**4. Hybridization of carbon atoms**

The recent materials discoveries at nano scale open new horizons in all science and engineering fields. One of the most important point of view reported in several literatures is depending on classify carbon materials according to their hybridization characteristics [24, 25].

The electron hybridization determines the ability of carbon atoms to arrange themselves in a wide variety of structures with linear, planar and tetrahedral symmetry forming different allotropes, such as carbyne/carbyte, graphene/ graphite and diamond. So, depending on hybridization type carbon structures can be classified from sub-molecular to macroscopic scales into three general families: carbyne- general family (sp1 family), this family includes carbon atoms with sp1 hybridization state from its nanostructured like carbyne or cyclo-carbon to its macrostructural crystalline form [26]. The second class called graphene general family (sp2 family), this family includes carbon atoms with sp2 hybridization state in their nano as well as macro-crystal structures with hexagonal and rhombohedral structures like graphene and graphite. The third class called diamond general family (sp3 family), the carbon within this family existing sp3 hybridization state like diamond structure in its nano and macro scales [27].

For more complexation, carbon atoms can be exist with other hybridization states called intermediate hybridizations with different degrees. The degree of hybridization in this case caused by the curvature of the sp2 hybridized structure, leading to produce strained C–C bonds. Usually carbon atoms with pure sp2 hybridization state shows an ideal flat structure. While in the case of atoms with curved structure, their hybridization degree should be >2 as in the case of fullerene carbon [14, 27].

On the other side, usually carbon atoms in sp2 hybridization state arrange themselves in hexagonal rings as well as in a various other polygonal rings. The non-hexagonal rings can leads to curving the flat sheet or keeping its flatness if the polygon arrangement fulfils certain symmetry rules [14].

**Figure 3.**

*The ternary carbon allotropy phase diagram based on hybridization type (reuse with permission Elsevier [14]).*

The pentagon rings induce a positive curvature while heptagon or octagon rings induce a negative curvature. Therefore, carbon materials with sp2 hybridization state can be exist into three types: positive curved fullerene-type, which includes carbon atoms with hexagonal and pentagonal rings and negative curved schwarzite-type, this type includes carbon atoms with hexagonal and either heptagonal or octagonal rings and the last one called zero-curvature graphene-type which includes carbon atoms with hexagonal rings only [14]. This procedure of classification carbon based- nanomaterials had been presented by a triangular carbon allotropes phase diagram, see **Figure 3**. In which, hypothetical carbon allotropes located at the corner of the diagram, and allotropes with intermediate hybridization states located at the edge of the diagram while carbon existing mixed hybridization states located inside the triangular diagram [14].

## **5. Fullerene and nanodiamond**

The recent discoveries of the nano-sized carbon materials leads to expand the list of carbon allotropes. In association with the ability of carbon atoms to form wide range of structures, carbon based- nanomaterials become widespread in the fields of nanoscience and nanotechnology [28].

Generally, Carbon-based nanomaterials possess effective physicochemical properties make them as a powerful tool in medicine. For example, graphene possess many promising properties due to its high surface area and high functionalization ability that make it suitable for drug delivery treatment, along with its high mechanical properties, graphene had been recommended for tissue engineering

**91**

*Fullerenes and Nanodiamonds for Medical Drug Delivery*

field. Carbon nano tubes CNTs had been suggested for different in vivo applications due to its strong optical absorption in the specific wave length and as an active tool for bi0 imaging and drug delivery applications. Recently, fullerene and nanodiamond had been investigated and received much attention to use as a drug delivery

In spite of the promising benefits of using carbon based- nanomaterial as medical tools for the treating of difficult to treat diseases, several challenges are involved within this technology such as, their toxicity, diffusion and distribution abilities throughout the body which may leading to unpredictable effects. So, in-depth and carefully studies around their nature and behavior in human body regarded the most important factors in this field. One of the great promises of nanotechnology in medicine is the local or targeted delivery of drugs. Efficient targeting would allow for a reduced systemic dosage meaning also a reduced toxicity while resulting in relatively higher or more efficient dosage at the desired

Several ideas, suggestions and observations in addition to physical and chemical experiments of clustered molecules were led to the way for discovery of C60 in 1985. In 1966, David Jones discussed the possibility of creating balloons made up from carbon atoms. Then in 1970, this idea was progressed by Eiji Osawa when he revealed the possibility of preparing molecule made up of 60 carbon atoms knowm as C60 molecule in a condensed icosahedron structure [30]. After that in 1971, Eiji Osawa and Zensho Yoshida enumerated the possible aromatic properties of the structured C60 molecule. Later, Bochva and co-worker studied the electronic structure of this molecule. Then in 1980, Davidson characterize the closed- hollow structure of this molecule using different theoretical techniques. Subsequently, in 1985, Kroto and Smalley and their team obtained carbon cluster through scientific experiment to study the suitable conditions at which carbon atoms nucleates in the atmosphere of the red gait star. The mass spectrometer analysis of the obtained clusters indicates that most of them had 60 carbon atoms

This carbon allotrope become the heart of nanotechnology and attracted significant attention of scientists. For that, in 1996, Kroto, Curl and Smalley were

Fullerene derived its name in the honor of the geodesic domes designer the artchitect Buckminster Fuller. Fullerene family usually represented by a formula of Cn, where n refers to the existing carbon atoms in the cage structure which can be up to several hundred atoms, the number of the carbon atoms existing within fullerene structure has a great influence on its structural geometry and its properties. C60 is the most dominant molecules within fullerene family [31].

The structure of C60 has truncated icosahedrons made up of 20 hexagonal rings located at the center of the icosahedral faces and a 12 pentagons located around the apexes. It is the most symmetric molecule. It has 2.fold, 3.fold and 5.fold rotational symmetry. The first one is through the edge center of 2- hexagons, the second one is from the center of 2-hexagons which facing each other, while the last one is through

Furthermore, fullerene molecules can be exist as a spherical, ellipsoid, tubular shapes consisting hexagonal, pentagonal and sometimes heptagonal rings. C60

rewarded by Nobel Prize in chemistry for their discovery of fullerene [31].

two pentagons centers which facing each other [30, 31].

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

carriers [29].

target site [29].

**6. Fullerene**

**6.1 History and structure**

and some of them had 70 ones [31].

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

field. Carbon nano tubes CNTs had been suggested for different in vivo applications due to its strong optical absorption in the specific wave length and as an active tool for bi0 imaging and drug delivery applications. Recently, fullerene and nanodiamond had been investigated and received much attention to use as a drug delivery carriers [29].

In spite of the promising benefits of using carbon based- nanomaterial as medical tools for the treating of difficult to treat diseases, several challenges are involved within this technology such as, their toxicity, diffusion and distribution abilities throughout the body which may leading to unpredictable effects. So, in-depth and carefully studies around their nature and behavior in human body regarded the most important factors in this field. One of the great promises of nanotechnology in medicine is the local or targeted delivery of drugs. Efficient targeting would allow for a reduced systemic dosage meaning also a reduced toxicity while resulting in relatively higher or more efficient dosage at the desired target site [29].

### **6. Fullerene**

*Materials at the Nanoscale*

The pentagon rings induce a positive curvature while heptagon or octagon rings

state can be exist into three types: positive curved fullerene-type, which includes carbon atoms with hexagonal and pentagonal rings and negative curved schwarzite-type, this type includes carbon atoms with hexagonal and either heptagonal or octagonal rings and the last one called zero-curvature graphene-type which includes carbon atoms with hexagonal rings only [14]. This procedure of classification carbon based- nanomaterials had been presented by a triangular carbon allotropes phase diagram, see **Figure 3**. In which, hypothetical carbon allotropes located at the corner of the diagram, and allotropes with intermediate hybridization states located at the edge of the diagram while carbon existing mixed hybridization

The recent discoveries of the nano-sized carbon materials leads to expand the list of carbon allotropes. In association with the ability of carbon atoms to form wide range of structures, carbon based- nanomaterials become widespread in the

Generally, Carbon-based nanomaterials possess effective physicochemical properties make them as a powerful tool in medicine. For example, graphene possess many promising properties due to its high surface area and high functionalization ability that make it suitable for drug delivery treatment, along with its high mechanical properties, graphene had been recommended for tissue engineering

hybridization

induce a negative curvature. Therefore, carbon materials with sp2

*The ternary carbon allotropy phase diagram based on hybridization type (reuse with permission* 

states located inside the triangular diagram [14].

fields of nanoscience and nanotechnology [28].

**5. Fullerene and nanodiamond**

**90**

**Figure 3.**

*Elsevier [14]).*

#### **6.1 History and structure**

Several ideas, suggestions and observations in addition to physical and chemical experiments of clustered molecules were led to the way for discovery of C60 in 1985.

In 1966, David Jones discussed the possibility of creating balloons made up from carbon atoms. Then in 1970, this idea was progressed by Eiji Osawa when he revealed the possibility of preparing molecule made up of 60 carbon atoms knowm as C60 molecule in a condensed icosahedron structure [30]. After that in 1971, Eiji Osawa and Zensho Yoshida enumerated the possible aromatic properties of the structured C60 molecule. Later, Bochva and co-worker studied the electronic structure of this molecule. Then in 1980, Davidson characterize the closed- hollow structure of this molecule using different theoretical techniques. Subsequently, in 1985, Kroto and Smalley and their team obtained carbon cluster through scientific experiment to study the suitable conditions at which carbon atoms nucleates in the atmosphere of the red gait star. The mass spectrometer analysis of the obtained clusters indicates that most of them had 60 carbon atoms and some of them had 70 ones [31].

This carbon allotrope become the heart of nanotechnology and attracted significant attention of scientists. For that, in 1996, Kroto, Curl and Smalley were rewarded by Nobel Prize in chemistry for their discovery of fullerene [31].

Fullerene derived its name in the honor of the geodesic domes designer the artchitect Buckminster Fuller. Fullerene family usually represented by a formula of Cn, where n refers to the existing carbon atoms in the cage structure which can be up to several hundred atoms, the number of the carbon atoms existing within fullerene structure has a great influence on its structural geometry and its properties. C60 is the most dominant molecules within fullerene family [31].

The structure of C60 has truncated icosahedrons made up of 20 hexagonal rings located at the center of the icosahedral faces and a 12 pentagons located around the apexes. It is the most symmetric molecule. It has 2.fold, 3.fold and 5.fold rotational symmetry. The first one is through the edge center of 2- hexagons, the second one is from the center of 2-hexagons which facing each other, while the last one is through two pentagons centers which facing each other [30, 31].

Furthermore, fullerene molecules can be exist as a spherical, ellipsoid, tubular shapes consisting hexagonal, pentagonal and sometimes heptagonal rings. C60

belongs to the spherical fullerene class which looks like a soccer ball, while C70 belongs to the ellipsoidal class which looks like rugby ball. In addition, several efforts have been reported to produce fullerene with high yields, in 1990, a method was discovered for producing macroscopic amounts of this distinctive material and this breakthrough allowed scientists to understand its chemistry and explore its properties [31].

Generally, fullerene can be classified into classical fullerene and non-classical fullerene. The first one containing 12 pentagons and any number of hexagons, while the second fullerene class can have heptagons, octagons, and an additional number of pentagons or squares [30, 31]. Due to the unique structure and properties of C60, scientists showed high interesting in synthesis both larger and smaller fullerenes. Therefore, the family of fullerenes has been expanded involving fullerene molecules with a wide range of carbon atoms number. Larger fullerenes that have an icosahedral- symmetry also can be constructed. While, the carbon cages structure smaller than C60 consist of adjacent pentagons. These smallest fullerenes are predicted to have unusual physical as well as mechanical properties due to the high curvature of their molecular surface. The smallest fullerene molecules is a dodecahedron consisting of 20 carbon atoms with only pentagon rings. The fundamental understanding of the size dependence of the closed carbon cage structures is important for tailoring these systems for possible nanotechnology applications [31].

Due to the electronegative nature of fullerene, fullerene can form different compounds with different structures. One of the most important fullerene species is derived from the cage- like structure in which there is an ability of trapping metal atom inside the cage and forming specific endohedral fullerene known as metallofullerene. Exohedral fullerene is another type of fullerene with enhanced solubility property, obtained due to the chemical reaction with chemical groups. On the other side, when one or more carbon atoms within cage structure are substituted by specific hetero atom a hetrofullerene is produced [31].

#### **6.2 Synthesis routes**

Synthesis of graphenic materials like fullerene have been studied and reported in many literatures. Different techniques have been adopted for fullerene synthesis, such as arc discharge technique [32], vapor deposition of carbon atoms technique [33] and laser technique using graphite [34]. The cage- like structure of fullerene was identified for the first time by Kroto and Smalley in 1985, their experiment depending on applying an intense pulsed laser on a rotating graphitic disk to vaporize carbon atoms in the presence of helium atmosphere, then the condensed material had been collected, some of these routes are shown in **Figure 4** [35].

In 1990, another method was used to prepare fullerene reported by Ajie and co-workers, this method depending on the principle of the resistive heating of carbonic rods in a partial helium atmosphere which leads to evaporating carbonic atoms and then condensing it into fullerene structure [36].

Another method was discussed in U.S Patent in 1991, using electric arc technique, through this process an electric arc is generated between graphitic rods in inert atmosphere leading to produce soot- like product in which fullerene molecules extracted from the soot using suitable solvents [37].

The previous methods were associated with producing fullerene with low yields and there is no temperature controlling zone which is required for graphitization step. To overcome these two limitations, in 1994, Smalley discussed a laser vaporization technique to prepare fullerene from graphite materials using a focused laser beam. This technique involving evaporating carbon atoms and retained it in a

**93**

**Figure 4.**

*Some synthesis routes of Fullerene.*

*Fullerenes and Nanodiamonds for Medical Drug Delivery*

temperature- controlled- zone for sufficient time in order to complete the growth

Furthermore, another method was reported by Boorm and co-workers in 2001 called the direct method. This method depending on using polycyclic aromatic hydrocarbons with fullerene- like- framework. Through this method fullerene was synthesized directly due to rolling- up of the hydrocarbons structure into fullerene structure via laser irradiation process under flash vacuum pyrolysis conditions [30]. Whereas, in 1993, fullerene has been synthesized in high yields via ablation technique of graphite rod with solar irradiation using solar- furnace. Through this technique graphite was vaporized under the action of direct exposure to high- fluxsolar- irradiation. Then, the carbonic vapor was entrained by helium flow and

Since the discovery of fullerene as an important carbonic allotrope, tremendous development have been made in nanoscience and nanotechnology in order to fill the urgent need for this materials in a wide variety of applications. But, the formation mechanism of the cage- like structure still as a mystery and not well known [36]. One attempt to explain fullerene formation mechanism was reported by Paul and co-workers in 2012. Through their experiment, they depending on the principle of the bottom- up technique to explain the growth mechanism of fullerene

by integration with carbon atoms and C2 using laser irradiation technique. A carbonic target made up from graphite or 13C amorphous carbon with fullerene content exposed to a single laser strike that leads to vaporizing carbonic target into atomic carbon and C2while fullerene molecules desorbed into carbonic vapor zone under the action of helium flow. Then an interaction takes place between C60 fullerene (98.9% 12C and 1.1% 13C) and enriched 13C carbonic vapor which involves the exchanging of the original 12C atom of fullerene structure with 13C atom of carbonic vapor [40]. Each ingesting of 13C atom into fullerene structure occurs parallel with ejecting 12C atom from its structure and this interaction will spurring bond rearrangement with fullerene structure. Then, the produced species leaves clustering zone and undergo to a supersonic expansion step. Hence, different fullerene isomer such as C70 can be formed and the ejected 12C atoms may be

Furthermore, the growth mechanism of fullerene via different techniques that rely on the interaction between carbon atom and C2 affected by several parameters such as the density of carbonic vaper, exposure time, the flow rate of

and annealing process of the produced structure [38].

cooled into dark- water- zone to form fullerene structure [39].

ingested or exchanged with another fullerene structure [36].

*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*

#### **Figure 4.** *Some synthesis routes of Fullerene.*

*Materials at the Nanoscale*

properties [31].

applications [31].

**6.2 Synthesis routes**

belongs to the spherical fullerene class which looks like a soccer ball, while C70 belongs to the ellipsoidal class which looks like rugby ball. In addition, several efforts have been reported to produce fullerene with high yields, in 1990, a method was discovered for producing macroscopic amounts of this distinctive material and this breakthrough allowed scientists to understand its chemistry and explore its

Generally, fullerene can be classified into classical fullerene and non-classical fullerene. The first one containing 12 pentagons and any number of hexagons, while the second fullerene class can have heptagons, octagons, and an additional number of pentagons or squares [30, 31]. Due to the unique structure and properties of C60, scientists showed high interesting in synthesis both larger and smaller fullerenes. Therefore, the family of fullerenes has been expanded involving fullerene molecules with a wide range of carbon atoms number. Larger fullerenes that have an icosahedral- symmetry also can be constructed. While, the carbon cages structure smaller than C60 consist of adjacent pentagons. These smallest fullerenes are predicted to have unusual physical as well as mechanical properties due to the high curvature of their molecular surface. The smallest fullerene molecules is a dodecahedron consisting of 20 carbon atoms with only pentagon rings. The fundamental understanding of the size dependence of the closed carbon cage structures is important for tailoring these systems for possible nanotechnology

Due to the electronegative nature of fullerene, fullerene can form different compounds with different structures. One of the most important fullerene species is derived from the cage- like structure in which there is an ability of trapping metal atom inside the cage and forming specific endohedral fullerene known as metallofullerene. Exohedral fullerene is another type of fullerene with enhanced solubility property, obtained due to the chemical reaction with chemical groups. On the other side, when one or more carbon atoms within cage structure are

Synthesis of graphenic materials like fullerene have been studied and reported in many literatures. Different techniques have been adopted for fullerene synthesis, such as arc discharge technique [32], vapor deposition of carbon atoms technique [33] and laser technique using graphite [34]. The cage- like structure of fullerene was identified for the first time by Kroto and Smalley in 1985, their experiment depending on applying an intense pulsed laser on a rotating graphitic disk to vaporize carbon atoms in the presence of helium atmosphere, then the condensed material had been collected, some of these routes are shown in **Figure 4** [35]. In 1990, another method was used to prepare fullerene reported by Ajie and co-workers, this method depending on the principle of the resistive heating of carbonic rods in a partial helium atmosphere which leads to evaporating carbonic

substituted by specific hetero atom a hetrofullerene is produced [31].

atoms and then condensing it into fullerene structure [36].

molecules extracted from the soot using suitable solvents [37].

Another method was discussed in U.S Patent in 1991, using electric arc technique, through this process an electric arc is generated between graphitic rods in inert atmosphere leading to produce soot- like product in which fullerene

The previous methods were associated with producing fullerene with low yields and there is no temperature controlling zone which is required for graphitization step. To overcome these two limitations, in 1994, Smalley discussed a laser vaporization technique to prepare fullerene from graphite materials using a focused laser beam. This technique involving evaporating carbon atoms and retained it in a

**92**

temperature- controlled- zone for sufficient time in order to complete the growth and annealing process of the produced structure [38].

Furthermore, another method was reported by Boorm and co-workers in 2001 called the direct method. This method depending on using polycyclic aromatic hydrocarbons with fullerene- like- framework. Through this method fullerene was synthesized directly due to rolling- up of the hydrocarbons structure into fullerene structure via laser irradiation process under flash vacuum pyrolysis conditions [30]. Whereas, in 1993, fullerene has been synthesized in high yields via ablation technique of graphite rod with solar irradiation using solar- furnace. Through this technique graphite was vaporized under the action of direct exposure to high- fluxsolar- irradiation. Then, the carbonic vapor was entrained by helium flow and cooled into dark- water- zone to form fullerene structure [39].

Since the discovery of fullerene as an important carbonic allotrope, tremendous development have been made in nanoscience and nanotechnology in order to fill the urgent need for this materials in a wide variety of applications. But, the formation mechanism of the cage- like structure still as a mystery and not well known [36].

One attempt to explain fullerene formation mechanism was reported by Paul and co-workers in 2012. Through their experiment, they depending on the principle of the bottom- up technique to explain the growth mechanism of fullerene by integration with carbon atoms and C2 using laser irradiation technique. A carbonic target made up from graphite or 13C amorphous carbon with fullerene content exposed to a single laser strike that leads to vaporizing carbonic target into atomic carbon and C2while fullerene molecules desorbed into carbonic vapor zone under the action of helium flow. Then an interaction takes place between C60 fullerene (98.9% 12C and 1.1% 13C) and enriched 13C carbonic vapor which involves the exchanging of the original 12C atom of fullerene structure with 13C atom of carbonic vapor [40]. Each ingesting of 13C atom into fullerene structure occurs parallel with ejecting 12C atom from its structure and this interaction will spurring bond rearrangement with fullerene structure. Then, the produced species leaves clustering zone and undergo to a supersonic expansion step. Hence, different fullerene isomer such as C70 can be formed and the ejected 12C atoms may be ingested or exchanged with another fullerene structure [36].

Furthermore, the growth mechanism of fullerene via different techniques that rely on the interaction between carbon atom and C2 affected by several parameters such as the density of carbonic vaper, exposure time, the flow rate of inert gas, therefore, there is a possibility of controlling the growth mechanism by these parameters [36].
