The size of primary particle of NDs obtained by the detonation technique is well suited for biomedical studies, the detonation products required to be extensively purified. Depending on the materials and matrices present during their production, detonation NDs can contain oxides and carbides, including those of iron, chromium, silicon, calcium, copper, potassium, titanium, and sulphur, in addition to carbon soot. To remove surface metallic impurities, NDs are treated with classic acidic treatments containing of sulfuric acid and its mixtures with nitric acid or potassium dichromate. A hydrofluoric acid and nitric acid combination also has been used to remove metallic contaminants from the particles. The oxidation and subsequent removal of sp2-bonded carbon structures, present either in amorphous or graphitic forms, is achieved by the use of liquid oxidizers such as sodium peroxide, a chromium trioxide and sulfuric acid mixture, or a nitric acid and hydrogen peroxide mixture7. Thermal oxidation process uses temperatures of 400°C–430°C to allow the oxidation of sp2-bonded carbon species in the air, with negligible alteration in sp3-bonded carbon structures. These temperature requirements for the selective oxidation of sp2-bonded carbon species were confirmed by authours.
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'The Size of Primary Particle of Nds'
The oxidation of NDs at a high temperature using air containing ozone is another approach that results in the major removal of the sp2-hybridized carbon structures. The ozone-air treatment, also known as the “gas phase treatment,” is ecological and efficient, as the purification of NDs is achieved without using the corrosive liquid oxidizers24.
Although the size, shape and surface properties of NDs are determined by the nature of explosion and purification conditions, their basic structure follows a core and shell model. The diamond carbon forms the inert core and the surface shell is partially containing of graphitic structures. In addition, a broad variation of functional groups such as carboxyl, hydroxyl, lactone, anhydride, ketone, and ether can be present on the surface of these ND particles. X-ray diffraction is one of the most utilized techniques for characterizing NDs, including in terms of their size, structure, and composition. Upon annealing the NDs at 1500°C for 10 minutes in a vacuum, the diamond X-ray diffraction peak disappears with the exposure of sp2 carbon structure peak. The crystal lattice parameters and the quality of NDs can vary depending upon the synthesis conditions, as determined by X-ray diffraction studies199.
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The economical large-scale production of detonation NDs give considerable impetus to technological applications. For example, the antifriction properties of NDs and their soot make them ideal candidates as wear-protective additives. The stability of these particles at extreme temperatures had led to applications in composite manufacturing. The large surface area of NDs is suitable for adsorbing biomolecules, presenting them as an attractive material for isolating proteins and pathogenic microorganisms, as shown in Table200.
