Carbon Nanoparticles and Nanostructures

The present chapter summarizes the recent advances in the production and the purification methods of nanodiamonds. The different strategies for seeding and patterning of surfaces are detailed. First reports of hybrids based on nanodiamonds are included like core shell particles or decoration with carbon dots or metallic atoms. Finally, an overview of applications for composites and nanomedicine is provided.

Chemical vapor deposition (CVD) is a powerful method to synthesize various carbon nanostructures (e.g., carbon nanotubes). A conventional CVD process has to be carried out at the temperatures over 600 °C. To extend the applications of carbon nanostructures, for example in the semiconductor industry, low-temperature synthesis processes are thus always pursued. In this chapter we review the CVD growth of carbon nanostructures at low temperatures (<450 °C). These growth processes are discussed in detail with respect to the applied catalyst system, carbon source, reaction atmosphere, catalyst faces, morphology control as well as unique structural characteristics of grown products. For the low-temperature CVD growth, catalytic reaction occurring on the low index faces of a metal catalyst is a crucial issue, and the growth is rate-limited by surface diffusion. Instead of the classical Vapor-Liquid-Solid (VLS) growth mechanism, the growth mechanism at low temperatures is interpreted with a novel Vapor-Facet-Solid (VFS) mechanism. Due to their unique features, the synthesized carbon nanostructures are promising to be applied for interconnects in large-scale integrated circuits, field emission, microwave adsorption, and as the anode material of lithium ion secondary battery, etc.

Carbon nanohorns, also called single-wall carbon nanohorns (SWNHs), are single-graphene tubules with horn-shaped tips, and were first reported by Iijima and colleagues in 1999 [1]. The tubule lengths and diameters range from 30 to 50 nm and 2 to 5 nm, respectively, and therefore, SWNHs are not uniform in size. Thousands of SWNHs assemble to form an aggregate, which in turn has an average diameter of ~80–100 nm. SWNHs are produced in large quantities (1 kg/day) by laser ablation of graphite. This process does not require a metal catalyst, and thus it is possible to prepare SWNHs with high purity (>95 %). Owing to their large surface area, molecular sieving effects and photo-thermal conversion characteristics, SWNHs show promise for applications in gas adsorption and storage, biosensor and nanomedicine such as drug delivery and photo-hyperthermia cancer therapy. In this chapter, we briefly introduce nanohorn production methods, biomaterial properties, and functionalization, and then highlight the potential use of SWNHs in various biological research fields. Issues concerning toxicity and biodegradation are also discussed.

Diamond nanoparticle hosting negatively-charged nitrogen vacancy (NV⁻) center has unique chemical, optical and spin properties in a wide range of nanotechnology applications. For instance, diamond nanoparticles containing NV centers have been well-known as Fluorescent NanoDiamond (FND) for fluorescence imaging. Recently the NV⁻ center has been applied for nanothermometry. In this chapter we are going to discuss the recent advances of the NV⁻ center for bioimaging and quantum sensing.

Polyglycerol (PG) functionalization on the surface of nanoparticle is one of the most effective methods to well disperse the particle in a physiological environment. The functionality also provides the nanoparticle with scaffold for further derivatization to add more functions. In this chapter, we will describe PG functionalization of nanoparticles including detonation nanodiamond (dND), superparamagnetic iron oxide nanoparticle (SPION) and fluorescence nanodiamond (fND), and their further derivatization for biomedical imaging agents in magnetic resonance and fluorescence imaging.

Carbon based dots (CDs) composed of sp² carbon structures and surface functional groups are a new kind of carbon nanomaterials, exhibiting unique luminescent properties due to the quantum confinement and edge effects. This chapter introduces CDs in detail from their synthetic strategies, morphological and structural characteristics, luminescent properties and mechanisms, and sensing applications. The synthesis methods are summarized as “top-down” and “bottom-up” approaches. Luminescent properties discussed include photoluminescence, upconversion luminescence, chemiluminescence, electrochemiluminescence. Sensing applications mainly refer to the chemical and biological sensors based on the luminescent properties of CDs. This chapter provides an overview of the research field and gives future perspectives for developing the exciting materials.

With unique and tunable photoluminescent properties, carbon nanodots (CNDs), as a new class of optical tags, have been extensively studied. In this chapter, we introduce the basic knowledge with respect to CNDs, including their structures and compositions, optical properties and applications in the bioimaging and biosensors. In particular, the photoluminescence (PL) mechanisms of CNDs, which are able to instructively improve its optical properties, have been emphasized and discussed in details. We hope to inspire research into the origins of the unique properties of CNDs and intrigue the researchers with different research backgrounds to participate in this field and explore the PL mechanisms of CNDs.

Carbon materials have been used for a long time in heterogeneous catalysis, which can satisfy most of the desirable properties required for a suitable catalyst support. Based on their significant advantages, such as low cost, huge amount, easy accessibility, high surface area, diverse porous structure, and resistance to acidic or basic environments, the carbon nanostructures are hungered for using as proper catalysts directly. Carbon dots (CDs), a new class of carbon nanomaterials with sizes below 10 nm, were also demonstrated to be efficient catalysts, such as, photocatalysts for selective oxidation, light-driven acid-catalysis and hydrogen bond catalysis. In this chapter, we will highlight the preparative methods, which have been used successfully to produce active, selective and durable CDs catalysts and look at their properties and the reactions which they promote. We then consider the catalysts design based on these new CDs and look into the future.

Macro-sized diamond films have been widely applied as the electrode for electrochemical and electroanalytical applications. Due to the non-uniform doping in diamond, boundary effects, and the varied ratios of graphite to diamond, only averaged electrochemical signals are detected over the full electrode. The studies of diamond electrochemistry at the nanoscale are thus highly required. In this chapter we overview recent progress and achievements about electrochemical properties and applications of diamond nanostructures and nanoparticles. After a brief introduction of the formation of these nanostructures and nanoparticles, electrochemical behavior of diamond nanostructures (e.g., diamond nanotexures, nanowires, networks, etc.) and nanoparticles (undoped, doped nanoparticles) in the presence/absence of redox probes is summarized. Their electroanalytical (e.g., electrochemical, biochemical sensing, etc.) and electrochemical (e.g., energy storage using capacitors and batteries, electrocatalysis, etc.) applications are shown. Diamond nanoelectrode array is introduced and highlighted as a promising tool to investigate diamond electrochemistry at the nanoscale as well.

Matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS) has become a widespread analytical tool for peptides, proteins and most other biomolecules. However, due to a competitive desorption of parasitic ions from the matrix, it is difficult to detect low molecular weight compounds (<700 Da). To enable desorption/ionization of small molecules, techniques operating in absence of an organic matrix were developed. These techniques known as surface assisted laser desorption/ionization mass spectrometry (SALDI-MS) rely on the use of nanostructured surfaces as laser desorption/ionization-assisted material. As compared to traditional MALDI-MS, SALDI-MS offers several advantages such as the ability to detect small molecules (<700 Da), easy sample preparation, low noise background, high salt tolerance and fast data collection. Carbon-based interfaces such as carbon-like graphite, carbon nanotubes, fullerenes or amorphous carbon have been employed as SALDI substrates for the detection of small macromolecules such as synthetic polymers and biomolecules. While the drawback of fullerenes and their derivatives is the general limited sensitivity, carbon nanotubes, which exhibit high sensitivities, are hardly soluble in aqueous solutions, limiting their use in bioanalytical applications. More recently, diamond-like carbon (DLC) and diamond nanowires have been successfully introduced as SALDI interfaces. This chapter summarizes recent developments in the use of carbon-based materials for SALDI-MS. A particular emphasis will be put on the use of diamond nanowires as novel SALDI substrates.