Synthesis, characterization, and enzymatic degradation of nitrogen-doped carbon nanomaterials

Carbon nanomaterials, especially the sp2 carbon allotropes such as carbon nanotubes (CNTs) and graphene, have gathered extensive research interest in the recent decades. Structurally, CNTs represent one dimensional (1D) tubes with single- or multiple-layer graphitic sidewalls; and graphene is two dimensional (2D) one-atom-thick sp2 carbon sheets. With their remarkable intrinsic physical, chemical, and electronic properties, carbon nanomaterials have revolutionary potential to make impact on various existing technologies in many fields from construction and energy to electronics and biomedicine. Current research activities are focused on harnessing the desired properties of carbon nanomaterials for practical applications by their rational functionalization.;Among different covalent or noncovalent chemical functionalization schemes, heteroatom doping into the graphitic lattice most fundamentally alters the intrinsic properties of carbon nanomaterials. Nitrogen-doped CNTs are the most studied doped carbon nanomaterials due to their excellent electrochemical catalytic activity toward oxygen reduction reaction (ORR). Moreover, nitrogen-doping in multiwalled carbon nanotubes (MWCNTs) results in hollow compartments resembling stacked cups. These nanocups, termed as nitrogen-doped carbon nanotube cups (NCNCs), may find potential applications as drug delivery carriers. We managed to efficiently separate individual nanocups from their stacks through chemical and physical separation methods. By functionalizing separated NCNCs with gold nanoparticles (GNPs), the nanocups can be effectively corked by GNPs on the cup opening. The GNP-corked NCNCs form self-enclosing nanocontainers with potential applications as drug delivery nanocarriers.;The increasing use of carbon nanomaterials in biological and industrial applications inevitably raises the risk of exposure to humans and the environment with potential toxicological and ecological issues. This research dissertation also studies the enzymatic degradation of carbon nanomaterials as a potential remedy measure to mitigate their negative impacts. Following previous studies on the enzymatic degradation of single-walled carbon nanotubes (SWCNTs) by horseradish peroxidase (HRP), we studied HRP degradation of MWCNTs and its underlying mechanism. Furthermore, by using a more potent peroxidase, myeloperoxidase (MPO), we found that MPO triggers the opening of the GNP-corked NCNCs and catalyzes the subsequent degradation of the NCNC shells. These findings allude to potential biological pathways of drug release and degradative clearance of the GNP-corked NCNCs in therapeutic applications.