Synthesis and integration of carbon nanotubes and graphene oxide nanostructures for energy storage and biomaterials applications
- Autores: Jesús David Núñez García
- Directores de la Tesis: Ana M. Benito (dir. tes.), Wolfgang K. Maser (dir. tes.)
- Lectura: En la Universidad de Zaragoza ( España ) en 2015
- Idioma: español
- Tribunal Calificador de la Tesis: Gerard Tobías Rossell (presid.), Raul Arenal de la Concha (secret.), Alan Brian Dalton (voc.)
- Materias:
- Texto completo no disponible (Saber más ...)
- Resumen
The present thesis is structured in two stages. The first involves the conception of novel synthesis procedures to optimise the production of multiwalled carbon nanotubes (MWCNT) and water dispersable graphene oxide (GO) flakes. The second comprises the evaluation of MWCNT-GO hybrid assemblies as suitable material for electrochemical energy storage applications as well as the synthesis of nanostructured bioactive composites of hydroxyapatite supported on MWCNT and GO.
A correlation between catalyst design and high yield MWCNT production is established based on the continuous exfoliation of MexMg1-xMoO4 (Me = Ni, Co) platelet-like catalyst systems by using chemical vapor deposition method. These phases are responsible for the formation of large bundles of MWCNTs in yields of more than 3000 wt. % providing important insights towards low-cost large-scale MWCNT production.
Chemisorbed water (CW) is recognized as a stabilizer of the layered structure of GO papers at the nanoscale. CW is responsible of the degradation of the carbon sp2 structure of GO by promoting steam reactions at temperatures beyond 200 ºC while hydrazine reduction treatment of GO decreases the amount of CW avoiding steam reactions. These results provide valuable contributions for the engineering of GO-based composites and hybrid materials. Flexible conductive RGO papers are obtained through direct and gentle annealing of parent GO papers. The disrupted carbon sp2 network of GO paper is recovered combining a pre-reduction treatment of hydrazine vapors with thermal treatment at 700 ºC in argon. The resulting RGO papers exhibit electrical conductivities up to 8.1 kS/m maintaining its prior structural integrity and mechanical flexibility. This approach proposes a cost-effective fabrication route for flexible conductive graphene-like papers.
A novel processing method for the fabrication of freestanding membranes base on in-situ self-assembly of GO and oxidized MWCNTs nanostructured hybrids (GOBucky) is reported. This GOBucky assembly proved to be an effective method to remove CW from the layered structure of GO flakes without disrupting the carbon sp2 structure of GO or modifying its chemical composition. GOBucky with 10-15 % loading of MWCNT improves the thermal stability and the electrical conductivity of conventional GO papers and facilitates the fabrication of conductive porous electrochemical electrodes with specific capacitances up to 156 F/g. These electrodes are considered a step forwards for the design of improved carbon-based energy storage devices.
Non-stoichiometric nanocrystalline hydroxyapatite (nHAp) with a composition similar to natural bone is grown on oxidized MWCNT and on GO resulting in corresponding biocomposites materials. Functionalization degree and morphology of MWCNTs and GO are referred as critical parameters controlling the shape and crystallinity of the self-assembled nHAp. Crystalline rod-like nHAp establish O-Ca-O interactions between calcium atoms from the crystallographic (300) planes of hydroxyapatite and oxygen atoms from functional groups located either at the sidewall of oxidized MWCNT or at the basal plane of GO. Relevantly, during the stage of bioactivity the integration degree of nHAp on the carbon support is altering with time due to the remineralization of the formed apatite nanoparticles. These findings underline the potential of GO as suitable carbon support material and the value of XPS for evaluating the integration degree. The obtained results are of great interest for the design of bone implants and tissue engineering applications.
