A Novel Method for Carbon Nanotube Production and the

Mechanisms Involved

Xinfeng Xie1

Barry Goodell1, Yuhui Qian1, Geoffrey Daniel2, Jody Jellison3

1Wood Science and Technology, University of Maine, Orono, USA2Wood Ultrastructure Research Centre, Swedish University of Agricultural Sciences,

Uppsala, Sweden3Biological Sciences, University of Maine, Orono, USA

Outline

Introduction

Objectives

Materials and Methods

Results and Discussion

Conclusions

Mechanical Properties of CNTs Compared with Other Materials

MaterialYoung's Modulus

(GPa)

Tensile Strength

(GPa)

Density(g/cm3)

SWNTs 1054 13-53 1.3

MWNTs 800 150 1.3Steel 208 0.65 7.8Wood 16 0.008 0.6

Scientists have designed a “Space Elevator” for travel from earth to the moon using CNTs as the construction materials. [httpwww.flickr.comphotosflyingsinger471698667]

Carbon nanotubes (CNTs) are highly sought-after materials due to their exceptional physical, mechanical, and electronic properties.

Introduction cont.

Last year, we reported a method to produce carbon nanotubes (CNTs) directly from plant materials using a cyclic oxidation process.

Oxidative carbonization of raw materials at 240°C in air;

Cyclic oxidation of the pretreated materials at 400°C.

Introduction cont.

40 nm

Structures observed after two cycles at 400 °C using Bamboo as the raw material.

Nanochannel

Tubular structure

Introduction cont.

During the first two cycles, formation of nanochannels was observed in the material. The diameters of these channels fell within the range of the cross sectional dimensions of the cellulose microfibrils in the plant cell wall

560nm x 16nm

CNTs from wood fiber after 35 cycles of oxidation at 400 °C.

Introduction cont.

After 35 cycles, single carbon nanotubes (CNTs) and CNT bundles were observed in samples. These CNTs are 10-20 nm in diameter and 500-600nm long.

Introduction cont.

Experimental setup with a new sliding devise and computer control system

Based on these results, we proposed that the formation of CNTs in the process occurred via template synthesis, with the nanochannels formed from the ablation of cellulose microfibrils functioning as a template.

Introduction cont.

Proposed Mechanism

Cellulose Microfibril

Lignin hemicellulosematrix

Introduction cont.

Multicyclic process under oxidative conditions

Low Temperature Partial Carbonization

Carbon from lignin hemicelulose matrix

Carbon from the microfibril

Carbon Vaporization

Channel formed by ablation of microfibril carbon

Carbon redeposition, rearrangement using the nanopore left by microfibrilablation as the template

The key point in the proposed mechanism is the differential ablation properties of the carbons derived from cellulose and matrix. Therefore the objectives of this study were to:

Examine the property differences between “cellulose carbon” and “lignin carbon” formed under identical experimental conditions

Determine how the carbonization temperature affects the properties of these two types of carbon

Objectives

Materials and Methods

Filter paper

&

Isolated lignin

Heat at 240°C in air for about 8 hours

Oxidative behaviors in air were studied using TGA (thermogravimetricanalysis).

Chemical compositions were monitored using FTIR

Specific surface area was tested using nitrogen adsorption at 77°K

Carbonization inArgon at • 400°C, • 500°C,• 700°C and • 1000°C for about 8 hours.

Materials and Methods cont.

ARTEn

dtd ln)1ln()ln( +−−= αα

where α is the fraction of carbon ablated at time t; n is the order of reaction; A is the frequency factor (min-1); R is the gas constant (8.314 J K-1 mol-1); T is the absolute temperature (K), and E is the activation energy (kJ mol-1).

In order to better understand the oxidative behaviors of the two types of carbons in this study, apparent kinetic parameters were determined using the relationship between mass loss rate and temperature using the Friedman equation:

DTG Curve TG Curve

(1)

ARTE

dtdn ln)ln()1ln( −=−− αα

Slope

(2)

Results and Discussion

DTG profiles for oxidation of 400°C cellulose carbon and lignin carbon in air.

400° C

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- 15

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0300 350 400 450 500 550 600

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Cel l ul ose Car bon Li gni n Car bon

73 °C

Considerable difference in oxidative mass change was observed when comparing cellulose carbon and lignin carbon prepared at 400°C and 500°C. (only 400°C shown)

TGA

Results and Discussion cont.

700° C

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0300 350 400 450 500 550 600

Temper at ur e ( ° C)

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Cel l ul ose Car bon Li gni n Car bon

DTG profiles for oxidation of 700°C cellulose carbon and lignin carbon in air

The difference in oxidative mass change between the two types of carbons decreased markedly in the 700°C and 1000°C samples. (700°C shown).

TGA

Results and Discussion cont.

Cellulose Carbon Lignin Carbon Process

Temperature n E (kJ mol-1) n E (kJ mol-1)

400°C 1.05 89.8 0.65 98.4500°C 0. 75 101.2 0.50 109.7700°C 0. 65 143.4 0.55 141.11000°C 0.55 167.3 0.50 165.8

Apparent kinetic parameters for samples prepared at different temperatures

The difference in oxidative behaviors between these two types ofcarbon was primarily due to the difference in the order of reaction. Higher n values indicated higher reactivity of the materials.

TGA

Results and Discussion cont.

Specific surface area and porosity for samples prepared at different temperatures

Total Pore Langmuir BET Volume (cm3 g-1) Surface Area (m2 g-1) Surface Area (m2 g-1)

Process Temperature

Cellulose Lignin Cellulose Lignin Cellulose Lignin400°C 0.0092 0.0011 2.943 0.089 2.602 1.321

500°C 0.0108 0.0087 2.376 0.221 5.244 0.846

700°C 0.2238 0.2221 546.11 557.21 437.63 448.10

1000°C 0.2256 0.2130 560.90 536.10 449.06 432.33

Specific surface area

From the perspective of pore structure and specific surface area, cellulose carbon promotes oxidative reactions more readily than lignin carbon because cellulose carbon has greater pore volume and a larger surface area.

Results and Discussion cont.FTIR

Infrared spectrum (absorption) of cellulose carbon

500 1000 1500 2000 2500 3000 3500 4000Wavenumber ( cm- 1)

Untreated

Oxidized at 240°CCarbonized at 400°CCarbonized at 500°C

Carbonized at 700°C

Carbonized at 1000°C

1723 C=O

1603 C=C (Ar)

1430 CH2

1225 C-O

-OH

Results and Discussion cont.FTIR

Infrared spectrum (absorption) of lignin carbon

500 1000 1500 2000 2500 3000 3500 4000Wavenumber ( cm- 1)

Untreated

Oxidized at 240°C

Carbonized at 400°C

Carbonized at 500°C

Carbonized at 700°C

Carbonized at 1000°C

Comparing the FTIR profiles of cellulose carbon and lignin carbon, we found that:

At carbonization temperatures lower than 500 °C, cellulose carbon had far more paraffinic structures than lignin carbon;When carbonization temperatures increased to 700 °C or greater, the two types of carbon possessed a similar degree of carbonization with respect to their chemical structures;These results are consistent with those of the TGA study and they support the concept that oxidative mass loss in these two types of carbons is dictated primarily by their chemical structures.

Results and Discussion cont.FTIR

[http://notexactlyrocketscience.wordpress.com/2006/11/19/carbon-nanotechnology-in-an-17th-century-damascus-sword/]

“These ‘Damascus blades’ were extraordinarily strong, but still flexible enough to bend from hilt to tip. And they were reputedly so sharp that they could cleave a silk scarf floating to the ground, just as readily as a knight’s body.”

The Damascus swords of the Middle East were legendarily sharp, strong and flexible.

[http://www.nytimes.com/2006/11/28/science/28observ.html]

Results and Discussion cont.CNTs in Damascus Swords

Remnant of cementite nanowiresencapsulated by carbon nanotubes. (Reibold et al. 2006)

Cementite(iron carbide) CNT

•Thermal cycling forging and annealing may lead to the growth of carbon nanotubes(CNTs), which in turn initiate formation of cementitenanowires.

Results and Discussion cont.CNTs in Damascus Swords

Oxidation of cellulose carbon and lignin carbon prepared at low temperatures (<500°C) follows different kinetic models, with cellulose carbon having a higher reaction order.

The mass loss behaviors of these two types of carbon are dictated primarily by their chemical structures.

The findings in this study support our earlier hypotheses on mechanisms for the production of carbon nanotubes in lignocellulose materials through the ablation of cellulose microfibrils within the lignin matrix of intact plant/wood cell walls at low carbonization temperatures.

This research has significance related to the discovery of plant fiber-derived carbon nanotubes, formed at low carbonization temperatures, that have previously been identified in other materials such as Damascus steel.

Conclusions

Acknowledgements

Prof. Dannis NagleDr. Dajie Zhang

Advanced Technology Laboratory (ATL) atJohns Hopkins University

THANK YOU !

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