This set of Nanotechnology Multiple Choice Questions & Answers (MCQs) focuses on “Functional Chemistry of Graphene – Set 2”.
1. Why does pristine graphene form irregular aggregates in solutions?
a) Conjugated structure and hydrophobicity
b) Hydrophilicity and Conjugated structures
c) Unconjugated structure and Hydrophobicity
d) Hydrophilicity and Unconjugated structures
View Answer
Explanation: Pristine graphene as well as reduced graphene oxides can easily form irregular aggregates in solution owing to their conjugated structures and hydrophobicity. Conjugated compounds usually possess polyaromatic rings and functional groups that attach to the sp2 network of graphene sheets. This leads to the stabilization of graphene sheets.
2. Which of the following is not an isomer of graphane?
a) Bicycle
b) Chair
c) Stirrup
d) Boat
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Explanation: Graphene forms many stable isomers. These include chair, stirrup, boat, tricycle, twist-boat configurations. Bicycle is however not an isomer of graphane.
3. What happens when graphene undergoes covalent functionalization?
a) Atomic and electronic structures remain unaltered
b) Distortion of the π-π conjugation system
c) Increase or decrease in electrical conductivity
d) Conversion of sp3 to sp2 hybridization of carbon atoms
View Answer
Explanation: Covalent functionalization of graphene is usually carried out by high energy reactants such as fluorine, hydrogen atoms, strong acids and radicals. The functionalization results in distortion of the π-π conjugation system of graphene basal plane.
4. Zero bandgap of graphene can be opened by applying adducts like aryl diazonium salts.
a) True
b) False
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Explanation: Free radical additions to graphene surmount its inert chemical nature. The most widely used adducts for free radical additions are aryl diazonium salts. The aryl radicals upon attacking the basal plane of graphene result in transfer of electrons from graphene to the radical. Thus, zero band gap of graphene is opened by the diazonium functionalization.
5. Why is the oxidation of graphene more complex than its hydrogenation or fluorination?
a) Oxygen is chemically more reactive than fluorine
b) Binding energy of C-F bonds is lower than C-H bond
c) Oxygen can form two covalent bonds instead of one
d) Presence of reversed dipole in C-F bond
View Answer
Explanation: Oxidation of graphene is one of the most fundamental and significant chemical reactions. It is a way more complex reaction than fluorination or hydrogenation of graphene. This is due to the fact that oxygen atom can form two covalent bonds rather than a single bond.
6. Find out the correct statement with respect to the asymmetric functionalization of graphene basal plane.
a) Chemical reactivity of graphene remains unaffected by these functionalities
b) Functionalities influence the surface wettability of graphene on one side
c) Asymmetric structures fail to control self-assembly of graphene sheets
d) Functionalities cannot break the symmetric restriction of graphene
View Answer
Explanation: Graphene undergoes bifacially asymmetric modifications of the basal plane. These functionalities influence the chemical reactivity on one side while the surface wettability on the other side of graphene surface. Moreover, the asymmetric structures are capable of controlling the self assembly of graphene sheets. This functionalization often breaks the symmetric restrictions of graphene, providing it with a non-zero bandgap.
7. Why does hydrogenation of graphene result in its higher elasticity?
a) Strong aromatic bond network is replaced with single σ bond
b) Lower surface roughness of graphane in comparison to graphene
c) Increase in strength of graphene after hydrogenation
d) Narrowing of the band gap
View Answer
Explanation: Hydrogenation is the most profusely researched and studied covalent functionalization of graphene basal planes. The functionalization alters both the electronic structure and properties of graphene. It also increases the elasticity of the graphene sheets owing to the replacement of the strong aromatic bond network with single σ bonds. Perfect graphane acts elastically upto at least 30% strains.
8. Find out the incorrect statement with regards to the free radical additions to graphene.
a) Decreased solubility of functionalized graphene in polar aprotic solvents
b) Modification of the conjugation length of the delocalized carbon lattice
c) Opening of bond gap of graphene using diazonium functionalization
d) Insert chemical nature of pristine graphene can be surmounted
View Answer
Explanation: Free radical addition to graphene results in covalent functionalization of graphene basal plane. It often overcomes the inert chemical nature of pristine graphene. The additions alter the conjugation length of the delocalized carbon lattice. They further enhance the solubility of graphene in polar aprotic solvents like DMF. Finally, the additions also result in opening of the band gaps in graphene.
9. What happens when only one side of graphene sheet is hydrogenated?
a) Rolling of graphene sheets
b) Shortening of the carbon-carbon(C-C) bonds
c) sp2 hybridization of carbon atoms remain unaltered
d) Balanced external stress
View Answer
Explanation: Graphene sheets can be partially as well as fully hydrogenated. Complete hydrogenation of graphene results in graphane where every carbon atom is covalently bonded to a hydrogen atom. Partial hydrogenation, on the other hand, results in formation of covalent bonds between hydrogen and carbon atoms of only one side of the graphene sheets. On partial hydrogenation, graphene sheets tend to roll into a tube due to the unbalanced external stress.
10. Which among the following is not a method of fluorination of graphene?
a) Treating graphene with XeF2
b) Chemical exfoliation of graphite fluoride
c) Treating graphene with (p-nitrophenyl) diazonium tetrafluoroborate
d) Mechanical exfoliation of graphite fluoride
View Answer
Explanation: Fluorination of graphene involves the binding of a fluorine atom to a carbon atom by a single covalent bond. The binding energy of C-F bond is low enough to allow the easier production of a saturated fluorographene. Fluorination can be performed by treating graphene with XeF2 and also by the chemical or mechanical exfoliation of graphite fluoride.
11. Which of the following doesn’t undergo covalent functionalization with graphene?
a) Fluorine
b) Aryl radical
c) PEGylated polymer
d) Dichlorocarbene
View Answer
Explanation: Graphene undergoes both covalent and non-covalent functionalization. Fluorine, aryl radicals and dichlorocarbene covalently bond with the carbon atoms present on the graphene basal plane rendering it functionality, while, amphiphilic polyethylene glycosylated (PEGylated) polymers are placed onto graphene sheets without the involvement of covalent bonds.
Sanfoundry Global Education & Learning Series – Nanotechnology.
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