Nanomaterials and their synthesis processes

Nanotechnology synthesis processes

1. Fullerene synthesis C60 is a molecule having 60 carbon atoms. The shape of C60 is like a soccer ball. There are 12 number of pentagons and 20 hexagons. If we put carbon atoms at all these 60 points, then we get structure of buckminsterfullerene.

2. Fullerene properties Each carbon atom is bonded to three others and is sp 2 hybridized. C60 behaves like an electron deficient alkenes and reacts readily with electron rich species. It avoid double bonds in the pentagonal rings, resulting in  poor electron  delocalisation.  As  a result, C60  behaves like  an  electron deficient alkene. Fullerenes are a class of closed-cage carbon molecule, C n , characteristically containing 12 pentagons and a variable number of hexagons. Hexagons = [(carbon atoms) – 20] / 2 Only C60 is more aromatic and highly stable. The highest stability of C60 is due to reduced strain in ring as twelve pentagons are isolated from each other.

3. Arc Vaporization of Graphite Kratschmer Huffman method Product : Large quantity fullerene containing soot

4. Components: High current electrical feed through—One movable electrode Water cooled surface to collect the soot Gas inlet Connection to vacuum Chamber evacuation up to  10 -3 torr and Helium filled at 150-250 torr High Quality graphite rod fitted to electrical feed through—Graphite rods are just touching---Low voltage AC or DC power supply For 6.25 mm graphite rod at 100-200 A results in efficient fullerene formation

5. The consumption of graphite is 5 -10 mm/min Crude carbon product/soot deposited on the inner surface is collected by hard brush Soot contains fullerene, higher fullerene and other carbon products Several experimental variables determine the yield of fullerene Vaporization current density and Helium partial pressure are two important parameters Vaporization of graphite is due to arc discharge— plasma formation —Cooling to fullerene clusters

6. Increase in current density increases the plasma temperature– increase in fullerene yield Increase in He pressure (150-500 torr ) ---increase in CNT yield

7. Laser Ablation Method Laser Ablation of graphite in Helium Atmosphere A very useful and powerful technique It was the first method attempted. The yield was too low The ablation is done at room temperature resulting in fast cooling. Rapidly cooling plasma does not get sufficient time for growing carbon structures to complete the formation of stable and closed fullerene structure. When the laser ablation is carried out at high temperature, fullerene in high yield is produced.

8. Laser ablation in high temperature furnace At high temperature the generated plasma cools more slowly and the growing carbon clusters have sufficient time to rearrange in to stable fullerene Fullerene production is more efficient at 1200 C At temp. higher that 1200 C, the yield may further increase Laser pulse energy and wavelength can be varied to modify the carbon plasma characteristics Gas pressure is another important variable which can also control carbon plasma and yield of pure fullerene

9. As the electrical connection has been dispensed with laser, minimum amount can be used efficiently for fullerene production Other methods of fullerene production Hydrocarbon combustion Low pressure helium sputtering Electron beam evaporation Inductively coupled RF evaporation of graphite target *** Only hydrocarbon combustion has been found to be satisfactory

10. Hydrocarbon combustion Benzene –oxygen mixture in laminar flow flame produce significant amount of C60 and C70 When benzene-oxygen ratio is 1 and diluted with 10% Helium it gives maximum yield of 0.3% C60 and C70 respectively Attractive Features Hydrocarbon process can be scaled up and also can be done as a continuous process In fact it can make large scale production process Variation in properties of flame can lead to systematic size distribution of fullerene Systematic doping can be easily studied as dopant can be mixed in benzene-oxygen mixture prior to burning

11. Fast atom bombardment mass spectrometry of soot from Arc Discharge Method

12. Separation of Fullerene clusters from others Fullerene is accompanied by higher hydrocarbon (> C60) species The crude mixture is unsuitable for further research or application work C60 needs to be separated from the crude mixture Flow chart outlining the principle of purification of crude soot to individual Fullerene

13. Soot in toluene is sonicated in a sonicator cleaning bath—C60 and higher fullerenes dissolve in toluene After sonication for 30-60 min the solution is filtered to remove insoluble carbon products Soot can be extracted by boiling toluene in a soxhlet separation experiment The method can be run continuously When toluene coming out after siphoning appear clear it indicates purification is near completion

14. Fullerene extracted by these methods contain about 15-20% of carbon soot produced The mass spectrum indicates dominant species are C60 and C70 along with mostly linear hydrocarbon impurities Removal of hydrocarbon impurity : Clue: Hydrocarbons are soluble in diethyl ether, whereas fullerenes are not. Step 1 : Remove toluene from toluene/fullerene extract in flash evaporator to get black residue Step 2 :Wash extensively the residue with diethyl ether The remaining solid is pure fullerenes

15. Separation of fullerenes All successful methods used to isolate individual fullerene is based on chromatography Neutral alumina as stationery phase and method is gravity feed Crude mixture fed on top of the column & eluted with 95:5 (v/v) mixture of hexane/toluene mixture In a good separation 3 distinct bands are visible Fast moving purple band (C60) has the highest mobility C70 deep red band comes next

16. Elution of C70 In the column chromatography after C60 is leached out the eluant composition is changed to hexane: toluene ratio of 50:50 Third yellow band contains higher fullerenes (<10%) *** Although chromatography is straightforward process, it takes several days to produce gram amount Ex. 1 g fullerene requires 10 kg alumina & 50L solvent Method 2: Alumina column is used along with soxhlation : Only 50% C60 is isolated

17. Method 3 : Activated carbon is packed over silica and mobile phase is pure toluene Elution is done under positive pressure 1g of pure C60 can be obtained in one hour Method 4 : HPLC: C60, C70 and higher fullerenes are well separated The collection at specific time from HPLC can lead to pure product Drawback : Functions at miligram level only HPLC chromatogram

18. Characterization by: NMR Mass Spectroscopy Optical spectroscopy HPLC 13 C NMR in C 6 D 6

19. Reactions of fullerene Fullerene dimers The C60 fullerene dimerizes in a formal [2+2] cycloaddition to a C120 bucky dumbbell in the solid state by mechanochemistry (high-speed vibration milling) with potassium cyanide as a catalyst. The trimer has also been reported using 4-aminopyridine as catalyst (4% yield) Heterofullerene In heterofullerenes at least one carbon atom is replaced by another element. Substitutions have been reported with boron, nitrogen, oxygen, arsenic, germanium, phosphorus, silicon, iron, copper, nickel, rhodium and iridium.

20. Open-cage fullerenes A part of fullerene research is devoted to so-called open-cage fullerenes whereby one or more bonds are removed chemically exposing an orifice. In this way it is possible to insert into it small molecules such as hydrogen, helium or lithium. The first such open-cage fullerene was reported in 1995. In endohedral hydrogen fullerenes the opening, hydrogen insertion and closing back up are possible. Electrophilic additions Fullerenes react in electrophilic additions as well. The reaction with bromine can add up to 24 bromine atoms to the sphere. The record holder for fluorine addition is C60F48

21. Hydroxylations Fullerenes can be hydroxylated to fullerenols or fullerols . Water solubility depends on the total number of hydroxyl groups that can be attached. One method is fullerene reaction in diluted sulfuric acid and potassium nitrate to C60 The maximum number of hydroxyl groups that can be attached (hydrogen peroxide method) stands at 36–40 Oxidations Although more difficult than reduction, oxidation of fullerene is possible for instance with oxygen and osmium tetraoxide .

22. Hydrogenations Fullerenes are easily hydrogenated by several methods. Examples of hydrofullerenes are C60H18 and C60H36. However, completely hydrogenated C60H60 is only hypothetical because of large strain. Nucleophilic additions Fullerenes react as electrophiles with a host of nucleophiles in nucleophilic additions Fullerene reacts with chlorobenzene and aluminium chloride in a Friedel -Crafts alkylation type reaction

23. FULLERENE APPLICATIONS The few of the applications of fullerenes are- Artificial photosynthesis Non-linear optics In cosmetics. In surface coatings Biological applications– Drug delivery

24. Porphyrinoid –Fullerene Hybrids as Candidates in Artificial Photosynthetic For natural photosynthesis, sequential photo-induced energy transfers are required, which are followed by an electron transfer process in the reaction center  This porphyrinoid -based scaffold is the light harvesting antenna system which absorbs sunlight and efficiently transfers it to the reaction center.  Light harvesting dye absorbs solar energy and transfer the energy to photosensitizer The photosensitizer transfer electron to the acceptor to form a charge separated state. Porphyrin is connected with an electron donor and acceptor Chromophore is energy donor and fullerene is electron acceptor Ferrocene-porphyrin-fullerene constitutes the most efficient artificial photosynthesis system.

25. Non-linear optics Two wave mixing, Frequency doubling, Parametric amplification etc. can function in 2 nd order NLO---T elecommunication Large number of conjugated double bond in fullerenes gives rise to 2nd and 3rd order non-linearity when push-pull functionalities are attached  -  + Conjugated

26. FULLERENE IN PERSONAL CARE PRODUCTS Fullerene C 60  is known to be able to inactivate hydroxyl radicals by attaching to double bonds   It is a powerful antioxidant, reacting readily and at a high rate with free radicals, which are often the cause of cell damage or death. It behaves like a " radical sponge ," as it can sponge-up and neutralize 20 or more free radicals per fullerene molecule. It possess a novel ability of selectively entering oxidation-damaged cerebral endothelial cells rather than normal endothelial cells and then protecting them from apoptosis (Cell death).

27.  In spite of their extreme conjugation, they behave chemically and physically as electron-deficient alkenes rather than electron rich aromatic systems The efficiency of these entities goes up to around 100 times the leading antioxidants

28. It enhances skin absorption and helps fight the appearance of fine lines, wrinkles sagging skin and dark spots caused by the oxidation of cells. UV Whitening Cream contains Fullerene RS™, a patented Nobel Prize technology, which is a superior radical scavenger with unparallel anti-oxidation effect that eliminates free radicals and inhibits UVA-Induced melanin formation .  `UV-induced melanin formation (tanning), traditionally thought to protect against skin cancer’ ** It is shown to be directly involved in melanoma formation in mammals

29. Fullerenes hold great promise also in non-physiological applications where oxidation and radical processes are destructive ( food spoilage, plastics deterioration, metal corrosion ).

30. Biological applications of fullerene . Factors That need to be kept in mind ! Compatibility Degree of its Usage in the body Target Area Effect after a Pre-Specified Time

31. Drug Delivery Vehicles

32. Fullerenes form an interesting system for Drug Delivery Derivatized Fullerenes are Strong Drug Adsorbents Water soluble Fullerene Derivatives which are localized closely to Mitochondria gave a new perspective on the use of Fullerenes in drug delivery systems. Nakamura and co-workers designed a Fullerene that is used to condense p-DNA Mitochondria are double walled fascinating structures that create energy to run the cell

33. Fullerene (C 60 ) derivatives extensively studied for a variety of medical applications, such as: Use as neuroprotective agents HIV-1 protease inhibitors Bone-disorder therapy agents X-ray contrast agents Slow-release agents for drug delivery C 60 -based reagents have also been examined as DNA transfection vectors (Delivery of DNA or RNA for higher expression or inhibition ) and tested for the ability to mediate gene transfer

34. Fullerenes in coatings Fullerene contributes positive tribological properties High friction coefficients of C 60  and C 70  films (0.55-0.8 m ) are due to the   tendency of the C 60  and C 70  particles to clump and   compress into high shear strength layers rather than due to   the impurities in the fullerenes. 

35. Buckminster fullerenes act as dry lubricants in coating application

36. Fullerene films as surfaces of uniform electric potential Continuous fullerene films (85% C 60 , 15% C 70 ) of thickness ∼10 nm have been sublimed on a metallic substrate previously coated with a 1‐nm‐thick Germanium sub layer . The films show no surface potential variations when scanned with a probe of 1 mV potential and 1 mm spatial resolutions. Transmission electron microscopy reveals the fullerene films to be amorphous.

37. Antibiofouling potential of a fullerene-coated surface *** Biofilm formation is prevented during water treatment using fullerene suspension However, as coating the biofilm is promoted Antibacterial fullerene-based particles, termed nC60, were coated onto a polystyrene surface to evaluate their ability to prevent biofilm formation by Pseudomonas mendocina If the surface is conducting, then it actually promotes biofilm formation The electronic properties of fullerenes and their apparent ability to encourage biofilm formation has potential for microbial fuel cell applications.

38. Inorganic Fullerenes (IF) Certain inorganic compounds such as WS 2 , MoS 2 , TiS 2 and NbS 2 that normally occur as large flat platelets can be synthesized into much smaller nano -spheres and nano -tubes ----Named as inorganic fullerene-like nanostructures In contrast to organic Fullerenes, IF is easier and much less expensive to produce, it is chemically stable and is less reactive and consequently less flammable. Organic Fullerenes are also considered to be highly toxic while IF materials have been tested extensively and deemed safe. One of the most interesting new IF properties is its extremely high degree of shock absorbing ability. Shock absorbing materials are commonly used in impact resistant applications such as ballistic protection personal body armor , bullet proof vests, vehicle armor , shields, helmets, and protective enclosures . The IF material has up to twice the strength of the best impact resistant materials as compared to highly efficient boron carbide and silicon carbide, Over 5 times stronger than steel. Mixing IF with highly elastic materials can lead to new compounds which are both flexible and shock-absorbing.