Rational design and synthesis of efficient Carbon and/or Silica functional nanomaterials for electrocatalysis and nanomedicine

In nanomaterials there is a strong correlation between structure and properties. Thus, the design and synthesis of nanomaterials with well-defined structures and morphology is essential in order to produce materials with not only unique but also tailorable properties. The unique properties of nanomaterials in turn can be taken advantage of to create materials and nanoscale devices that can help address important societal issues, such as meeting renewable energy sources and efficient therapeutic and diagnostic methods to cure a range of diseases. In this thesis, the different synthetic approaches I have developed to produce functional nanomaterials composed of earth-abundant elements (mainly carbon and silica) at low cost in a very sustainable manner are discussed. In Chapter 1, the fundamental properties of nanomaterials and their properties and potential applications in many areas are introduced. In chapter 2, a novel synthetic method that allows polymerization of polyaniline (PANI), a conducting polymer, inside cylindrical channel pores of nanoporous silica (SBA-15) is discussed. In addition, the properties of the III resulting conducting polymer in the confined nanochannel spaces of SBA-15, and more importantly, experimental demonstration of the use of the resulting hybrid material (PANI/SBA-15 material) as electocatalyst for electrooxidation reactions with good overpotential, close to zero, are detailed. In chapter 3, the synthetic approach discussed in Chapter 2 is further extended to afford nitrogen- and oxygen-doped mesoporous carbons. This is possible by pyrolysis of the PANI/SBA-15 composite materials under inert atmosphere, followed by etching away their silica framework. The high catalytic activity of resulting carbon-based materials towards oxygen reduction reaction despite they do not possess any metal dopants is also included. The potential uses of nanomaterials in areas such as nanomedicine need deep understanding of the biocompatibility/ toxicity of the materials. In Chapter 4, comparative in vitro and in vivo assessments of the biological properties and murine lung toxicity (biocompatibility) of the carbon-based nanomaterials synthesized above and in core-shell architectures containing carbon, silica and cobalt is presented. The results indicate that silica shell is essential for biocompatibility. Furthermore, cobalt oxide is the preferred phase over the zero valent Co(0) phase to impart biocompatibility to cobalt-based nanoparticles. This study is a result of collaboration between Asefa's research group at Rutgers University and Souid's research group at United Arab Emirates University. In Chapter 5, a new synthetic method to carbon nanoneedles (or a new class of carbon nanomaterials with high aspect ratios) is presented. In the work, cellulose nanocrystals are prepared and used as precursor for carbon nanostructures. Unlike other types of carbon nanomaterials, carbon IV nanoneedles possess high surface area and large proportion of edge planes, which have outstanding charge transfer and catalytic properties. The resulting metal-free, carbon nanoneedles are shown to serve as effective electrocatalysts for oxidation of hydrazine. In Chapter 6, the synthesis of amorphous carbon nanoneedles containing cobalt and their catalytic activities for oxygen reduction reaction is discussed. Even though the activity of the materials is lower than the one discussed in Chapter 3 for polyaniline-derived mesoporous carbons, the result and discussion in this chapter provides new insights on the effects and advantages of carbon nanoneedles on the electrocatalytic activity of the materials. In addition, the effects of cobalt content and nanoneedles' structures on the catalytic activity of the materials are described. In chapter 7, the synthesis of very small Au nanoparticles within SBA-15 mesoporous silica host materials by galvanic exchange reactions is described. The resulting Au/SBA-15 materials with different size Au nanoparticles are shown to have very interesting surface plasmon resonance (SPR) activity as a result of the confinement of large numbers of Au nanoparticles side-to-side in a row within the cylindrical channel pores of SBA-15 and the many SPR hot spots they formed. The surface enhanced Raman scattering (SERS) property of the materials in form of powder, showing reasonably high SERS enhancement factor for analytes is discussed. Finally in Chapter 8, Conclusions and Future Prospects are discussed.