Oxidation nanodiamond surface

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. 

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,... 

Here we describe how to employ in situ Raman spectroscopy to determine the conditions for selective oxidation and purification of carbon nanotubes (CNT) and nanodiamond (ND) measure and control their crystal size and improve the fundamental understanding of effects of temperature, quantum confinement, and surface chemistry on Raman spectra of nanocrystalline materials. 

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... 

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. 

For C-based QDs, nanodiamond and carbon dots are most extensively reported. Synthesis techniques include surface modification, oxidation with concentrated acid, electrochemistry, laser ablation, organic carbonization, and template methods. ... 

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