-controlled process [40] a linear relation withhigh relative coefficient (R 0985 ple 0001) was obtained asshown in Figure 8(b) and is expressed as follows

ln Ip (0883 plusmn 0099)ln v +(minus0577 plusmn 0477) (3)

+en its slope of 0883 is close to 1 +en it was con-cluded that the oxidation of Pb(II) on the modified electrodewas an adsorption-controlled process

Effective surface area of the modified electrode could beobtained based on the relation between current-potentialcharacteristics According to the Bard and Faulkner equation[41] the relation between current and potential of the oxidationirreversible process is described by the following equation

Ip 0227 middot FAC expαF

RTmiddot Ep1113874 1113875 (4)

where Ip is the current peak (A) Ep is the potential peak (V)A is the effective surface area (cm2) C is the bulk con-centration of Pb(II) (ppb) α is the electron transfer co-efficient F is equal to 96493 (C molminus1) R is the gas constant

0

50

100

150I (μA

)

E (V)

ν = 20 mVsν = 40 mVsν = 50 mVsν = 75 mVsν = 100 mVs

ν = 200 mVsν = 300 mVsν = 400 mVsν = 500 mVs


(a)

0 100 200 300 400 5000

20

40

60

80

100

120

140

Ip (μ

A)

ν (mVsndash1)

(b)

Figure 7 (a) CVs of BiFNafZiF-8GCE with an increase in the scan rate from inner to outer 20ndash500mVmiddotsminus1 (b) linear regression of Ipversus v

0

40

80

120

I p (μ

A)

ν120 5 10 15 20 25

(a)

3 4 5 6

2

3

4

5

lnI p

lnν

(b)

Figure 8 Dependence of anodic peak current (Ip) on potential scan rate12 (v12) (a) plot of ln Ip against ln v (b)


to 8314 (JmiddotKminus1 molminus1) and T is the temperature in Kelvin(298K)

Natural logarithm (4) obtained the dependence below

ln Ip ln(0227 middot FAC) +αF

RTmiddot Ep (5)

Plot of the linear relation between ln Ip and Ep providesa linear regression equation as follows

ln Ip minus2527 + 6431 middot Ep R 0999 (6)

Effective surface area of the modified electrode which wasobtained for the intercept of linear regression linewas 4834 cm2+e geometry surface area of the electrode is 0065 cm2 (di-ameter of the electrode 28mm) +en effective surface areawas 780 times the geometry surface area of the electrode +emodified electrode with increased surface is due to the presenceof ZIF-8 +e larger effective surface area results in more activesites and leads to a higher signal-to-nose ratio [42]

+e electron transfer rate constant (ks) was calculatedbased on the Laviron equation [43]

Ep Eo +RTαnF

lnαnFRTKs

+RTαnF

ln v (7)

where n is the electron transfer number+e plot of anodic peak potential (Ep) against ln v gives

the linear regression equation as followsEp(V) minus0641 + 0024 ln v (8)

+e linear regression with high relative coefficient(R 0996) was obtained +e value of nα is 107 which wasobtained from the slope of the regression equation

+e relation between Eap and v could be analyzed by themodel

y y0 + A1 middot eminusxt1 + A2 middot e

minusxt2 (9)

+e nonlinear regression through this model providedthe following equation

Eap minus0478 +(minus0050) middot eminus]298

+(minus0071) middot eminus]3246

R 0998

(10)

+e high relative coefficient confirmed that this modelfitted well experimental data +e standard potential(E0

Pb2+Pb minus0599 V) with reference electrode AgAgClKCl1M can be the deduced intercept of Ep versus v on theordinate by extrapolating the line to v 0+e valueKs 027 sminus1could be obtained from the value of intercept and nα 107Since the value of α is assumed to be equal to 05 which iscommonly employed for a totally irreversible system [44] thevalue of n was calculated to be 214 +erefore the averagenumber of electrons transferred n was 2 which confirmed againthat two electrons and one protonwere involved in the oxidationof Pb(II) on the ZIF-8-based modified electrode

+e imime groups of imidazole in ZIF-8 bind Pb(II) tosurface complexes because of its high affinity to Pb(II) ions[45]+e Pb(II) were accumulated in the electrode due to thereduction reaction and then dissolved in solution throughthe oxidation reaction +e electrochemical reactions couldoccur as follows

Complex step ZIFminus 8 + (Pb(II))harrZIFminus 8(Pb(II))Accumulation stepZIFminus 8(Pb(II)) + 2eharrZIFminus 8(Pb0)Stripping stepZIFminus 8(Pb0) + H2OharrZIFminus 8 + Pb(OH)+ + H+ + 2e

N

N

N

N

Zn

Zn

Zn

N

N

N

N

NN

N

N

N

N

N N

N

N

i (microA

)

U (V)

ndash(Pb(OH) ndash + H ndash ndash2e)

+H2 O

+2e

+Pb(II)

Pb

Pb

Figure 9 Proposed mechanisms of electrochemistry process for Pb(II) determination at the ZiF-8-based modified electrode by DP-ASV


+e electrochemistry process at the ZIF-8-based modi-fied electrode was illustrated in Figure 9

323 Repeatability Reproducibility Accuracy Linear Rangeand Limit of Detection (LOD) +e repeatability of NafBiFZIF-8GCE for DP-ASV was checked with the solution of 20and 100 ppb Pb (II)+e detection of 20 and 100 ppb Pb (II) ineach signal was estimated by successive measurements for seventimes+eobtainedRSD for 20 and 100ppbwere 708 and 392respectively that were lower than the 12 RSDHorwitz predicted [46]Such reasonable RSD of successive measurements demonstratedthat the NafBiFZIF-8GCE could be repeatedly used for thedetection of Pb(II) in either low concentration range or highconcentration range +e reproducibility was also estimatedwith five NafBiFZIF-8GCEs in detection of 20ppb Pb(II)under the optimized conditions +e results exhibited a goodreproducibility with the RSD of the current responses as 70+e expectable RSD for five independent electrodes confirmedthe good reproducibility of the obtained NafBiFZIF-8GCE

+e accuracy of the method was estimated through therecovery of a spike of Pb(II) +e solution with knownconcentration was prepared from stock solution +e 100 μLof 10 ppm Pb(II) 30mL of 100 ppm Bi(III) and 1mL of05M B-R buffet (pH 32) were mixed together and dilutedto 100mL +is solution was split into two portions +econcentration of one portion evaluated by DP-ASV underoptimal condition was 959 ppb +e other was spiked for

increasing the concentration by 10 ppb+e concentration ofPb(II) in spiked solution determined by DP-ASV underoptimum conditions was 2069 ppb Recovery ( Rev) was1101 +is result suggested that the determination of Pb(II) employing the DP-ASV with BiFNaf-ZiF-8GCE pos-sessed acceptable error [35]

Under the optimal conditions the linear range of leaddetection with a ZIF-8- modified electrode was conducted+e response current peak (Ip) was linear in the concen-tration range 12 ppb to 100 ppb (R 0999) as shown inFigure 10(a) Linear regression equation of the calibrationcurves was Ip (minus2601plusmn 0697) + (0290plusmn 0012) CPb(II)(Figure 10(b)) Sensitivity obtained from the slope of thecalibration curve was 0290 μAppb +e limit of detection(LOD) was calculated based on the concentration from12 ppb to 100 ppb As shown in Figure 10(b) the LOD wascalculated from 3 Syb where Sy is the standard deviation ofy-residuals and b is the slope of linearity +e LOD wasfound to be 416 ppb +e limit of quantitation (LOQ)calculated from 10 Syb was 139 ppb

+e obtained detection limits and the linear ranges inthis work were compared with the results reported pre-viously in which the electrode was modified with goldnanoparticle-graphene-cysteine composite chitosan MIL-100 polyaniline bismuth nanoparticles and mercapto-diatomite composite [47ndash52] A comparison was listed inTable 1 It could be noticed that the detection limit of Pb(II)from the NafionBiFZIF-8GCE electrode was lower or

ndash08 ndash07 ndash06 ndash05 ndash04 ndash03 ndash02

0

10

20

30

40

I (microA

)

E (V)

12 ppb

100 ppb

(a)

20 40 60 80 1000

10

20

30

I p (micro

A)

CPb(II) (ppb)

(b)

Figure 10 (a) +e DP-ASV curves of Pb(II) with increasing Pb(II) from 12 to 100 ppb (b) the linear regression of Ip versus CPb(II)

Table 1 A comparison of Pb(II) detection using modified electrodes

Modified electrodes Method Linear range (ppb) LOD (ppb) ReferencesMIL-101(Cr)GCE SW-ASV 0ndash207 911 [47]GACTSCNTPE SW-AdSV 20ndash414 1179 [48]NPC-nafionBiGCE DP-ASV 7ndash70 080 [49]BiNPsGCE DP-ASV ABS 50ndash600 080 [50]Diatomite-MPTMSGCE DP-ASV ABS 20ndash150 690 [51]AuNPsGCE DP ASV ABS mdash 1120 [52]BiFNaf-ZIF-8GCE DP-ASV 12ndash100 416 +is studyAuNPs gold nanoparticles GA glutaraldehyde CPE carbon paste electrode BiNPs nanoparticles bismuth MPTMS 3-mercaptopropyl trimethoxysilaneGNFs graphite nanofibers CNTPE carbon nanotube paste electrode CTS chitosan SW-AdSV square-wave adsorptive stripping voltammetry DP-ASVdifferential pulse-anodic stripping voltammetry GCE glass carbon electrode NPC nanoporous carbon material


comparable with those results based on modified electrodesin previous papers +e ZIF-8-modified electrode exhibitedbetter than some of the electrodes based on kaoliniteMPTMS-diatomite or gold nanoparticles but failed to someothers Overall the ZIF-8 was proved to be an effectiveelectrode modifier for the detection of Pb(II) in aqueoussolution

4 Conclusions

A novel electrode modifier named zeolite imidazoleframework-ZIF-8 has been prepared by a hydrothermalprocess ZIF-8 was stable in ambient atmosphere and waterIt is stable in pH ranging from 3 to 12 and exhibits theremarkable chemical resistance to some boiling organicsolvents +e obtained ZIF-8 was applicable to the fabri-cation of an BiF-NafZIF-8GCE composite electrode whichgave a good performance in the determination of Pb(II)using the DP-ASV technique due to a combination of theadvantages of ZIF-8 with high surface area hierarchicalporous structure and thermal and chemical stabilities +epeak current of Pb(II) was linearly proportional to itsconcentration over the range of 12 to 100 ppb +e limit ofdetection and the limit of quantitation were as low as412 ppb and 1250 ppb respectively +ese results showedthat ZIF-8 is a potential electrode modifier for lead de-termination in aqueous solution

Conflicts of Interest

+e authors declare that they have no conflicts of interest

Acknowledgments

+is work was supported by the project B2016-DHH-20sponsored by the Ministry of Education and TrainingVietnam

References

[1] L C Jesse R Andrew R Millward K S Park andO M Yaghi ldquoHydrogen sorption in functionalized metal-minusorganic frameworksrdquo Journal of the American ChemicalSociety vol 126 no 18 pp 5666-5667 2004

[2] I Luz F X Llabres i Xamena and A Corma ldquoBridginghomogeneous and heterogeneous catalysis withMOFs ldquoclickrdquoreactions with Cu-MOF catalystsrdquo Journal of Catalysisvol 276 no 1 pp 134ndash140 2010

[3] M Opanasenko A Dhakshinamoorthy M Shamzhy et alldquoComparison of the catalytic activity of MOFs and zeolites inKnoevenagel condensationrdquo Catalysis Science and Technol-ogy vol 3 no 2 pp 500ndash507 2013

[4] R Banerjee A Phan B Wang C Knobler H Furukawa andM OrsquoKeeffe ldquoHigh-throughput synthesis of zeolitic imida-zolate frameworks and application to CO2 capturerdquo Sciencevol 319 no 5865 pp 939ndash943 2008

[5] S R Venna and M A Carreon ldquoHighly permeable zeoliteimidazolate framework-8 membranes for CO2CH4 separa-tionrdquo Journal of the American Chemical Society vol 132 no 1pp 76ndash78 2010

[6] A K Kida M Okita K Fujita S Tanaka and Y MiyakeldquoFormation of high crystalline ZIF-8 in an aqueous solutionrdquoCrystEng Comm vol 15 no 9 pp 1794ndash1801 2013

[7] D Yamamoto T Maki S Watanabe H TanakaM T Miyahara and K Mae ldquoSynthesis and adsorptionproperties of ZIF-8 nanoparticles using a micromixerrdquoChemical Engineering Journal vol 227 pp 145ndash150 2013

[8] H Bux A Feldhoff J Cravillon M Wiebcke Y-S Li andJ Caro ldquoOriented zeolitic imidazolate framework-8 mem-brane with sharp H2C3H8 molecular sieve separationrdquoChemistry of Materials vol 23 no 8 pp 2262ndash2269 2011

[9] H Wu W Zhou and T Yildirim ldquoHydrogen storage ina prototypical zeolitic imidazolate framework-8rdquo Journal of theAmerican Chemical Society vol 129 no 17 pp 5314-5315 2007

[10] B Assfour S Leoni G Seifer and J Phys ldquoHydrogen ad-sorption sites in zeolite imidazolate frameworks ZIF-8 andZIF-11rdquo Journal of Physical Chemistry C vol 114 no 17pp 13381ndash13384 2010

[11] M T Luebbers T Wu L Shen and R I Masel ldquoEffects ofmolecular sieving and electrostatic enhancement in the adsorp-tion of organic compounds on the zeolitic imidazolate frameworkZIF-8rdquo Langmuir vol 26 no 19 pp 15625ndash15633 2010

[12] U P N Tran K K A Le and N T S Phan ldquoExpandingapplications of metalminusorganic frameworks zeolite imidazolateframework ZIF-8 as an efficient heterogeneous catalyst for theknoevenagel reactionrdquo ACS Catalysis vol 1 no 2 pp 120ndash1272011

[13] C M Miralda E E Macias M Zhu P Ratnasamy andM A Carreon ldquoZeolitic imidazole framework-8 catalysts inthe conversion of CO2 to chloropropene carbonaterdquo ACSCatalysis vol 2 no 1 pp 180ndash183 2012

[14] M M Abdel-Galeil M M Ghoneim H S El-DesokyT Hattori and A Matsuda ldquoAnodic stripping voltammetrydetermination of lead ions using highly sensitive modifiedelectrodes based on multi-walled carbon nanotuberdquo Journalof Chemistry and Biochemistry vol 2 no 2 pp 25ndash43 2014

[15] S Morante-Zarcero A Sanchez M Fajardo I Hierro andI Sierra ldquoVoltammetric analysis of Pb(II) in natural watersusing a carbon paste electrode modified with 5-mercapto-1-methyltetrazol grafted on hexagonal mesoporous silicardquoMicrochimica Acta vol 169 pp 57ndash64 2010

[16] F Barbosa F J Krug and E C Lima ldquoOn-line coupling ofelectrochemical preconcentration in tungsten coil electro-thermal atomic absorption spectrometry for determination oflead in natural watersrdquo Spectrochimica Acta Part B AtomicSpectroscopy vol 54 no 8 pp 1155ndash1166 1999

[17] J Vogl and K G Heumann ldquoDetermination of heavy metalcomplexes with humic substances by HPLCICP-MS couplingusing on-line isotope dilution techniquerdquo Freseniusrsquo Journalof Analytical Chemistry vol 359 no 4-5 pp 438ndash441 1997

[18] D W grzynek and B Hołynska ldquoSimultaneous analysis oftrace concentrations of lead and arsenic by energy-dispersiveX-ray fluorescence spectrometryrdquo Applied Radiation andIsotopes vol 44 no 8 pp 1101ndash1104 1993

[19] A Phan C J Doonan F J Uribe-Romo C B KnoblerM OrsquoKeeffe and O M Yaghi ldquoSynthesis structure andcarbon dioxide capture properties of zeolitic imidazolateframeworksrdquo Accounts of Chemical Research vol 43 no 1pp 58ndash67 2010

[20] L Xiao H Xu S Zhou et al ldquoSimultaneous detection of Cd(II)and Pb(II) by differential pulse anodic stripping voltammetry ata nitrogen-doped microporous carbonNafionbismuth-filmelectroderdquo Electrochimica Acta vol 143 pp 143ndash151 2014


[21] A Walcarius ldquoMesoporous materials-based electrochemicalsensorsrdquo Electroanalysis vol 27 no 6 pp 1303ndash1340 2015

[22] A Magheara M Etienne M Tertis R S Andulescu andA Walcarius ldquoClay-mesoporous silica composite films gen-erated by electro-assisted self-assemblyrdquo Electrochimica Actavol 112 pp 333ndash341 2013

[23] V P Pattar and S T Nandibewoor ldquoElectroanalytical methodfor the determination of 5-fluorouracil using a reducedgraphene oxidechitosan modified sensorrdquo RSC Advancesvol 5 no 43 pp 34292ndash34301 2015

[24] J I Gowda and S T Nandibewoor ldquoSimultaneous electro-chemical determination of 4-aminophenazone and caffeine atelectrochemically pre-treated graphite pencil electroderdquoAnalytical Methods vol 6 pp 5147ndash5154 2014

[25] A M Bagoji and S T Nandibewoor ldquoElectrocatalytic redoxbehavior of graphene films towards acebutolol hydrochloridedetermination in real samplesrdquo New Journal of Chemistryvol 40 no 4 pp 3763ndash3772 2016

[26] V P Pattar and S T Nandibewoor ldquoStaircase voltammetricdetermination of 2-thiouracil in pharmaceuticals and humanbiological fluids at polyaniline and polypyrrole film modifiedsensorsrdquo Sensors and Actuators A Physical vol 250pp 40ndash47 2016

[27] J Mao L Yang P Yu X Wei and L Mao ldquoElectrocatalyticfour-electron reduction of oxygen with copper (II)-basedmetal-organic frameworksrdquo Electrochemistry Communica-tions vol 19 pp 29ndash31 2012

[28] H Hosseini H Ahmar A Dehghani A Bagheri A R Fakhariand M M Amini ldquoAu-SH-SiO2 nanoparticles supported onmetal-organic framework (Au-SH-SiO2Cu-MOF) as a sensorfor electrocatalytic oxidation and determination of hydrazinerdquoElectrochimica Acta vol 88 pp 301ndash309 2013

[29] Y Wang H Ge Y Wu G Y H Chen and X Hu ldquoCon-struction of an electrochemical sensor based on amino-functionalized metal-organic frameworks for differentialpulse anodic stripping voltammetric determination of leadrdquoTalanta vol 129 pp 100ndash105 2014

[30] A Samadi-Maybodi S Ghasemi and H Ghaffari-Rad ldquoAnovel sensor based on Ag-loaded zeolitic imidazolateframework-8 nanocrystals for efficient electrocatalytic oxi-dation and trace level detection of hydrazinerdquo Sensors andActuators B Chemical vol 220 pp 627ndash633 2015

[31] N H Phong M T+anh D C Tien M X Tinh N P Hungand D Q Khieu ldquoAssess the status of exposure workers tobenzene toluene by analysis the metabolites products in theurinerdquo VNU Journal of Science Natural Sciences and Tech-nology vol 32 no 1 pp 198ndash206 2016

[32] H-Y Cho J Kim S-N Kim and W-S Ahn ldquoHigh yield 1-Lscale synthesis of ZIF-8 via a sonochemical routerdquo Micro-porous and Mesoporous Materials vol 169 pp 180ndash184 2013

[33] M Zhua D Srinivas S Bhogeswararao P Ratnasamy andM A Carreon ldquoCatalytic activity of ZIF-8 in the synthesis ofstyrene carbonate from CO2 and styrene oxiderdquo CatalysisCommunications vol 32 pp 36ndash40 2013

[34] M Zhu S R Venna J B Jasinski and M A Carreon ldquoRoom-temperature synthesis of ZIF-8 the coexistence of ZnO nano-needlesrdquo Chemistry of Materials vol 23 no 16 pp 3590ndash35922011

[35] D Harvey Modern Analytical Chemistry McGraw-HillHigher Education New York NY USA 2000

[36] S Eslava L Zhang S Esconjauregui et al ldquoMetal-organicframework ZIF-8 films as low-κ dielectrics in microelectronicsrdquoChemistry of Materials vol 25 no 1 pp 27ndash33 2013

[37] Y Du R Z Chen J F Yao and H T Wang ldquoFacile fab-rication of porous ZnO by thermal treatment of zeoliticimidazolate framework-8 and its photocatalytic activityrdquoJournal of Alloys and Compounds vol 551 pp 125ndash130 2013

[38] F TormaMKadar K Toth andETatar ldquoNafionreg22prime-bipyridyl-modified bismuth film electrode for anodic stripping voltam-metryrdquoAnalytica Chimica Acta vol 619 no 2 pp 173ndash182 2008

[39] L Fotouhi M Fatollahzadeh and M M Heravi ldquoRETRAC-TED ldquoMahendra Yadav Sushil Kumar Indra Bahadur DereshRamjugernath Electrochemical and quantum chemical studieson synthesized phenylazopyrimidone dyes as corrosion in-hibitors for mild steel in a 15 HCl Solution [Int J Electro-chem Sci 9 (2014) 3928 - 3950]rdquordquo International Journal ofElectrochemical Science vol 7 pp 3919ndash3928 2012

[40] J Soleymani M Hasanzadeh N Shadjou et al ldquoA newkineticndashmechanistic approach to elucidate electrooxidation ofdoxorubicin hydrochloride in unprocessed human fluidsusing magnetic graphene based nanocomposite modifiedglassy carbon electroderdquoMaterials Science and Engineering Cvol 61 pp 638ndash650 2016

[41] A J Bard and L R Faulkner Fundamentals and ApplicationsElectrochemical Methods John Wiley amp Sons Inc HobokenNJ USA 2nd edition 2001

[42] G Yang X Qu M Shen C Wang Q Qu and X HuldquoElectrochemical behavior of lead(II) at poly(phenol red)modified glassy carbon electrode and its trace determinationby differential pulse anodic stripping voltammetryrdquo Micro-chimica Acta vol 160 no 1-2 pp 275ndash281 2008

[43] E Laviron ldquoGeneral expression of the linear potential sweepvoltammogram in the case of diffusionless electrochemicalsystemsrdquo Journal of Electroanalytical Chemistry and In-terfacial Electrochemistry vol 101 pp 19ndash28 1979

[44] C Li ldquoElectrochemical determination of dipyridamole ata carbon paste electrode using cetyltrimethyl ammoniumbromide as enhancing elementrdquo Colloids and Surfaces BBiointerfaces vol 55 pp 77ndash83 2007

[45] D Mallick U Panda S Jana C Sen T K Mondal andC Sinha ldquoLead(II) complexes of 1-alkyl-2-(arylazo)imidazolesynthesis structure photochromism and metallomesogenicpropertiesrdquo Polyhedron vol 117 pp 318ndash326 2016

[46] W Horwitz and R Albert ldquoQuality issues the concept ofuncertainty as applied to chemical measurementsrdquo Analystvol 122 no 6 pp 615ndash617 1997

[47] DWang Y KeDGuoHGuo and J Chen ldquoFacile fabrication ofcauliflower-like MIL-100(Cr) and its simultaneous determinationof Cd2+ Pb2+ Cu2+ and Hg2+ from aqueous solutionrdquo Sensorsand Actuators B Chemical vol 216 pp 504ndash510 2015

[48] F C Vicentini T A Silva A Pellatieri and B C Janegitz ldquoPb(II) determination in natural water using a carbon nanotubespaste electrode modified with crosslinked chitosanrdquo Micro-chemical Journal vol 116 pp 191ndash196 2014

[49] L Xiao S ZhouGHuH Xu YWang andQ Yuan ldquoOne-stepsynthesis of isoreticular metalndashorganic framework-8 derivedhierarchical porous carbon and its application in differentialpulse anodic stripping voltammetric determination of Pb(ii)rdquoRSC Advances vol 5 no 94 pp 77159ndash77167 2015

[50] D Yang L Wang Z Chen M Megharaj and R NaiduldquoAnodic stripping voltammetric determination of traces of Pb(II) and Cd(II) using a glassy carbon electrode modified withbismuth nanoparticlesrdquo Microchimica Acta vol 181 no 11-12 pp 1199ndash1206 2014

[51] D Q Khieu B H Son V T T Chau P D Du N H Phongand N T D Chau ldquo3-Mercaptopropyltrimethoxysilane Mod-ified Diatomite Preparation and Application for Voltammetric


Determination of Lead (II) and Cadmium (II)rdquo Journal ofChemistry vol 2017 article 9560293 10 pages 2017

[52] X Xu G Duan Y Li et al ldquoFabrication of gold nanoparticlesby laser ablation in liquid and their application for simul-taneous electrochemical detection of Cd2+ Pb2+ Cu2+Hg2+rdquo ACS Applied Materials and Interfaces vol 6 no 1pp 65ndash71 2014


TribologyAdvances in

Hindawiwwwhindawicom Volume 2018


International Journal ofInternational Journal ofPhotoenergy


Journal of

Chemistry


Advances inPhysical Chemistry

Hindawiwwwhindawicom

Analytical Methods in Chemistry

Journal of

Volume 2018

Bioinorganic Chemistry and ApplicationsHindawiwwwhindawicom Volume 2018

SpectroscopyInternational Journal of


Hindawi Publishing Corporation httpwwwhindawicom Volume 2013Hindawiwwwhindawicom

The Scientific World Journal

Volume 2018

Medicinal ChemistryInternational Journal of


NanotechnologyHindawiwwwhindawicom Volume 2018

Journal of

Applied ChemistryJournal of



Biochemistry Research International


Enzyme Research


Journal of

SpectroscopyAnalytical ChemistryInternational Journal of


MaterialsJournal of



BioMed Research International Electrochemistry

International Journal of


Na

nom

ate

ria

ls


Journal ofNanomaterials

Submit your manuscripts atwwwhindawicom

(DP-ASV) as one kind of the ASVmethod has been appliedfor the determination of trace heavy metal ions because ofits remarkably high sensitivity Glassy carbon electrodeschemically modified with porous materials such as modifiedmesoporous materials [21] clay-mesoporous silica composite[22] multiwall carbon nanotubes [14] reduced grapheneoxidechitosan [23] pretreated graphite pencil [24] graphenefilms [25] and polyaniline and polypyrrole film [26] havereceived considerable attention for ASV because they exhibitsignificant improvements in terms of fast response highselectivity low detection limit and renewability

Due to high surface areas highly order structure andhigh reactive site density the usage of MOFs-based com-posite for the electrochemical field is becoming increasingMao et al [27] reported the usage of copper (II)-22prime-bipyridine-benzene-135-tricarboxylate (Cu(II) basedMOF-199) as selective electrocatalysts for the reduction ofO2 and CO2 MOF modified by Au-SH-SiO2 nanoparticleswas utilized to determinate hydrazine and L-cysteine byelectrochemistry analysis [28] +e amino-functionalizedMOF-199 material could provide an excellent modifier fordeveloping a sensitive electrode for the determination of leadtrace [29] Ag-loaded ZIF-8 nanocrystals were used as anelectrode modifier to detect hydrazine AgZIF-8CPE(carbon paste electrode) performed a good catalytic per-formance toward hydrazine oxidation [30] Xiao et al [20]reported the nitrogen-doped microporous carbon preparedfrom pyrolysis of ZIF-8 as an excellent electrode modifier todetermine Pb(II) and Cd(II) in aqueous solution

In the previous paper [31] we demonstrated the using ofZIF-8-modified electrode to determine Pb(II) in aqueoussolution In the present work we continue to refine the studyon the use of ZIF-8 as an electrode modifier for the de-termination of Pb(II) by the voltammetric technique +estability of ZIF-8 over time in several solvents and in dif-ferent pH solutions was studied ZIF-8 has been used tomodify the glassy carbon electrode (GCE) for Pb(II) de-termination using DP-ASV methods Several parametersrelated to the electrode performance were studied and op-timized for using in the analysis To our knowledge this isthe first report on using modified electrode-based ZIF-8material for the determination of lead by the DP-ASV

2 Experimental

21 Materials Zinc nitrate hexahydrate (Zn(NO3)2middot6H2ODaejung Korea) methanol (CH3OH Merck Germany)and 2-methylimidazole (C4H6N2 Aldrich USA) were utilizedin the synthesis of ZIF-8 For electrochemistry performancebismuth(III) nitrate pentahydrate (Bi(NO3)3middot5H2O Sigma-Aldrich USA) was used to prepare the bismuth film Nafionsolution was prepared from stock solution (5d 0874 gmiddotmLminus1 Aldrich USA) and ethanol (96 MerckGermany) with a volume ratio VnafionVethanol 14BrittonndashRobinson buffer solution (B-R BS) of pH 47was prepared from 004M H3BO3 004M H3PO4 and004M CH3COOH (Merck Germany) pH of the B-R BSwas adjusted by the addition of 10M sodium hydroxidesolutions into the B-R BS and then checked by the pH

meter +e working solution of Pb(II) was prepared dailyfrom stock solution (1000 ppm Merck Germany)

22 Synthesis of ZIF-8 ZIF-8 was synthesized according to[32ndash34] Briefly zinc nitrate (28mmol) was dissolved inmethanol (14mL) 2-Methylimidazole (644mmol) wasdissolved in methanol (14mL) and this solution was addedto the zinc solution under sonication condition for 30minutes and then vigorously stirred for 24 h at roomtemperature Finally this solution was centrifuged at300 rpm and washed thoroughly with methanol +iswashing procedure was repeated 5 times +e resultingcrystals were dried overnight at 120degC

23 Voltammetric Procedure

231 Preparation of Working Electrode-Modified Electrodes+e preparation procedure was carried out as in [28] Inbrief glassy carbon electrode (GCE) was first polished with005 μm Al2O3 slurry on a polishing cloth and then rinsedultrasonically with 2MHNO3 absolute ethanol and double-distilled water Subsequently the GCE was electrochemicallycleaned by a cyclic potential scan between minus11 V and +03Vin 05M acetate buffer solution pH 45 with the scan rate of010Vmiddotsminus1 After that the electrode was rinsed with double-distilled water +e nafionZIF-8 composite was prepared bydispersing 25mg ZIF-8 into 10mL nafion (01 wt) andsonicated+eGCEwas coated with 5 μL of the nafionZIF-8composite and dried under the room temperature (sim25degC)(denoted as NafZIF-8GCE) For the same procedure theGCE modified by nafion was denoted as NafGCE Bis-muth film (BiF) was formed simultaneously with Pb(II)preconcentration +e bismuth deposition was conductedat minus12 V potential under stirring for 120 s +e GCENafGCE and NafZIF-8GCE modified by BiF weredenoted as BiFGCE NafBiFGCE and NafBiFZIF-8GCE respectively

232 Voltammetric Procedure Solution under study (finalvolume of 10mL) containing 004M B-R BS (pH 47) and200 ppb Pb(II) was transferred into the electrochemical cellwith the 3 electrodes +en voltammetric measurement wasconducted as follows

(i) For surveying voltammetric characteristics of Pb(II)on the modified GCE Pb(II) was accumulated on thesurface of the modified electrode at a potential ofminus12V (Eacc) for an accumulated time of 120 s (tacc)During this step the electrode was rotated ata constant rate of 1000 rpm After that the electroderotation was off and then cyclic voltammograms(CVs) were recorded from ndash11V to +03V (forwardpotential scan) and then from +03V to minus11 V(reverse potential scan) at a scan rate of 01 Vmiddotsminus1

(ii) For differential pulse anodic stripping voltammetric(DP-ASV) determination of Pb(II) on modifiedGCE during the DP-ASV procedure Pb(II) wasaccumulated on the surface of the rotating modified















0 10 20 30 40 50 60

334

134

01302

211

200

201

1

233

222

114

500

Cps

Inte

nsity

(au

)

2θ (degree)





100 nm

(a)

1500

00100 1000

Diameter (nm)1000

00

1000

Und

ersiz

e

q (

)

(b)



ZIF-8 (1 months)

ZIF-8

500

Cps

Inte

nsity

(arb

)

2θ (degree)5 10 15 20 25 30 35

(a)

5 10 15 20 25 30


ZIF-8 (C6H6)

ZIF-8

500

Cps

Inte

nsity

(arb

)

2θ (degree)

(b)



ZIF-8

ZIF-8 (14 days)

500

Cps

Inte

nsity

(arb

)

2θ (degree)5 10 15 20 25 30

(a)

5 10 15 20 25 30 35


1000

Cps

ZIF-8ZIF-8 (pH = 120)

Inte

nsity

(arb

)

2θ (degree)

(b)







10

15

20

25

30

35

40

I (microA

)




(a)

10

15

20

25

30

35

40 RSDIp ()Solvent

DMF 093H2O 091C2H5OH 135

I (microA

)


(b)

10 100 300 500 700 10000

10

20

30

40

I pP

b (microA

)

[BiIII] (ppb)

(c)





(R minus09651 ple 0001)(1)







ndash30

ndash20

ndash10

0

10

20

30

I (microA

)

E (V)

pH = 27pH = 32pH = 36pH = 41

pH = 46pH = 49pH = 56


(a)

0

5

10

15

20

25

I p (micro

A)

pH27 32 36 41 4649 56

(b)

2 3 4 5 6

ndash060

ndash055

ndash050

E p (V

)

pH

(c)




Ip (0048 plusmn 0001)v12

+(minus0641 plusmn 0004) (2)







RTmiddot Ep1113874 1113875 (4)


0

50

100

150I (μA

)

E (V)




(a)

0 100 200 300 400 5000

20

40

60

80

100

120

140

Ip (μ

A)

ν (mVsndash1)

(b)


0

40

80

120

I p (μ

A)

ν120 5 10 15 20 25

(a)

3 4 5 6

2

3

4

5

lnI p

lnν

(b)






RTmiddot Ep (5)





Ep Eo +RTαnF

lnαnFRTKs

+RTαnF

ln v (7)






minusxt2 (9)




R 0998

(10)





N

N

N

N

Zn

Zn

Zn

N

N

N

N

NN

N

N

N

N

N N

N

N

i (microA

)

U (V)


+H2 O

+2e

+Pb(II)

Pb

Pb










0

10

20

30

40

I (microA

)

E (V)

12 ppb

100 ppb

(a)

20 40 60 80 1000

10

20

30

I p (micro

A)

CPb(II) (ppb)

(b)






4 Conclusions




Acknowledgments


References






























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls

















0 10 20 30 40 50 60

334

134

01302

211

200

201

1

233

222

114

500

Cps

Inte

nsity

(au

)

2θ (degree)





100 nm

(a)

1500

00100 1000

Diameter (nm)1000

00

1000

Und

ersiz

e

q (

)

(b)



ZIF-8 (1 months)

ZIF-8

500

Cps

Inte

nsity

(arb

)

2θ (degree)5 10 15 20 25 30 35

(a)

5 10 15 20 25 30


ZIF-8 (C6H6)

ZIF-8

500

Cps

Inte

nsity

(arb

)

2θ (degree)

(b)



ZIF-8

ZIF-8 (14 days)

500

Cps

Inte

nsity

(arb

)

2θ (degree)5 10 15 20 25 30

(a)

5 10 15 20 25 30 35


1000

Cps

ZIF-8ZIF-8 (pH = 120)

Inte

nsity

(arb

)

2θ (degree)

(b)







10

15

20

25

30

35

40

I (microA

)




(a)

10

15

20

25

30

35

40 RSDIp ()Solvent

DMF 093H2O 091C2H5OH 135

I (microA

)


(b)

10 100 300 500 700 10000

10

20

30

40

I pP

b (microA

)

[BiIII] (ppb)

(c)





(R minus09651 ple 0001)(1)







ndash30

ndash20

ndash10

0

10

20

30

I (microA

)

E (V)

pH = 27pH = 32pH = 36pH = 41

pH = 46pH = 49pH = 56


(a)

0

5

10

15

20

25

I p (micro

A)

pH27 32 36 41 4649 56

(b)

2 3 4 5 6

ndash060

ndash055

ndash050

E p (V

)

pH

(c)




Ip (0048 plusmn 0001)v12

+(minus0641 plusmn 0004) (2)







RTmiddot Ep1113874 1113875 (4)


0

50

100

150I (μA

)

E (V)




(a)

0 100 200 300 400 5000

20

40

60

80

100

120

140

Ip (μ

A)

ν (mVsndash1)

(b)


0

40

80

120

I p (μ

A)

ν120 5 10 15 20 25

(a)

3 4 5 6

2

3

4

5

lnI p

lnν

(b)






RTmiddot Ep (5)





Ep Eo +RTαnF

lnαnFRTKs

+RTαnF

ln v (7)






minusxt2 (9)




R 0998

(10)





N

N

N

N

Zn

Zn

Zn

N

N

N

N

NN

N

N

N

N

N N

N

N

i (microA

)

U (V)


+H2 O

+2e

+Pb(II)

Pb

Pb










0

10

20

30

40

I (microA

)

E (V)

12 ppb

100 ppb

(a)

20 40 60 80 1000

10

20

30

I p (micro

A)

CPb(II) (ppb)

(b)






4 Conclusions




Acknowledgments


References






























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls






100 nm

(a)

1500

00100 1000

Diameter (nm)1000

00

1000

Und

ersiz

e

q (

)

(b)



ZIF-8 (1 months)

ZIF-8

500

Cps

Inte

nsity

(arb

)

2θ (degree)5 10 15 20 25 30 35

(a)

5 10 15 20 25 30


ZIF-8 (C6H6)

ZIF-8

500

Cps

Inte

nsity

(arb

)

2θ (degree)

(b)



ZIF-8

ZIF-8 (14 days)

500

Cps

Inte

nsity

(arb

)

2θ (degree)5 10 15 20 25 30

(a)

5 10 15 20 25 30 35


1000

Cps

ZIF-8ZIF-8 (pH = 120)

Inte

nsity

(arb

)

2θ (degree)

(b)







10

15

20

25

30

35

40

I (microA

)




(a)

10

15

20

25

30

35

40 RSDIp ()Solvent

DMF 093H2O 091C2H5OH 135

I (microA

)


(b)

10 100 300 500 700 10000

10

20

30

40

I pP

b (microA

)

[BiIII] (ppb)

(c)





(R minus09651 ple 0001)(1)







ndash30

ndash20

ndash10

0

10

20

30

I (microA

)

E (V)

pH = 27pH = 32pH = 36pH = 41

pH = 46pH = 49pH = 56


(a)

0

5

10

15

20

25

I p (micro

A)

pH27 32 36 41 4649 56

(b)

2 3 4 5 6

ndash060

ndash055

ndash050

E p (V

)

pH

(c)




Ip (0048 plusmn 0001)v12

+(minus0641 plusmn 0004) (2)







RTmiddot Ep1113874 1113875 (4)


0

50

100

150I (μA

)

E (V)




(a)

0 100 200 300 400 5000

20

40

60

80

100

120

140

Ip (μ

A)

ν (mVsndash1)

(b)


0

40

80

120

I p (μ

A)

ν120 5 10 15 20 25

(a)

3 4 5 6

2

3

4

5

lnI p

lnν

(b)






RTmiddot Ep (5)





Ep Eo +RTαnF

lnαnFRTKs

+RTαnF

ln v (7)






minusxt2 (9)




R 0998

(10)





N

N

N

N

Zn

Zn

Zn

N

N

N

N

NN

N

N

N

N

N N

N

N

i (microA

)

U (V)


+H2 O

+2e

+Pb(II)

Pb

Pb










0

10

20

30

40

I (microA

)

E (V)

12 ppb

100 ppb

(a)

20 40 60 80 1000

10

20

30

I p (micro

A)

CPb(II) (ppb)

(b)






4 Conclusions




Acknowledgments


References






























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls








10

15

20

25

30

35

40

I (microA

)




(a)

10

15

20

25

30

35

40 RSDIp ()Solvent

DMF 093H2O 091C2H5OH 135

I (microA

)


(b)

10 100 300 500 700 10000

10

20

30

40

I pP

b (microA

)

[BiIII] (ppb)

(c)





(R minus09651 ple 0001)(1)







ndash30

ndash20

ndash10

0

10

20

30

I (microA

)

E (V)

pH = 27pH = 32pH = 36pH = 41

pH = 46pH = 49pH = 56


(a)

0

5

10

15

20

25

I p (micro

A)

pH27 32 36 41 4649 56

(b)

2 3 4 5 6

ndash060

ndash055

ndash050

E p (V

)

pH

(c)




Ip (0048 plusmn 0001)v12

+(minus0641 plusmn 0004) (2)







RTmiddot Ep1113874 1113875 (4)


0

50

100

150I (μA

)

E (V)




(a)

0 100 200 300 400 5000

20

40

60

80

100

120

140

Ip (μ

A)

ν (mVsndash1)

(b)


0

40

80

120

I p (μ

A)

ν120 5 10 15 20 25

(a)

3 4 5 6

2

3

4

5

lnI p

lnν

(b)






RTmiddot Ep (5)





Ep Eo +RTαnF

lnαnFRTKs

+RTαnF

ln v (7)






minusxt2 (9)




R 0998

(10)





N

N

N

N

Zn

Zn

Zn

N

N

N

N

NN

N

N

N

N

N N

N

N

i (microA

)

U (V)


+H2 O

+2e

+Pb(II)

Pb

Pb










0

10

20

30

40

I (microA

)

E (V)

12 ppb

100 ppb

(a)

20 40 60 80 1000

10

20

30

I p (micro

A)

CPb(II) (ppb)

(b)






4 Conclusions




Acknowledgments


References






























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls






(R minus09651 ple 0001)(1)







ndash30

ndash20

ndash10

0

10

20

30

I (microA

)

E (V)

pH = 27pH = 32pH = 36pH = 41

pH = 46pH = 49pH = 56


(a)

0

5

10

15

20

25

I p (micro

A)

pH27 32 36 41 4649 56

(b)

2 3 4 5 6

ndash060

ndash055

ndash050

E p (V

)

pH

(c)




Ip (0048 plusmn 0001)v12

+(minus0641 plusmn 0004) (2)







RTmiddot Ep1113874 1113875 (4)


0

50

100

150I (μA

)

E (V)




(a)

0 100 200 300 400 5000

20

40

60

80

100

120

140

Ip (μ

A)

ν (mVsndash1)

(b)


0

40

80

120

I p (μ

A)

ν120 5 10 15 20 25

(a)

3 4 5 6

2

3

4

5

lnI p

lnν

(b)






RTmiddot Ep (5)





Ep Eo +RTαnF

lnαnFRTKs

+RTαnF

ln v (7)






minusxt2 (9)




R 0998

(10)





N

N

N

N

Zn

Zn

Zn

N

N

N

N

NN

N

N

N

N

N N

N

N

i (microA

)

U (V)


+H2 O

+2e

+Pb(II)

Pb

Pb










0

10

20

30

40

I (microA

)

E (V)

12 ppb

100 ppb

(a)

20 40 60 80 1000

10

20

30

I p (micro

A)

CPb(II) (ppb)

(b)






4 Conclusions




Acknowledgments


References






























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls





Ip (0048 plusmn 0001)v12

+(minus0641 plusmn 0004) (2)







RTmiddot Ep1113874 1113875 (4)


0

50

100

150I (μA

)

E (V)




(a)

0 100 200 300 400 5000

20

40

60

80

100

120

140

Ip (μ

A)

ν (mVsndash1)

(b)


0

40

80

120

I p (μ

A)

ν120 5 10 15 20 25

(a)

3 4 5 6

2

3

4

5

lnI p

lnν

(b)






RTmiddot Ep (5)





Ep Eo +RTαnF

lnαnFRTKs

+RTαnF

ln v (7)






minusxt2 (9)




R 0998

(10)





N

N

N

N

Zn

Zn

Zn

N

N

N

N

NN

N

N

N

N

N N

N

N

i (microA

)

U (V)


+H2 O

+2e

+Pb(II)

Pb

Pb










0

10

20

30

40

I (microA

)

E (V)

12 ppb

100 ppb

(a)

20 40 60 80 1000

10

20

30

I p (micro

A)

CPb(II) (ppb)

(b)






4 Conclusions




Acknowledgments


References






























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls







RTmiddot Ep (5)





Ep Eo +RTαnF

lnαnFRTKs

+RTαnF

ln v (7)






minusxt2 (9)




R 0998

(10)





N

N

N

N

Zn

Zn

Zn

N

N

N

N

NN

N

N

N

N

N N

N

N

i (microA

)

U (V)


+H2 O

+2e

+Pb(II)

Pb

Pb










0

10

20

30

40

I (microA

)

E (V)

12 ppb

100 ppb

(a)

20 40 60 80 1000

10

20

30

I p (micro

A)

CPb(II) (ppb)

(b)






4 Conclusions




Acknowledgments


References






























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls











0

10

20

30

40

I (microA

)

E (V)

12 ppb

100 ppb

(a)

20 40 60 80 1000

10

20

30

I p (micro

A)

CPb(II) (ppb)

(b)






4 Conclusions




Acknowledgments


References






























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls





4 Conclusions




Acknowledgments


References






























































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls












































Journal of

Chemistry





Journal of

Volume 2018






Volume 2018




Journal of






Enzyme Research


Journal of



MaterialsJournal of






Na

nom

ate

ria

ls




synthesisandvoltammetricdeterminationofpb(ii)using azif-8 … · 2019. 7. 30. · researcharticle...

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