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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Deri
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ve M
ass
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in)
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)
Deri
vati
ve M
ass
(%/m
in)
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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