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SYNTHESIS OF SILVER– AND CADMIUM SELENIDE NANOPARTICLES–DECORATED REDUCED GRAPHENE OXIDES AND THEIR APPLICATION IN DETERMINATION OF SOME BIOLOGICAL COMPOUNDS and ETHANOL ELECTROOXIDATION AT ZINC OXIDE/PALLADIUM NANOPARTICLES-MODIFIED CARBON PASTE ELECTRODE

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M.Sc. Dissertation

In Analytical Chemistry

SYNTHESIS OF SILVER– AND CADMIUM SELENIDE NANOPARTICLES–DECORATED REDUCED GRAPHENE OXIDES AND THEIR APPLICATION IN DETERMINATION OF SOME BIOLOGICAL COMPOUNDS

and

ETHANOL ELECTROOXIDATION AT ZINC OXIDE/PALLADIUM NANOPARTICLES-MODIFIED CARBON PASTE ELECTRODE

ABSTRACT

An electrochemical sensor based on modification of carbon paste electrode by reduced graphene oxide-silver nanocomposite (RGO-Ag/CPE) was prepared for voltammetric determination of acetaminophen (AP). The electrochemical behaviors of acetaminophen on RGO-Ag/CPE were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). AP was determined in the range of 5.0 – 480.0 µM, and the limit of detection was determined as 0.18 µM using DPV.

A reduced graphene oxide (RGO) decorated thioglycolic acid capped cadmium selenide quantum dots (CdSe) modified glassy carbon electrode (RGO-CdSe/GCE) was prepared for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The electrode was fabricated by a simple drop-casting method. Peak separations of 135, 150, and 285 mV between DA and AA, DA and UA, and UA and AA, respectively, allow simultaneous detection of DA, AA, and UA by DPV using RGO-CdSe/GCE as working electrode.

The ethanol electrooxidation reaction was investigated on zinc oxide-palladium nanoparticles modified carbon paste electrode (ZnO-Pd/CPE). This reaction was studied by CV and was used for ethanol determination by chronoamperomeric method. The results showed that Pd/CPE electrocatalysts lonely had activity for ethanol electrooxidation. The result showed that the adding ZnO enhances the anti-poison ability of ZnO-Pd/CPE catalyst. The sensor has the advantages of low detection limit (20.3 mM), good linear range (1.99 mM – 3.35 M), ease of renewing the electrode surface, good long-term stability and reproducibility for ethanol determination.

ABSTRACT

An electrochemical sensor based on modification of carbon paste electrode by reduced graphene oxide-silver nanocomposite (RGO-Ag/CPE) was prepared for voltammetric determination of acetaminophen (AP). The electrochemical behaviors of acetaminophen on RGO-Ag/CPE were investigated by cyclic voltammetry (CV) and differential pulse voltammetry (DPV). AP was determined in the range of 5.0 – 480.0 µM, and the limit of detection was determined as 0.18 µM using DPV.

A reduced graphene oxide (RGO) decorated thioglycolic acid capped cadmium selenide quantum dots (CdSe) modified glassy carbon electrode (RGO-CdSe/GCE) was prepared for simultaneous determination of ascorbic acid (AA), dopamine (DA) and uric acid (UA). The electrode was fabricated by a simple drop-casting method. Peak separations of 135, 150, and 285 mV between DA and AA, DA and UA, and UA and AA, respectively, allow simultaneous detection of DA, AA, and UA by DPV using RGO-CdSe/GCE as working electrode.

The ethanol electrooxidation reaction was investigated on zinc oxide-palladium nanoparticles modified carbon paste electrode (ZnO-Pd/CPE). This reaction was studied by CV and was used for ethanol determination by chronoamperomeric method. The results showed that Pd/CPE electrocatalysts lonely had activity for ethanol electrooxidation. The result showed that the adding ZnO enhances the anti-poison ability of ZnO-Pd/CPE catalyst. The sensor has the advantages of low detection limit (20.3 mM), good linear range (1.99 mM – 3.35 M), ease of renewing the electrode surface, good long-term stability and reproducibility for ethanol determination.

Keyword: Acetaminophen, Graphene, Reduced Graphene Oxide, Silver, QD, CdSe, ZnO, Pd, Dopamine, Ascorbic Acid, Uric Acid, Ethanol, Direct Alcohol Fuel Cell.

دسته: زبان خارجه, زبان خارجه برچسب: Ascorbic Acid, CdSe, Direct Alcohol Fuel Cell., Dopamine, Ethanol, Graphene, Keyword: Acetaminophen, Pd, QD, Reduced Graphene Oxide, Silver, Uric Acid, ZnO

توضیحات

LIST OF CONTENTS

CONTENT ……………………….……………..……………………… PAGE

CHAPTER ONE.. 1

Introduction. 2

1.1. Nanomaterials. 2

1.1.1. Nanomaterial in electrochemistry. 2

1.1.1.1. Metal and metal oxide nanoparticles. 3

1.1.1.1.1. Zinc oxide. 4

1.1.1.1.2. ZnO-Pd nanoparticles. 5

1.2. Fuel cells. 8

1.3. Modified electrodes. 11

1.4. Carbon electrodes. 11

1.4.1. Carbon paste electrode (CPE). 12

1.5. Graphene-based materials. 14

1.6. Bioelectrochemistry. 15

1.6.1. Brain chemistry. 16

1.6.1.1. Dopamine. 16

1.6.1.2. Ascorbic acid. 17

1.6.2. Uric acid. 17

1.6.3. Acetaminophen. 17

CHAPTER TWO.. 19

Literature Review.. 20

CONTENT …………………….…………………….………… PAGE

2.1. Determination of Acetaminophen by Reduced Graphene oxide-Silver Modified Carbon Paste Electrode. 20

2.2. Ethanol Electrooxidation at Zinc Oxide/Palladium Nanoparticles Modified Carbon Paste Electrode. 22

2.3. Simultaneous Determination of Ascorbic acid, Dopamine and Uric acid by Reduced Graphene oxide-CdSe Modified Glassy Carbon Electrode. 25

2.4. Objective of the present work. 27

CHAPTER THREE.. 28

EXPERIMENTAL.. 29

3.1. Determination of Acetaminophen by Reduced Graphene oxide – Silver Nanocomposite Modified Carbon Paste Electrode. 29

3.1.1. Reagent and solutions. 29

3.1.2. Apparatus. 29

3.1.3. Synthesis of reduced graphene oxide – silver nanocmposite. 30

3.1.4. Modified Electrode Preparation. 30

3.1.5. General procedure. 31

3.2. Ethanol Electrooxidation at Zinc Oxide/Palladium Nanoparticles Modified Carbon Paste Electrode. 32

3.2.1. Chemicals. 32

3.2.2. Apparatus. 32

3.2.3. Synthesis of zinc oxide – palladium nanocomposite. 32

3.2.4. Modified Electrode Preparation. 33

CONTENT ………………………..……………………………… PAGE

3.3. Simultaneous Determination of Ascorbic acid, Dopamine and Uric acid by Reduced Graphene oxide-CdSe modified Glassy Carbon Electrode. 34

3.3.1 Chemicals. 34

3.3.2. Apparatus. 34

3.1.3. Synthesis of reduced graphene oxide – cadmium selenide nanocomposite 35

3.3.4. Modified Electrode Preparation. 35

3.3.5. General procedure. 36

CHAPTER FOUR.. 37

RESULTS AND DISCUSSION.. 38

4.1. Determination of acetaminophen by reduced graphene oxide-silver nanocomposite modified carbon paste electrode. 38

4.1.1. Structural characterization of RGO – Ag nanocomposite. 38

4.1.2. Electrochemical behaviour of acetaminophen on RGO-Ag/CPE.. 41

4.1.3. Optimization of RGO – Ag percentage in composite electrode. 43

4.1.4. Effects of pH on the response of the electrode. 44

4.1.5 Effect of scan rate on the response of RGO-Ag/CPE.. 46

4.1.6. Voltammetric determination of acetaminophen on RGO-Ag modified CPE 46

4.1.7. Repeatability and reproducibility. 48

4.1.8. Effect of coexisting electroactive species. 49

CONTENT ……………………………………….…………… PAGE

4.1.9 Real sample analysis. 49

4.1.10. Conclusions. 50

4.2. Ethanol Electrooxidation at Zinc Oxide/Palladium Nanoparticles Modified Carbon Paste Electrode. 51

4.2.1. Preliminary study. 51

4.2.2. Physical characterization of ZnO-Pd nanocomposite. 52

4.2.2. Voltammetric studies. 54

4.3.3. Chronoamperometric studies. 60

4.4.4. Determination of real surface area of ZnO-Pd modified carbon paste electrode 62

4.4.5. Amperometric determination of ethanol in alkaline media. 64

4.4.6. Repeatability, reproducibility and stability of the ZnO-Pd modified carbon paste Electrode. 66

4.4.7. Interference study. 67

4.4.8. Real sample analysis. 68

4.4.9. Conclusions. 68

4.3. Simultaneous Determination of Ascorbic acid, Dopamine and Uric acid by Reduced Graphene oxide-CdSe modified Glassy Carbon Electrode. 70

4.3.1. Characterization of CdSe QDs decorated on the reduced graphene oxide nanocomposite 70

4.3.2. Cyclic voltammetric detection of AA, DA, and UA.. 72

4.3.3. Effect of pH on the electrochemical behavior of AA, DA and UA.. 75

CONTENT ……………………….…………………………… PAGE

4.3.4. Effect of scan rate on the electrochemical behavior of single AA, DA and UA 78

4.3.5. Differential pulse voltammetry. 80

4.3.6. Real sample analysis. 83

4.3.7. Conclusion. 83

REFERENCES. 84

LIST OF FIGURES

FIGURE ……………………………………………………… PAGE

Figure 1.1. Schematic representation of ZnO crystal structures: wurtzite and zinc blende. 5

Figure 1.2. (a) Structure and electronic properies of NS-Zinc oxide: Zn_1+xO (Metal excess, creation of metal Frenkel-like defects by adding Zn atoms that are incorporated in interstitial sites. Zn_i oxidized to Zn_i²⁺ and Zn²⁺ in lattice sites reduced to Zn⁺). (b) Electronic structure and electrical conductivity. 6

Figure 1.3. Schematic diagram of Pd/ZnO sensing mechanism. 8

Figure 1.4. Schematic representation of an individual fuel cell 9

Figure 4.1.1. XRD spectra of (a) GO and (b) RGO, and RGO-Ag. 39

Figure 4.1.2. FTIR spectra of samples GO, RGO, and RGO-Ag. 40

Figure 4.1.3. TEM image of RGO-Ag nanocomposites. 41

Figure 4.1.4. Electrochemical behavior of electrode in the presence and absence of acetaminophen in 0.1 M PBS pH 4.0 at the scan rate of 50mV s^-1. 42

Figure 4.1.5. Electrooxidation behaviour of 0.4 mM AP at bare CPE (a), RGO/CPE (b) and RGO – Ag/CPE (c) in 0.1 M PBS pH 4.0 at the scan rate of 50mV s^-1. 43

Figure 4.1.6. Optimization of RGO – Ag percentage in composite electrode. 0.4 mM AP in 0.1 M PBS pH 4.0 at the scan rate of 50mV s^-1. 44

Figure 4.1.7. Differential pulse voltammograms of 0.4 mM acetaminophen at RGO – Ag/CPE, in buffer solution with various pHs. Scan rate: 50 mV s⁻¹ . Inset is the plot of peak potential vs. pH value. 45

FIGURE ……………………………………………………… PAGE

Figure 4.1.8. CVs of 0.4 mM AP on RGO-Ag/CPE at different scan rates from 10 to 250 mV/s. Inset is the plot of peak current vs. square root of scan rate. 46

Figure 4.1.9. Relationship of current responses to acetaminophen concentration on RGO-Ag/CPE for different acetaminophen concentrations in 0.1 M phosphate buffer (pH=4). 47

Figure 4.2.1. CVs of ZnO-Pd/CPE (a) before, and (b) after applied potential step in 1.0 M ethanol+1.0 M KOH at scan rate of 50 mV s^-1. 52

Figure 4.2.2. XRD pattern of (a) nano ZnO, and (b) Pd-modified ZnO nanoparticles 53

Figure 4.2.3. TEM image of ZnO-Pd (a) after and (b) before reduction. 54

Figure 4.2.4. CVs for (a) ZnO/CPE, (b) Pd/CPE, and (c) ZnO-Pd/CPE in 1.0 M KOH at scan rate of 50 mV s^-1. Inset is CV of ZnO/CPE in 1.0 M KOH. 55

Figure 4.2.5. CVs of ZnO-Pd/CPE in (a) 1.0 M 2-propanol+1.0 M KOH, (b) 1.0 M methanol+1.0 M KOH, and (c) 1.0 M ethanol+1.0 M KOH at scan rate of 50 mV s^-1. 56

Figure 4.2.6. CVs of (a) ZnO/CPE, (b) Pd/CPE, and (c) ZnO-Pd/CPE in 1.0 M KOH containing 1.0 M ethanol at scan rate of 50 mV S^-1. 57

Figure 4.2.7. Consecutive scans in 1.0 M ethanol + 1.0 M KOH at ZnO-Pd/CPE, scan rate 50 mV S^-1. 59

Figure 4.2.8. Effect of potential on electrocatalytic signal of 1.0 M ethanol on ZnO-Pd/CPE. 61

FIGURE ……………………………………………………… PAGE

Figure 4.2.9. Chronoamperometry of ZnO-Pd/CPE in (a) 1.0 M KOH and (b) 1.0 M ethanol+1.0 M KOH. The electrode potential was held at -0.25 V. 62

Figure 4.2.10. (a) CVs of ZnO-Pd/CPE in 1.0 M KOH at different switching potentials from 0.0 to 0.4 V at scan rate of 50 mV S^-1. (b) Reduction charge (C) of Pd oxides as a function of switching potential. 63

Figure 4.2.11. Amperometric responses for increasing ethanol concentrations at ZnO-Pd/CPE in 1.0 M KOH for (a) whole range with complete calibration curve and (b) two calibration ranges. 65

4.3.1. XRD patterns of GO, RGO-CdSe, RGO, and CdSe. 71

Figure 4.3.2. TEM image of the (a) GO, and (b) RGO -CdSe QD nanocomposites. 72

Figure 4.3.3. Cyclic voltammograms of 99 µM dopamine in phosphate buffer solution pH 7 at GCE, RGO/GCE and RGO-CdSe/GCE. Scan rates were 50 mV s^-1. 73

Figure 4.3.4. Cyclic voltammograms of 99 µM ascorbic acid in phosphate buffer solution pH 7 at GCE, RGO/GCE and RGO-CdSe/GCE. Scan rates were 50 mV s^-1. 74

Figure 4.3.5. Cyclic voltammograms of 99 µM uric acid in phosphate buffer solution pH 7 at GCE, RGO/GCE and RGO-CdSe/GCE. Scan rates were 50 mV s^-1. 75

Figure 4.3.6. The effects of pH on the oxidation peak current of (a) AA, (b) DA and (c) UA. Insets are the plots of peak potential vs. pH. 77

Figure 4.3.7. Cyclic voltammograms of (A) 0.4 mM AA, (B) 0.04 mM DA and (C) 0.04 mM UA at different scan rates 10 to 100 mV s^-1. 79

FIGURE ……………………………………………………… PAGE

Figure 4.3.8. Differential pulse voltammograms (baseline subtracted) of a ternary mixtures of DA (4.0×10^-5M), AA (4.0×10^-4 M) and UA (4.0×10^-5M) at RGO-CdSe/GCE in phosphate buffer solution, pH 7. Pulse time: 50 ms, potential step: 5 mV, Sweep rate: 10 mV s^-1. 81

Figure 4.3.9. Differential pulse voltammetry of RGO-CdSe/GCE in 0.1 M PBS (pH 7.0) (a) Containing 14.9 µM DA, 14.9 µM UA and different concentrations of AA from 3.9×10^-4to 1.0×10^-3M. (b) Containing 1.0 mM AA, 14.8 µM UA and different concentrations of DA from 4.94×10^-6to 7.36×10^-5M. (C) Containing 1.0 mM AA, 4.9 µM DA and different concentrations of UA from 9.0×10^-6to 1.2×10^-4M. Pulse time: 50 ms, potential step: 5 mV, Sweep rate: 10 mV s-1. 82

LIST OF TABLES

TABLE …..…………………………………………………… PAGE

Table 4.1.1. Comparison of the electroanalytical data for determination of AP. PANI: polyaniline, MWCNT: multi-walled carbon nanotube, BDD: Boron-Doped Diamond. 48

Table 4.1.2. Determination of AP in real samples using RGO-Ag as working electrode by DPV technique. 49

Table 4.2.1. Comparison of electrochemical performance of different electrodes in a solution containing 1 M KOH and 1 M ethanol. 57

Table 4.2.2. Comparison of the electrochemical performance of oxidation of ethanol (1.0 M) in alkaline solution (1.0 M KOH) on different catalysts. 60

Table 4.2.3. A comparison of basic parameters for amperometric ethanol sensors. CNF: carbon nanofiber; AOD: alcohol oxidase; GCE: glassy carbon electrode; PVA: poly(vinyl alcohol); MWCNT: multiwall carbon nanotube; ADH: Alcohol dehydrogenase; PNR: Poly(neutral red); SiNWs: silicon nanowires; CNT: carbon nanotubes; IL: ionic liquid; NiCFP: nickel nanoparticle-loaded carbon fiber paste; MCP: microchannel-plate. 66

Table 4.2.4. Results of interference study for the determination of 20.0 mM ethanol. 67

Table 4.2.5. Applicability of ZnO-Pd/CPE electrode for ethanol determination in a human blood serum sample. 68

Table 4.3.1. Determination of DA, AA and UA in real sample (Synthetic Urine sample). 83

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