**7. Nanodiamond ND**

#### **7.1 History**

Recently, nanodiamond ND with its novel structure opened a new path in the creating and developing materials field. Nanodiamond is a new member of carbon- base- nanomaterials consisting nano tetrahedral network [37]. Naturally, nanoparticles of diamond have been found in meteorites as well as they have been found as inclusions in the old crust fragment of the earth [38].

The history of nanodiamond discovery starts since the second half of the last century via several successful and unsuccessful attempts in the synthesis and analysis of nanodiamond ND or ultra-dispersion diamond UDD begins in 1956 by Yu. Ryabinin using dynamic synthesis approach [39]. In 1961, diamond have been detected in a preserved shock compressed graphite in a plane ampoule by P.J.De Carli and co-workers. Then, in 1962, diamond was produced via shock compression using carbon black and graphite as starting material in cylindrical and spherical storage ampoule with up to 2% yields. Later, diamond was synthesized in explosion chamber using graphite, through this process graphite was placed directly into cylindrical charge containing of a troty- hexogen mixture and the charge was enveloped in a water jacket in order to inhibit graphitization process.

During 1963–1965, the effect of explosion conditions on the produced UDD was studied and indicate that the DP cooling as a result of conversion of the potential energy of diamond particles into kinetic energy of the envelope surrounding the charge plays a decisive role in the UDD synthesis [29]. Then, in 1976, Dupon co. used a cylindrical ampoules to produced diamond micropowder in commercial production rates by compressing a mixture made up from graphite and copper with charge. After that several scientific experiment were carried out to produce UDD with high yields using large mass charges. Another attempts were carried out in 1994 by V.V.Danilenko and co-workers to sintering UDD under static conditions [39].

Furthermore, a wide variety of techniques have been reported and employed to prepare micro and nano diamond particles. But on the other hand, the main drawback of most of these techniques are their requirement for high temperature and high pressure conditions, also, it was found that the produced material is a mixture made up from diamond and nan-diamond phases and some procedures leads to precipitate a amorphous carbon films at the grain boundaries of the produced nanodiamond [40]. After that, several techniques were suggested to produce nanodiamond at lower temperature and pressure conditions [41].

In this area, many researchers compete to synthesis ND with higher yields using advanced techniques in order to use it for a wide range of applications such as in drug delivery, biotechnology and tissue engineering fields [42].

#### **7.2 Structure and properties**

ND have unique properties, for this reason it is attracted the desire and interest of scientists and researchers in the physics and chemistry of nano- materials. It is believed that the structure of ND consisting of single or more diamond crystal surrounding by a shell containing graphenic carbons sp2C, amorphous diamond

**95**

**Figure 5.**

*Representation of ND structure.*

applications.

*Fullerenes and Nanodiamonds for Medical Drug Delivery*

functional groups have been found, see **Figure 5** [43].

dispersion ability comparing carboxylic- ND [48].

sp3C in addition to surface- state- carbons. The latter made up from chains of trans- polyacetylene TPA and graphene/fullerene fragments. In addition, different

However, some of the existing sp2carbon and amorphous diamond can be discarded by specific techniques such as thermal oxidation technique [44], while some graphene/fullerene fragments of the shell are an intrinsic components formed through the re-arrangement of the diamond surface. So, it is believed that the collected information about the structure is necessary in order to understand the nature of interaction between ND particles on one side and with other compounds on another side [43]. It is worth mentioning that the shell's constituents will have a

In the last decades, it was supposed that the shape of ND particles were quasispherical, but the modern microscope confirmed they are a polyhedral with distinct faceting shape and about half of the presented carbon atoms in ND are located at their surfaces. Hence, ND particles have bonding ability with different functional groups that effecting on its stability [46]. ND particles were required for a wide variety of applications, in lubricant industry, composites, medical therapy and others, this is due to the nature of their surface chemistry which depending on the chemical history of the material and the synthetic process [47]. For example, oxygen- rich- functional groups like hydroxyl, lactone and carboxyl have been found on the ND particle's surface produced via detonation technique [48]. Several efforts were reported about the surface modification process by functionalization with different groups which regarded as an effective strategy for reducing the size of ND aggregations. For example, functionalization with long chains of alkyl leads to reducing their aggregation size and enhancing their dispersion ability in organic solvents. Similar effects have been achieved via functionalization with boran. Furthermore, functionalization with Lysine molecules showed better water

Another type of ND is called hydrogenated ND, in which the surface of nanoparticles were wholly hydrogenated, hydrogenation process involves of linking a hydrogen atom with carbonic specie, then hydrogen atom will take its active role in etching of ND particles such as graphenic/fullerene carbon sp2 C or amorphous carbon, discarding oxygen-rich-groups as well as forming C-H bonds at ND surface [47, 49]. In fact all these benefits make this type more attracted for the most critical

great influence on the properties of ND particles with smaller sizes [45].

*DOI: http://dx.doi.org/10.5772/intechopen.97867*

#### *Fullerenes and Nanodiamonds for Medical Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.97867*

*Materials at the Nanoscale*

by these parameters [36].

**7. Nanodiamond ND**

**7.1 History**

conditions [39].

**7.2 Structure and properties**

inert gas, therefore, there is a possibility of controlling the growth mechanism

Recently, nanodiamond ND with its novel structure opened a new path in the creating and developing materials field. Nanodiamond is a new member of carbon- base- nanomaterials consisting nano tetrahedral network [37]. Naturally, nanoparticles of diamond have been found in meteorites as well as they have been

The history of nanodiamond discovery starts since the second half of the last century via several successful and unsuccessful attempts in the synthesis and analysis of nanodiamond ND or ultra-dispersion diamond UDD begins in 1956 by Yu. Ryabinin using dynamic synthesis approach [39]. In 1961, diamond have been detected in a preserved shock compressed graphite in a plane ampoule by P.J.De Carli and co-workers. Then, in 1962, diamond was produced via shock compression using carbon black and graphite as starting material in cylindrical and spherical storage ampoule with up to 2% yields. Later, diamond was synthesized in explosion chamber using graphite, through this process graphite was placed directly into cylindrical charge containing of a troty- hexogen mixture and the charge was

During 1963–1965, the effect of explosion conditions on the produced UDD was studied and indicate that the DP cooling as a result of conversion of the potential energy of diamond particles into kinetic energy of the envelope surrounding the charge plays a decisive role in the UDD synthesis [29]. Then, in 1976, Dupon co. used a cylindrical ampoules to produced diamond micropowder in commercial production rates by compressing a mixture made up from graphite and copper with charge. After that several scientific experiment were carried out to produce UDD with high yields using large mass charges. Another attempts were carried out in 1994 by V.V.Danilenko and co-workers to sintering UDD under static

Furthermore, a wide variety of techniques have been reported and employed to prepare micro and nano diamond particles. But on the other hand, the main drawback of most of these techniques are their requirement for high temperature and high pressure conditions, also, it was found that the produced material is a mixture made up from diamond and nan-diamond phases and some procedures leads to precipitate a amorphous carbon films at the grain boundaries of the produced nanodiamond [40]. After that, several techniques were suggested to produce nanodiamond at lower temperature and pressure conditions [41].

In this area, many researchers compete to synthesis ND with higher yields using advanced techniques in order to use it for a wide range of applications such as in

ND have unique properties, for this reason it is attracted the desire and interest of scientists and researchers in the physics and chemistry of nano- materials. It is believed that the structure of ND consisting of single or more diamond crystal surrounding by a shell containing graphenic carbons sp2C, amorphous diamond

drug delivery, biotechnology and tissue engineering fields [42].

found as inclusions in the old crust fragment of the earth [38].

enveloped in a water jacket in order to inhibit graphitization process.

**94**

sp3C in addition to surface- state- carbons. The latter made up from chains of trans- polyacetylene TPA and graphene/fullerene fragments. In addition, different functional groups have been found, see **Figure 5** [43].

However, some of the existing sp2carbon and amorphous diamond can be discarded by specific techniques such as thermal oxidation technique [44], while some graphene/fullerene fragments of the shell are an intrinsic components formed through the re-arrangement of the diamond surface. So, it is believed that the collected information about the structure is necessary in order to understand the nature of interaction between ND particles on one side and with other compounds on another side [43]. It is worth mentioning that the shell's constituents will have a great influence on the properties of ND particles with smaller sizes [45].

In the last decades, it was supposed that the shape of ND particles were quasispherical, but the modern microscope confirmed they are a polyhedral with distinct faceting shape and about half of the presented carbon atoms in ND are located at their surfaces. Hence, ND particles have bonding ability with different functional groups that effecting on its stability [46]. ND particles were required for a wide variety of applications, in lubricant industry, composites, medical therapy and others, this is due to the nature of their surface chemistry which depending on the chemical history of the material and the synthetic process [47]. For example, oxygen- rich- functional groups like hydroxyl, lactone and carboxyl have been found on the ND particle's surface produced via detonation technique [48]. Several efforts were reported about the surface modification process by functionalization with different groups which regarded as an effective strategy for reducing the size of ND aggregations. For example, functionalization with long chains of alkyl leads to reducing their aggregation size and enhancing their dispersion ability in organic solvents. Similar effects have been achieved via functionalization with boran. Furthermore, functionalization with Lysine molecules showed better water dispersion ability comparing carboxylic- ND [48].

Another type of ND is called hydrogenated ND, in which the surface of nanoparticles were wholly hydrogenated, hydrogenation process involves of linking a hydrogen atom with carbonic specie, then hydrogen atom will take its active role in etching of ND particles such as graphenic/fullerene carbon sp2 C or amorphous carbon, discarding oxygen-rich-groups as well as forming C-H bonds at ND surface [47, 49]. In fact all these benefits make this type more attracted for the most critical applications.

**Figure 5.** *Representation of ND structure.*

#### **7.3 Synthesis routes**

Graphite is the most stable carbon allotrope at ambient conditions of temperature and pressure. While, diamond formation requires more severe conditions. For example, the conditions for naturally formed diamond are (>1000°C) temperature and (4.5–6) Gpa pressure. After diamond formation, the reverse transition to graphite structure will not occur due to the high- energybarrier for phase transition. Although, graphite is the favored allotrope from thermodynamic point of view, but about 0.4 eV energy barrier must be overcome to transfrom sp2 C structure to sp3 C structure and this fact makes diamond as a metastable allotrope. But the transition kinetic to graphitic structure is not allowed [50].

Nowadays, a wide variety synthetic techniques for ND are available. In the following a brief description of the main techniques.


#### *7.3.1 Detonation technique*

In detonation technique an explosives with a negative- oxygen- balance and a source for carbon atoms (graphite or molecules driven from the used explosive materials) were placed inside the detonation chamber which is a closed metallic chamber. The driving force for diamond formation obtained from the explosion energy. During detonation, carbon atoms released and then condensed and transform into nanoclusters of crystals. In association with the generated high pressure and temperature, a crystallization of nanoclusters will occur and ND particles will form and grow into aggregations with size about (4–5) nm. The used coolant agent can exist as gas (dry detonation) or as water (wet detonation) [38, 39, 49].

The final produced soot-like material is usually consisting of diamond core with sp3 C surrounded by sp2C. The main advantages of this technique is its ability to produce ND with wide range of particle size, structure and surface- functional- groups these features makes this technique useful for a wide variety of applications as polymer filler for nanocomposites, polishing and coating purposes and others. While on the other side, the main associated disadvantage is the contamination of the produced ND with fragments from chamber wall [49]. So in order to eliminate the unwanted sp2C, to discard metal contamination and to breakup ND aggregations, a post- treatment step will be an essential to produce pure, de- aggregated ND with sp3C [39, 49].

Formation mechanism of detonation ND has been proposed by Danilenko. He suggested that the required temperature to form liquid carbon from its nano scale is lower than that from its bulk scale. So, he is suggested that the liquid carbon region is shifted to low- temperature region while the stability region of ND is shifted to high- pressure. This situation leads to a homogeneous nucleation of ND in carbon supersaturated vapor region followed by crystallization of the produced carbonic liquid [50].

#### *7.3.2 Chemical vapor deposition technique*

Till this day, CVD technique is widely used in the preparation of ND as powder or thin film with a wide range of sizes. The required carbon atoms for ND formation

**97**

*Fullerenes and Nanodiamonds for Medical Drug Delivery*

is derived from the decomposition of gaseous phases (usually methane in hydrogen excess) and a carbon-rich species. During decomposition process, the released carbon atoms were deposited on a silicon substrate covered with a detonation nanodiamond DND acting as a seeding sites for nucleation of ND [51].

For further illustration, several sources of energy can be used to activate the gas phase such as hot filament [52], plasma and flames [53]. Due to decomposition of gas phase, radicals will forms and then each two adjacent carbon atoms located at the surface of the used diamond-coat are left with the dangling bonds after hydrogen abstraction by H• radical. After that these bonds will be full with CH3 radicals then the adjacent carbon atoms will bond together and locked within

The main advantage of this technique is its ability to produce ND particle or ND thin film with a wide range of size (10–200) nm, in addition, to the possibility of controlling on the structure and morphology characteristics of ND. Also there is possibility to produce ND doped with different species that can inserted within diamond structure through growth process. In fact these possibilities enabled this technique to produce ND with modified electrical and optical properties required

This technique is one of the most attractive used technique for synthesis ND in liquid [38]. This technique including directing an intense laser beam on the graphite target immersed in a liquid medium, usually water. The directed laser beam with high energy induces target surface melting and turning it into superheated liquid. Due to the highly increased temperatures, a phase explosion will takes place and nanodroplets will be forms [57]. At these conditions, the emission of plasma plume with ablation will occur and an extremely high pressure and temperature conditions are created. Then through cooling of the ablation plume with the liquid medium a rapid quenching will takes place. In fact this situation of rapid and sudden decreasing in temperature creates the appropriate conditions for carbonic

This technique presents good benefits such as the ability to produce ND with high purity, while the main drawback is the high cost with low production rates [39]. On the other hand, several attempts have been reported to overcome such undesired features one of these attempts is called (Light Hydro- Dynamic Effect) LHDE. This technique used laser beam with higher power cross a fluid with a specific refractive index. The direction of laser beam produces white light flash and generates acoustic waves which leads to form high- power- hydro- shock [39]. This technique produced ND with high yields in association with good controlling on its size and surface functional groups. Moreover, it is found that the produced material possess outstanding thermal property make it suitable for

Nano-sized diamond have been synthesized via different techniques as previously discussed. In spite of the expected stability of the produced material, hightemperature and high- pressure are the main requirements for these techniques. In addition, the produced material is usually consisting sp3 and sp2 carbon and some of these techniques leads to produce ND with contaminates which requires additional purification steps and hence the overall cost will be increase. Therefore, several studies have been reported to prepare ND at ambient conditions [60, 61].

nanodroplets formation within few nanoseconds [49–59].

nanocomposites applications require heat dissipation property [58].

**7.4 Nanodiamonds at ambient conditions**

*DOI: http://dx.doi.org/10.5772/intechopen.97867*

diamond lattice [54, 55].

for many applications [54, 56].

*7.3.3 Laser technique*

#### *Fullerenes and Nanodiamonds for Medical Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.97867*

is derived from the decomposition of gaseous phases (usually methane in hydrogen excess) and a carbon-rich species. During decomposition process, the released carbon atoms were deposited on a silicon substrate covered with a detonation nanodiamond DND acting as a seeding sites for nucleation of ND [51].

For further illustration, several sources of energy can be used to activate the gas phase such as hot filament [52], plasma and flames [53]. Due to decomposition of gas phase, radicals will forms and then each two adjacent carbon atoms located at the surface of the used diamond-coat are left with the dangling bonds after hydrogen abstraction by H• radical. After that these bonds will be full with CH3 radicals then the adjacent carbon atoms will bond together and locked within diamond lattice [54, 55].

The main advantage of this technique is its ability to produce ND particle or ND thin film with a wide range of size (10–200) nm, in addition, to the possibility of controlling on the structure and morphology characteristics of ND. Also there is possibility to produce ND doped with different species that can inserted within diamond structure through growth process. In fact these possibilities enabled this technique to produce ND with modified electrical and optical properties required for many applications [54, 56].

#### *7.3.3 Laser technique*

*Materials at the Nanoscale*

**7.3 Synthesis routes**

allowed [50].

1.Detonation technique.

3.Laser technique.

*7.3.1 Detonation technique*

2.Chemical Vapor technique.

Graphite is the most stable carbon allotrope at ambient conditions of temperature and pressure. While, diamond formation requires more severe conditions. For example, the conditions for naturally formed diamond are (>1000°C) temperature and (4.5–6) Gpa pressure. After diamond formation, the reverse transition to graphite structure will not occur due to the high- energybarrier for phase transition. Although, graphite is the favored allotrope from thermodynamic point of view, but about 0.4 eV energy barrier must be overcome to transfrom sp2 C structure to sp3 C structure and this fact makes diamond as a metastable allotrope. But the transition kinetic to graphitic structure is not

Nowadays, a wide variety synthetic techniques for ND are available. In the

In detonation technique an explosives with a negative- oxygen- balance and a source for carbon atoms (graphite or molecules driven from the used explosive materials) were placed inside the detonation chamber which is a closed metallic chamber. The driving force for diamond formation obtained from the explosion energy. During detonation, carbon atoms released and then condensed and transform into nanoclusters of crystals. In association with the generated high pressure and temperature, a crystallization of nanoclusters will occur and ND particles will form and grow into aggregations with size about (4–5) nm. The used coolant agent can exist as

The final produced soot-like material is usually consisting of diamond core with sp3 C surrounded by sp2C. The main advantages of this technique is its ability to produce ND with wide range of particle size, structure and surface- functional- groups these features makes this technique useful for a wide variety of applications as polymer filler for nanocomposites, polishing and coating purposes and others. While on the other side, the main associated disadvantage is the contamination of the produced ND with fragments from chamber wall [49]. So in order to eliminate the unwanted sp2C, to discard metal contamination and to breakup ND aggregations, a post- treatment step will be an essential to produce pure, de- aggregated ND with sp3C [39, 49]. Formation mechanism of detonation ND has been proposed by Danilenko. He suggested that the required temperature to form liquid carbon from its nano scale is lower than that from its bulk scale. So, he is suggested that the liquid carbon region is shifted to low- temperature region while the stability region of ND is shifted to high- pressure. This situation leads to a homogeneous nucleation of ND in carbon supersaturated vapor region followed by crystallization of the produced carbonic

Till this day, CVD technique is widely used in the preparation of ND as powder or thin film with a wide range of sizes. The required carbon atoms for ND formation

following a brief description of the main techniques.

gas (dry detonation) or as water (wet detonation) [38, 39, 49].

**96**

liquid [50].

*7.3.2 Chemical vapor deposition technique*

This technique is one of the most attractive used technique for synthesis ND in liquid [38]. This technique including directing an intense laser beam on the graphite target immersed in a liquid medium, usually water. The directed laser beam with high energy induces target surface melting and turning it into superheated liquid. Due to the highly increased temperatures, a phase explosion will takes place and nanodroplets will be forms [57]. At these conditions, the emission of plasma plume with ablation will occur and an extremely high pressure and temperature conditions are created. Then through cooling of the ablation plume with the liquid medium a rapid quenching will takes place. In fact this situation of rapid and sudden decreasing in temperature creates the appropriate conditions for carbonic nanodroplets formation within few nanoseconds [49–59].

This technique presents good benefits such as the ability to produce ND with high purity, while the main drawback is the high cost with low production rates [39]. On the other hand, several attempts have been reported to overcome such undesired features one of these attempts is called (Light Hydro- Dynamic Effect) LHDE. This technique used laser beam with higher power cross a fluid with a specific refractive index. The direction of laser beam produces white light flash and generates acoustic waves which leads to form high- power- hydro- shock [39].

This technique produced ND with high yields in association with good controlling on its size and surface functional groups. Moreover, it is found that the produced material possess outstanding thermal property make it suitable for nanocomposites applications require heat dissipation property [58].

#### **7.4 Nanodiamonds at ambient conditions**

Nano-sized diamond have been synthesized via different techniques as previously discussed. In spite of the expected stability of the produced material, hightemperature and high- pressure are the main requirements for these techniques. In addition, the produced material is usually consisting sp3 and sp2 carbon and some of these techniques leads to produce ND with contaminates which requires additional purification steps and hence the overall cost will be increase. Therefore, several studies have been reported to prepare ND at ambient conditions [60, 61].

#### *Materials at the Nanoscale*

Proceeding from the chemical principles, the chemical reaction depending on the energy- materials interaction degree and require specific energy to proceed. Some of these studies suggested the possibility of using ultrasonic irradiation technique as a source for the required energy [60].

So, ultrasonic irradiation technique has been candidate to prepare ND. This technique improves the chemical reaction in solution via production of holeconstituent micro-bubbles [60]. During this process, a liquid media is irradiated with ultrasound and bubbles will be creates and oscillates under the action of the alternating compressive and expansive acoustic waves. Then, these bubbles will grow to a critical size and collapse leading to release an intense- localize energy about (5000 K and 1000 bar) within a very short period of time which is enough for synthesis of nanodiamond particles [61, 62].

The features of this technique were taken by researchers to produce micro and nano diamonds. In 2008, Khachatry and co-workers used graphite organic liquid suspension to synthesis microcrystalline diamond with degree of purity, cubicstructure and size range about (6–9) μm via ultrasound- cavitation process [63].

In 2019, researchers used a suitable method to synthesis nanocrystalline diamond via ultrasound waves. Through their experiment, graphene oxide was synthesized by modified Hummer's method then the prepared GO dispersion is activated by ultrasound waves which impacts its morphology and chemistry leads to produce graphene sheets. On the other hand, the generated shear forces leads to convert some of the produced graphene sheets into graphenic nanoscrolls with Mn2O7 had been inserted within its cavity. After decomposition of the unstable Mn2O7 a localized damage at the nanoscroll structure takes place which then undergoing to self-healing and as a result, ND seeds was formed and warped into nanoclusters of diamond, see **Figures 6** and **7** [62].

Other studies have been shown that the nucleation of ND is preferred inside the structure of carbon nanotubes under the action of surface tension property as a result of the carbon nanostructured curvature [64]. In association of founding some carbonates such as Li2CO3, Na2CO3 and K2CO3 as inclusions in natural diamond. Kamali and co-workers made their study in 2015 to produce nanocrystalline diamond from lithium- carbonate containing nanostructured carbon by simple heat treatment and at atmospheric pressure. In this study, CNTs produced by electrochemical process in lithium chlorite melt using graphite material. Through the experiment, lithium ions discharge on the cathode and inserted between the layers of graphene of the graphite structure under the influence of the cathodic which led to initiated enough stress to pulling graphene sheets from graphite structure into the melt and then these sheets will rolling up into CNTs. And after simple oxidation of the produced CNTs at temperatures range (420–550) °C and at atmospheric pressure, ND was formed, see **Figure 8** [64].

Another methodology was reported by Maia and co-workers in 2015. Their strategy depending on using dynamic compression as a tool for carbon structured transformation process under the action of accumulation of ultra- short laser pulses assisted by the formation of onion-like carbon structure as intermediate phase. Basically, the accumulation of free-electrons with high densities at the grain boundaries of graphite absorbed the applied energy which leads to creation a super ex cited region and then an ablation takes place followed by the propagation of non- thermal shockwave. After that, heating and thermal equilibrium takes place. In fact, these sequences of effects happened at each strike of laser which leading to destroy the lattice in continuous manner and causes more carbonic order to form. The formation of latter structure considered as intermediate phase with lower energy barrier to allotrope transition while the degree of crystallinity increases at each strike of shockwave [65, 66].

**99**

**8. Drug delivery system**

*permission Royal Society of Chemistry [64]).*

*(a-b) SEM image of Nanodiamond ND.*

Nanotechnology is the nano-sized materials science, involves materials manipulation at atomic and molecular scale in order to produce materials, systems and devices with unprecedented features. Recently, nanotechnology become the most promising technology in a wide variety of fields, one of these fields is medicine field. In fact, the employment of nanotechnology in medicine field is called

*SEM images of the micro and nano sized diamond particles after heating CNTs to 550°C in air (reuse with* 

*Fullerenes and Nanodiamonds for Medical Drug Delivery*

*DOI: http://dx.doi.org/10.5772/intechopen.97867*

*SEM images of nanodiamond at its cauliflower stage.*

**Figure 6.**

**Figure 7.**

**Figure 8.**

*Fullerenes and Nanodiamonds for Medical Drug Delivery DOI: http://dx.doi.org/10.5772/intechopen.97867*

*Materials at the Nanoscale*

source for the required energy [60].

synthesis of nanodiamond particles [61, 62].

nanoclusters of diamond, see **Figures 6** and **7** [62].

pressure, ND was formed, see **Figure 8** [64].

each strike of shockwave [65, 66].

Proceeding from the chemical principles, the chemical reaction depending on the energy- materials interaction degree and require specific energy to proceed. Some of these studies suggested the possibility of using ultrasonic irradiation technique as a

So, ultrasonic irradiation technique has been candidate to prepare ND. This technique improves the chemical reaction in solution via production of holeconstituent micro-bubbles [60]. During this process, a liquid media is irradiated with ultrasound and bubbles will be creates and oscillates under the action of the alternating compressive and expansive acoustic waves. Then, these bubbles will grow to a critical size and collapse leading to release an intense- localize energy about (5000 K and 1000 bar) within a very short period of time which is enough for

The features of this technique were taken by researchers to produce micro and nano diamonds. In 2008, Khachatry and co-workers used graphite organic liquid suspension to synthesis microcrystalline diamond with degree of purity, cubicstructure and size range about (6–9) μm via ultrasound- cavitation process [63]. In 2019, researchers used a suitable method to synthesis nanocrystalline diamond via ultrasound waves. Through their experiment, graphene oxide was synthesized by modified Hummer's method then the prepared GO dispersion is activated by ultrasound waves which impacts its morphology and chemistry leads to produce graphene sheets. On the other hand, the generated shear forces leads to convert some of the produced graphene sheets into graphenic nanoscrolls with Mn2O7 had been inserted within its cavity. After decomposition of the unstable Mn2O7 a localized damage at the nanoscroll structure takes place which then undergoing to self-healing and as a result, ND seeds was formed and warped into

Other studies have been shown that the nucleation of ND is preferred inside the structure of carbon nanotubes under the action of surface tension property as a result of the carbon nanostructured curvature [64]. In association of founding some carbonates such as Li2CO3, Na2CO3 and K2CO3 as inclusions in natural diamond. Kamali and co-workers made their study in 2015 to produce nanocrystalline

diamond from lithium- carbonate containing nanostructured carbon by simple heat treatment and at atmospheric pressure. In this study, CNTs produced by electrochemical process in lithium chlorite melt using graphite material. Through the experiment, lithium ions discharge on the cathode and inserted between the layers of graphene of the graphite structure under the influence of the cathodic which led to initiated enough stress to pulling graphene sheets from graphite structure into the melt and then these sheets will rolling up into CNTs. And after simple oxidation of the produced CNTs at temperatures range (420–550) °C and at atmospheric

Another methodology was reported by Maia and co-workers in 2015. Their strategy depending on using dynamic compression as a tool for carbon structured transformation process under the action of accumulation of ultra- short laser pulses assisted by the formation of onion-like carbon structure as intermediate phase. Basically, the accumulation of free-electrons with high densities at the grain boundaries of graphite absorbed the applied energy which leads to creation a super ex cited region and then an ablation takes place followed by the propagation of non- thermal shockwave. After that, heating and thermal equilibrium takes place. In fact, these sequences of effects happened at each strike of laser which leading to destroy the lattice in continuous manner and causes more carbonic order to form. The formation of latter structure considered as intermediate phase with lower energy barrier to allotrope transition while the degree of crystallinity increases at

**98**

**Figure 6.** *SEM images of nanodiamond at its cauliflower stage.*

**Figure 7.** *(a-b) SEM image of Nanodiamond ND.*

**Figure 8.**

*SEM images of the micro and nano sized diamond particles after heating CNTs to 550°C in air (reuse with permission Royal Society of Chemistry [64]).*
