Hierarchical Three Dimensional Carbon Nanotube Nanostructures: Designing, Surface Modifications and Applications for Supercapacitors and Photocatalysis

Abstract

Motivated by the fantastic size-dependent properties of nano-sized structures, this thesis mainly describes the designing, surface modifications and applications of the Si pillar assisted hierarchical three dimensional (3D) carbon nanotube (CNT) structures. The author begins with an introduction of the basic background knowledge about CNTs and the reasons that motivated the chosen research path of designing, surface modification and exemplary applications of hierarchical 3D CNT structures. PartⅠand partⅡseparately introduce the Si pillar assisted three-dimensional carbon nanotube web (3DCNW) and curtain (3DCNC) structures which have been investigated by author’s research group during the recent decade. PartⅠ furnishes the research processes of 3DCNW, from its evolution history, fabrication process, properties characterization to rational CNT surface modifications and applications. Compared with conventional CNTs which have been used by other researchers, the 3DCNW gained more attention because of its unique hierarchical structure which is comprised of interconnected SWNTs between Si pillars. 3DCNW has been successfully applied as a new type of microfluidic platform for nanoparticle filtration and streptavidin capturing. However, also because of its unique structure, how to modify the CNTs without destroying the structure is always a challenge. Physical vapor depositions (like ion sputtering, thermal evaporation, and atomic layer deposition), polymer coating (like high polymer molecule wrapping, π-π conjugation, and plasma induced polymerization), and electrochemical depositions (like metal/metal oxides, polymers) have been applied for the surface modification of 3DCNW. In this part, author mainly described two representative modification methods (aniline π-π conjugation and polymerization and Cu2O crystal electrochemical deposition) and their related applications (supercapacitors and photocatalysis, respectively). PartⅡ presents the study of pillar assisted 3DCNC. Starting from a pillar structured Si substrate, highly ordered and regular CNT “curtain” microstructure is obtained by introducing chemically induced capillary force assembly on vertically aligned CNTs. Morphological and surface properties of the formed CNT curtains are investigated by SEM, Raman spectra, static contact angle and XPS. A “spring-block” type computer simulation model is used for understanding the pattern forming process and mechanism. The obtained dynamics in simulation matches well the experimental in-situ observations. Such highly ordered and regular microstructures could be of great potential for many applications in biomedicine, biosensors, cell seeding, etc...