NMR Characterization of NMR Characterization of Sidewall Functionalized Sidewall Functionalized

SWNTSWNT

By By

Heather RhoadsHeather Rhoads

AbstractAbstract

Since the discovery of SWNT (Single walled carbon Since the discovery of SWNT (Single walled carbon nanotubes) there has been an intense effort to nanotubes) there has been an intense effort to characterize, understand, and exploit their properties.characterize, understand, and exploit their properties.1, 21, 2 To achieve the full potential of SWNT, they must be To achieve the full potential of SWNT, they must be debundled into individual SWNTs. Debundling is achieve debundled into individual SWNTs. Debundling is achieve through several techniques including sidewall through several techniques including sidewall functionalization. The functionalization must be proven functionalization. The functionalization must be proven but currently utilized techniques give little information but currently utilized techniques give little information about the functionalization. More recently nuclear about the functionalization. More recently nuclear magnetic resonance (NMR) has been utilized to prove magnetic resonance (NMR) has been utilized to prove functionalization and the structure of the functionalized functionalization and the structure of the functionalized SWNT. This paper gives background, theory, review of SWNT. This paper gives background, theory, review of the literature, and future directions.the literature, and future directions.

BackgroundBackground

SWNT discovery Iijima in 1991SWNT discovery Iijima in 1991Avg Diameter of 1 nmAvg Diameter of 1 nmLength up to 5 cmLength up to 5 cmProduced by Produced by

Arc dischargeArc dischargeLaser ablationLaser ablationChemical vapor deposition (CVD)Chemical vapor deposition (CVD)

Literature ReviewLiterature Review

First utilized on Multiwalled carbon nanotubesFirst utilized on Multiwalled carbon nanotubes3-53-5

Theoretical background calculationsTheoretical background calculations6-106-10

Location of SWNT in Location of SWNT in 1313C NMRC NMR Separation of types of SWNTSeparation of types of SWNT

PropertiesProperties Structural, electronic, phase transitions, and Structural, electronic, phase transitions, and

dynamicsdynamics1111

Theoretical separation of metallic and Theoretical separation of metallic and semiconductingsemiconducting1212

Cutting, bending twisting and defects effect electronic Cutting, bending twisting and defects effect electronic propertiesproperties13-1413-14

Literature Review (cont)Literature Review (cont)

Growth Mechanism studyGrowth Mechanism study15-1715-17

Monitor opening and closing of SWNTMonitor opening and closing of SWNT1818

Hydrogen gas storageHydrogen gas storage19-2319-23

Adsorption sites and mechanismAdsorption sites and mechanism24-2724-27

Lithium and Cesium IntercalatedLithium and Cesium Intercalated28-3328-33

Polymers and SWNT interactionsPolymers and SWNT interactions34-4234-42

Desired Properties of SWNTDesired Properties of SWNT

Electrical – 1000x greater than copperElectrical – 1000x greater than copperMechanical - specific strength is aprox. Mechanical - specific strength is aprox.

200x greater than steel200x greater than steelElastic – 5x greater than steelElastic – 5x greater than steel

Characteristics of SWNTCharacteristics of SWNT

SWNT is a rolled up graphene sheet SWNT is a rolled up graphene sheet Composed of spComposed of sp22 hybirderized carbon hybirderized carbonHexagonal patternHexagonal patternRolling along the hexagonal pattern forms Rolling along the hexagonal pattern forms

along chiral vector aalong chiral vector a1, 1, aa22 giving units (n, m) giving units (n, m)Given by the following equation:Given by the following equation:

CChh = n (a = n (a11) + m (a) + m (a22))

Vector units of SWNTVector units of SWNT

Figure 1. The n and m coordinates of SWNT structure.

Properties Determined by Chiral VectorProperties Determined by Chiral Vector

Diameter - Diameter - ddt = (Ö3/p)t = (Ö3/p) ac ac-c (-c (mm22 + + mnmn + + nn22))1/21/2;;

Metallic - n-m/3 = integer: 1, 2,3…Metallic - n-m/3 = integer: 1, 2,3…Semiconducting – all other casesSemiconducting – all other casesType of SWNTType of SWNT

Arm chair – n=mArm chair – n=mZigzag – m=0Zigzag – m=0Chiral – all other combinations of (n, m)Chiral – all other combinations of (n, m)

Forms of SWNTForms of SWNT

Figure 2. Top) armchair SWNT, Middle) zigzag SWNT, Bottom) chiral SWNT. 43-44

ProblemProblem

SWNT can not over come van der Waals SWNT can not over come van der Waals effectseffects

Form bundles (range from 5 to 40 nm)Form bundles (range from 5 to 40 nm)Dramatically decrease desired propertiesDramatically decrease desired properties

SolutionsSolutions

Dispersing in Organic solventsDispersing in Organic solventsDispersing with Surfactant InteractionDispersing with Surfactant InteractionFunctionalization of the SWNTFunctionalization of the SWNT

EndEndSidewallSidewall

NoncovalentNoncovalentCovalentCovalent

Characterization TechniquesCharacterization Techniques

Raman spectroscopyRaman spectroscopyOptical absorptionOptical absorptionTransmission Electron Microscopy (TEM)Transmission Electron Microscopy (TEM)Functionalization = DefectFunctionalization = DefectNuclear Magnetic Resonance (NMR)Nuclear Magnetic Resonance (NMR)

Nuclear Magnetic ResonanceNuclear Magnetic Resonance

NMR is a phenomenon which occurs when NMR is a phenomenon which occurs when the nuclei of certain atoms are immersed the nuclei of certain atoms are immersed in a static magnetic field and exposed to a in a static magnetic field and exposed to a second oscillating magnetic field.second oscillating magnetic field.55, 5655, 56

Neutrons, protons, and electrons posses Neutrons, protons, and electrons posses spinspin

This creates a magnetic field around the This creates a magnetic field around the nucleus nucleus

NMR backgroundNMR background

Unpaired protons create NMR signals Unpaired protons create NMR signals Nucleus posses magnetic moment, Nucleus posses magnetic moment, μμ, ,

given by the following:given by the following:

I=spin; I=spin; γγ = = gyromagentic ratio; h = gyromagentic ratio; h = Planck’s constPlanck’s const

Energy of NMREnergy of NMR

Energy of particle is changing, which is Energy of particle is changing, which is detected in NMR through the following detected in NMR through the following equation:equation:

BB is the strength of the magnetic field at is the strength of the magnetic field at the nucleusthe nucleus

Transition stateTransition state

E = - m B cos q

Spin – Lattice RelaxationSpin – Lattice Relaxation

Given by TGiven by T11 is dependent upon time for return is dependent upon time for return

along z axisalong z axis Given by the following equationGiven by the following equation

MMzz = M = Moo (1 - e-t/T (1 - e-t/T11))

Provides structural informationProvides structural information Number of other similar atomsNumber of other similar atoms Functional group informationFunctional group information

Spin – Spin RelaxationSpin – Spin Relaxation

Spin-spin relaxation is found by the Spin-spin relaxation is found by the following:following:

1/T1/T22* = 1/T* = 1/T22 + 1/T + 1/T22inhomo inhomo

Information givenInformation givenNumber of identical substituentsNumber of identical substituentsPosition of probed atom in comparison to Position of probed atom in comparison to

other probed atomsother probed atoms

Current Applications: NoncovalentCurrent Applications: Noncovalent

Nakashima et al reported pyrene carrying ammonium ion Nakashima et al reported pyrene carrying ammonium ion noncovalent sidewall functionalization, which was noncovalent sidewall functionalization, which was determined by proton NMR.determined by proton NMR.5757

Li et al reported an interaction with the porphine THPP Li et al reported an interaction with the porphine THPP and SWNT, which could been seen by peak and SWNT, which could been seen by peak broadening.broadening.5858

Wong and Banerjee formed a new type of Wilkinson’s Wong and Banerjee formed a new type of Wilkinson’s catalyst with SWNT and observed the mechanism with catalyst with SWNT and observed the mechanism with 11H, H, 3131P, and P, and 1313C NMR.C NMR.5959

These noncovalent bonding methods are being utilized These noncovalent bonding methods are being utilized to separate semiconducting from metallic SWNT, to separate semiconducting from metallic SWNT, building materials in aqueous solutions, and new sources building materials in aqueous solutions, and new sources for catalyst material.for catalyst material.

Covalent: RadicalsCovalent: Radicals Covalently bonded SWNT are more prevalent Covalently bonded SWNT are more prevalent Radical reactions are one type of reaction Radical reactions are one type of reaction Umek et al reported the addition of carbon Umek et al reported the addition of carbon

radicals, which is confirmed with line broadening radicals, which is confirmed with line broadening in proton NMR.in proton NMR.5050

A photoinduced radical addition of perfluorinated A photoinduced radical addition of perfluorinated alkyl radicals to SWNT was monitored with alkyl radicals to SWNT was monitored with 1919F F NMR.NMR.6060

Billups et al reports alkyl addition from radical Billups et al reports alkyl addition from radical ions generated from varying salts; the material ions generated from varying salts; the material was then characterized with solid state was then characterized with solid state 1313C C NMR.NMR.6161

Covalent: Photosensitive and Covalent: Photosensitive and Electrical circuits with single bondsElectrical circuits with single bonds

The protonation of SWNT induced by pH change The protonation of SWNT induced by pH change was observed in 13C NMR, which showed a was observed in 13C NMR, which showed a downfield shift and new peak.downfield shift and new peak.6262

Zhang et al reported functionalizing SWNT with Zhang et al reported functionalizing SWNT with aniline in a ratio 360:1 SWNT to aniline, which aniline in a ratio 360:1 SWNT to aniline, which structure is proven by with an chemical shift and structure is proven by with an chemical shift and broadening of the proton NMR spectra.broadening of the proton NMR spectra.6363

Silylation of SWNT was determined by an Silylation of SWNT was determined by an downfield shift and broadening of peaks in downfield shift and broadening of peaks in 2929Si Si NMR.NMR.6464

These materials are being utilized as These materials are being utilized as photosensor materials and electronic circuitsphotosensor materials and electronic circuits

Covalent: cycloadditionCovalent: cycloaddition

The classic cycloaddition, Diels-Alder reaction, The classic cycloaddition, Diels-Alder reaction, has been utilized to functionalize SWNT with o-has been utilized to functionalize SWNT with o-quinodimethane under microwave irradiation.quinodimethane under microwave irradiation.6565

Zhang et al has performed a similar Diels-Alder Zhang et al has performed a similar Diels-Alder reaction excepted the SWNT are fluorinated.reaction excepted the SWNT are fluorinated.6666

The NMR proves the structure with broadening The NMR proves the structure with broadening of the peaks, chemical shift, and generation of of the peaks, chemical shift, and generation of new peak.new peak.

These materials are the precursors for polymer These materials are the precursors for polymer functionalization and photoelectrical materials.functionalization and photoelectrical materials.

Covalent: Nitrenes and Carbenes Covalent: Nitrenes and Carbenes CycloaddtionCycloaddtion

Holzinger et al has performed an extensive study utilizing Holzinger et al has performed an extensive study utilizing the cylcoaddition of nitrene with a large range of R the cylcoaddition of nitrene with a large range of R groups to SWNT. The groups to SWNT. The 11H NMR displayed an upfield shift H NMR displayed an upfield shift and broadening of peaks from the starting material.and broadening of peaks from the starting material.60,6760,67

Nitrene cycloaddition is utilized to attach carborane Nitrene cycloaddition is utilized to attach carborane cages to the sidewalls of SWNTs. cages to the sidewalls of SWNTs. 1313C NMR shows a C NMR shows a downfield shift, which is the result of the spdownfield shift, which is the result of the sp22 carbon carbon changing to spchanging to sp33 carbon attached to an nitrogen. carbon attached to an nitrogen.6868

The Bingel Reaction was utilized to create a carbene, The Bingel Reaction was utilized to create a carbene, which was tagged with fluorine and observed with which was tagged with fluorine and observed with 1919F F NMR.NMR.6969

Materials utilized new polymers, target drug for cancers, Materials utilized new polymers, target drug for cancers, and sensors, respectivelyand sensors, respectively

Covalent: 1, 3 dipolar additionCovalent: 1, 3 dipolar addition

1, 3 dipolar addition of nitrile oxide.1, 3 dipolar addition of nitrile oxide.7070

1,3 dipolar addition of nitrile amine.1,3 dipolar addition of nitrile amine.7171

Both confirm with proton NMRBoth confirm with proton NMRPeak broadeningPeak broadeningUpfield shiftUpfield shift

PhotomaterialsPhotomaterialsSensorSensorVoltaic cellVoltaic cell

ConclusionsConclusions

Determine Sidewall Determine Sidewall Functionalization Functionalization through NMRthrough NMR Peak broadeningPeak broadening Chemical ShiftChemical Shift

New materialsNew materials SeparationsSeparations PolymersPolymers DrugsDrugs SolarSolar CircuitsCircuits CatalystCatalyst

Future WorkFuture Work

Functionalized SWNT are proven to be an Functionalized SWNT are proven to be an essential part of several fields such as medical, essential part of several fields such as medical, electronical, and mechanical. electronical, and mechanical.

The vast goal of utilizing NMR to characterize The vast goal of utilizing NMR to characterize SWNT is to identify the functional groups and SWNT is to identify the functional groups and their structure, so the reaction conditions can be their structure, so the reaction conditions can be tailored for specific target needs. tailored for specific target needs.

The refinement of characterization techniques The refinement of characterization techniques for functionalized SWNT is essential for these for functionalized SWNT is essential for these materials to become the part of our everyday materials to become the part of our everyday life. life.

AcknowledgementsAcknowledgements

Dr. Grady, Dr. Cheville, Dr. Ford, and Dr. Dr. Grady, Dr. Cheville, Dr. Ford, and Dr. TeetersTeeters

Dr. ReitenDr. ReitenDr. NelsonDr. NelsonHeather Beem and Jason WatkinsHeather Beem and Jason WatkinsMy FamilyMy Family

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