Der elektrochemische Nachweis von polycyclischen aromatischen Kohlenwasserstoffen (PAK), zu denen Anthracen und Pyren gehören, bietet eine kostengünstigere, einfachere und schnellere alternative Analysemethode als herkömmliche Methoden wie GC und HPLC. Im Vergleich zu diesen Methoden weist er jedoch nach wie vor eine geringere Empfindlichkeit auf. Einige neuere Bemühungen haben an einem Mangel an Selektivität gelitten, entweder aufgrund der elektrodenmodifizierende Schicht mit hohem Hintergrundstrom oder der Wahl eines Leitelektrolyten, der die Detektion stört. Bei dem vorliegenden Versuch wurden Pt-Pd-Nanopartikel (NPs) und MWCNTs verwendet, um eine Glaskohlenstoffelektrode (GCE) zum empfindlichen Nachweis von Anthracen und Pyren zu modifizieren. Die verwendeten NPs wurden unter Verwendung eines wässrigen Extrakts aus Blättern von E. grandis synthetisiert, einem nachhaltigen und umweltfreundlichen Syntheseweg. Durch einer Optimierung der Mengen an Pt- und Pd-Ionen im Vorläufer wurden NPs mit einer durchschnittlichen Größe von 10 nm erhalten, wobei ein Verhältnis von 1 Pt-Ion zu 3 Pd-Ionen die kleinste Größe ergab. Durch XPS wurde festgestellt, dass die Zusammensetzung der NPs von Pt2+ und Pd0 dominiert wird. Die XRD-Analyse ergab eine kristalline Natur mit einer flächenzentriert-kubischen Struktur. Die Pt-Pd-NPs bewirkten eine Erhöhung des Spitzenstroms um 94 % für Pyren, führten jedoch zu niedrigeren Spitzenströmen für Anthracen. Wenn die NPs weiter mit MWCNTs zum Nachweis von Pyren verwendet wurden, wurde eine Spitzenstromsteigerung von etwa 200 % mit einem Dynamikbereich von 66–130 μM und einer LOD von 23 μM beobachtet. Es wurde auch festgestellt, dass der elektrochemische Prozess gemischt diffusions- und adsorptionskontrolliert ist. Aufgrund des Einflusses der Adsorption musste die Akkumulationszeit im Analyseverfahren berücksichtigt werden. MWCNTs wurden beim Nachweis von Anthracen angewendet, wobei eine Erhöhung des Spitzenstroms um 74 % und eine Verringerung des Überpotentials um 53 mV beobachtet wurde. Ein dynamischer Bereich von 50–146 µM und eine LOD von 42 µM wurden bestimmt. Niedrigere Konzentrationen wurden mit einer Leitungswasserprobe gemessen, die mit Anthracen versetzt war, hauptsächlich wegen der geringen Löslichkeit von PAK in Wasser. Der Einfluss der Säurebehandlung von MWCNTs auf den Nachweis von Anthracen und Pyren wurde ebenfalls untersucht. Die Säurebehandlung ermöglichte das Laden von mehr Material ohne Ablösen der modifizierten Schicht, was zu höheren Spitzenstromverbesserungen für Anthracen (533 %) und Pyren (448 %) führte. Für Anthracen und Pyren wurden LODs von 40 µM bzw. 14 µM bestimmt, die nur geringfügig niedriger sind als die bei MWCNTs/GCE und Pt-PdNPs/MWCNTs/GCE beobachteten Werte. Der Nachweis von Anthracen wurde durch die Anwesenheit von Pyren und gewöhnlichen Ionen gestört, während die LOD für Pyren in Gegenwart von Anthracen 18 µM betrug. Es wurde festgestellt, dass die auf MWCNTs basierende elektrochemische Nachweisplattform eine bessere Reaktion auf Pyren aufweist.:Bibliographische Beschreibung i Referat i Abstract iii Zeitraum, Ort der Durchführung v Acknowledgements vi Dedication vii Table of Contents viii List of Abbreviations and Symbols xii Chapter 1 1 Introduction 1 1.1 Overview 1 1.2 Polycyclic Aromatic Hydrocarbons 2 1.3 Electrochemical Sensors 7 1.3.1 General Response Curve for Chemical Sensors 10 1.4 Carbon Nanotubes 13 1.5 Use of Nanoparticles in Electrochemical Detection 18 1.6 Green Synthesis of Nanoparticles and The Rationale Behind It 21 1.7 Previous Efforts in the Electrochemical Detection of Polycyclic Aromatic Hydrocarbons 24 1.8 Objectives of the Study 26 Chapter 2 28 Experimental 28 2.1 Chemicals 28 2.1.1 Preparation of Anthracene and Pyrene Solutions 28 2.2 Collection and Preparation of Plant Material 29 2.3 Synthesis and Preparation of Materials 29 2.3.1 Synthesis of Metallic Nanoparticles 29 2.3.2 Acid Treatment of Multi-walled Carbon Nanotubes 30 2.4 Characterization of the Nanomaterials 30 2.4.1 UV-Vis Spectrophotometry 30 2.4.2 SEM/EDX and TEM Analysis 30 2.4.3 Powder X-ray Diffractometry 31 2.4.4 XPS Analysis 31 2.5 Electrochemical Measurements 31 2.5.1 Preparation of the Bare and Modified Glassy Carbon Electrode 32 2.5.2 Characterization of the Bare and the Modified Glassy Carbon Electrode 33 2.5.3 Electrocatalytic Oxidation of Anthracene on the Bare and Modified GCEs 33 2.5.4 Electrocatalytic Oxidation of Pyrene on the Bare and Modified GCEs 34 Chapter 3 35 Synthesis, Characterization, and Application of Pt-Pd Nanoparticles in the Electrochemical Detection of Anthracene and Pyrene 35 3.1 Test for Flavonoids and Polyphenols in the E. grandis Leaves’ Extract 35 3.2 Synthesis of Nanoparticles 35 3.3 Characterization of Nanoparticles 37 3.3.1 TEM Analysis 37 3.3.2 SEM Analysis 40 3.3.3 EDX Analysis 41 3.3.4 Powder X-Ray Diffraction Analysis 45 3.3.5 XPS Analysis of Pt-Pd Particles 46 3.4 Impedance Measurements of the Bare and Nanoparticle-modified Glassy Carbon Electrode 49 3.5 Electrochemical Oxidation of Anthracene and Pyrene at the Bare and Nanoparticles-modified Glassy Carbon Electrode 51 3.6 Conclusions 53 Chapter 4 55 Pt-PdNPs/MWCNTs-Modified GCE for the Detection of Pyrene 55 4.1 Impedance Measurement with Pt-PdNPs/MWCNTs/GCE 55 4.2 Electrochemical Oxidation of Pyrene on Pt-PdNPs/MWCNTs/GCE 56 4.3 Analysis of Varying Concentrations of Pyrene on Pt-PdNPs/MWCNTs/GCE 59 4.4 Selectivity 61 4.5 Conclusions 62 Chapter 5 64 Exploring Multi-walled Carbon Nanotubes for the Detection of Anthracene 64 5.1 Impedance Measurement of MWCNT-Modified Glassy Carbon Electrode 64 5.2 Electrochemical Oxidation of Anthracene on MWCNT/GCE 65 5.3 Analysis of Varying Concentrations of Anthracene Using MWCNTs/GCE 68 5.4 Detection of Anthracene in Tap Water 71 5.5 Conclusions 72 Chapter 6 73 Effect of Acid Treatment of Multi-walled Carbon Nanotubes on the Detection of Anthracene and Pyrene 73 6.1 Characterization of fMWCNTs 74 6.2 Electrochemical Oxidation of Anthracene on fMWCNTs/GCE 75 6.2.1 Effect of Change in Scan Rate 76 6.2.2 Effect of Accumulation Time 77 6.2.3 Application of fMWCNTs/GCE in the Analysis of Varying Concentrations of Anthracene 77 6.3 Electrochemical Oxidation of Pyrene on fMWCNTs/GCE 79 6.4 Selectivity 82 6.4.1 Co-detection of Anthracene and Pyrene at fMWCNTs/GCE 83 6.4.2 Interference of Some Common Ions 85 6.5 Detection of Pyrene in Tapwater using fMWCNTs/GCE 86 6.6 Conclusions 87 Chapter 7 88 Summary and Outlook 88 7.1 Summary 88 7.2 Outlook 90 References 92 Selbständigkeitserklärung 101 Curriculum Vitae 102 / Electrochemical detection of polycyclic aromatic hydrocarbons (PAHs), which include anthracene and pyrene, offers a cheaper, simpler, and faster alternative method of analysis than conventional methods like GC and HPLC. However, it still is not as sensitive as these methods. Some recent efforts have suffered from lack of selectivity, either from the electrode modifying layer having high background current or from the choice of supporting electrolyte interfering with the detection. In this work, Pt-Pd nanoparticles (NPs) and MWCNTs were used to modify a glassy carbon electrode (GCE) for sensitive detection of anthracene and pyrene. The NPs used were synthesized using an aqueous extract from E. grandis leaves, a sustainable and environmentally friendly synthetic route. NPs with an average size of 10 nm were obtained by optimizing the amounts of Pt- and Pd-ions in the precursor, with a ratio of 1:3 Pt to Pd-ions producing the smallest size. Through XPS, the composition of the NPs was established to be dominated by Pt2+ and Pd0. XRD analysis revealed a crystalline nature with a face-centered cubic structure. The Pt-Pd NPs produced 94 % enhancement in the peak current for pyrene but resulted in lower peak currents for anthracene. When the NPs were further used with MWCNTs for the detection of pyrene, about 200% peak current enhancement was observed with a dynamic range of 66–130 µM and LOD of 23 µM. The electrochemical process was also established to be mixed diffusion- and adsorption-controlled. The influence of adsorption necessitated the employment of accumulation time in the analysis procedure. MWCNTs were applied in the detection of anthracene and a 74 % peak current enhancement and a reduction in the overpotential by 53 mV were observed. A dynamic range of 50–146 µM and LOD of 42 µM were determined. Lower concentrations were recovered from a tap water sample that was spiked with anthracene, mainly because of the low solubility of PAHs in water. Effect of acid treatment of MWCNTs on the detection of anthracene and pyrene was also investigated. Acid treatment allowed for loading of more material without peeling off of the modified layer which resulted in higher peak current enhancements for anthracene (533%) and pyrene (448%). LODs of 40 µM and 14 µM were determined for anthracene and pyrene respectively, which are only slightly lower than what was observed at MWCNTs/GCE and Pt-PdNPs/MWCNTs/GCE. Detection of anthracene was interfered by the presence of pyrene and common ions, while the LOD for pyrene in the presence of anthracene was 18 µM. The MWCNTs based electrochemical detection platform was found to have a better response towards pyrene.:Bibliographische Beschreibung i Referat i Abstract iii Zeitraum, Ort der Durchführung v Acknowledgements vi Dedication vii Table of Contents viii List of Abbreviations and Symbols xii Chapter 1 1 Introduction 1 1.1 Overview 1 1.2 Polycyclic Aromatic Hydrocarbons 2 1.3 Electrochemical Sensors 7 1.3.1 General Response Curve for Chemical Sensors 10 1.4 Carbon Nanotubes 13 1.5 Use of Nanoparticles in Electrochemical Detection 18 1.6 Green Synthesis of Nanoparticles and The Rationale Behind It 21 1.7 Previous Efforts in the Electrochemical Detection of Polycyclic Aromatic Hydrocarbons 24 1.8 Objectives of the Study 26 Chapter 2 28 Experimental 28 2.1 Chemicals 28 2.1.1 Preparation of Anthracene and Pyrene Solutions 28 2.2 Collection and Preparation of Plant Material 29 2.3 Synthesis and Preparation of Materials 29 2.3.1 Synthesis of Metallic Nanoparticles 29 2.3.2 Acid Treatment of Multi-walled Carbon Nanotubes 30 2.4 Characterization of the Nanomaterials 30 2.4.1 UV-Vis Spectrophotometry 30 2.4.2 SEM/EDX and TEM Analysis 30 2.4.3 Powder X-ray Diffractometry 31 2.4.4 XPS Analysis 31 2.5 Electrochemical Measurements 31 2.5.1 Preparation of the Bare and Modified Glassy Carbon Electrode 32 2.5.2 Characterization of the Bare and the Modified Glassy Carbon Electrode 33 2.5.3 Electrocatalytic Oxidation of Anthracene on the Bare and Modified GCEs 33 2.5.4 Electrocatalytic Oxidation of Pyrene on the Bare and Modified GCEs 34 Chapter 3 35 Synthesis, Characterization, and Application of Pt-Pd Nanoparticles in the Electrochemical Detection of Anthracene and Pyrene 35 3.1 Test for Flavonoids and Polyphenols in the E. grandis Leaves’ Extract 35 3.2 Synthesis of Nanoparticles 35 3.3 Characterization of Nanoparticles 37 3.3.1 TEM Analysis 37 3.3.2 SEM Analysis 40 3.3.3 EDX Analysis 41 3.3.4 Powder X-Ray Diffraction Analysis 45 3.3.5 XPS Analysis of Pt-Pd Particles 46 3.4 Impedance Measurements of the Bare and Nanoparticle-modified Glassy Carbon Electrode 49 3.5 Electrochemical Oxidation of Anthracene and Pyrene at the Bare and Nanoparticles-modified Glassy Carbon Electrode 51 3.6 Conclusions 53 Chapter 4 55 Pt-PdNPs/MWCNTs-Modified GCE for the Detection of Pyrene 55 4.1 Impedance Measurement with Pt-PdNPs/MWCNTs/GCE 55 4.2 Electrochemical Oxidation of Pyrene on Pt-PdNPs/MWCNTs/GCE 56 4.3 Analysis of Varying Concentrations of Pyrene on Pt-PdNPs/MWCNTs/GCE 59 4.4 Selectivity 61 4.5 Conclusions 62 Chapter 5 64 Exploring Multi-walled Carbon Nanotubes for the Detection of Anthracene 64 5.1 Impedance Measurement of MWCNT-Modified Glassy Carbon Electrode 64 5.2 Electrochemical Oxidation of Anthracene on MWCNT/GCE 65 5.3 Analysis of Varying Concentrations of Anthracene Using MWCNTs/GCE 68 5.4 Detection of Anthracene in Tap Water 71 5.5 Conclusions 72 Chapter 6 73 Effect of Acid Treatment of Multi-walled Carbon Nanotubes on the Detection of Anthracene and Pyrene 73 6.1 Characterization of fMWCNTs 74 6.2 Electrochemical Oxidation of Anthracene on fMWCNTs/GCE 75 6.2.1 Effect of Change in Scan Rate 76 6.2.2 Effect of Accumulation Time 77 6.2.3 Application of fMWCNTs/GCE in the Analysis of Varying Concentrations of Anthracene 77 6.3 Electrochemical Oxidation of Pyrene on fMWCNTs/GCE 79 6.4 Selectivity 82 6.4.1 Co-detection of Anthracene and Pyrene at fMWCNTs/GCE 83 6.4.2 Interference of Some Common Ions 85 6.5 Detection of Pyrene in Tapwater using fMWCNTs/GCE 86 6.6 Conclusions 87 Chapter 7 88 Summary and Outlook 88 7.1 Summary 88 7.2 Outlook 90 References 92 Selbständigkeitserklärung 101 Curriculum Vitae 102