Oxidation, nanodiamond

One method of oxidizing nanodiamond surfaces has already been presented in Section 5.3.4 as a means of sample purification. The differing reactivity of graphitic and diamond carbon is utilized here. The unordered graphitic structures are oxidized and removed as gaseous products, whereas diamond particles are only modified on their surface. 

Wehling J, et al. Bactericidal activity of partially oxidized nanodiamonds. ACS Nano 2014 8(6) 6475-83. 

Other meteorite classes like C2, CO and ordinary chondrites contain much smaller inclusions less than 1 mm (MacPherson et al. 1988) and require ion microprobe techniques to evaluate the isotopic compositions. On the least metamorphosed side. Cl have very few inclusions or oxide grains, but are the carrier of the greatest amounts of stellar nanodiamond and other carbides (Anders and Zirmer 1993). As will be shown for Cr anomalies in carbonaceous chondrites, the survival of the mineral carriers of the anomalies also depends on the metamorphic grade of the meteorites. Nevertheless, isotopic anomalies have also been formd in higher metamorphic grade from other classes, especially in the reduced enstatite chondrites. 

Graphene has been prepared by different methods pyrolysis of camphor under reducing conditions (CG), exfoliation of graphitic oxide (EG), conversion of nanodiamond (DG) and arc evaporation of SiC (SG). The samples were examined by X-ray diffraction (XRD), transmission electron microscopy, atomic force microscopy, Raman spectroscopy and magnetic measurements. Raman spectroscopy shows EG and DG to exhibit smaller in-plane crystallite sizes, but in combination with XRD results EG comes out to be better. The CG, EG and DG samples prepared by us have BET surface areas of 46,... 

Graphene was prepared by four different methods, namely the reductive pyrolysis of camphor (CG), exfoliation of graphitic oxide (EG),4 conversion of nanodiamond (DG)5 and arc evaporation of SiC (SG).6 In the first method, to prepare CG, camphor was pyrolysed over nickel particles under a reducing atmosphere. The reaction was carried out in a two-stage furnace and camphor was slowly sublimed (170 °C) by heating from the first furnace to the second furnace held at 770 °C where the... 

In situ Raman spectroscopy during heating in a controlled environment allows for a time-resolved investigation of the oxidation kinetics of carbon nanomaterials and can identify changes in material structure and composition during oxidation. In this chapter, we describe the application of in situ Raman spectroscopy to determine conditions for selective oxidation and purification of carbon nanotubes (CNT) and nanodiamond (ND). 

Until recently, selective oxidation of carbon nanomaterials has not been optimized or was considered not feasible as in the case of ND [2]. However, for the production and application of nanostructures on an industrial scale, it is very important to develop a simple and efficient route to selectively remove sp -bonded carbon from nanodiamond and amorphous carbon from nanotubes with minimal or no loss of diamond or nanotubes. 

The stmctural diversity of carbon at the nanoscale exceeds that of all other materials [1]. Detailed information on the nature of the material and the structure-dependency of the oxidation kinetics is thus crucial for providing the required selectivity. While some nanomaterials, such as carbon nanotubes, have been studied extensively and are generally well understood, other nanostructures such as nanodiamond (ND) have received much less attention. However, in order to study their properties and open avenues for new applications, one has to provide a material of high purity and defined composition. 

Chiganov AS (2004) Selective inhibition of the oxidation of nanodiamonds for their cleaning. Phys Solid State 46(4) 595-787... 

Osswald S, Yushin G, Mochalin V, Kucheyev S et al (2006) Control of sp2/sp3 carbon ratio and surface chemistry of nanodiamond powders by selective oxidation in air. J Am Chem... 

Osswald S, Havel M, Mochalin V, Yushin G et al (2008) Increase of nanodiamond crystal size by selective oxidation. Diamond Related Mater 17(7-10) 1122-1126... 

In some cases, the oxidative purification is followed by a thermal treatment that is, heating the sample to ca. 700 C in an atmosphere of argon. It helps annealing surface defects and, partially, causes a thermal removal of functional groups from the surface, too. However, it also leads to a further graphitization of the surface. Hence careful consideration is required whether graphitized or functionalized nanodiamond is more advantageous for a certain experiment or application. 

Contrary to bulk diamond, the spin density is increased by sample purification because the treatment, for example, with concentrated oxidizing mineral acids, removes the graphitic layer from the surface of the nanoparticles (Section 5.3.4). In this way new, unsaturated bonding sites are generated. A part of the spin density, however, is localized in the crystal lattice for nanodiamond as well, and again nitrogen centers and other defects give rise to the unpaired electrons. 

The carboxyl groups available from oxidation of the diamond surface also represent good anchoring sites for further functionalizations. Derivatives can be obtained by acid-catalyzed esterification as well as by a base-catalyzed formation of amides (Figure 5.41). Employing bifunctional alcohols or amines allows for subsequent grafting steps. In principle, the same compounds can be used here like in the modification of chlorinated nanodiamond with alcohols or amines. 

Oxidized samples of nanodiamond carry many polar functional groups leading to a preferred interaction with polar compounds. The bonding is achieved via... 

The high thermal conductivity can be employed for nanodiamond applications as well. It is possible to prepare, for example, heat-conducting pastes. The material demand is only l-10gm here. Another positive effect of using the nontoxic nanodiamond powder is to avoid the customary, very poisonous paste of beryUium oxide in some of these applications. 

H-B. Cho, S.T. Nguyen, T. Nakayama, M.T.T. Huynh, H. Suematsu, T. Suzuki, et al.. Oxidation of nanodiamonds and modulation of their assembly in polymer-based nanohybrids by field-inducement,/owrna/ of Materials Science, 48 (12), 4151-4162, 2013. 

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