Former prepared by static high-pressure and high-temperature (HPHT)

Former to the development of application-specific surface revisal strategies for ND particles, it is important to know that there are no universal “nanodiamond particles” with well-defined structure and properties. There are many different types of method for the synthesis of ND particle, but only two major types of NDs are commercially available as a result can be considered for specific applications now. Nanodiamond particles of nanoscale size are produced by detonation of carbon-containing explosives so-called detonation nanodiamonds (DNDs) or by grate of micron-sized diamond powders prepared by static high-pressure and high-temperature (HPHT) synthesis in hydraulic presses (Figure 3)24. These two different types of ND particles have different structures and compatible different applications. Major differences between DND and HPHT ND, which influence their applications, are the size of primary particles (monocrystallites), state and content of nitrogen impurities present in the core of the particles. Besides, due to the difference in the methods of synthesis (bottom-up versus top-down approaches), the DND and HPHT NDs have seperate morphological differences. Primary particles of DND of few nanometer size have advantages in the production of the material at industrial scale in tons quantities annually25. As produced DNDs from tight inseparable, sonication, aggregates the primary particles. Based on recent advancement in DND deaggregation through milling of colloidal solutions the primary ND particles of size 4–5 nm in diameter are become available. Processing of HPHT synthetic diamond produced monocrystalline ND particles with the smallest average particle size around 10–20 nm; these particles exhibit blocky shapes. HPHT NDs consist nitrogen as a natural impurity in the form of substitutional nitrogen (Ns) with a typical concentration of 100–200 ppm (for HPHT ND type Ib). ND produced by crashing of natural diamond type Ia (Ns concentration up to 3000 ppm) is also available. High-energy irradiation by type Ib ND form vacancies followed by annealing causes creation of NV centres along red emission, whereas Ia ND exhibits green luminescence generated from formation of nitrogen-vacancy nitrogen (NVN) centres after irradiation and annealing26.