ABSTRACT
New allotropes and forms of carbon are now known that distinguish themselves from three-dimensional (3D) diamond, graphite, and amorphous carbon. The new allotropes and forms include fullerenes (1985), 1D carbon nanotubes (CNTs) (1991), 2D graphene (G) derivatives and graphene oxide (GO), and 0D graphene quantum dots (GQDs) and carbon dots (CDs). These materials have been the subject of intense research due to their relevance in nanoscience and engineering, nanotechnology, and for their growing presence, importance, and emerging uses in society. Closely related to the carbon allotropes are the so-called BCN materials formed by boron, carbon, and nitrogen, such as 1D boron nitride nanotubes (BNNTs), ribbons, and nanofibers, 2D boron nitride nanosheets (BNNSs), boron and nitrogen doped graphenes, as well as 3D boron nitrides and carbides. Collectively, these materials have already demonstrated the potential to provide new and challenging opportunities in radiochemical nanomaterial
labeling and tracking research, and in emerging applications in areas such as nanomedicine, nuclear medicine, health care, energy, catalysis, electronics, photonics, spintronics, sensing, toxicology, and environment. The emerging role of radiolabeled nanoparticles (NPs) and nanostructures (NSs) in nanomedicine, for example, is discussed by de Barros et al. [1].Although these materials constitute NSs rather than NPs, per se, their inclusion in the present monograph is justified by the enormous potential impact that these materials offer in labeling research and applications due to the present and emerging global importance of these materials in society. Accordingly, we present a short introduction to the materials in this chapter along with some common methods of preparation and examples of some of their applications. 4.1 IntroductionThe past several decades have witnessed an explosive growth in chemical, physical, and biological research on low dimensional carbon forms, with G and CNTs in the forefront. Research has already expanded to include large scale production of graphene, for example, using green energy techniques and low-cost starting materials, which attest to the already-demonstrated and increasing importance of this material and its derivatives in applications across broad sectors of society from the nano to the macro scale.Although some 15 isotopes of carbon are known, ranging from 8C to 22C, only 12C and 13C are stable, while 14C appears to be the only radioactive carbon isotope found in nature. Since some of these isotopes presently lend themselves to labeling and tracking applications, their extension to use in low dimensional carbon structures is inevitable. 11C, with a half-life of ~20 min, decays predominantly via positron emission, 11C 11B + e+ + ne and is thus potentially valuable in positron emission tomography (PET) imaging. Both isotopes, especially 14C, are important tracer elements and can be made artificially by thermal neutron bombardment (14C) or with a cyclotron or linear accelerator (11C) using, for example, boron, in 11B(p, n)11C, or nitrogen, in 14N(p, a)11C. 14C is available in many forms, for example, as carbonates, gases, and organic
compounds, such as 14C-labeled glucose [2]. 13N provides a short-lived, but nonetheless usable additional isotope for labeling BCN materials. 4.2 Background and Description
4.2.1 Graphene (G) and Graphene Oxide (GO)Graphene in pure form, with formula Cn, consists of sp2-hybridized carbon atoms arranged in hexagonal form in stable, one-atom-thick, 2D sheets akin to a monolayer of graphite. Because of its atomic thickness, ~0.35 nm, G is considered to be a 2D nanostructure. Under different fabrication conditions, monolayers of G may be planar, corrugated, rippled, pleated, curled, or folded, as depicted in Fig. 4.1. Monolayers of G are commonly polycrystalline and consist of single crystalline grains separated by grain boundaries that can adversely affect their physical properties in applications of G-bearing devices. Edwards et al. reviewed the G film growth on polycrystalline metals, including groups 8 through 11 metals, stainless steel, and other alloys [3]. The uniform growth of single-crystal G over wafer-scale areas is currently a hotly pursued topic that, if successful, could have major technological and societal impact [4-7].The graphene community generally distinguishes between single, bi and tri layer G, few-layer (< ~10), and multilayer G, which begins to exhibit electronic properties similar to those of thin-layer graphite. Few-and multilayered G may show rhombohedral rotational faulting, ordered (e.g., Bernal ABA and rhombohedral ABC), or disordered (turbostratic) stacking [8, 9]. Although the lateral dimensions of G sheets may range over many microns (G microsheets), when the dimensions are <100 nm, the G nanosheets are generally referred to as GQDs.Several excellent books and reviews are now available on the physics, chemistry, and applications of G, GO, and GQDs. For a general overview of G and its derivatives, see references [3, 10, 16-40]. For general works on 2D NSs and low-dimensional carbon materials see, for example, [37, 38], respectively. For an accurate historical account of key events in the nearly 175-year history of graphite-graphene-like materials, see [41].
