Preparation and characterization of surfaces modified with carbon nano-onions. Biomedical and environmental applications
- Autores: Julio César Zuaznabar Gardona
- Directores de la Tesis: Alex Fragoso (dir. tes.)
- Lectura: En la Universitat Rovira i Virgili ( España ) en 2021
- Idioma: español
- Tribunal Calificador de la Tesis: Arben Merkoçi (presid.), Mayreli Ortiz Rodríguez (secret.), Marta E. Płońska Brzezińska (voc.)
- Programa de doctorado: Programa de Doctorado en Nanociencia, Materiales e Ingeniería Química por la Universidad Rovira i Virgili
- Materias:
- Enlaces
- Tesis en acceso abierto en: TDX
- Resumen
The focus of the present thesis is to prepare and characterize surfaces modified with carbon nano-onions (CNOs) to develop electrocatalytic systems and electrochemical (bio)sensors for biomedical and environmental applications.
In the first chapter, it is presented a general introduction to the topics that will be discussed in this thesis. It covers general information about carbon materials with emphasis in the preparation, characterization, functionalization and electrochemical (bio)sensing applications of CNOs. The second chapter covers the dispersion study of CNOs in 20 solvents of different polarities.These solvents were classified as “good” or “bad” to determine the Hansen solubility parameters (HSPs) for CNOs using various optimization approaches. These parameters were further used to predict the dispersion behavior of CNOs in other solvents with a very good agreement between expected and observed dispersibilities. The third chapter was dedicated to study the effect of two oxidation treatments on the electronic structure and the surface chemical composition of CNOs. Pristine, physical and chemical oxidized CNOs were analyzed by using ultraviolet photoelectron spectroscopy (UPS) and X-ray photoelectron spectroscopy (XPS). It was found that each oxidative treatment affects the electronic structure and the surface chemical composition of CNOs in different ways. The interfacial energy diagrams for pristine and oxidized CNOs are also provided and used to explain some electronic interfacial properties of these materials. In the fourth chapter, it is provided the electrochemical data for pristine CNOs, radio frequency Ar/O2 plasma oxidized CNOs (CNO-RF) and chemically oxidized CNOs (CNO-OXI) cast on glassy carbon (GC) electrodes. The electrochemical response was evaluated by cyclic voltammetry using [Fe(CN)6]3-, [Ru(NH3)6]3+, [Fe(H2O)6]2+ and ferrocenemethanol (FcCH2OH) as redox probes. The results indicate the electron transfer kinetics for these probes was influenced by the nature of functional groups on the electrode material, adsorption processes and the electrostatic interactions between the redox probes and the surface of the different carbon nano-onions. The Chapter 5 is a deeper understanding of the electrochemical behaviour of FcCH2OH and [Fe(CN)6]3- redox probes at unmodified and CNOs modified GC electrodes. Cyclic voltammetry experiments were used to demonstrate that the electrochemical response of [Fe(CN)6]3- is a fully diffusion-controlled process, while for FcCH2OH a weak adsorption of its reduced form takes place on the GCE/CNO electrodes and in higher extension than on bare GC electrode. Double potential step chronocoulometry was used to obtain the empirical adsorption isotherms which were found to respond to the Sips model isotherm. In Chapter 6, it is explored the electrocatalytic properties of CNO, CNO-RF and CNO-OXI modified electrodes. At these surfaces, the electroreduction of O2 to H2O2 in acid media and the electrooxidation of H2O2, ascorbic acid (AA), dopamine (DA) and uric acid (UA) was studied by cyclic voltammetry and differential pulse voltammetry. The modified electrodes displayed excellent electrocatalytic activity to these molecules. The results demonstrate that CNOs enhance the electroactive properties of redox molecules and are thus promising materials for electrochemical detection and metal-free electrocatalysts of different reactions. Chapter 7 introduces a novel potentiometric pH sensor based on polydopamine films coated on a CNOs conductive surface. Glassy carbon electrodes containing a carbon nano-onion layer were modified by electropolymerization and self-polymerization of dopamine. The modified surfaces were characterized by ESEM, Raman spectroscopy and cyclic voltammetry. The modified electrodes displayed an almost Nernstian potentiometric response over the pH range 2-10. Furthermore, the pH sensors exhibit a fast and reversible behavior toward variations of pH and negligible interference effects from monovalent cations. The sensors showed an excellent correspondence between the pH values obtained using the GCE/CNO/PDA electrodes and those measured with glass electrodes. Chapter 8 explores the possibility to uses the co-electropolymerization of DA and L-3,4-dihydroxyphenylalanine (L-DOPA) on CNOs modified electrodes as versatile platform to develop electrochemical immunosensors. Mixtures of DA and L-DOPA at different molar rations were co-electropolymerized on CNOs-modified glassy carbon electrodes to form a poly(L-DOPA/DA) film. This platform was applied to the electrochemical detection of IgA antibodies using both a HRP-based sandwich type assay and label-free detection based on [Fe(CN)6]3-/4- signal blocking. The sandwich and the label-free assays showed a wide linear response and suitable LOD to allow the detection of serum IgA deficiency. Most remarkably, the incorporation of CNOs layer led to a significant improvement (three-orders of magnitude) of the analytical performance of these immunosensors.
Overall, the presented thesis has contributed to expand the current knowledge on the dispersibility, electronic structure, surface chemical composition and electrochemical properties of CNOs. Novel electrocatalytic properties and electrochemical (bio)sensing applications of these materials were also explored and systematized to understand their relationship with the electronic structure of CNOs. The results presented here illustrate the advantages of incorporating CNOs in the design of electrochemical systems to improve their performance. These results might also help to fabricate tailor made surfaces with unique properties to realize high potential of CNOs to the maximum and to open new application possibilities in areas such as electrochemical energy storage and electroanalytical methods.
