Nanotechnology Questions and Answers – Purification of Fullerene

This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Purification of Fullerene”.

1. Choose the correct order for the purification of fullerene.
a) Column chromatography ➔ Residue re-dissolved in toluene ➔ Solvent extraction ➔ Filtration ➔ Evaporation
b) Solvent extraction ➔ Filtration ➔ Evaporation ➔ Residue re-dissolved in toluene ➔ Column chromatography
c) Filtration ➔ Evaporation ➔ Column chromatography ➔ Residue re-dissolved in toluene ➔ Solvent extraction
d) Evaporation ➔ Column chromatography ➔ Filtration ➔ Solvent extraction ➔ Residue redissolved in toluene
View Answer

Answer: b
Explanation: The purification process begins with extraction of soot enriched fullerenes in solvents such as toluene, benzene etc. This is followed by their filtration using a filter paper. Solvent is then subjected to evaporation and the residue of toluene-soluble soot fraction is re-dissolved in solvent. This solution is further led to the column for carrying out liquid chromatography.

2. Why is STG method so useful for separating higher fullerenes?
a) Ineffective for Endohedral fullerenes
b) Does not use inert buffer gas
c) Do not involve solvents
d) A quite inexpensive process
View Answer

Answer: c
Explanation: The separation and purification of fullerenes by sublimation in a temperature gradient (STG) does not involve solvents as used in liquid chromatography. This is very advantageous since endohedral and higher fullerenes tend to be less soluble in organic solvents than C60 and C70. Moreover, contamination from the solvents used in various solvent based purification method, can be avoided.

3. On what basis does liquid chromatography separate fullerene molecule?
a) Colour
b) Vibration spectra
c) Molecular Weight
d) Optical spectra
View Answer

Answer: c
Explanation: Liquid chromatography is a wet chemical method which involves a liquid mobile phase and a solid stationary phase. The separation of molecules of fullerene occurs in accordance to their weights. This method is useful in separating a single allotrope or isolating isomers having different molecular shapes but same molecular weight.

4. Which was the first available method for purification of C60 fullerene?
View Answer

Answer: a
Explanation: High performance liquid chromatography (HPLC) was the first available method for purification of C60 fullerene. HPLC relies on pumps that passes the pressurized solution (mobile phase) through a column filled with the high surface area solid (stationary phase). This leads to the separation of fullerene molecules from the solution.

5. Which of the following is a method of fullerene purification?
a) Reverse Osmosis
b) Liquid chromatography
c) Steam distillation
d) Crystallization
View Answer

Answer: b
Explanation: One of the major methods for fullerene purification is liquid chromatography. This method involves both mobile phase and stationary phase. The separation occurs on the basis of the interactions of the sample with the mobile (liquid) and stationary (high surface area solid) phases.

6. Find out the incorrect statement regarding purification of fullerenes from the following option.
a) Soxhlet extraction uses toluene as a solvent
b) In column chromatography alumina is the stationary phase
c) One-stop separation of higher fullerene is highly feasible
d) Polystyrene gel acting as a stationary phase is completely unreactive towards fullerene
View Answer

Answer: c
Explanation: The most common method for purification of fullerene is solvent extraction. Soxhlet extraction is a type of solvent extraction that uses toluene, hexane or heptane as solvents. Another common method is liquid chromatography which uses alumina as the stationary phase and hexane/toluene as eluent. Polystyrene gel can be used in place of alumina as stationary phase as it is completely unreactive towards fullerene. Thus, a good separation of fullerenes can be obtained with toluene as mobile phase. However, a one-step separation of higher fullerenes is impossible owing to the pronounced tailing effect of the preceding fullerenes.

7. What was the major drawback of flash column chromatography for fullerene purification?
a) Absence of stationary phase
b) Higher fullerenes could not be purified
c) Absence of the mobile phase
d) Abundant quantities of solvent formed
View Answer

Answer: d
Explanation: Flash column chromatography has remained as a predominant method for separation of fullerenes over the years. It includes separation of raw fullerenes in a column chromatography packed with neutral alumina as stationary phase and hexane or hexane/toluene (95:5) as the mobile phase. Since fullerene is not very soluble in hexane, abundant quantities of alumina and solvents are required. The solvents are different to recycle which makes the method inefficient.

8. Why is toluene preferred over benzene as an eluting solvent for recovery of C60 fullerenes?
a) Greater and easier availability of toluene
b) Less toxic in nature than benzene
c) Has lower boiling point than benzene
d) Toluene is less expensive than benzene
View Answer

Answer: b
Explanation: There are different suitable eluting solvents such as aromatic, heteroaromatic and halogenated hydrocarbons used for the recovery of fullerenes. Certain aromatic solvents in which fullerenes are soluble include benzene, toluene, xylene and mesitylene. Out of these, toluene is preferred more since it is less toxic than benzene and it has lower boiling point than xylene.

9. Which among the following is not an advantage for celite used for the purification of fullerene?
a) Very light weight
b) Inexpensive material
c) Permits passage of heavier fullerenes
d) High porosity
View Answer

Answer: c
Explanation: Celite is a soft, naturally occurring sedimentary rock that is often referred to as diatomaceous earth. It is a source of silica that easily crumbles into fine powder. It is a cheap and light material having high porosity. It, along with silica and carbon gel, can be used for efficient purification of fullerene. It possesses good pores that hold back the heavier fullerenes while allowing the lighter ones to pass through the column in liquid chromatography method of fullerene separation.

10. Liquid chromatography involves both physical and chemical interactions.
a) True
b) False
View Answer

Answer: a
Explanation: Liquid chromatography indulges in both physical and chemical interactions between a certain molecule and the stationary phase (solid) that is packed in a column. The interactions either reduce or raise the migration rate of molecules through the column. These are also responsible for increasing or decreasing the retention time of the molecule.

Sanfoundry Global Education & Learning Series – Nanotechnology.

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Manish Bhojasia - Founder & CTO at Sanfoundry
Manish Bhojasia, a technology veteran with 20+ years @ Cisco & Wipro, is Founder and CTO at Sanfoundry. He lives in Bangalore, and focuses on development of Linux Kernel, SAN Technologies, Advanced C, Data Structures & Alogrithms. Stay connected with him at LinkedIn.

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