Control of sp 2 /sp 3 Carbon Ratio and Surface Chemistry of Nanodiamond Powders by Selective Oxidation in Air
ABSTRACT The presence of large amounts of nondiamond carbon in detonation-synthesized nanodiamond (ND) severely limits applications of this exciting nanomaterial. We report on a simple and environmentally friendly route involving oxidation in air to selectively remove sp(2)-bonded carbon from ND. Thermogravimetric analysis and in situ Raman spectroscopy shows that sp(2) and sp(3) carbon species oxidize with different rates at 375-450 degrees C and reveals a narrow temperature range of 400-430 degrees C in which the oxidation of sp(2)-bonded carbon occurs with no or minimal loss of diamond. X-ray absorption near-edge structure spectroscopy detects an increase of up to 2 orders of magnitude in the sp(3)/sp(2) ratio after oxidation. The content of up to 96% of sp(3)-bonded carbon in the oxidized samples is comparable to that found in microcrystalline diamond and is unprecedented for ND powders. Transmission electron microscopy and Fourier transform infrared spectroscopy studies show high purity 5-nm ND particles covered by oxygen-containing surface functional groups. The surface functionalization can be controlled by subsequent treatments (e.g., hydrogenization). In contrast to current purification techniques, the air oxidation process does not require the use of toxic or aggressive chemicals, catalysts, or inhibitors and opens avenues for numerous new applications of nanodiamond.
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ABSTRACT: The standard enthalpies of formation at 25 °C of onion-like carbons (OLC) with different structural ordering have been investigated by high-temperature oxidation calorimetry. In terms of enthalpy and depending on the degree of structural ordering, OLC can be up to 16 kJ mol À1 less stable than graphite but up to 27 kJ mol À1 more stable than their fullerene allotropes. Furthermore, OLC are approximately 5–9 kJ mol À1 less stable than single-wall carbon nanotubes (SWCNTs). The samples prepared at 1800 °C are energetically less stable than samples made at 1300 and 1500 °C. These changes in energetics may stem from oxy-gen-containing functional groups bonded to the structure or from the creation of topolog-ical defects (polygonization and pentagon formation) whose concentration increases with increasing temperature and whose higher energy is balanced by configurational entropy.Carbon 04/2014; 69:490. DOI:10.1016/j.carbon.2013.12.053 · 6.16 Impact Factor
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ABSTRACT: Nanoparticles have recently emerged as an important group of materials used in numerous disciplines within the life sciences, ranging from basic biophysical research to clinical therapeutics. Luminescent nanoparticles make excellent optical bioprobes significantly extending the capabilities of alternative fluorophores such as organic dyes and genetically engineered fluorescent proteins. Their advantages include excellent photostability, tunable and narrow spectra, controllable size, resilience to environmental conditions such as pH and temperature, combined with a large surface for anchoring targeting biomolecules. Some types of nanoparticles provide enhanced detection contrast due to their long emission lifetime and/or luminescence wavelength blue-shift (anti-Stokes) due to energy upconversion. This topical review focuses on four key types of luminescent nanoparticles whose emission is governed by different photophysics. We discuss the origin and characteristics of optical absorption and emission in these nanoparticles and give a brief account of synthesis and surface modification procedures. We also introduce some of their applications with opportunities for further development, which could be appreciated by the physics-trained readership.Journal of Physics Condensed Matter 04/2013; 25(19):194101. DOI:10.1088/0953-8984/25/19/194101 · 2.22 Impact Factor
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ABSTRACT: Chemically modified 5-nm detonation diamond nanoparticles (DNPs) are characterized by grazing angle reflectance (GAR) Fourier transform infrared spectroscopy (FTIR), Kelvin force microscopy (KFM), and X-ray photoelectron spectroscopy (XPS). Using GAR-FTIR we discuss the surface chemistry and stability of the as-received DNPs, and compare them with DNPs modified by annealing in air or by oxygen plasma treatment. Infrared spectra of the as-received DNPs are dominated by C–H bonds and carboxylic groups (COOH), probably related to the wet chemical treatment in acids. Annealing in air and oxygen plasma lead to a significant enhancement of C=O groups and vanishing C–H groups. After short-term (10 min) oxygen plasma treatment, infrared peaks change in intensity and position indicating a spontaneous reactivity of DNPs, probably due to the partial erosion of the graphitic shell. Prolonged oxygen plasma treatment (40 min) or annealing in air at 450 °C for 30 min provides a stable DNPs surface. Surface potentials of DNPs obtained by KFM are well correlated with the GAR-FTIR measurements. XPS characterization corroborates DNPs compositional changes after the modification procedures.Journal of Nanoparticle Research 04/2013; 15(4). DOI:10.1007/s11051-013-1568-7 · 2.28 Impact Factor