Detonation nanodiamonds (DNDs) is found as a member in the class of carbon family nanoparticles. Detonation method was first used to produce nanodiamonds. The oxygen-deficient explosive mixture of trinitrotoluene /hexogen (in the proportion 60:40) is detonated in an enclosed chamber in the atmosphere of inert gas along with H2O or even ice. To avoid the conversion of diamond into graphite at high-temperature during detonation, the cooling rate of the reaction outcome must be minimum i.
e 3000 K/min. Detonation nanodiamonds are formed at the front of detonation wave in a fraction of a microsecond. They contain carbon content predominantly in diamond phase upto an extent of 80-88%. The important aspect of the detonation nanodiamonds structure is the presence of different functional groups such as carboxyl, hydroxyl, lactone, anhydride, ketone and ether on the surface of the particles (often called “a coat of functional groups”). These groups are formed in detonation synthesis in a very short time (microsecond) during the explosion and the non-stationary arrangement of detonation nanodiamonds failed to stabilize their electron shell. The yield of produced detonation nanodiamonds depends on the heat capacity of the cooling medium in detonation chamber28. The diamonds are extracted from the soot by the use of liquid oxidants such as HNO3, a mixture of H2SO4 and HNO3, K2Cr2O7 in H2SO4, or HClO4.
The product is subjected to HCl for removing the non-carbon impurities. Non-diamond carbon can be oxidized by ozone-rich air at high temperatures is the cheapest and more ecological alternative method. Ozone-purified DNDs have a smaller aggregate size in aqueous dispersions and higher content of single particles as compared to purified with the help of liquid oxidants. Single DND particles have diameters of 4–5 nm. Firstly, aggregates are formed from single DND particles by coherent and non-coherent boundaries with C-C bonds (directly under explosion conditions). The aggregation continues as a result of realized bonds between functional groups on the surface of DND particles and due to Vander Waals forces.
Another theory, the aggregation mediated through graphitic soot6. Graphitic soot embryos which are obtained after lowering of the temperature, and the pressure start to coagulate and are arranged like an irregular graphitic shell around the particle before formed a core aggregate of DNDs. Another methods of synthesis of ND are: laser ablation, plasma assisted chemical vapour deposition (CVD), autoclave synthesis from supercritical fluids, chlorination of carbides, ion irradiation of graphite, electron irradiation of carbon ‘onions’ and ultrasound cavitation29,30.