Electrochemical Detection of Atrazine by Platinum Nanoparticles

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Electrochemical Detection of Atrazine by Platinum Nanoparticles/ Carbon Nitride Nanotubes with Molecularly Imprinted Polymer Mehmet Lütfi Yola, and Necip Atar Ind. Eng. Chem. Res., Just Accepted Manuscript • DOI: 10.1021/acs.iecr.7b01379 • Publication Date (Web): 20 Jun 2017 Downloaded from http://pubs.acs.org on June 23, 2017

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Industrial & Engineering Chemistry Research

Electrochemical Detection of Atrazine by Platinum Nanoparticles/Carbon Nitride Nanotubes with Molecularly Imprinted Polymer

Mehmet Lütfi Yola*† and Necip Atar‡

†

Iskenderun Technical University, Faculty of Engineering and Natural Sciences, Department

of Biomedical Engineering, Hatay, Turkey ‡

Pamukkale University, Faculty of Engineering, Department of Chemical Engineering,

Denizli, Turkey

* To whom correspondence should be addressed: Dr. Mehmet Lütfi YOLA Iskenderun Technical University Tel.: +903266135600 ; Fax: +903266135613 E-mail: [email protected]

0 ACS Paragon Plus Environment


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ABSTRACT: In this report, a new electrochemical sensor based on molecular imprinting polymer (MIP) and platinum nanoparticles (Pt NPs)/carbon nitride nanotubes (C3N4 NTs) nanocomposite was developed for atrazine (ATR) analysis. Firstly, the structures of prepared nanocomposites and surfaces were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), x-ray diffraction (XRD) and energy dispersive x-ray analysis (EDX). After the characterization studies, ATR imprinted glassy carbon electrode (GCE) based on Pt NPs/C3N4 NTs nanocomposite was developed by 100 mM phenol containing 25 nM ATR. The linearity range and the detection limit of the molecular imprinted sensor were calculated as 1.0×10-12 – 1.0×10-10 and 1.5×10-13 M, respectively. In addition, the voltammetric sensor was applied to wastewater samples with high recovery. Keywords: Atrazine; Platinum nanoparticles; Carbon nitride nanotubes; Molecular imprinting; Electrochemical detection


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1. INTRODUCTION The carcinogenic and cytotoxic drugs is utilized to control insects and some pests. However, their residues can easily go into the food chain through water and soil. Owing to these reasons, they result in crucial health problems and affect ecosystems 1-3. ATR, 1-Chloro3-ethylamino-5-isopropylamino-2,4,6-triazine, takes part in triazine groups and one of the most common pesticides

4, 5

. The extensive usage of ATR causes lots of release into

wastewater and many water sources. Because of this, the ecosystem and human health are negatively affected 6. Hence, the development of sensitive and selective analytical methods for ATR analysis is crucial in real samples. Recently, many analytical methods were developed such as gas chromatography–mass spectrometry 7, thin-layer chromatography 8 and high-performance liquid chromatography. Nevertheless, when we want to investigate these methods in terms of material consumption, complexity and expensiveness, there are many negative situations. Due to these reasons, more sensitive, favorable portability, low-cost, simple and selective sensors based on nanomaterials are needed in terms of environmental safety. Hence, the highly selective methods for sensitive sensor applications have been presented. Molecular imprinting technology (MIT) is a method based on the formation of MIP 9

. It is the polymerization method in presence of monomer and target molecule. In the

literature, the effective sensor techniques were developed by MIT for determination of ATR. Firstly, the method was developed on formation of molecularly imprinted core-shell nanoparticles. The high recovery was obtained as 93.4% and 79.8% for ATR separation in spiked corn and lettuce samples, respectively

10

. Secondly, we reported quartz crystal

microbalance (QCM) sensor by fabricating ATR imprinted polymer on gold chip. The detection limit was obtained as 0.028 nM by QCM 11. Moreover, the MIP sensor was prepared by polymerizing methacrylic acid and ethylene glycol dimethacrylate on gold surface

12

. In

the other work, the electrochemical MIP film was developed by electropolymerization of o-



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phenylenediamine in the presence of ATR 13. After that, molecularly imprinted polymer has been electrochemically synthesized onto a platinum electrode for ATR detection. The molecular imprinted sensor has large linear range (from 1.0×10-9 M to 1.5×10-2 M)

14

. In

addition, the amperometric sensor was prepared by GCE with MIP membrane for ATR detection and detection limit was obtained as 9.0×10-7 M 15. In the development of electrochemical nanosensor, the nanomaterials such as graphene/graphene oxide, carbon and carbon nitride nanotubes are utilized to improve the sensitivity

16-18

. These nanomaterials have important advantages such as high surface area,

electrical conductivity, thermal and mechanical stability. Especially, the pesticides cause significant health and ecosystem problems. Owing to these reasons, the selective and sensitive analytical methods based on the nanomaterials and MIP are needed for early diagnosis. We reported several analytical assays relating to pesticides. A novel molecular imprinted electrochemical sensor based on Pt NPs on polyoxometalate/multi-walled carbon nanotubes was developed for simazine detection

17

and carbon nitride nanotubes decorated with

graphene quantum dots was prepared for the determination of chlorpyrifos 19. Graphitic carbon nitride (g-C3N4) is one of the most stable carbon nitride materials. It has layered structure. There are van der waals interactions between C-N layers. Like graphene/graphene oxide, it is utilized for the nanotechnology applications such as photocatalysis or biosensing

20-22

. The ultra-thin graphitic carbon nitride (utg-C3N4) is

different from bulk structure. utg-C3N4 has atomic-scale thickness and facilitates the charge transfer

23, 24

. Like utg-C3N4, carbon nitride nanotubes can increase electron transfer and

reduce mass transfer resistance due to the active sites 25, 26. Owing to technological interest of Pt NPs, their applications were crucial during last years

27

. The films with Pt NPs can be

utilized for various applications such as optical applications and catalytic activity

28, 29

addition, the stable forms of Pt NPs have significant role to develop efficient fuel cells


. In

30, 31

.

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Morever, Pt NPs are utilized for manufacturing of conductive thick films and electrochemically active surface

18

and increase the sensitivity for the electrochemical

determination of pesticides 32. In this study, the molecular imprinting technique 33 was used for formation of selective active sites relating to ATR. Firstly, platinum nanoparticles/carbon nitride nanotubes nanocomposite was prepared by hydrothermal treatment. After that, ATR imprinted electrodes were formed on platinum nanoparticles/carbon nitride nanotubes modified electrode by cyclic voltammetry (CV). Finally, the prepared electrode was applied to wastewater samples for ATR detection. According to the results, the minimal waste formation in preparation of platinum nanoparticles/carbon nitride nanotubes is obtained. The prepared sensor is sensitive, selective, fast and cheap. In addition, ATR analysis with high recovery in wastewater samples is firstly performed by MIP/Pt NPs/C3N4 NTs/GCE. We can say that the analytical method in this report can be preferred in comparison with the other methods. 2. EXPERIMENTAL SECTION 2.1. Materials. ATR, simazine (SIM), 1,3,5-triazine (TRZ) and prometryn (PRO) were obtained from Sigma–Aldrich. The stock solutions of ATR (1.0 mM) were prepared by distilled water and the stock solution was diluted with 0.1 M phosphate buffer solution (PBS) (pH 7.0). Chloroplatinic acid (H2PtCl6), phenol, melamine, acetonitrile (MeCN), ethanol, isopropyl alcohol (IPA) and activated carbon were purchased from Sigma–Aldrich (USA). 2.2. Instrumentation. Square wave voltammetry (SWV) and CV were employed by IviumStat (U.S) equipped with C3 cell stand. PHI 5000 Versa Probe (Φ ULVAC-PHI, Inc., Japan/USA) was utilized for XPS analysis with Al Kα radiation (1486.6 eV) at 50 W. JEOL 2100 HRTEM (JEOL Ltd., Tokyo, Japan) and ZEISS EVO 50 SEM (GERMANY) analytic microscopies were utilized for the characterization of nanocomposites. A Rigaku Miniflex X-



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ray diffractometer (Japan) using monochromatic CuKα radiation at a voltage of 30 kV was utlized for X-ray diffraction measurement. 2.3. Preparation of g-C3N4, utg-C3N4, C3N4 NTs and Pt NPs/C3N4 NTs. The g- C3N4, utgC3N4 and C3N4 NTs were prepared according to our previous report 16. Pt NPs/C3N4 NTs was synthesized by one-step hydrothermal treatment. Firstly, g-C3N4 (1.0 g) was dispersed into H2PtCl6 solution (1.0 mM). After the stirring for 30 min, the suspension was subject to hydrothermal treatment at 150 °C. The suspension was dried at 60 °C and Pt NPs/C3N4 NTs was finally obtained. 2.4. Procedure for the electrode preparation. The electrodes such as bare GCE, utgC3N4/GCE, C3N4 NTs/GCE and Pt NPs/C3N4 NTs/GCE were cleaned and employed according to the our previous report 17. 2.5. Preparation of ATR imprinted electrochemical sensor. The development of the ATR imprinted electrochemical sensor is given in Scheme 1. The ATR imprinted electrochemical sensor (MIP/Pt NPs/C3N4 NTs/GCE) was prepared by CV for 10 cycles in 100 mM phenol containing 25 nM ATR (Supporting electrolyte: 0.1 M, pH 7.0 PBS). In addition, for a control experiment, the imprinted electrochemical sensor without ATR (NIP) was prepared.

Here Scheme 1.

2.6. ATR removal from electrode surface. The 1.0 M NaCl was used as desorption solution for eliminating hydrogen bonds interactions between phenol and ATR molecules. ATR imprinted electrode was dipped into 25 mL NaCl solution. After 15 min, the electrode was dried with nitrogen gas. 2.7. Sample preparation. The sample was prepared according to the protocol

11

: The

collected wastewater sample (Denizli/TURKEY) in pre-cleaned amber glass bottles was


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transferred to the laboratory for storage at 4 °C. The sample was centrifuged at 4500 rpm for 5 min. After that, it was filtrated by a 0.45 m syringe filter. Finally, the filtrate was diluted with 0.1 M PBS (pH 7.0). 3. RESULTS AND DISCUSSION 3.1. Characterization of nanostructures by SEM, TEM, EDX, XPS and XRD. Figure 1A indicates the bulk structure of g-C3N4 like graphite structure. In the bulk structure of g-C3N4, the clear and crisp edges were observed. SEM image of g-C3N4 shows irregular morphology and varying sizes of the sample. In addition, it suggests that g-C3N4 intensively agglomerates about several micrometers in size. After the ultrasonication, the utg-C3N4 was successfully formed (Figure 1B). After the hydrothermal treatment of utg-C3N4 at 150 °C, the formation of tubular carbon nitride occurred. Figure 1C confirms the hollow and tubular structure of C3N4 NTs. According to Figure 1C, the hollow and tubular nanostructure was formed by curling utg-C3N4 at 150 °C. During the hydrothermal treatment, the large quantity of C3N4 NTs in the aligned arrangements occurred. Figure 1C also showed that C3N4 NTs had open ends. These C3N4 NTs have diameters ranging from 75 to 150 nm. The presence of Pt NPs on a lighter and tubular structure is seen clearly (Figure 1D). The average diameters of spherical Pt NPs as dark dots are 15-20 nm. Hence, we can say that Pt NPs/C3N4 NTs nanostructure is successfully prepared by one-step hydrothermal treatment. In addition, the formation of Pt NPs/C3N4 NTs nanostructure was confirmed by SEM image (Figure 1E). In Figure 1E, a dense layer of spherical Pt NPs was covered on C3N4 NTs nanostructure, demonstrating successful combination. After the formation of ATR imprinted polymer on Pt NPs/C3N4 NTs/GCE, SEM image of MIP/Pt NPs/C3N4 NTs modified surface was obtained (Figure 1F). According to Figure 1F, the intensive polymer layer was seen on the Pt NPs/C3N4 NTs modified surface. This situation indicates that the ATR imprinted electrochemical sensor is successfully prepared. The SEM image of NIP/Pt NPs/C3N4 NTs/GCE was also obtained



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(Figure 1G). It has a less porous structure in comparison with ATR imprinted electrochemical surface. In addition, EDX analysis confirms the formation of Pt NPs/C3N4 NTs nanostructure. The C, N and Pt elements in the nanohybrid were observed in Figure 1H.

Here Figure 1.

In addition, the XPS analysis of Pt NPs/C3N4 NTs nanostructure was performed to confirm its structure (Figure 2A). The two peaks at the binding energies of 288.02 eV and 285.09 eV are seen in the C1s spectrum. The peak at 288.02 eV is corresponded to the carbon atom binding with three nitrogen atoms and the peak at 285.09 eV is assigned to C-C bond. The three peaks at 400.12, 399.87 and 398.79 eV in N1s spectrum confirms C–N groups of the nanostructure 34

. The peaks at 70.62 eV and 74.61 eV were assigned to Pt4f7/2 and Pt4f5/2 on Pt NPs/C3N4 NTs

nanostructure. According to XRD analysis (Figure 2B), C3N4 NTs show one strong peak at 27.5°, corresponding to the reflection from (002) plane of C3N4 NTs 35. Compared with C3N4 NTs, Pt NPs/C3N4 NTs nanocomposite demonstrates two additional peaks at 40.0°, and 46.1°, corresponding to 111 and 200 faces of platinum, respectively. These results prove that Pt NPs aggregate into C3N4 NTs during hydrothermal treatment. XPS analysis of MIP/Pt NPs/C3N4 NTs nanostructure was carried out (Figure 2C). The peaks in the C1s, N1s and Pt4f7/2 spectra are the same as the peaks of Pt NPs/C3N4 NTs nanostructure. In addition, the peak at 532.18 eV is corresponded to the C–O groups on phenol monomer.

Here Figure 2.


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3.2. The CV and EIS characterizations of the modified GCE. [Fe(CN)6]3- solution (1.0 mM) containing 0.1 M KCl as the redox probe was used for the characterizations of electrodes such as bare GCE, utg-C3N4/GCE, C3N4 NTs/GCE and Pt NPs/C3N4 NTs/GCE. The obvious reversible peaks of 1.0 mM [Fe(CN)6]3-/4- with 200 mV of peak potential difference (∆Ep) is seen at bare GCE (curve a of Figure 3A). After modification of bare GCE with utg-C3N4, ∆Ep decreased to 150 mV with a small increase in the peak current (curve b of Figure 3A). The more catalytic increase was shown when C3N4 NTs/GCE was used as working electrode (∆Ep = 120 mV on curve c of Figure 3A). Finally, when Pt NPs/C3N4 NTs/GCE as working electrode was used, the more catalytic ability and the less ∆Ep were obtained against redox probe (∆Ep = 80 mV on curve d of Figure 3A). The obtained results were confirmed by EIS experiments. Figure 3B shows the impedance plot of (a) bare GCE, (b) utg-C3N4/GCE, (c) C3N4 NTs/GCE and (d) Pt NPs/C3N4 NTs/GCE in 1.0 mM [Fe(CN)6]3/4-

(1:1) solution containing 0.1 M KCl. The charge transfer resistance (Rct) values of the

prepared electrodes are 130.0 ohm, 90.0 ohm, 65.0 and 45.0 ohm, respectively. According to Figure 3A and Figure 3B, Rct values are consistent with CV results. These enhanced performances can be resulted from the electrode surface area and the synergistic effect between carbon nitride nanotubes and metal nanoparticles. In addition, the effective surface areas of the electrodes were calculated by CV in presence of 1.0 mM [Fe(CN)6]3- solution containing 0.1 M KCl. The equation of ip = 2.69×105 A n3/2 D1/2 C v1/2, where ip is the signal, C is the concentration of [Fe(CN)6]3-, v is the scan rate and A is the surface area (cm2), was utilized for calculation of surface area (n = 1, D = 7.6×10-6 cm2 s-1) 36. Consequently, the electrode areas of bare GCE, utg-C3N4/GCE, C3N4 NTs/GCE and Pt NPs/C3N4 NTs/GCE were obtained as 0.070 cm2, 0.243 cm2, 0.419 cm2 and 0.822 cm2, respectively. Hence, it is clear that the highest electrode area and the highest conductivity were obtained by Pt NPs/C3N4 NTs/GCE.



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Here Figure 3.

3.3. MIP formation on Pt NPs/C3N4 NTs/GCE by CV and evaluation of imprinted/nonimprinted electrodes by SWV and EIS. The polymerization on modified electrode was carried out by CV in 0.1 M PBS (pH 7.0) and the voltammogram is given in Figure 4A. According to Figure 4A, the maximum signal was obtained at first cycle. After that, the signals decreased with the cycles. 100 mM phenol containing 25 nM ATR was oxidized at 0.72 V. During scanning, the signal began to decrease. This situation showed the formation of imprinted film on Pt NPs/C3N4 NTs/GCE. After the monomer polymerization on Pt NPs/C3N4 NTs/GCE, charge transfer resistance was obtained as 250 ohm (curve a of Figure 4B). After performing of desorption of 25 nM ATR, the value decreased to 90 ohm (curve b of Figure 4B). Hence, the formation of imprinted film between active electrode area and redox probe demonstrates obvious obstruction effect. When the template molecule was rebinded to imprinted film, the value of Rct is 210 ohm (curve c of Figure 4B). As a result, the ATR molecules block the electrochemical reaction of redox probe. The responses of different imprinted electrodes are compared by SWV (Figure 4C). The performance of MIP/Pt NPs/C3N4 NTs/GCE (curve a of Figure 4C) is better than that of the MIP/C3N4 NTs/GCE (curve b of Figure 4C) and MIP/GCE (curve c of Figure 4C). Hence, we can again say that C3N4 NTs/Pt NPs nanocomposite can increase sensitivity and conductivity in comparison with C3N4 NTs. In addition, NIP/Pt NPs/C3N4 NTs/GCE was prepared to investigate the imprinting effect. NIP/Pt NPs/C3N4 NTs/GCE shows a small response (curve d of Figure 4C). The non-specific interaction between monomer and electrode surface resulted in the small response. In addition, the surface areas of the MIP/Pt NPs/C3N4


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NTs/GCE and NIP/Pt NPs/C3N4 NTs/GCE were calculated from Randles-Sevcik equation as 0.883 cm2 and 0.154 cm2, respectively.

Here Figure 4.

3.4. Optimization studies 3.4.1. The effect of pH. The effect of pH on analysis conditions in the range of 3.0-9.0 was investigated. There are hydrogen bonds interactions between ATR molecules and monomer (phenol) (Scheme 2). The response of ATR on electrode surface decreased at low and high pH conditions. Due to the protonation of monomer and template molecules at the low pH, the recovery of ATR molecules decreases. Owing to the ionic forms of monomer and template molecules at the high pH, this situation causes negative extraction efficiency 37. According to Figure 5A, the optimum and efficient signals were obtained at pH 7.0. Hence, we can say that ATR molecules diffuse easily to electrode surface at pH 7.0.

Here Scheme 2.

3.4.2. The effect of the mole ratio template molecule to monomer. The effect of the mole ratio (ATR/monomer) was evaluated in the range from 1:2 to 1:6 (Figure 5B). According to Figure 5B, the template response increased when the monomer amount increased up to 100 mM. The increase resulted from increase of the number of binding site. However, when the monomer amount reached to the higher levels, the thicker polymer on the electrode surface formed. This situation causes non-specific interactions between monomer and template. Hence, the optimum mole ratio was selected as 1:4.



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3.4.3. The effect of elution time. The effect of elution time was investigated (Figure 5C). The response of analyte molecule increased up to the 15 min. After 15 min, it stayed constant. Hence, after 15 min, there is no analyte molecule on the electrode surface and the elution of ATR molecule finished. 3.4.4. The effect of scan cycle. Especially, the scan cycle has important effect on sensitivity of prepared sensor. The five imprinted electrodes were developed (Scan cycle: 5, 10, 15, 20 and 25) (Figure 5D). The maximum response was obtained with 10 of scan cycle. If scan cycle is higher than 10, the thicker polymer surface forms. Hence, the template molecule is not completely removed from this electrode surface. If scan cycle is lower than 10, the number of binding site is less. Hence, the number of scan cycle was selected as 10.

Here Figure 5.

3.5. Linearity range of proposed sensor. The square wave voltammograms with different concentrations (Figure 6) show that the signals increase linearly with amount of ATR. The calibration graph was related to the mean value of six measurements. The regression equation (inset of Figure 6) is y (µA) = 55.923x (nM) + 0.2164. Limit of quantification (LOQ) and limit of detection (LOD) for ATR were obtained as 1.0×10-12 M and 1.5×10-13 M, respectively.

Here Figure 6.

In addition, the prepared electrochemical sensor in this study was compared with the other available sensors in the literature (Table 1). We presented the several advantages of the proposed method: Firstly, the molecular imprinted polymer on QCM chip was developed by


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us11. In the QCM methods, the polymer film breaks on gold chip frequently occur in comparison with GCE. Hence, many imprinted chips are needed in sensor applications 38. In this study, the molecular imprinted electrochemical sensor with high selectivity was prepared. The obtained selectivity is better in comparison with mercury film

39

and bismuth film

40

electrodes. The nanocomposite was prepared by hydrothermal treatment in this study. According to the results, minimal waste formation in preparation of platinum nanoparticles/carbon nitride nanotubes is obtained and the cheaper, eco-friendly and highly efficient nanomaterial was obtained in comparison with multi-walled carbon nanotubes and carbon aerogel

41

. Gas chromatography and solid phase micro extraction methods were

developed for the determination of triazine herbicides in water 42, 43. However, there are many negative situations such as material consumption, complexity and expensiveness in these methods. In addition, the expensive electrodes including troublesome cleaning such as gold were used for formation of molecular imprinting polymer 12, 13. Finally, according to Table 1, MIP/Pt NPs/C3N4 NTs/GCE in this study (LOD: 1.5×10-13 M) shows more sensitivity in comparison with the other analytical methods 44, 45.



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Table 1. Comparison of the prepared sensor in this study with the other analytical methods Material or Method MIP/QCM MIT/CA Mercury film SPME GC/MIP/SPME Mixed-bed SPE/MIP MIP/o-PD MIP/Au MWCNTs/HPLC PZC–BSA SiO2@atrazine-MIP Potentiometric/MIP Biomimetic/MIP RAFT-MIPs BiFE/DPASV MIP/Pt NPs/C3N4 NTs

Linear Range (M) 8.0×10-11 – 1.3×10-9 1.2×10-7 – 9.3×10-7 2.0×10-9 – 2.8×10-7 4.1×10-8– 3.9×10-7 2.3×10-7– 4.1×10-5 2.3×10-8– 9.2×10-7 5.0×10-9 – 1.4×10-7 1.0×10-6 – 1.0×10-5 9.2×10-10 – 4.6×10-7 4.6×10-9 – 9.3×10-5 0 – 1.0×10-4 3.0×10-5 – 1.0×10-3 1.0×10-7 – 1.0×10-2 2.3×10-7 – 2.3×10-5 6.7×10-7 – 2.0×10-5 1.0×10-12 – 1.0×10-10

LOD (M) 2.8×10-11 8.0×10-9 1.0×10-10 1.9×10-7 9.2×10-8 6.2×10-9 1.0×10-9 1.0×10-6 1.0×10-10 1.2×10-10 1.8×10-6 2.0×10-5 5.0×10-7 1.3×10-8 1.4×10-7 1.5×10-13

Reference 11 46 39 43 42 37 13 12 41 38 47 48 45 44 40

This study

MIP: molecularly imprinted polymer, QCM: quartz crystal microbalance, CA: Carbon aerogel, MIT: Molecularly imprinted TiO2, SPME: Solid phase micro extraction, GC: Gas chromatography, SPE: Solid micro extraction, o-PD: o-phenylenediamine, Au: Gold, MWCNTs: Multi-walled carbon nanotubes, HPLC: Highperformance liquid chromatography, PZC: Piezoelectric quartz crystals, BSA: Bovine serum albumin, SiO2: Silicon dioxide, RAFT: Reversible addition–fragmentation transfer, BiFE: Bismuth film electrode, DPASV: Differential pulse adsorptive stripping voltammetry

3.6. Recovery. The United States Environmental Protection Agency states that the maximum contaminant amount of ATR is 1.4×10-8 M in water supplies 49. ATR was found as 0.022×10-9 M in this report (Table 2). The presence of ATR is owing to its accumulation in soil. Hence, ATR goes into surface waters. Nevertheless, it was still lower than the legal limit 49. As seen in Table 2, the values of recovery are very close to 100.00%. According to the results, we can say that the ATR imprinted electrochemical sensor in this report has high selectivity. In addition, to verify the high selectivity, the standard addition technique was applied to the wastewater samples. The obtained equation is y (µA) = 56.179x (nM) + 11.7938. Hence, the effect of interference was not importantly seen in wastewater sample.


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Table 2. The recovery of ATR in wastewater samples (n=7) Sample Added ATR Found ATR

Wastewater

Recovery

(M)

(M)

(%)

-

0.022×10-9

-

0.005×10-9

0.028×10-9

103.70

0.010×10-9

0.031×10-9

96.88

0.050×10-9

0.073×10-9

101.39

3.7. Selectivity, Stability, Repeatability, Reproducibility and Reusability of MIP/Pt NPs/C3N4 NTs. To confirm the selectivity of MIP/Pt NPs/C3N4 NTs/GCE, the other experiment in the presence of SIM, TRZ and PRO was performed (Figure 7A and 7B). ATR imprinted electrochemical sensor was more selective at 3.0, 6.0 and 12.0 times for ATR than SIM, TRZ and PRO, respectively. These results confirmed the standard addition technique and the recovery experiments. The stability of one electrode (MIP/Pt NPs/C3N4 NTs/GCE) was examined. During 50 days, the signal was frequently measured. The mean value is 99.12% of the first signal. The mean value indicates that MIP/Pt NPs/C3N4 NTs/GCE is utilized in long-term. In order to show the repeatability of MIP/Pt NPs/C3N4 NTs/GCE, twenty voltammograms were obtained in the presence of 0.1 nM ATR. According to the obtained voltammograms, MIP/Pt NPs/C3N4 NTs/GCE showed the repeated signals at about 5.8 µA. The reproducibility test was performed with ten different MIP/Pt NPs/C3N4 NTs modified electrodes. These imprinted electrodes were fabricated independently by the same procedure. The value of relative standard deviation is 0.38% for current signal in presence of 0.1 nM ATR. This situation indicates the reliability of the sensor preparation procedure. Finally, the reusability of MIP/Pt NPs/C3N4 NTs/GCE was investigated. MIP/Pt NPs/C3N4 NTs/GCE is not a disposable sensor. It can be used at least 10 times by washing with 0.1 M PBS (pH 7.0). Here Figure 7.



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4. CONCLUSION In this report, ATR imprinted electrochemical sensor based on platinum nanoparticles/carbon nitride nanotubes was prepared and the sensor was applied to wastewater samples. Firstly, platinum

nanoparticles/carbon

nitride

nanotubes

nanocomposite

was

prepared

by

hydrothermal treatment. In this treatment, the minimal waste formation was observed. After that, ATR imprinted electrochemical sensor based on platinum nanoparticles/carbon nitride nanotubes was developed by CV. The linearity range, LOQ and LOD values of proposed sensor were calculated. Finally, the sensor shows high selectivity and sensitivity in wastewater sample in comparison with the other analytical methods. ■ AUTHOR INFORMATION Corresponding Author Tel.: +903266135600; Fax: +903266135613, E-mail: [email protected] Notes The authors declare no competing financial interest. ■ REFERENCES (1)

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Figure Caption

Scheme 1. The preparation of MIP/Pt NPs/C3N4 NTs/GCE



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Scheme 2. Schematic illustration of hydrogen bond interactions between ATR molecules and phenol


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Figure 1. SEM images of (A) g-C3N4; (B) utg-C3N4 nanolayers; (C) C3N4 NTs; (D) TEM image of Pt NPs/C3N4 NTs nanostructure, (E) SEM image of Pt NPs/C3N4 NTs nanostructure, (F) SEM image of MIP/Pt NPs/C3N4 NTs modified surface, (G) SEM image of NIP/Pt NPs/C3N4 NTs modified surface, (H) EDX image of Pt NPs/C3N4 NTs nanostructure



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Figure 2. (A) Narrow region XPS spectra of Pt NPs/C3N4 NTs, (B) XRD patterns of C3N4 NTs and Pt NPs/C3N4 NTs, (C) Deconvolution spectra of the O1s of MIP/Pt NPs/C3N4 NTs nanostructures


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Figure 3. (A) Cyclic voltammograms at (a) bare GCE,

(b) utg-C3N4/GCE,

(c) C3N4

NTs/GCE, (d) Pt NPs/C3N4 NTs/GCE; (B) EIS response at (a) bare GCE, (b) utg-C3N4/GCE, (c) C3N4 NTs/GCE, (d) Pt NPs/C3N4 NTs/GCE. Redox probe: 1.0 mM [Fe(CN)6]3- solution containing 0.1 M KCl, Scan rate: 100 mV s-1



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Figure 4. (A) The polymerization of 100 mM phenol containing 25 nM ATR on Pt NPs/C3N4 NTs/GCE (Scan rate: 50 mV s-1); (B) EIS of (a) MIP/Pt NPs/C3N4 NTs/GCE (with template molecule), (b) MIP/Pt NPs/C3N4 NTs/GCE (removing template), (c) MIP/Pt NPs/C3N4 NTs/GCE (after rebinding of ATR) in 1.0 mM [Fe(CN)6]3-/4- solution containing 0.1 M KCl; (C) SWV curves of different imprinted and non-imprinted electrodes in 0.1 M PBS (pH 7.0) after rebinding of 0.1 nM ATR (a) MIP/Pt NPs/C3N4 NTs/GCE, (b) MIP/C3N4 NTs/GCE, (c) MIP/GCE, (d) NIP/Pt NPs/C3N4 NTs/GCE (frequency of 50 Hz, pulse amplitude of 20 mV, scan increment of 3 mV)


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Figure 5. Effect of (A) pH, (B) mole ratio (ATR/monomer), (C) elution time, (D) scan cycle (in the presence of 0.1 nM ATR)



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Figure 6. SWV curves of MIP/Pt NPs/C3N4 NTs/GCE (from 0.001 nM ATR to 0.1 nM ATR in pH 7.0 of PBS: Inset: The calibration curves of ATR (frequency of 50 Hz, pulse amplitude of 20 mV, scan increment of 3 mV)


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Figure 7. (A) SWV curves of the MIP/Pt NPs/C3N4 NTs/GCE for 0.1 nM ATR, SIM, TRZ and PRO; (B) The values of peak current of 0.1 nM ATR, SIM, TRZ and PRO (frequency of 50 Hz, pulse amplitude of 20 mV, scan increment of 3 mV)



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Electrochemical Detection of Atrazine by Platinum Nanoparticles

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