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Supersensitive Detection of Chlorinated Phenols by Multiple Amplification Electrochemiluminescence Sensing Based on Carbon Quantum Dots/Graphene Shanli Yang, Jiesheng Liang, Sheng-Lian Luo, Chengbin Liu, and Yanhong Tang Anal. Chem., Just Accepted Manuscript • DOI: 10.1021/ac400874h • Publication Date (Web): 24 Jul 2013 Downloaded from http://pubs.acs.org on July 29, 2013

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Analytical Chemistry

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Supersensitive Detection of Chlorinated Phenols by Multiple

2

Amplification Electrochemiluminescence Sensing Based on Carbon

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Quantum Dots/Graphene

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Shanli Yang a, Jiesheng Liang a, Shenglian Luo a,*, Chengbin Liu a,*, Yanhong Tang b

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a

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Changsha 410082, P. R. China

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b

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State Key Laboratory of Chemo/Biosensing and Chemometrics, Hunan University,

College of Materials Science and Engineering, Hunan University, Changsha 410082,

P. R. China

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————————————

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*

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E-mail: [email protected].(S.L. Luo); [email protected] (C.B. Liu)

Corresponding authors. Tel.: +86 731 88823805; Fax: +86 731 88823805

23 1

ACS Paragon Plus Environment


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ABSTRACT

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A novel electrochemiluminescence (ECL) sensor based on carbon quantum dots

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(CQDs) immobilized on graphene (GR) has been firstly developed for the

4

determination of chlorinated phenols (CPs) in water. The detection is based on the

5

ECL signals from the interaction between the analytes and the excited CQDs (C*+)

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using S2O82− as coreactant. GR facilitates both C•− and SO4•− production, resulting in a

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high yield of C*+, and the multistage amplification effect leads to a nearly 48-fold

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ECL amplification. Pentachlorophenol (PCP) is often monitored as an important

9

indicator for CPs in real environmental samples, but its ultra-trace and real-time

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analysis is an intractable issue in environmental monitoring. The resulting ECL sensor

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enables the real-time detection of PCP with unprecedented sensitivity reaching 1.0 ×

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10−12 M concentration in a wide linear range from 1.0 × 10−12 to 1.0 × 10−8 M. The

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ECL sensor showed high selectivity to CPs, especially to PCP. The practicability of

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the sensing platform in real water sample showed ideal recovery rates. It is envisaged

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that the eco-friendly and recyclable sensor could be employed in the identification of

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key CPs in the environment.

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Keywords:

PCP

ultra-trace

detection;

Carbon

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Electrochemiluminescence; Multistage amplification

quantum

20

2


dots;

Graphene;

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INTRODUCTION

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Chlorinated phenols (CPs) are a typical group of persistent organic pollutants in

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the environment, and several of them have been listed as priority pollutants by the US

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Environmental Protection Agency and classified as a group 2B environmental

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carcinogen by International Agency for Research on Cancer.1−3 One of the most

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commonly used and strongest carcinogens in the CPs family is pentachlorophenol

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(PCP), which not only poses a health threat, but is also of great environmental concern

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because of soil and water contamination. The content of PCP correlates well with the

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total CPs content in contaminated environmental samples, and thus PCP is often

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monitored as a model compound for CPs in real environmental samples. Moreover,

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due to the strict restrictions on the maximum admissible concentration of CPs in

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drinking water by European Union and the US Environmental Protection Agency (0.5

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ppb and 1 ppb respectively), extensive work has been carried out on the trace and

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ultra-trace detection of CPs in the last decade.4−8 However, those methods are usually

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time-consuming, and require bulky equipment, tedious sample preparation and an

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expert operator. In addition, considering critical importance for practical use, those

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systems lack the ability to perform a real-time analysis since they cannot be

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miniaturized.

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Quantum dots (QDs) based electrochemiluminescence (ECL) sensor is a

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powerful potential detection method, owing to its miniaturization, inexpensive

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instrumentation, excellent detection sensitivity and high selectivity.9 Its applications

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for the detection of chemical and biological species have been widely reported.10−12

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However, reports on concerning the environmental detection utilizing QDs based ECL

2

sensor are relatively scarce though the ECL sensor has so many advantages. The

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reasons are mainly attributed to the following factors: 1) inherently high toxicity of

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Cd-based QDs used in ECL;13−15 2) high cost and complex experimental design of

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ECL involved in Cd-based QDs and non-recycle of these solution-phase QDs;10−15

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and 3) most importantly, poor reversibility and low ECL intensity due to the poor

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stability of Cd-based QDs at high excited electrochemical potentials. Therefore,

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nontoxicity, low cost, and reproducibility are urgently needed for the development of

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QDs based ECL sensors in environmental monitoring.

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The newly emerging carbon quantum dots (CQDs) may be a promising

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alternative because of their low toxicity, low cost, high stability and good ECL

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reversibility.16 To the best of our knowledge, CQDs based ECL sensors have rarely

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been reported, which is hampered by the low ECL intensity of CQDs and the

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non-recycle of CQDs in aqueous system. Although extrinsic coreactant S2O82− has

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been employed to enhance CQDs ECL intensity,16 it is hard to satisfy the trace and

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ultra-trace detection of CPs in the environment. Thus, the key point lies in how to

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further amplify CQDs ECL signal and solve the non-recyclable problem

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simultaneously.

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Graphene (GR), a two-dimensional sp2-hybridized carbon sheet, has recently

20

attracted great attention due to its unique electrical, optical, and mechanical properties

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as well as potential use in various fields such as electronics, sensors and composite

22

materials.17−19 Benefiting from the large surface-to-volume ratio, good chemical

4


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stability and ﬂexibility, GR is a suitable immobilization platform for many

2

nanostructural materials;20,21 moreover, due to its good electrical conductivity and

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excellent electrocatalytic activity, GR could efficiently amplify the ECL signal of

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CdSe QDs.22

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Herein, for the first time, a novel one-step electrochemical reduction technology is

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proposed for the preparation of carbon quantum dots/graphene (CQDs/GR) hybrid

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(See Supporting Information, Scheme S1), and an advanced ECL sensor based on the

8

CQDs/GR hybrid was fabricated for the supersensitive, rapid, and real-time detection

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of CPs through multistage amplification of the CQDs ECL signal by GR and S2O82−.

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GR serves as both the ECL amplification reagent and the immobilization platform for

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CQDs, which can not only enhance the detection sensitivity, but also achieve the

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recyclability of CQDs.

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METERIALS AND METHODS

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Materials. Titanium foil (99.8%, 0.127 mm thickness) was purchased from

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Aldrich (Milwaukee, WI). Graphite powder in size of about 50 µm was purchased

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from Shanghai Carbon Co., Ltd. Graphite oxide was synthesized from graphite

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powder by the Hummers’ method,23 and then the prepared graphite oxide was

19

dissolved in 0.067 M PBS (pH 7) to form 1 mg/mL GO solution. Wood based

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activated carbon powder (200 mesh) and 1−30 kDa molecular weight cut off (MWCO)

21

membranes (Amicon Ultra-4, Millipore) were purchased from the local suppliers, and

22

the oxidized carbon quantum dots (OCQDs) was synthesized from activated carbon

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powder by the Dong’s method.24 Other chemicals of analytical reagent grade were

2

obtained from commercial sources and used without further purification. Ultrapure

3

water was used throughout the experiments.

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Fabrication of CQDs/GR hybrid. 1 mL of OCQDs (5 mg) and 9 mL of GO

5

(9mg) solution were mixed under stirring for 1 h to form OCQDs/GO solution. A

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titanium ribbon (1.0 cm×3.5 cm ) was ultrasonically cleaned in a dilute HF solution

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and then in water for 5 min each. The top part of the titanium ribbon was used as the

8

electrical contact position, and an electrically insulated Pt wire was attached on the

9

top by jointing. The as-prepared titanium ribbon was immersed into the above

10

OCQDs/GO solution under stirring and then subjected to scanning from −1.4 to +1.0

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V at 50 mV/s with 10 electrodeposition cycles to obtain CQDs/GR hybrid. Based on

12

the measurement of electrochemical properties, the above conditions were optimized.

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The morphologies of CQDs/GR hybrid were characterized on a scanning electron

14

microscope (SEM, JSM-6700F, JEOL, Japan) and a transmission electron microscope

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(TEM, JEM-3010, JEOL, Japan). Photoluminescence (PL) spectra were acquired with

16

F-2500 fluorescence spectrometer (Hitachi, Japan). Electrochemical measurements

17

were carried out on CHI-660D electrochemistry station (Chenhua Instrument Inc.,

18

China) with a three-electrode system where the modified titanium ribbon (1.0 cm×

19

3.5 cm) was used as the working electrode with a Pt foil as the counter electrode and a

20

saturated calomel electrode (SCE) as the reference electrode.

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ECL Measurements. The ECL of CQDs/GR in PBS solution containing 100 mM

22

K2S2O8 was measured with a MPI-E multifunctional chemiluminescent analyzer

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(Xi’an Rimax Electronics Co. Ltd., China) with a photomultiplier tube voltage set at

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600 V, using CQDs/GR modified titanium ribbon, a Pt foil,and a SCE as the working

3

electrode, the counter electrode and the reference electrode, respectively. During the

4

measurements, the potential supplied by the MPI-E electrochemical analyzer was

5

applied to the CQDs/GR working electrode by a cyclic voltammetric technique with a

6

potential range from −1.6 to +0.2 V at 400 mV/s. At the same time, the ECL emission

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was recorded by the MPI-E multifunctional chemiluminescence analyzer.

8 9

RESULTS AND DISCUSSIONS

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Characterization and Evaluation of CQDs/GR Hybrid. Recently, Dong et al.

11

reported a new kind of oxidized carbon quantum dots (OCQDs) with an abundant of

12

-COOH groups on their surfaces, showing a good dispersity in aqueous solution.24

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Inspired by this, utilizing the difference in solubility of OCQDs (good dispersity in

14

aqueous solution) and CQDs (insoluble in aqueous solution), we can speculate that

15

when the OCQDs in direct contact with an electrode accept electrons to suffer from

16

electroreduction to CQDs, the resulted insoluble CQDs will directly attach onto the

17

electrode surface. We would like to point out that, to the best of our knowledge, it is

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the first report about CQDs immobilization by directly utilizing the solubility

19

difference between OCQDs and CQDs and also about CQDs/GR hybrid construction

20

by one-step electrochemical reduction technique.

21

The cyclic voltammograms (CVs) for OCQDs electrolysis on titanium ribbon

22

electrode and on the more sensitive glassy carbon electrode (GCE) are shown in

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1

Figure S1A and S1B (See Supporting Information), respectively. Both of the

2

reduction currents regularly decreased with successive sweeps, highlighting the

3

persistent deposition of poor conductive CQDs onto the electrodes. The GCE after

4

OCQDs electrolysis was then scanned in PBS buffer solution (Figure S1C) where

5

there is no irreversible electroreduction peak of OCQDs to CQDs at −1.3 V (peak III

6

in Figure S1B), showing that part of oxygen-containing groups of OCQD had been

7

irreversibly reduced during OCQDs electrolysis. Figure S1D shows the Fourier

8

transform infrared reflectance (FTIR) spectra of OCQDs and CQDs where the

9

absorption intensities of C=O, C-O, and O-H in OCQDs were much stronger than

10

those in CQDs, confirming the electroreduction of OCQDs to CQDs. The CQDs were

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in an average size of 7.5 nm on the electrode surface (Figure S1E). The cyclic

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voltammogram (CV) for GO electrolysis on titanium ribbon is shown in Figure S1F

13

where the cathodic peak at −1.0 V was attributed to the irreversible electrochemical

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reduction of GO to GR;25 moreover, in the Raman spectra of GO and GR (Figure

15

S1G), there appeared a decreased intensity ratio (ID/IG) of D band and G band, which

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further confirmed the electroreduction of GO to GR. Figure S1H shows the CV for

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OCQDs/GO co-electrolysis on titanium ribbon retaining the reduction peak of GO.

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Notably, the peak currents persistently decreased with the successive co-deposition of

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GR and CQDs but it is remarkably larger than that of individual GO or OCQDs

20

deposition, indicating the higher conductivity of CQDs/GR hybrid than that of GR or

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CQDs. It is thought that the insertion of CQDs between GR sheets prevented GR

22

sheets from agglomeration and increased the surface area of GR, thus resulting in the

8


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improved electrochemical activity. This inference is in agreement with the CV results

2

of GR, CQDs, and CQDs/GR on titanium ribbon in PBS buffer solution (Figure S2A)

3

and the redox probe Fe(CN)63−/4− solution (Figure S2B), respectively.

4

Figure 1A and B show the SEM and TEM images of CQDs/GR on titanium

5

ribbon, respectively. The CQDs particles in a size of about 7.5 nm were

6

homogeneously and densely distributed on the surface of GR sheets. Figure 1C shows

7

the PL spectra of GR (curve a), CQDs (curve b) and CQDs/GR hybrid (curve c). No

8

obvious excitation and emission peaks were observed for only GR, while being

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excited at 365 nm, both CQDs and CQDs/GR demonstrate dramatic emission peaks at

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about 420 nm, which were attributed to PL emission of CQDs. The PL peaks of both

11

CQDs/GR and CQDs were sharp, reflecting the homogeneous size distribution of

12

CQDs on the GR surface, consistent with the SEM and TEM results. No luminescence

13

from the supernatant after centrifugation of the CQDs/GR hybrid (curve d) suggested

14

the robust adhesion of CQDs to GR.

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Multistage Amplified ECL of Carbon QDs. As shown in Figure 2A, in the

16

presence of coreactant S2O82−, there was no ECL on bare titanium ribbon (curve a)

17

and GR/titanium ribbon (curve b), while there was one ECL emission peak at −1.5 V

18

on both CQDs/titanium ribbon (curve c) and CQDs/GR/titanium ribbon (curve d),

19

resulting from the reaction between CQDs and S2O82−.16,24 The ECL intensity of

20

CQDs/GR is 7 times higher than that of CQDs, indicating that GR is a good ECL

21

signal amplifier. Notedly, the ECL intensity of CQDs/GR with S2O82− is 48 times

22

higher than that of CQDs in the absence of GR and S2O82− (Figure S3), indicating that

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1

the proposed multistage amplification strategy is efficient in greatly enhancing the

2

ECL of CQDs. It is also worth noting that the ECL curve of the CQDs/GR shows an

3

onset potential at about −0.75 V that is more positive than that of CQDs (−0.9 V).

4

This indicates that the presence of GR decreased the potential barrier of the ECL

5

reduction due to the accelerated electron transport between the electrode and CQDs

6

by GR.22 The CVs of the CQDs and CQDs/GR electrodes were recorded

7

simultaneously (Figure 2A, inset), and both of them showed only one cathodic peak

8

attributed to the reduction of S2O82−.10,26 The more positive reduction potential and

9

higher reduction current of CQDs/GR electrode again suggest that GR could

10

accelerate electron transfer between the electrode and S2O82−. Figure 2B shows the

11

ECL emission of CQDs/GR with S2O82− under continuous 22 cyclic voltammetric

12

sweeps. The ECL emission is highly repeatable, meaning a good stability of the

13

proposed ECL multistage amplification system for CQDs.

14

Condition Optimization. The ECL emission intensity is closely related with the

15

performance of ECL detection. Accordingly, before the ECL detection of PCP, it is

16

necessary to investigate the factors that influence the ECL emission intensity.

17

Generally, the ECL emission intensity is dependent on the pH value of solution and

18

the concentration of coreactant S2O82−. Figure S4A shows that the strongest ECL

19

intensity was observed at pH 7. In acidic solution, the reduction of proton to hydrogen

20

would occur at the applied negative potential, which might inhibit the reduction of

21

S2O82−, while in basic solution, the intermediate SO4•− from S2O82− reduction would be

22

scavenged by OH•−, resulting in a decrease in the ECL intensity.27 Figure S4B shows

10


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that the ECL intensity increased with the concentration of S2O82− in the range from 25

2

mM to the saturated concentration of 200 mM. As the ECL intensity obtained in 200

3

mM S2O82− reached the upper detection limit of the instrument, 100 mM S2O82− was

4

chosen to ensure an adequate sensitivity. Figure S4C shows that the ECL intensity

5

obviously increased with the increasing electrodeposition cycle from 1 to 10, but

6

when the electrodeposition cycle was more than 10, the ECL intensity kept basically

7

stable. So the optimum electrodeposition cycle was chosen to be 10.

8

ECL Detection of PCP. Figure 4 shows that the ECL intensity decreased with

9

increasing PCP concentration under the optimum condition. Taking the relative

10

intensity change of I−I0 / I0 as the function of the concentration of PCP, where I0 was

11

the initial intensity and I−I0 was the PCP-induced decrease in ECL intensity, the I−I0 /

12

I0 was linear dependent on the logarithm of PCP concentration in the range of 1.0 ×

13

10−12 -1.0 × 10−8 M with a correlation coefficient of 0.995 (Figure 4 inset) and the

14

limit of detection (LOD) was 1.0×10−12 M (S/N=3). Besides, the achieved LOD has

15

been much lower than the reported values: 8.6×10−8 M from a molecularly imprinted

16

polymer-based room-temperature phosphorescence optosensor,28 1.9×10−9 M from a

17

spectrophoto-metricassay,29 and 1.9×10−7 M from a gas chromatography–mass

18

spectrometry.30

19

The selectivity of the ECL sensor was also investigated by measuring the ECL

20

responses to the addition of some common cations and anions, 2,4,6-trinitrophenol

21

(2,4,6-TNP), p-dioxybenzene (p-DOB), p-chlorophenol (p-CP), 2,6-dichlorophenol

22

(2,6-DCP), 2,4,6-trichlorophenol (2,4,6-TCP) and PCP, respectively. As shown in

11



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1

Table 1, several points are noteworthy: 1) comparing the ECL inhibition ratio of the

2

common ions (cations and anions) and the non-chlorinated phenols (2,4,6-TNP and

3

p-DOB) with those of the chlorinated phenols (CPs) (p-CP, 2,6-DCP, 2,4,6-TCP and

4

PCP), the ECL sensor showed high selectivity to CPs, especially to PCP; 2) the

5

compound with higher oxidation potential (Figure S5) made less decrease in the ECL

6

intensity, which suggested a oxidization detection mechanism; and 3) as the analogs

7

of PCP, p-CP, 2,6-DCP and 2,4,6-TCP showed less ECL inhibition ratios than PCP

8

due to their more stable chemical properties,31 making them harder to be oxidized.

9

The low LOD and high selectivity of the proposed sensor will guarantee the quick

10

scanning of PCP. PCP in the concentrations of 0 M, 5×10−11 M, 10×10−11 M, and

11

20×10−11 M was respectively spiked in real soil samples, including the sludge from

12

Taozi Lake and the soil from the experimental field nearby Xiangjiang River. All the

13

naturally dried soil samples (5.0 g) were extracted, respectively, with a mixture of

14

methanol/ethylene glycol (4:1, v/v), and then the extraction solutions were tested

15

using the proposed method and GC-MS, respectively. The testing results of PCP in

16

the sludge and the farmland soil by the proposed method were good agreement with

17

those achieved by GC-MS (Table 2), indicating that the ECL sensing system could be

18

employed in the identification of CPs in the environment.

19

Detection Mechanism. In ECL system, there are two proposed mechanisms: one

20

is cationic and anionic radical annihilation ECL and the other is coreactant ECL.16

21

Figure 3 shows the ECL transients of CQDs by applying 1 Hz potential steps between

22

−1.8 and +1.5V without S2O82−. At the first positive step, only cationic CQD radical

12


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1

(C•+) was produced without ECL signals; however, both anodic and cathodic ECL

2

signals were evidently observed at the subsequent potential steps, indicating that both

3

cationic CQD radical (C•+) and anionic CQD radical (C•−) are stable enough to

4

produce ECL via the annihilation between C•+ and C•−. However, it was noteworthy

5

that the ECL signals was much lower than that of the CQDs with S2O82− (Figure S3),

6

indicating that S2O82− played an important role in the ECL process where the

7

coreactant ECL dominantly contributed to the whole ECL. Furthermore, due to the

8

extraordinary electron transport ability of GR (Figure 2A), electrons were transferred

9

from electrode to CQDs and S2O82− through GR in the cathodic ECL process,

10 11 12

promoting the generation of C•− and SO4•−. By referencing the proposed model,32 the possible ECL detection mechanism is elucidated as below:

13

C + e−

C•−

14

S2O82− + e-

15

2SO4•− + C•−→ 2SO42− + C*+

(3)

16

C*+ + e− → C + hν

(4)

17

C*+ + PCP → C + TCQ

(5)

18

Scheme 1 intuitively shows the mechanism. Primarily, electrons were transferred

19

from electrode to the CQDs and S2O82− through GR, resulting the generation of C•−

20

and SO4•− (reactions 1 and 2). The cathodic ECL herein was originated from the

21

formation of excited-state CQDs (C*+) via electron transfer annihilation of C•− and

22

SO4•− radicals (reactions 3 and 4). While PCP was added, the PCP would be absorbed

(1) SO42− + SO4•−

(2) 

13



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1

onto the CQDs surface, and be oxidized by C*+ resulting in a decrease in ECL

2

(reaction 5). The chloranil (TCQ) produced during the oxidization of PCP was

3

determined by mass spectroscopy analysis (not shown here), confirming the

4

oxidization detection mechanism.

5 6

CONCLUSION

7

In conclusion, a novel ECL sensing platform based on CQDs/GR hybrid was

8

fabricated by one-step electrochemical reduction technology. The new ECL sensor

9

exhibited the supersensitive and selective detection of PCP through a multistage

10

CQDs ECL signal amplification mechanism by combining GR with coreactant S2O82−.

11

Moreover, the sensing system is eco-friendly and recyclable. This work may present

12

an important strategy to design QDs ECL sensors and expanded their applications of

13

ultra-trace environmental sensing.

14 15

ACKNOWLEDGMENTS

16

This work was supported by the National Natural Science Foundation of China

17

(51178173, 51202065, 51078129), Innovation Research Team in University

18

(IRT1238), Program for New Century Excellent Talents in University (11-0126), the

19

Key Program of National Natural Science Foundation of China (51238002), and

20

Hunan Province graduate student scientific research innovation plan (No.

21

521298769).

22

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1

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Anal. Chem. 2010, 82, 9749–9754.

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(14) Ding, S. N.; Xu, J. J.; Chen, H. Y. Chem. Commun. 2006 , 34, 3631–3633.

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(27) Yamashita, K.; Yamazaki-Nishida, S.; Harima, Y.; Segawa, A. Anal. Chem. 1991, 63, 872–876.

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(28) Wang, H. F.; He, Y.; Ji, T. R.; Yan, X. P. Anal. Chem. 2009, 81, 1615–1621.

4

(29) Mufeed Awawdeh, A.; Harmon, H. J. Biosens. Bioelectron. 2005, 20,

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1595–1601.

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(30) Gremaud, E.; Turesky, R. J. J. Agric. Food Chem. 1997, 45, 1229–1233.

7

(31) Li, C. C.; Kang, Q.; Chen, Y. F.; Li, J. X.; Cai, Q. Y.; Yao, S. Z. Analyst 2010,

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135, 2806–2810. (32) Li, J. X.; Yang, L. X.; Luo, S. L.; Chen, B. B.; Li, J.; Lin, H. L.; Cai, Q. Y.; Yao, S. Z. Anal. Chem. 2010, 82, 7357–7361.

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Page 18 of 25

Figures and Tables

1 2

(A) C

e-

C

eee-

(B)

ECL Signals

C·-

hv

*+

C

eeee-

h+

SO4·S2O82- SO42-

CQDs:

C C·-

h+

SO4·S2O82-

*+

PCP

hv TCQ

SO42-

ECL quenching

ECL emission RG:

ECL Signals

PCP:

TCQ:

3 4

Scheme 1 Illustrative ECL detection mechanism for PCP with CQDs/GR in S2O82−

5

solution.

6

18


Page 19 of 25

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1 2

Figure 1 (A) SEM and (B) TEM images of CQDs/GR. (C) Photoluminescence of (a)

3

GR, (b) CQDs, (c) CQDs/GR and (d) the supernatant after centrifugation of the

4

CQDs/GR hybrid.

5

19



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

2 3

Figure 2 (A) ECL–potential curves of (a) bare titanium ribbon, (b) GR, (c) CQDs,

4

and (d) CQDs/GR on titanium ribbon in 0.067 M pH 7 PBS containing 100 mM

5

S2O82−. Inset: CVs of (a) CQDs and (b) CQDs/GR on titanium ribbon. (B) ECL

6

emission from CQDs/GR with 100 mM S2O82− under continuous 22 cycles of cyclic

7

voltammetry.

8 20


Page 20 of 25

Page 21 of 25

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1 2

Figure 3 ECL transients of CQDs by applying 1 Hz potential steps between −1.8 and

3

+1.5 V without S2O82−.

4

21



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1 2

Figure 4 The ECL intensity response of CQDs/GR in 100 mM S2O82− solution (pH 7)

3

at different concentration of PCP (×10−12 M): (a) 1, (b) 10, (c) 100, (d) 1000, and (e)

4

10000; the insert plot is the calibration curve for PCP determination.

5

22


Page 22 of 25

Page 23 of 25

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1


Table 1

The interferences on PCP detection.

Substance

Concentration /M

I−I0 / I

Na+

3.0×10−11

0.1%

K+

3.0×10−11

0.1%

Ca2+

3.0×10−11

0.2%

Mg2+

3.0×10−11

0.1%

Cl-

3.0×10−11

0.2%

NO3-

3.0×10−11

0.1%

HCO32-

3.0×10−11

0.3%

SO42-

3.0×10−11

0.2%

2,4,6-TNP

3.0×10−11

2.1%

p-DOB

3.0×10−11

3.2%

p-CP

3.0×10−11

6.2%

2,6-DCP

3.0×10−11

7.3%

2,4,6-TCP

3.0×10−11

9.1%

PCP

3.0×10−11

21.4%

CPs analogs

2

23



1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60

1

Table 2

Page 24 of 25

Recovery study for PCP with various real soil samples.

Sample

PCP

Proposed method

GC-MS

Added

Found

Found

(10−11 M)

(10−11 M)

(10−11 M)

0

3.2±0.2

2.8±0.1

5.0

7.9±0.1

7.8±0.2

10.0

13.1±0.3

12.5±0.4

20.0

22.9±0.5

22.4±0.3

0

2.1±0.1

1.7±0.2

5.0

7.2±0.3

6.9±0.1

10.0

11.9±0.2

11.4±0.3

20.0

19.9±0.6

19.7±0.2

sludge

farmland soil

2

24


Page 25 of 25

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60


for TOC only

1 2 (A) eeee-

(B)

ECL Signals

C

C*+

C·-

hv

C eeee-

h+

SO4·S2O82- SO42-

3

ECL Signals

C·-

C*+ h+

SO4·S2O82-

PCP SO42-

ECL quenching

ECL emission

25


hv TCQ

Supersensitive Detection of Chlorinated Phenols by Multiple ... - NSFC

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