Diamond, surface groups

Diamond surfaces after anodic oxidation treatment involve oxygen-containing surface functional groups. The electron-transfer kinetics for ions and polar molecules are expected to be quite different. Fe(CN)l /4 was highly sensitive to the surface termination of diamond. For an anionic reactant, there was an inhibition of the electron transfer for the oxygen-terminated diamond electrodes compared with the hydrogen-terminated diamond electrodes, and there was also an acceleration of the electron transfer for oxygen-terminated diamond for some cationic reactants such as Ru(NH3) +/3+ and Fe2+/3+. These results can be explained by electrostatic effects, which interact between the ionic... 

The amount of adsorbed atomic oxygen also changes considerably. Maximum quantity of atomic oxygen was observed temperature 500°C. It is established that as atomic oxygen is connected to a diamond surface.The atomic oxygen are formed at dissociations of chemical connected OH groups. 

A perfect stoichiometric crystal with complete absence of defects is considered neutral, which implies that the surface will be neutral too, thus there is no net surface charge. This is true for diamond. As soon as the surface is oxidized, hydroxyl and other groups form that develop a charge as soon as it is immersed in a protic liquid. Eor any material, there are four major sources of this charge ionization or dissolution of surface groups, specific ion adsorption, ion exchange, and solution of specific ions out of the surface. 

Upon treating nanodiamond with alkoxy silanes, a condensation occurs between one or more alkoxy functions of the silane and the hydroxyl groups situated on the diamond surface. The resulting compounds feature a C-O-Si-bonding of the organic residues to the diamond surface (Figure 5.35). 

Figure 5.42 Reactions of hydroxyl groups on the diamond surface.

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. 

Hydroxyl groups situated on the diamond surface can be reacted too, for example, in ester formations with acid chlorides. Again these esters may carry a variety of residues or feature multiple functionalities. A direct coupling of carboxylic acids is possible, too (Figure 5.42). Last, but not least, as mentioned in Section... 

The formation of O-acyl groups on the surface can also be realized starting from hydrogenated diamond. To this purpose, it is initiaUy treated with a diacyl peroxide like dibenzoyl or dUauroyl peroxide. The reagent is thermally cleft to give two radicals that can generate radical centers on the diamond surface by hydrogen abstraction. These positions may then be reacted with a variety of... 

In this way, it is possible to attach both aromatic and aliphatic carboxyUc acids to nanodiamond. The reaction is conducted wet-chemically in a suitable dispersing agent like hexane, cyclohexane, THF, or DMF. In acetonitrile, a reaction occurs with the solvent itself The radical initiator abstracts a hydrogen atom of the methyl group and the resulting alkyl is attached to a radical center on the diamond surface (Figure 5.44). This allows for estabhshing nitriles on the diamond that constitute valuable for further syntheses. 

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