A Study of Electrocatalytic and Photocatalytic Activity of Cerium

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A Study of Electrocatalytic and Photocatalytic Activity of Cerium Molybdate Nanocubes Decorated Graphene Oxide for the Sensing and Degradation of Antibiotic Drug: Chloramphenicol Karthik Raj, Vinoth Kumar Jeyaraj, Shen-Ming Chen, Chelladurai Karuppiah, Yi-Hui Cheng, and Muthuraj V ACS Appl. Mater. Interfaces, Just Accepted Manuscript • DOI: 10.1021/acsami.6b14242 • Publication Date (Web): 27 Jan 2017 Downloaded from http://pubs.acs.org on January 28, 2017

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ACS Applied Materials & Interfaces

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A Study of Electrocatalytic and Photocatalytic Activity of Cerium Molybdate Nanocubes

2

Decorated Graphene Oxide for the Sensing and Degradation of Antibiotic Drug:

3

Chloramphenicol

4

Raj Karthik1, Jeyaraj Vinoth Kumar2, Shen-Ming Chen1*, Chelladurai Karuppiah3

5

Yi-Hui Cheng1, Velluchamy Muthuraj2*

6

1

7

3, Chung-Hsiao East Road, Taipei 106, Taiwan, ROC.

8

2

Department of Chemistry, VHNSN College, Virudhunagar – 626001, Tamilnadu, India.

9

3

Department of Chemistry, National Taiwan University, No. 1, Sec. 4, Roosevelt Road, Da’an

10

Department of Chemical Engineering, National Taipei University of Technology, No. 1, Section

District, Taipei, Taiwan-10617.

11 12

* Authors for Correspondence

13

E-mail:[email protected], Tel: +886 2270 17147, Fax: +886 2270 25238.

14

E-mail: [email protected], Tel: +919940965228

15 16

1 ACS Paragon Plus Environment


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ABSTRACT

2

In this present work, “killing two birds with one arrow” strategy was performed for the

3

electrochemical trace level detection and photocatalytic degradation of antibiotic drug

4

chloramphenicol (CAP) using Ce(MoO4)2 nanocubes/graphene oxide (CeM/GO) composite for

5

the first time. The CeM/GO composite was synthesized via simple hydrothermal treatment

6

followed by sonication process. The successful formation of CeM/GO composite was confirmed

7

by several analytical and spectroscopic techniques. The CeM/GO composite modified GCE

8

showed excellent electrocatalytic activity towards the reduction of CAP in terms of decrease the

9

potential and increase the cathodic peak current in comparison with different modified and

10

unmodified electrodes. The electrocatalytic reduction of CAP based on the CeM/GO modified

11

GCE exhibited high selectivity, wide linear ranges, lower detection limit and good sensitivity of

12

0.012-20 & 26-272 µM, 2 nM and 1.8085 µAµM-1 cm-2, respectively. Besides, CeM/GO/GCE

13

was used to analyze the CAP in real samples such as honey and milk, the satisfactory recovery

14

results were obtained. On the other hand, the CeM/GO composite played excellent catalyst

15

towards the photodegradation of CAP. The obtained results from the UV-Vis spectroscopy

16

clearly suggested that CeM/GO composite had high photocatalytic activity compared than

17

pristine Ce(MoO4)2 nanocubes. The degradation efficiency of CeM/GO toward CAP is observed

18

about 99% within 50 min under visible irradiation and it shows a good stability by observing the

19

reusability of the catalyst. The enhanced photocatalytic performance was attributed to the

20

increased migration efficiency of photo-induced electrons and holes.

21 22

Keywords: Cerium Molybdate, Graphene oxide, Antibiotics, Chloramphenicol,

23

Electrochemistry, Photodegradation


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1. INTRODUCTION

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Antibiotics are the significant drug in the global medicine market that have been used for

3

the treatment of bacterial disease and other microbes in the 20th century. Unfortunately, the

4

universal need for these antibiotic drugs, specifically antibacterial resistance or antibacterial

5

agents produces some important negative impact on human beings as well as in soil and water

6

sources. Therefore, numerous analytical methods have been developed to scrutinize the presence

7

of antibiotics in the environment, human and pharmaceutical formulations1. A number of

8

significant antibiotics generally occur and/or made from living organisms such as

9

chloramphenicol (CAP), macrolides, benzyl penicillin, tetracyclines and streptomycin2-4. Among

10

them, CAP is a valuable broad-spectrum antimicrobial agent (resistance) and it was naturally

11

derived from the streptomy cesvenezuelae bacterium. CAP has been widely used in treatment

12

against the infection of various types of microorganism as well as fungi, bacteria and tetracycline

13

resistant viberio cholera or vancomycin resistant enterococcus 5,6. Predominantly, CAP is used in

14

food-producing animals, superficial eye infection, veterinary medicine, domestic poultry and

15

aqua-agriculture farming

16

effects to human such as neurotoxic reactions (mental confusion, headache and mild depression),

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hypersensitivity reactions (typhoid fever, angioedema, vesicular and macular rashes), gray baby

18

syndrome (cyanosis and hypotension), leukemia (cancer of bone marrow or blood), bone marrow

19

suppression (mitochondria) and aplasmatic anemia 9. To contain these extreme side effects, the

20

CAP has been banned in many countries such as USA, European Union, China and Switzerland

21

for in agriculture and food animal production 10. However, it is yet being used in some countries

22

and a minimum amount of CAP usage (0.3 µg Kg-1 set by the European Union) was strongly

23

regulated for all food-producing materials in animals. Therefore, the analytical chemists have

7, 8

. However, the widespread usage of CAP can cause significant side



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taken the challenge to develop a methodology for the accurate determination of CAP. There are

2

several analytical techniques available for the determination of CAP; among these,

3

electrochemical techniques are preferred due to its simplicity, rapid response, excellent

4

selectivity, low cost, reliability and offer excellent sensitivity 11, 12. On the other hand, the long-

5

term release of CAP into the environment through improper disposal treatment from

6

manufacturing industries or hospitals, human and animal feces causes chronic toxicity to

7

bacteria, microorganism and aquatic vertebrates

8

aquatic and soil environment is another major concern. Several traditional methods including

9

adsorption, coagulation, sonolysis and ozonation have been used to remove CAP from the

10

pharmaceutical waste water. Instead of these, photocatalysis is a green approach and low-cost

11

method as well as powerful technique to remove CAP from the environment

12

structure and IUPAC name of the CAP as depicted in Fig.S1.

13, 14

. Hence, the removal of CAP from the

15

.The chemical

13

As an essential material, transition metal-based molybdates (M = Zn, Mn, Mg, Sr, Ba, Ni,

14

Co, Pb, Ca, Cd, Cu etc.,) have been established and significantly applied in diverse fields such as

15

photocatalyst, catalyst, illumination, optical fibers, lasers, scintillation crystal, phytoremediation,

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Li-ion storage batteries, magnetic properties, supercapacitors, photoluminescence and humidity

17

sensor 16–30. In recent times, several metal molybdates with different size and morphologies have

18

been reported including flower-like mesocrystal, superstructures, nanowires, nanoplates, nest-

19

like nanostructures, thin film, nanorods, dendrites, doughnut-shaped microstructures, and

20

nanopowders, and so on

21

because of their feasible application in thermal expansion materials, phosphors and catalysts 36.

22

In specific, cerium molybdate (Ce(MoO4)2) is a significant family of an inorganic material and it

23

has a huge attraction to the researchers owing to their unique properties including high

26, 31–35

. However, the rare earth molybdates are extremely significant


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photostability, good catalytic-convertor and corrosion inhibitor. Due to these properties,

2

Ce(MoO4)2 is widely used in many important applications particularly in the field of catalysis 37,

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corrosion industry for suppressing the corrosion of aluminum alloys in a corrosive environment

4

38

5

(GO) has been considered as an excellent platform for the preparation of nanocomposite due to

6

its attractive properties including effective surface area, unique structures, mechanical and

7

thermal stability, outstanding charge-transfer characteristics as well as its enhancing of

8

electrocatalytic and photocatalytic activity could be the results of GO properties. Moreover, the

9

oxygen functionalities of GO is more responsible for the incorporation of metal and metal based

, plastics and ceramics and inorganic pigments in paints 39. On the other hand, graphene oxide

40

10

materials by the electrostatic attraction

. For that aforementioned unique properties, GO has

11

been used in many important applications such as sensor, supercapacitors, nanoelectronics,

12

nanomaterials, catalysis and nanophotonics. Hence, we have chosen GO as a supporting matrix

13

which decorated with Ce(MoO4)2 nanocubes and used for the electrochemical detection as well

14

as photocatalytic degradation of CAP for the first time. Because, GO has an excellent electric

15

conductivity and high specific surface area and it has been widely used as an essential supporting

16

materials in composite preparation to achieve an efficient catalytic activity.

17

In the present study, surfactant free CeM nanocubes was prepared via a simple

18

hydrothermal route and as well, CeM/GO composites were synthesized by simple sonication

19

method. As-formed CeM and CeM/GO composite were investigated by different spectroscopic

20

and analytical techniques and further evaluated for electrochemical sensing and photocatalytic

21

degradation of CAP. Interestingly, we found that the as-prepared CeM/GO composite exhibited a

22

highly active catalyst for the electrochemical determination of CAP, similar to its photocatalytic



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degradation of CAP antibiotic from the environmental samples that were briefly investigated

2

with high degradation rate.

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2. EXPERIMENTAL SECTION

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2.1. Materials Ammonium

5

cerium

nitrate

(Ce(NH4)2(NO3)6),

ammonium

molybdate

6

((NH4)6Mo7O24.4H2O), commercial TiO2, raw graphite (average diameter about >20 mm) and

7

chloramphenicol were obtained from Sigma-Aldrich. Other biological substances, common

8

metal ions and other chemicals were purchased from Sigma-Aldrich and Alfa Aesar, Taipei,

9

Taiwan and which are used without further purification. The supporting electrolyte utilized for

10

all experiments were prepared by using 0.05 M Na2HPO4 and NaH2PO4 solutions. All other

11

chemicals were of analytical grade and the required solutions were prepared with de-ionized

12

water.

13

2.2. Synthesis of CeM nanocubes

14

In

a

typical

synthesis,

5

mmol

of

(Ce(NH4)2(NO3)6)

and

5

mmol

of

15

((NH4)6Mo7O24.4H2O) were dissolved in 30 mL of distilled water separately and stirred to obtain

16

a homogeneous solution. Then, the solution ((NH4)6Mo7O24.4H2O) was slowly added to the

17

(Ce(NH4)2(NO3)6) solution with constant stirring and the mixture was kept stirred for 1 h.

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Subsequently, the resulting mixture was transferred into Teflon-lined sealed stainless steel

19

autoclave and treated at 160 °C for 5 h and then the autoclave was cooled down the room

20

temperature. The obtained light yellow products were washed with water and ethanol, and then

21

dried at 80 °C for 12 h. Finally, the dried products were calcined at 500 °C for 2 h.

22

2.3. Synthesis of GO and CeM/GO composite


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The GO was synthesized by the modified Hummer’s method as reported previously

41

.

2

The GO (5 mg/mL) was dispersed in 200 mL of de-ionized water and ultrasonicated for 30 min.

3

Then, 0.5 g of as-prepared CeM was added into the suspended GO solution and the mixture was

4

again ultrasonicated for an hour. Sequentially, the mixture was allowed to settle down and

5

removed the decanted solution. The collected residue was dried at room temperature and

6

designated as CeM/GO composite. Afterward, the CeM/GO composite was further used as the

7

electro- and photo-catalyst in this study. The overall synthesis process and applications was

8

schematically represented in Fig.1.

9 10

Fig.1. The synthesis route for CeM, CeM/GO composite and its application for electrochemical

11

sensor and photocatalytic activity.

12

2.4. Characterization

13

The X-ray diffraction patterns of the composite were analyzed in a XRD, XPERT-PRO

14

spectrometer (PANalytical B.V., The Netherlands) with Cu Kα radiation (λ = 1.5406 Å) and the

15

FTIR spectra were collected by using a Thermo Nicolet Nexus 670 spectrometer in the range of 7 ACS Paragon Plus Environment


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4000–400 cm–1. Raman spectroscopy was performed using an HR-800 (JobinYvon-Horiba,

2

France) spectrometer integrated with a confocal microscope. Scanning electron microscope

3

(SEM) and Energy dispersive X-ray (EDX) spectral studies have been done by using Hitachi S-

4

3000 H scanning electron microscope (SEM Tech Solutions, USA) and HORIBA EMAX X-

5

ACT, respectively. The X-ray photoelectron spectroscopy (XPS) spectrum was recorded using a

6

PHI 5000 Versa Probe instrument. UV-Visible diffused reflectance (DRS) spectrum of the

7

products was analyzed by using Shimadzu UV-2600 spectrophotometer and BaSO4 was used as

8

a reflectance reference material. The absorption spectra in the photocatalytic degradation process

9

were conducted by Shimadzu 2100 UV-Visible spectrometer. Total organic carbon (TOC) was

10

analyzed by Shimadzu TOC-L analyzer. The electrochemical measurements (cyclic voltammetry

11

and amperometric (i-t)) were carried out by using CHI 405a electrochemical work station and

12

analytical rotator AFMSRX (PINE instrument, USA), respectively. All the electrochemical

13

measurements were carried out using a three conventional electrode cell system with GCE as a

14

working electrode (working area with = 0.071 cm2), Ag/AgCl as a reference electrode and Pt

15

wire as a counter electrode.

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2.5. Fabrication of modified electrode

17

Before CeM/GO composite modification on the GCE, the GCE was well polished with

18

0.05 µM alumina slurry. Then, 5 mg/mL of the as-prepared composite was redispersed in DI

19

water. Afterward, about 8 µL (optimized concentration) of CeM/GO composite was drop casted

20

on the mirror polished GCE after that, it was allowed to dry at room temperature. The obtained

21

CeM/ GO/GCE were used for the further electrochemical measurements.

22

2.6. Photocatalytic experiments


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The photocatalytic performances of the as-synthesized products were performed towards

2

the degradation of CAP aqueous solution under visible light irradiation. In a typical experiment,

3

50 mg of the catalysts were dispersed in 100 mL of CAP solution (20 mg/L, solution pH= 5) in

4

the dark and stirred for 1 h to reach adsorption-desorption equilibrium of the working solution.

5

Then, the suspension was irradiated under visible light, A 500 W tungsten lamp equipped with a

6

UV cut-off filter (λ > 400 nm) was used as the visible light source. At certain time intervals, 5

7

mL of aliquot was collected and the change in concentration of CAP was measured by UV-Vis

8

spectrophotometer. The photocatalytic degradation rate was evaluated using C/Co, where C-

9

major absorption peak intensity of the CAP aqueous solution and Co- initial absorption intensity

10

of the CAP aqueous solution. In reusability test, the photocatalyst was collected after the

11

photodegradation experiments by centrifugation and washed with alcohol and dried.

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3. RESULT AND DISCUSSION

13

3.1. Characterization of CeM/GO composite

14

The functional groups present in the composite materials were identified by using FTIR

15

analysis. Fig.2A shows the FTIR spectra of the as-synthesized CeM, GO and CeM/GO

16

composite. The broad absorption bands in the range of 620-910 cm-1 were attributed to the Mo-

17

O-Mo symmetric stretching vibrations of Ce(MoO4)2 42 (curve a), which reveals the absence of

18

hydroxyl and organic matters. The FTIR spectra of GO (curve b) depicts the peaks at 1048,

19

1220, 1404, 1624, 1729 and 3393 cm-1. The peaks at 3393 and 1404 cm-1are related to the O-H

20

stretching and deformation vibrations, respectively. The skeletal vibrations of non-oxidized

21

graphitic domains represent the peak at 1624 cm-1. The bands at 1729, 1220 and 1048 cm-1 were

22

ascribed to the C=O, C-OH and C-O stretching vibrations, respectively, which clearly confirms

23

the successful oxidation of graphite 43. The CeM/GO composite (curve c) shows the presence of



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Fig.2. (A) FTIR (B) XRD and (C) Raman spectra and (D) XPS survey spectrum of as

3

synthesized CeM/GO composite

4

both absorption bands correspond to the CeM and GO, which reveals the formation of strong

5

bonding between the CeM and GO sheets in the CeM/GO composite.

6

The crystalline quality and phase structure of CeM, GO and CeM/GO were determined

7

by X-ray diffraction analysis (XRD), as depicted in Fig.2B. The distinctive major diffraction

8

peak was observed in the 2θ range at 28.60°, 34.19°, 46.97°, 49.10°, 54.01° and 57.92° which

9

correspond to the (112), (200), (204), (220), (116) and (303) crystallographic planes of tetragonal

10

phase CeM and these results are good agreement with the Joint Committee on Powder


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1

Diffraction Standards data [JCPDS No. 330330]. No other extra peaks related to the CeO2 or

2

MoO3 were observed which indicated the high purity of as-synthesized Ce(MoO4)2. For pure

3

GO, an abrupt peak at 11.5° attributed to the (001) plane with an interlayer spacing of 8.02Å.

4

The diffraction peaks of CeM/GO composite can be comfortably indexed to the (112), (200),

5

(204), (220), (116) and (303) planes of CeM and the very low intense (001) plane of GO,

6

indicates the successful construction of composite.

7

Raman spectroscopy is an important diagnostic tool to analyze the structure and quality

8

of the carbonaceous material and it is considered a direct and non-destructive technique. The

9

Raman spectrum of pure CeM/GO composite, which is presented in Fig.2C, shows the bands at

10

190, 333 and 786 cm-1 attributed to the Mo-O-Mo deformation, Mo=O bending and Mo-O-Mo

11

asymmetric stretching vibrations respectively 44. The two distinctive peaks at 1253 and 1511 cm-

12

1

13

band) and E2g phonons of carbon sp2 domains (G band) of GO, respectively

14

results confirm the successful formation of CeM/GO composite.

were observed which correspond to the k-point phonons breathing mode of A1g symmetry (D 45

. The observed

15

Furthermore, the existence of elements and their oxidation states of the materials were

16

accurately investigated by X-ray photoelectron spectroscopy (XPS) and the spectrum was

17

presented in Fig.2D and Fig.3. The XPS survey spectra of CeM/GO composite demonstrates the

18

corresponding the signals of molybdenum, carbon, oxygen, and cerium, which confirms the

19

formation CeM/GO composite and well agreed with EDX analysis which is described in the

20

prospective section. Fig.3 (A-D) displays the high-magnification XPS spectra of Ce 3d, Mo 3d,

21

O 1s and C 1s, respectively. From the Fig.3A, the distinctive peaks centered at 898.4 and 917.3

22

eV ascribed to the binding energies of Ce 3d5/2 and Ce 3d3/2, illustrating that Ce is in Ce4+ state 46.

23

In the enlarged view of Mo 3d core level spectrum in Fig.3B, the peaks were obtained at 232.2



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and 235.1 eV which belongs to the Mo 3d5/2 and Mo 3d3/2 spin-orbit splitting of Mo6+ state

2

The strong intense peak at 530.8 eV can be considered as the characteristic peak of O 1s (Fig.3C)

3

in CeM/GO composite and its Gaussian deconvolution peaks at the binding energies of 529.2

4

and 530.3 eV is due to the presence of lattice oxygen into the CeM/GO composites. In addition,

5

the peaks at 531.5 and 532.4 eV are attributed to the presence of chemisorbed oxygen or

6

hydroxyl groups and adsorbed water molecule on the surface of the CeM/GO composite

7

Fig.3D shows the high-resolution C 1s XPS spectrum can be deconvoluted into the three main

8

peaks at 285.6 and 288.2 eV which were attributed to C-C, C-O (hydroxyl carbon) and O-C=O

9

(carboxyl carbon) groups, respectively 49. The obtained binding energy values for each element

10

proves the successful formation of CeM/GO composite and it is in good agreement with the

11

FTIR, XRD and Raman studies.


47

48

.

.

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1 2

Fig.3. (A) High-resolution XPS spectra of (A) Ce 3d, (B) Mo 3d, (C) O 1s and (D) C 1s.

3

The surface morphology of the as-synthesized CeM, GO and CeM/GO composites were

4

examined using scanning electron microscopy (SEM), as shown in Fig.4. The SEM micrograph

5

of pure CeM (Fig.4A) displays the formation of cube-like structure and furthermore the cubes

6

are arranged to get together with clean and smooth surfaces. Fig.4A inset shows the enlarged

7

view of the cube-like structure of CeM and its corresponding EDX spectra is shown in Fig.4E

8

which portrayed the presence of Ce, Mo and O elements without any other impurities. In

9

addition, the flat and wrinkled bundle sheets-like morphology was observed for GO (Fig.4B).



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1

The SEM images of CeM/GO composite (Fig.4C&D) illustrates the nanocube-like structure of

2

CeM still retained with slight aggregation and randomly embedded on the surface of GO sheets,

3

which is favorable for the electronic interaction between CeM nanocubes and GO sheets. The

4

corresponding EDX spectrum shows the presence of Ce, Mo, O and C which further confirmed

5

the formation of CeM/GO composite elements (Fig.4F). Furthermore, the data on the elemental

6

mapping of the CeM/GO composite are provided in Fig. S2. This elemental mapping further

7

proves the presence of CeM and GO in the nanocomposite.

8

Fig.5. portrays the UV-Vis spectrum of CeM and CeM/GO composite. In comparison

9

with CeM, the CeM/GO composite increases the intensity of absorption as well as the red shift

10

was observed in the visible region (Fig.5A). The red shift primarily caused by the charge transfer

11

transition between CeM and GO. The bandgap value was determined by applying Tauc’s

12

equation, as shown in Fig 5B. The band gap of CeM and CeM/GO was determined to be 2.52

13

and 2.47 eV, respectively, which proposed that CeM/GO composite had broad visible-light

14

absorption capability that encourages the photodegradation efficiency.

15


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1 2

Fig.4. SEM micrographs of (A) CeM (B) GO (C&D) CeM/GO composite and (E & F)

3

corresponding EDX spectra of A and C.

4



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1 2

Fig.5. (A) UV-Vis diffuse reflectance spectra (DRS) and (B) Energy gap spectra of pristine CeM

3

and CeM/GO composite.

4

3.2. Electrochemical behavior of CAP

5

The electrochemical performance of CAP on various modified and unmodified GCE was

6

investigated using cyclic voltammetry (CV). Fig.6. reveals the electrochemical performance of

7

CAP on bare GCE, CeM/GCE, GO/GCE and CeM/GO/GCE in 0.05M phosphate buffer (PB)

8

solution containing absence (Fig.6A) and presence (Fig.6B) of 200 µM CAP at a scan rate 50

9

mVs-1. The CeM/GO modified GCE shows high capacitive current than the other modified GCE

10

indicates the large specific surface area of the composite. On the other hand, as seen in Fig.6B,

11 16 ACS Paragon Plus Environment

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1

Fig.6. (A) The CVs of bare GCE, CeM/GCE, GO/GCE and CeM/GO/GCE in 0.05 M PB

2

solution in the absence and (B) presence of 200 µM CAP at a scan rate 50 mVs-1.

3

the electrocatalytic reduction of CAP on CeM/GO/GCE was observed in the presence of 200 µM

4

CAP containing PB solution. A well-defined irreversible cathodic peak (R1) is obtained at the

5

potential of -0.53 V, which is attributed to the direct reduction of CAP (scheme 1a) to

6

phenylhydroxylamine (scheme 1b) with four electrons and four proton transfer process

7

Furthermore, two more peaks are obtained during the reverse scan and it is designated as O1 (-

8

0.02 V) and R2 (-0.04 V). The O1 and R2 peaks are the reversible redox couple of hydroxyl

9

group to nitroso derivative (scheme 1c) with two electron and two proton transfer process. The

10

overall electrochemical reduction mechanism of CAP can be described as scheme 1. The peak

11

current of O1 and R2 is lower than R1, which suggests that the CAP reduction at CeM/GO/GCE

12

is more favored to form arylhydroxylamine in neutral or more alkaline medium. Furthermore, the

13

higher cathodic peak current was observed at CeM/GO/GCE, which is 5.3-fold, 3-fold and 2-fold

14

higher than the bare GCE, CeM and GO modified GCE, respectively. Besides, the cathodic peak

15

potential of CAP on CeM/GO/GCE is lower when compared to aforementioned modified

16

electrodes. This result confirms that the effective catalytic behavior of CeM/GO composite

17

which is due to the strong interaction of CAP with GO and more active sites of the CeM 51.


50

.


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Page 18 of 39

1 2

Scheme1 Electrochemical reduction mechanism of CAP.

3

3.3. Effect of scan rate and pH

4

The impact of scan rate on CeM/GO modified GCE toward CAP reduction was studied

5

by CV in 0.05 M PB solution containing 200 µM of CAP by changing the different sweeping

6

rates from 20 to 260 mVs-1 (Fig. 7A, curve a to m). The cathodic peak current of the CAP was

7

increased when increasing the scan rate and the cathodic peak potential was shifted to the more

8

negative potential side. This relocated potential was influenced by the size of the diffusion layer

9

which depends on the scan rate. At lower scan rates, the thickness of the diffusion layer is high

10

and it has been grown much further from the electrode surface. In contrast, the thickness of

11

diffusion layer is considerably low at high scan rates. As a result, the altering flux is drastically

12

lower at the electrode surface when sweeping the potential at lower scan rates, hence, the peak

13

potential was shifted. As well, the cathodic peak current (Ipc, R1) of CAP was plotted against the


Page 19 of 39

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1

scan rate and it can be seen in Fig.7B. The obtained plot suggested that the CAP reduction

2

showed a good linearity in scan rate vs. cathodic peak current with linear regression equation of

3

Ipc (µA) = -0.37 ν (mVs-1) - 48.06 (µA) and the correlation coefficient of R2 = 0.997. This result

4

confirms that the electrocatalytic reduction of CAP at CeM/GO/GCE is an adsorption controlled

5

process.

6 7

Fig.7. (A) CVs of 200 µM CAP at CeM/GO/GCE with different scan rates (20 -260 mVs-1; a-m)

8

in 0.05 M PB solution (pH 7.0). (B) The plots of peak current vs. scan rate. (C) The CV

9

responses of the reduction of CAP at CeM/GO/GCE in various pHs ranging from 3.0 to 11.0. (D)

10

Plot of peak current vs. pH, (E) Plot of peak potential (Epc) vs. pH. 19 ACS Paragon Plus Environment


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Page 20 of 39

1

The pH of the electrolyte significantly influenced the electrochemical behavior of CAP.

2

Thus, the reduction of CAP was examined by CV in the various pH (pH = 3.0 to 11.0) solutions

3

containing 200 µM CAP at a scan rate of 50 mVs-1 (Fig.7C). The maximum cathodic peak

4

current (Ipc, R1) was observed only at pH 7.0 (Fig.7D), whereas the peak current was decreased

5

when increasing or decreasing the pH

6

electrochemical measurements. Moreover, the cathodic peak potential (Epc, R1) was shifted to

7

more negative potential when increasing the pH from 3.0 to 11.0. The cathodic peak potential

8

was plotted against the pH (Fig.7E) with the linear regression equation of Epc (V) = -0.03 pH –

9

0.31; R2 = 0.996. The slope value, 30 mV/pH, indicates the one proton and two electrons are

10

transferred onto the electrode surface 66.

11

3.4. Determination of CAP

52

. Hence, the pH 7.0 was chosen for the further

12

Under the optimized condition of CV, to estimate the electrochemical detection of CAP,

13

the CeM/GO modified rotating disc glassy carbon electrode (RDGCE) was performed by

14

amperometric (i-t) technique. Fig.8A reveals the amperometric current response of CAP

15

reduction on CeM/GO/GCE at an applied potential of -0.53 V and the rotation speed of 1200

16

rpm with the successive addition of various concentrations (0.002 – 272 µM) of CAP into the

17

continuous stirring 0.05 M PB solution (pH 7.0). The inset (Fig.8A) shows the enlarged view of

18

i-t response for CAP reduction in low concentrations of CAP. It confirms that the stepwise

19

increasing current has good agreement with CAP addition and it reaches a steady state current

20

within 2 s. As a result, two linear ranges were observed from this CAP electrocatalysis, first

21

linear ranges (lower concentrations) is 0.012 – 20 µM with linear regression equation of I (µA) =

22

0.36 [CAP]/µM +2.12; correlation coefficient R2 = 0.9951 (Fig.8B). However, at higher

23

concentrations, the second linear range was obtained in the range of 26 – 272 µM with linear


Page 21 of 39

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1

regression equation of I (µA) = 0.12 µM + 6.87; correlation coefficient R2 = 0.9992. From the

2

lower concentration linear range, the limit of detection (LOD) was calculated to be 2 nM. The

3

sensitivity of the CeM/GO modified RDGCE was calculated about 1.8085 µA µM-1 cm-2.

4

Interestingly, we achieved a very low LOD, wide linear range and good sensitivity for the

5

detection of CAP that are more comparable with previously reported modified electrodes, as

6

listed in Table 1.

7 8

Fig.8 (A) Amperometric i-t responses obtained for CAP at CeM/GO/RDGCE with the

9

consecutive addition of different concentrations of CAP from 0.002 to 272 µM in 0.05 M PB

10

(pH 7.0), and the inset illustrates the enlarged view of the nM detection of CAP. (B) The

11

calibration plot of the linear range for the steady-state current against the concentration of CAP. 21 ACS Paragon Plus Environment


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1

(C) Amperometric i-t responses for CAP at CeM/GO/RDGCE with successive additions of 50

2

µM CAP (a) 100 fold excess of common metal ions Ca2+ (b), Zn2+ (c), Cu2+ (d), Fe2+ (e), Ni2+ (f),

3

Na+ (g), Co2+ (h), No3- (i), I- (j), Br- (k), Cl- (l), 100 fold excess of UA (m), AA (n), DA (o),

4

glucose (p), 20 fold excess of nitro-aromatic substances 4 AP (q), 4 ACP (r), 4 NB (s), 4 NP (t)

5

and 4 NA (u). (D) Steady-state response observed at CeM/GO/RDGCE CAP sensors for the

6

addition of 50 µM CAP in 0.05 M PB (pH 7.0) up to 2500 s; Applied potential = -0.53 V;

7

Rotation speed = 1200 rpm.

8

3.5. Selectivity, stability, repeatability and reproducibility

9

The selectivity is very important for the electrochemical sensor and biosensor application.

10

In order to study the selectivity of CAP on CeM/GO/RDGCE, a number of possible interfering

11

substances such as common metal ions, biologically co interfering compounds and nitroaromatic

12

derivatives were investigated. Fig.8C reveals the amperometric (i-t) current response of CAP

13

reduction in 0.05 M PB solution containing 50 µM of (a) CAP with 100-fold concentration of

14

common metal ions such as (b) Ca2+, (c) Zn2+, (d) Cu2+, (e) Fe2+, (f) Ni2+, (g) Na+, (h) Co2+, (i)

15

NO3-, (j) I-, (k) Br-, (l) Cl- which does not affect the CAP signal. Although, 100-fold excess

16

concentration of biologically co-interfering substances such as (m) uric acid (UA), (n) ascorbic

17

acid (AA), (o) dopamine (DA) and (p) glucose were added into the same solution, resulting no

18

such interfering effect was observed. Moreover, the interference effect was also examined using

19

20-fold of nitro-aromatic and phenolic substances such as (q) 4-aminophenol (4-AP), (r) 4-

20

acetaminophen (4-ACP), (s) 4-nitrobenzene (4-NB), (t) 4-nitrophenol (4-NP) and (u) 4-

21

nitroaniline (4-NA). Notably, a little current response was observed while adding nitrobenzene

22

and nitrophenol due to the identical functional group. Besides, the CAP detection was studied

23

with other existing antibiotics including (v) ofloxacin, (w) thiamphenicol, (x) norfloxacin, (y)

24

ciprofloxacin, (z) amoxicillin and (a’) metronidazole (Fig.S3). These antibiotics do not affect the


Page 23 of 39

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1

CAP reduction signal. Hence, the obtained results are suggesting the good selectivity of

2

CeM/GO/RDGCE towards CAP.

3

The stability of CeM/GO/RDGCE (Fig.8D) was investigated by the amperometric (i-t)

4

technique towards CAP in the presence of 50 µM CAP. The current response of CAP reduction

5

was recorded over a long operational period of 2500 s which is retained about 92.7 % of its

6

original current. This study confirms the operational stability of the CeM/GO composite.

7

Furthermore, the CeM/GO composite was fabricated on GCE and monitored the CAP reduction

8

response for 3 weeks. The as-fabricated sensor achieved 94.3% of efficiency towards the

9

detection of CAP, reveals the excellent long term stability. Besides, to study the reliability and

10

reproducibility, the reliability was observed for 10 consecutive measurements in the presence of

11

50 µM CAP with relative standard deviation (RSD) of 3.2% suggesting an acceptable reliability

12

of the CeM/GO modified electrode. In addition, we have chosen three independent CeM/GO

13

modified electrodes for the determination of CAP with RSD of 2.8% which displayed a good

14

reproducibility.

15

3.6. Determination of CAP in honey and milk samples

16

To evaluate the practical feasibility of the electrochemical sensor, the determination of

17

CAP was examined in honey and milk samples. The honey and milk samples were purchased

18

from the local market in Taipei, Taiwan. The samples were prepared by the appropriate dilution

19

with distilled water and spiked with the known amount of CAP. The same experimental

20

condition (from section 3.4) was used to determine the CAP in real samples. The amperometric

21

response of the CAP determination was given in Fig.S4. The recovery results for the real sample

22

analysis was calculated using standard addition method. The obtained results are summarized in

23

Table S1 and the recoveries are observed from 97.3 to 103.7 %. The noteworthy recoveries were



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Page 24 of 39

1

achieved in honey and milk samples for the determination of CAP, which reveals the CeM/GO

2

modified composite had good practical ability in the real sample analysis.

3

3.7. Photocatalytic activity

4

The photocatalytic performance of CeM nanocubes and CeM/GO composites was

5

assessed for the photodegradation of CAP drug under visible light irradiation. The photocatalytic

6

degradation of CAP was monitored by examining the major absorption peak in the UV-vis

7

spectra at 278 nm. From Fig.9A, CeM/GO nanocomposite were used as a photocatalyst, it was

8

clearly observed that the intensity of the major absorption peak gradually decreased almost equal

9

to zero within 50 min of visible light irradiation in the presence of CeM/GO nanocomposites.

10

The results showed that the 99% of the CAP solution was degraded which is significantly higher

11

compared to that of CeM nanocubes (65 %) and pristine GO (38 %) as illustrated in Fig.9B and

12

9C respectively. The significant enhancement in the photocatalytic efficacy indicated that the

13

GO plays an essential role in the degradation of CAP. The higher photodegradation efficiency of

14

CeM/GO composite is mainly due to the GO which act as an electron acceptor and transfer

15

channel to help the separation and migration of photogenerated electrons

16

significant peaks observed in the spectrum which suggested that CeM/GO nanocomposite did not

17

alter the photodegradation reaction pathway of CAP solution 60.

58, 59

. There were no

18

For comparison, direct photolysis of CAP was evaluated under the same identical

19

conditions in the absence of photocatalyst and the absence of light. It was found that CAP

20

degradation was trifling in the absence of photocatalyst under visible light irradiation as well as

21

in the absence of light. Fig.9C presents CeM/GO composite showing higher photocatalytic

22

performance towards the degradation of CAP solution than the parent CeM nanocubes, GO and

23

commercial TiO2 under the visible light irradiation.


Page 25 of 39

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1 2

Fig.9. (A) Absorption spectrum of CAP in the presence of 50 mg CeM/GO composite and (B)

3

pristine Ce(MoO4)2 under visible light illumination, (C) Photodegradation of CAP in the

4

presence of different catalysts, (D) Effect of different amount of catalyst dosage on the

5

photodegradation of CAP.

6

The suitable amount of catalyst dosage is an important parameter that is significantly

7

influences the rate of photodegradation efficiency. The amount of CeM/GO photocatalyst dosage

8

was varied from 10 to 125 mg/mL for the degradation of CAP solution and the other reaction

9

parameters were kept constant (concentration of CAP solution and light source and pH=5) as

10

shown in Fig.9D. It is obvious that the rate of photocatalytic degradation increased while the 25 ACS Paragon Plus Environment


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Page 26 of 39

1

amount of photocatalyst increased from 10 to 50 mg/mL. Upon increasing the amount of

2

photocatalyst, the generation of number of photons adsorbed on the surface of the photocatalyst

3

was increased. However, the rate of photocatalytic degradation decreased over the 50 mg/mL of

4

the photocatalyst dosage, which might be due to the accumulation of photocatalyst that hindered

5

the light penetration into the photocatalyst. Moreover, due to the over usage of photocatalyst, the

6

accumulated particles are leading to form as an aggregated particles. Hence, 50 mg/mL of the

7

photocatalyst is a suitable amount for the proficient photodegradation of CAP solution.

8

The effect of initial concentration of CAP solution on the photodegradation rate was

9

investigated by various concentration of CAP from 15 to 30 mg/L under the same identical

10

conditions and the results are displayed in Fig.10A. The photodegradation rate was decreased

11

with increasing the concentration of CAP solution. In the present study, the CeM/GO showed 99

12

% photodegradation against 20 mg/L concentration of CAP solution and over the 20 mg/L, the

13

degradation efficiency was decreased. However, at higher CAP concentration, more quantity of

14

organic molecules that present in the CAP solution is adsorbed on the surface of CeM/GO

15

photocatalyst. Therefore, most of the light intensity is hindered by the CAP solution and fewer

16

photons are able to arrive at the CeM/GO surface. As a result, the generation of electron-hole

17

pairs highly reduced which causes the poor degradation performance imputable to the lack of

18

oxidizing species.

19

The effect of pH is another significant factor for the photodegradation of CAP because

20

the pharmaceutical waste water could be acidic or basic nature. Therefore, we carried out a series

21

of experiments under different pH values from 3 to 11 (3, 5, 7, 9 and 11) and the results are

22

display in Fig.10B. The initial pH of the CAP solution were controlled by using 0.1 M HCl (for

23

acidic) and KOH (for basic). As from the Fig.10B, we observed that the highest degradation


Page 27 of 39

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1

efficiency was obtained at lower acidic medium (pH=3). Because, at lower pH condition, the

2

surface of the photocatalyst becomes highly protonated and more positive

3

initial solution pH value led to remarkable decrease in photocatalytic degradation efficiency. At

4

higher solution pH, the surface of the photocatalyst becomes more negative, which could inhibit

5

further reactions

6

the photodegradation of CAP 63, 64. Thus, acidic conditions were more favorable for the removal

7

of CAP than neutral and alkaline conditions.

62

61

. The increasing

. The result was similar to the previous reports showing that low pH favored

8

In order to identify the involvement of primary active species for the degradation of CAP

9

solution, we performed the control experiments with the addition of scavengers for electrons (e-),

10

holes (h+), superoxide radicals (O2˙-) and hydroxyl radicals (•OH)

65

11

potassium persulfate (K2S2O8), ammonium oxalate (AO), acryl amide (AA) and tert-butanol (t-

12

BuOH) were used as a scavenger for e-, h+, O2 and OH• radicals. As presented in Fig.10 C, the

13

efficiency of photodegradation achieved about 99% for the absence of scavengers. Whereas, a

14

little changes were observed on the degradation rate while using the scavengers. The rate of

15

photodegradation was suppressed when using the AA as the singlet oxygen quencher, which

16

indicates the active involvement of O2˙-. The •OH radical scavenger, t-BuOH generally decrease

17

the rate of the photocatalytic reaction, mainly proceeded by the •OH. In the present study, it was

18

observed that the huge decrement in the photocatalytic reaction rate in the presence of AA which

19

clearly indicated that the active involvement of O2˙- in the reaction. Moreover, the addition of

20

AO and K2S2O8 slightly retarded the photodegradation efficiency. Hence, the results suggested

21

that O2˙- as well as •OH play major dynamic role and e- plays a minor role for the effective

22

degradation of CAP.

. In the present system,

-.



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Page 28 of 39

1

Furthermore, the mineralization efficiency of CAP over CeM/GO composite under

2

optimized identical condition, TOC (Total Organic Carbon) and COD (Chemical Oxygen

3

Demand) experiments were carried out and the results are depicted in Fig.S5. The results shows

4

that the removal of organics in the CAP solution increases with increasing the irradiation time.

5

After the 50 min of irradiation, the TOC (Fig.S5A) and COD Fig.S5B) removal efficiency was 68

6

and 71%, respectively. The results suggested that the CeM/GO composite not only having CAP

7

photodegradation efficiency but also having good mineralization performances.

8

For long-term use in practical application of CeM/GO nanocomposite photocatalyst, the

9

stability and durability is top priority. Herein, the photocatalytic stability of the CeM/GO

10

nanocomposite evaluated for five consecutive recycle experiments under identical reaction

11

conditions as represented in Fig.10D. Fascinatingly, the results revealed that only 9 % of

12

photodegradation efficiency was lost during the fifth cycle, which proved that CeM/GO

13

nanocomposite photocatalyst possessed superior stability and reusability efficiency. A slight

14

decrement in the photodegradation efficiency of the recycling experiment might be due to the

15

some intermediates of the CAP solution adsorbed on the surface of the catalyst.

16

17


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1 2

Fig.10. (A) Effect of initial CAP concentration on the photodegradation, (B) Effect of pH on the

3

photodegradation of CAP (C) Effect of different scavengers on the photodegradation of CAP and

4

(D) Reusability of the CeM/GO composite.

5

CONCLUSIONS

6

In summary, we developed a novel CeM/GO composite tailored via simple template-

7

free hydrothermal route followed by the sonication process and characterized by FTIR, XRD,

8

Raman, XPS, SEM, UV-DRS and CV techniques. The as-synthesized CeM/GO composite was

9

scrutinized for its electrochemical reduction and photocatalytic degradation performances

10

towards neurotoxicity antibiotic drug CAP. The electrochemical studies demonstrated the as29 ACS Paragon Plus Environment


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Page 30 of 39

1

synthesized CeM/GO composite showed a good analytical performance towards the

2

determination of CAP including wide linear range, low LOD, excellent selectivity and good

3

sensitivity. The practical ability of CAP towards the real sample analysis was assessed in honey

4

and milk samples with good recoveries. Moreover, as-formed CeM/GO nanocomposite showed

5

an excellent photocatalytic activity for the degradation of CAP under visible light illumination

6

with high degradation rate of 99% after 50 min. The obtained electrocatalytic and photocatalytic

7

activities revealed that the CeM/GO composites can be used as a proficient electrode as well as

8

excellent photocatalytic material for the other electrochemical and photocatalytic applications.

9 10

Table 1 Comparison between proposed sensor with previously reported electrochemical modified electrodes for the determination of CAP Modified Electrode

Method

Linear range (µM)

LOD (µM)

References

AuNPs/GO

Amperometry

1.5–2.95

0.25

50

MoS2/f-MWCNTs

Amperometry

0.08 - 1392

0.015

53

SWV

0.1 - 10

0.047

54

DPV

0.1 - 1000

0.065

55

LSV

2-80

0.059

56

CV

0.05- 100

0.02

57

Amperometry

0.012- 20

0.002

This work

Activated carbon fibre microelectrodes MoS2/self-doped polyaniline N-doped graphene/AuNPs Titanium nitride/RGO CeM/GO/GCE

26-272 11 12 13 14

AuNPs- Gold nanoparticles: GO – Graphene oxide: MoS2 – Molybdinum sulfide: f-MWCNT – functionalized- Multiwalled carbon nanotubes: RGO – Reduced graphene oxide: CeM – Cerium molybdate; LSV- Linear sweep voltammetry: SWV-square wave voltammetry: CV- Cyclic voltammetry: DPV- Differential pulse voltammetry.

15


Page 31 of 39

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1

ASSOCIATED CONTENT

2

Supporting Information

3

The Supporting Information is available free of charge on the ACS Publications website

4

at DOI: xxxxxxx

5

The chemical structure of the CAP, EDX elemental mapping, amperometry of interference

6

study, amperometry of real sample, TOC & COD analysis and real sample Table 1.

7 8

AUTHOR INFORMATION

9

Corresponding Authors

10

*E-mail: [email protected] (S.-M. Chen).

11

*E-mail: [email protected] (V. Muthuraj).

12

Notes

13

The authors declare no competing financial interest.

14

ACKNOWLEDGEMENTS

15

This project was supported by the National Science Council and the Ministry of Education of

16

Taiwan, ROC. We are grateful to thank the University of Grant Commission (UGCF. No. 42-

17

348/2013 (SR) & 01.04.2013), New Delhi, India. We also express our gratitude to the College

18

Managing Board, Principal and Head of the Department of Chemistry, VHNSN College,

19

Virudhunagar for providing research facilities.

20 21 22



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REFERENCES [1] S. Morais, L. A. T. Genaro, T. A. Chover, R. Puchades, A. Maquieira, Multiplexed Microimmunoassays on a Digital Versatile Disk. Anal. Chem, 2009, 81, 5646–5654. [2] E. S. Elmolla, M. Chaudhuri, Photocatalytic Degradation of Some Antibiotics in Aqueous Solution, water Malaysia, 2009, 19-21. [3] Y. Zhou, New Insights In To the Structure, Function and Evolution of Tetr Family Transcriptional Regulator, University of Toronto, 2009, 1-16. [4] S. E. Kaya, A. Filazi, Determination of Antibiotic Residues in Milk Samples. Kafkas Univ Vet Fak Derg, 2010, 31-35, DOI:10.9775/kvfd.2009.1174.

10

[5] G. S. Bezanson, R. MacInnis, G. Potter, T. Hughes, Presence and potential for horizontal

11

transfer of antibiotic resistance in oxidase-positive bacteria populating raw salad

12

vegetables. Int. J. Food Microbiol, 2008, 127, 37-42.

13

[6] P. W. Rose, A. Hamden, A. B. Brueggemann, R. Perera, A. Sheikh, D. Crook, D. Mant,

14

Chloramphenicol treatment for acute infective conjunctivitis in children in primary care:

15

a randomised double-blind placebo-controlled trial. Lancet, 2005, 366, 37-43.

16

[7] A. Hailemichael, L. Hlalele. Voltammetric Determination of Chloramphenicol at

17

Electrochemically Pretreated Glassy Carbon Electrode, Bull. Chem. Soc. Ethiop, 2007,

18

21, 1-12.

19 20

[8] [S. Schwarz, E. C. Dancla, Use of antimicrobials in veterinary medicine and mechanisms of resistance. Vet. Res, 2001, 32, 201–225.

21

[9] J. A. Turton, A. C. Havard, S. Robinson, D. E. Holt, C. M. Andrews, R. Fagg, T. C.

22

Williams, An assessment of chloramphenicol and thiamphenicol in the induction of

23

aplastic anaemia in the BALB/c mouse. Food Chem. Toxicol, 2000, 38, 925–938.

24 25

[10] Council Regulation (EEC) 1430/94 of 22 June 1994, Off. J. Eur. Commun. 1994, L156, 6-8.

26

[11] P. Jakubec, V. Urbanova, Z. Medrikova, R. Zboril, Advanced sensing of antibiotics with

27

magnetic gold nanocomposite: Electrochemcial detection of chloramphenicol. Chem.

28

Eur. J. 2016, 22, 14279-14284.

29

[12] R. Karthik, Y. S. Hou, S. M. Chen, A. Elangovan, M. Ganesan, P. Muthukrishnan, Eco-

30

friendly synthesis of Ag-NPs using Cerasus serrulata plant extract–Its catalytic,


Page 33 of 39

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

electrochemical reduction of 4-NPh and antibacterial activity. J. Ind. Eng. Chem, 2016,

2

37, 330–339.

3

[13] M. C. Dodd, A. D. Shah, U. V. Gunten, C. H. Huang, Interactions of Fluoroquinolone

4

Antibacterial Agents with Aqueous Chlorine: Reaction Kinetics, Mechanisms, and

5

Transformation Pathways. Environ. Sci. Technol, 2005, 39, 7065–7076.

6 7

[14] G. Carlsson, S. Orn, D. G. J. Larsson, Effluent from bulk drug production is toxic to aquatic vertebrates. Environ. Toxicol. Chem, 2009, 28, 2656–2662.

8

[15] J. V. Kumar, R. Karthik, S. M. Chen, V. Muthuraj, K. Chelladurai, Fabrication of

9

potato-like silver molybdate microstructures for photocatalytic degradation of chronic

10

toxicity ciprofloxacin and highly selective electrochemical detection of H2O2. Sci. Rep,

11

2016, 6 (34149), 1-13.

12

[16] A. S. Nasab, M. Maddahfar, S. M. H. Mashkani, Ce(MoO4)2 nanostructures: Synthesis,

13

characterization, and its photocatalyst application through the ultrasonic method. J. Mol.

14

Liq, 2016, 216, 1–5.

15

[17] M. Shen, X. Zhang, K. Dai, H. Chen, T. Peng, Hierarchical PbMoO4 microspheres:

16

hydrothermal synthesis, formation mechanism and photocatalytic properties. CrystEng

17

Comm, 2013, 15, 1146–1152.

18

[18] S. Driscoll, U. S. Ozkan, Isotopic Labeling Studies on Oxidative Coupling of Methane

19

over Alkali Promoted Molybdate Catalysts. Stud. Surf. Sci. Catal, 1994, 82, 367–375.

20 21

[19] A. Kumar, J. Kumar, Perspective on europium activated fine-grained metal molybdate phosphors for solid state illumination. J. Mater. Chem, 2011, 21, 3788–3795.

22

[20] J. P. Liu, X. T. Huang, Y. Y. Li, Z. K. Li, A general route to thickness-tunable

23

multilayered sheets of sheelite-type metal molybdate and their self-assembled films. J.

24

Mater. Chem, 2007, 17, 2754–2758.

25

[21] J. G. Rushbrooke, R. E. Ansorge, Optical fibre readout and performance of small

26

scintillating crystals for a fine-grained gamma detector. Nucl. Instrum. Methods

27

Phys.Res. Sect A, 1989, 280, 83–90.

28

[22] R. Sundaram, K. S. Nagaraja, Solid state electrical conductivity and humidity sensing

29

studies on metal molybdate–molybdenum trioxide composites (M = Ni2+, Cu2+ and

30

Pb2+). Sens. Actuators B, 2004, 101, 353–360.



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

Page 34 of 39

[23] V. B. Mikhailik, H. Kraus, Performance of scintillation materials at cryogenic temperatures. Phys. Status Solidi. B, 2010, 247, 1583–1599.

3

[24] J. Qu, L. Wang, X. Yuan, Q. Cong, S. S. Guan, Effects of ammonium molybdate on

4

phytoremediation by alfalfa plants and (im)mobilization of toxic metals in soils.

5

Environ. Earth Sci, 2011, 64, 2175–2182.

6

[25] G. Schwarz, J. Schulze, F. Bittner, T. Eilers, J. Kuper, G. Bollmann, A. Nerlich, H.

7

Brinkmann, R. R. Mendel, The Molybdenum Cofactor Biosynthetic Protein Cnx1

8

Complements Molybdate-Repairable Mutants, Transfers Molybdenum to the Metal

9

Binding Pterin, and Is Associated with the Cytoskeleton. Plant Cell, 2000, 12, 2455–

10

2471.

11

[26] W. Xiao, J. S. Chen, C. M. Li, R. Xu, X. W. Lou, Synthesis, Characterization, and

12

Lithium Storage Capability of AMoO4 (A = Ni, Co) Nanorods. Chem. Mater, 2010, 22,

13

746–754.

14

[27] Y. Ding, S. H. Yu, C. Liu, Z. A. Zang, 3D Architectures of Iron Molybdate: Phase

15

Selective Synthesis, Growth Mechanism, and Magnetic Properties. Chem. Eur. J, 2007,

16

13, 746–753.

17

[28] Z. Zhang, Y. Liu, Z. Huang, L. Ren, X. Qi, X. Wei, J. Zhong, Facile hydrothermal

18

synthesis

of

NiMoO4@CoMoO4

hierarchical

nanospheres

19

applications. Phys ChemChem Phys, 2015, 17, 20795–20804.

for

supercapacitor

20

[29] B. Senthilkumar, K. V. Sankar, R. K. Selvan, M. Danielle, M. Manickam, Nano α-

21

NiMoO4 as a new electrode for electrochemical supercapacitors. RSC Adv, 2013, 3,

22

352–357.

23

[30] J. H. Ryu, J. W. Yoon, C. S. Lim, W. C. Oh, K. B. Shim, Microwave-assisted synthesis

24

of CaMoO4 nano-powders by a citrate complex method and its photoluminescence

25

property. J. Alloys Compd, 2005, 390, 245–249.

26

[31] Y. Mi, Z. Y. Huang, F. L. Hu, Y. F. Li, J. Y. Jiang, Room-Temperature Synthesis and

27

Luminescent Properties of Single-Crystalline SrMoO4 Nanoplates. J. Phys. Chem. C,

28

2009, 113, 20795-20799.

29

[32] Y. S. Luo, W. D. Zhang, X. J. Dai, Y. Yang and S. Y. Fu, Facile Synthesis and

30

Luminescent Properties of Novel Flowerlike BaMoO4 Nanostructures by a Simple

31

Hydrothermal Route. J. Phys. Chem. C, 2009, 113, 4856-4863. 34 ACS Paragon Plus Environment

Page 35 of 39

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

[33] Y. Cheng, Y. S. Wang, D. Q. Chen, F. Bao, Evolution of Single Crystalline Dendrites

2

from Nanoparticles through Oriented Attachment. J. Phys. Chem. B, 2005,109, 794-798.

3

[34] W. S. Wang, Y. X. Hu, J. Goebl, Z. D. Lu, L. Zhen, Y. D. Yin, Shape- and Size-

4

Controlled Synthesis of Calcium Molybdate Doughnut-Shaped Microstructures. J. Phys.

5

Chem. C, 2009,113, 16414-16423.

6

[35] B. Moreno, E. Chinarro, M. T. Colomer, J. R. Jurado, Combustion Synthesis and

7

Electrical Behavior of Nanometric β-NiMoO4. J. Phys. Chem. C, 2010, 114, 4251-4257.

8

[36] M.K. Xu, Z.H. Ouyang, Z.R. Shen, Topological evolution of cerium(III) molybdate

9

microflake assemblies induced by amino acids. Chin. Chem. Lett, 2016, 27, 673-677.

10

[37] W. Kuang, Y. Fan, Y. Chen, Catalytic properties of ultrafine molybdenum–cerium oxide

11

particles prepared by the sol–gel method. Catal. Lett, 1998, 50, 31–35.

12

[38] I.A. Kartsonakis, G. Kordas, Synthesis and characterization of cerium molybdate

13

nanocontainers and their inhibitor complexes. J. Am. Ceram. Soc, 2010, 93, 65–73.

14

[39] K.J. Sreeram, R. Srinivasan, J.M. Devi, B.U. Nair, T. Ramasami, Cerium molybdenum

15

oxides for environmentally benign pigments. Dyes Pigm, 2007, 75, 687–692.

16

[40] M. Chen, Y. Meng, W. Zhang, J. Zhou, J. Xie, G. Diao, ) β-Cyclodextrin polymer

17

functionalized reduced-graphene oxide: Application for electrochemical determination

18

imidacloprid. Electrochim Acta, 2013, 108, 1-9.

19

[41] D. Rajkumar, R. Karthik, S. M. Chen, M.A. Ali, V. Mani, B.S. Lou, F. M. A. Al-

20

Hemaid, Enzymatic glucose biosensor based on bismuth nanoribbons electrochemically

21

deposited on reduced graphene oxide. Microchim. Acta, 2015, 182, 2165–2172.

22

[42] J. Zhao, Q.S. Wu, M. Wen, Temperature-controlled assembly and morphology

23

conversion of CoMoO4·3/4H2O nano-superstructured grating materials. J. Mater. Sci,

24

2009, 44, 6356–6362.

25

[43] D.C. Marcano, D.V. Kosynkin, J.M. Berlin, A. Sinitskii, Z.Z. Sun, A.S. Slesarve, L.B.

26

Alemany, W. Lu, J.M. Tour, Improved Synthesis of Graphene Oxide. ACS Nano, 2010,

27

4, 4806–4814.

28 29 30 31

[44] G. Mestl, T. K. K. Srinivasan, Raman Spectroscopy of Monolayer-Type Catalysts: Supported Molybdenum Oxides. Catal. Rev. Sci. Eng, 1998, 40, 451-570. [45] Y. Song, M.Feng, H. Zhan, Geometry-dependent electrochemistry of graphene oxide family. Electrochem. Commun, 2015, 56, 38-42. 35 ACS Paragon Plus Environment


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

[46] N. S. Arul, D. Mangalaraj, R. Ramachandran, A. N. Grace, J. I. Han, Fabrication of

2

CeO2/Fe2O3 composite nanospindles for enhanced visible light driven photocatalyst and

3

supercapacitor electrode. J. Mater. Chem. A, 2015, 3, 15248-15258.

Page 36 of 39

4

[47] Z. Xu, Z. Li, X. Tan, C. M. B. Holt, L. Zhang, B. S. Amirkhiz, D. Miltin,

5

Supercapacitive carbon nanotube-cobalt molybdate nanocomposites prepared via

6

solvent-free microwave synthesis. RSC Adv, 2012, 2, 2753-2755.

7

[48] X. Tong, S. Chen, C. Guo, X. Xia, X.Y. Guo, Mesoporous NiCo2O4 Nanoplates on

8

Three-Dimensional Graphene Foam as an Efficient Electrocatalyst for the Oxygen

9

Reduction Reaction, ACS Appl. Mater. Interfaces, 2016, 8, 28274–28282..

10

[49] M. Gopiraman, S. G. Babu, Z. Khatri, K. Wei, Y. A. Kim, M. Endo, R. Karvembu, I. S.

11

Kim, Dry Synthesis of Easily Tunable Nano Ruthenium Supported on Graphene:

12

Novel Nanocatalysts for Aerial Oxidation of Alcohols and Transfer Hydrogenation of

13

Ketones, J. Phys. Chem. C. 2013, 117, 23582−23596.

14

[50] R. Karthik, M. Govindasamy, Shen-Ming Chen , V. Mani, B. S. Lou, R.

15

Devasenathipathy, Y. S. Hou, A. Elangovan, Green synthesized gold nanoparticles

16

decorated graphene oxide for sensitive determination of chloramphenicol in milk,

17

powdered milk, honey and eye drops. J. Colloid Interf. Sci, 2016, 475, 46–56.

18

[51] X. Zhou, C. Yuan, D. Qin, Z. Xue, Y. Wang, J. Du, L. Ma, L. Ma and X. Lu, Pd

19

Nanoparticles on Functionalized Graphene for Excellent Detection of Nitro aromatic

20

Compounds. Electrochim. Acta, 2014, 119, 243–250.

21

[52] N. Karikalan, M. Velmurugan, S. M Chen, C. Karuppiah, K. M. Al-Anazi, M. Ajmal

22

Ali, B. S. Lou, Flame synthesis of nitrogen doped carbon for the oxygen reduction

23

reaction and non-enzymatic methyl parathion sensor. RSC Adv., 2016, 6, 71507-71516.

24

[53] M. Govindasamy, S.M. Chen, V. Mani, R. Devasenathipathy, R. Umamaheswari, K. J.

25

Santhanaraj, A. Sathiyan, Molybdenum disulfide nanosheets coated multiwalled carbon

26

nanotubes composite for highly sensitive determination of chloramphenicol in food

27

samples milk, honey and powdered milk. J. Colloid. Interf. Sci, 2016, 485, 129-136.

28

[54] L. Agui, A. Guzman, P. Y. Sedeno, J. Pingarron, Voltammetric determination of

29

chloramphenicol in milk at electrochemically activated carbon fibre microelectrodes.

30

Anal. Chimi. Acta, 2002, 461, 65-73.


Page 37 of 39

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

[55] R. Yang, J. Zhao, M. Chen, T. Yang, S. Luo, K. Jiao, Electrocatalytic determination of

2

chloramphenicol based on molybdenum disulfide nanosheets and self-doped

3

Polyaniline. Talanta, 2015, 131, 619-623.

4

[56] J. Borowiec, R. Wang, L. Zhu, J. Zhang, Synthesis of nitrogen-doped graphene

5

nanosheets decorated with gold nanoparticles as an improved sensor for electrochemical

6

determination of chloramphenicol. Electrochim. Acta, 2013, 99, 138-144.

7

[57] F. Y. Kong, T. T. Chen, J. Y. Wang, H. L. Fang, D. H. Fan, W. Wang, UV-assisted

8

synthesis of tetrapods-like titanium nitride-reduced graphene oxide nanohybrids for

9

electrochemical determination of chloramphenicol. Sens. Actuators B, 2016, 225, 298-

10

304.

11

[58] J.G. Yu, J. Jin, B. Cheng, M. Jaroniec, A noble metal-free reduced graphene oxide–CdS

12

nanorod composite for the enhanced visible-light photocatalytic reduction of CO2 to

13

solar fuel. J. Mater. Chem. A, 2014, 2, 3407-3416.

14

[59] W.J. Wang, J.C. Yu, D.H. Xia, P.K. Wong, Y.C. Li, Graphene and g-C3N4 Nanosheets

15

Cowrapped Elemental α-Sulfur As a Novel Metal-Free Heterojunction Photocatalyst for

16

Bacterial Inactivation under Visible-Light. Environ. Sci. Technol, 2013, 47, 8724-8732.

17

[60] L. P. Zhu, G. H. Liao, N. C. Bing, L. L. Wang, Y. Yang, H. Y. Xie, Self-assembled 3D

18

BiOCl hierarchitectures: tunable synthesis and

19

2010, 12, 3791–3796.

20

characterization. Cryst Eng Comm,

[61] D. Xiao, K. Dai, Y. Qu, Y. Yin, H. Chen, Hydrothermal synthesis of α-Fe2O3/g-C3N4

21

composite

and

its

efficient

photocatalytic

22

visible light. Appl. Surf. Sci., 2015, 358, 181-187.

reduction

of

Cr(VI)

under

23

[62] G. N. Jovanovic, P. Z. Plazl, P. Sakrittichai, K. A. Khaldi, Dechlorination of p-

24

chlorophenol in a microreactor with bimetallic Pd/Fe catalyst. Ind. Eng. Chem. Res.

25

2005, 44, 5099–5106.

26

[63] Z. Q. Fang, J. H. Chen, X. H. Qiu, X. Q. Qiu, W. Cheng, L. C. Zhu, Effective removal

27

of antibiotic metronidazole from water by nanoscale zero-valent iron particles.

28

Desalination, 2011, 268, 60–67.

29 30

[64] X. Zhang, Y. M. Lin, Z. L. Chen, 2,4,6-Trinitrotoluene reduction kinetics in aqueous solution using nanoscale zero-valent iron. J. Hazard. Mater., 2009, 165, 923–927.



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

Page 38 of 39

1

[65] S. J. Liang, S. Y. Zhu, Y. Chen, W. M. Wu, X. C. Wang, L. Wu, Rapid template-free

2

synthesis and photocatalytic performance of visible light-activated SnNb2O6

3

nanosheets. J. Mater. Chem, 2012, 22, 2670–2678.

4

[66] N. S. Lawrence, R. P. Deo, J. Wang, Electrochemical determination of hydrogen

5

sulfide at carbon nanotube modified electrodes. Analytica Chimica Acta, 2004,

6

517, 131–137.

7


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