Nanostructured carbohydrate-derived carbonaceous materials [Elektronische Ressource] / Shiori Kubo. Betreuer: Markus Antonietti

Nanostructured carbohydrate-derived carbonaceous materials [Elektronische Ressource] / Shiori Kubo. Betreuer: Markus Antonietti

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Max-Planck-Institut für Kolloid- und Grenzflächenforschung Nanostructured Carbohydrate-Derived Carbonaceous Materials Dissertation zur Erlangung des akademischen Grades "doctor rerum naturalium" (Dr. rer. nat.) in der Wissenschaftsdisziplin "Physikalische Chemie" eingereicht an der Mathematisch-Naturwissenschaftlichen Fakultät der Universität Potsdam von Shiori KUBO Potsdam, den 16, 02, 2011 Published online at the Institutional Repository of the University of Potsdam: URL http://opus.kobv.de/ubp/volltexte/2011/5315/ URN urn:nbn:de:kobv:517-opus-53157 http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-53157 Nanostructured Carbohydrate-Derived Carbonaceous Materials Shiori KUBO Contents 1. Introduction..................................................................................................................... 1 2. Nanostructured Carbonaceous Materials ........................................................................ 7 2.1 Carbonisation Chemistry ...........................................................................................7 2.1.1 Classical Carbonisation (Pyrolysis)7 2.1.2 Hydrothermal Carbonisation...................................................................................9 2.2. Nanostructured Carbonaceous Materials .................................

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Max-Planck-Institut
für Kolloid- und Grenzflächenforschung






Nanostructured Carbohydrate-Derived
Carbonaceous Materials









Dissertation


zur Erlangung des akademischen Grades
"doctor rerum naturalium"
(Dr. rer. nat.)
in der Wissenschaftsdisziplin "Physikalische Chemie"


eingereicht an der
Mathematisch-Naturwissenschaftlichen Fakultät
der Universität Potsdam




von
Shiori KUBO




Potsdam, den 16, 02, 2011













































Published online at the
Institutional Repository of the University of Potsdam:
URL http://opus.kobv.de/ubp/volltexte/2011/5315/
URN urn:nbn:de:kobv:517-opus-53157
http://nbn-resolving.de/urn:nbn:de:kobv:517-opus-53157
Nanostructured Carbohydrate-Derived
Carbonaceous Materials

Shiori KUBO

Contents






1. Introduction..................................................................................................................... 1


2. Nanostructured Carbonaceous Materials ........................................................................ 7
2.1 Carbonisation Chemistry ...........................................................................................7
2.1.1 Classical Carbonisation (Pyrolysis)7
2.1.2 Hydrothermal Carbonisation...................................................................................9
2.2. Nanostructured Carbonaceous Materials ................................................................13
2.2.1 Activated Carbon ..................................................................................................14
2.2.2. Carbon Aerogels from the Carbonisation of Organic Aerogels...........................14
2.2.3. Carbon Aerogels from Biomass Derivatives .......................................................15
2.3 Nanocasting Methods...............................................................................................16
2.3.1. Soft Templating (endo-templating)......................................................................17
2.3.2. Hard Templating (exo-temp19


3. Characterisation Techniques......................................................................................... 21
3.1 Electron Microscopy................................................................................................21
3.1.1 Transmission Electron Microscopy (TEM) ..........................................................21
3.1.2 High Resolution Transmission Electron Microscopy (HR-TEM) ........................23
3.1.3 Scanning Electron Microscopy (SEM) .................................................................24
3.2 Small Angle X-ray Scattering (SAXS) ....................................................................26
3.3 Gas sorption .............................................................................................................31
3.3.1 Determination of surface area...............................................................................33
3.3.2 Assessment of Mesopore Size Distribution35
3.3.3 Assessment of Micr .........................................................36
3.3.4 Density Functional Theory (DFT) for Determination of Pore Chracteristics.......37
3.3.5. Quenched Solid Density Functional Theory (QSDFT) method ..........................38
3.4 Fourier Transform Infrared Spectroscopy (FTIR) ...................................................39


4. Hydrothermal Carbonisation of Carbohydrates in the presence of Inorganic Sacrificial
Templates.......................................................................................................................... 43
4.1. Introduction.............................................................................................................43 4.2. Silica as a Sacrificial Template...............................................................................46
4.2.1. Hard-Templating of Mesoporous Silica Beads for the Production of
Hydrothermal Carbon Sphere ....................................................................................46
4.2.2 Hydrothermal Carbon Monoliths..........................................................................53
4.3 Macroporous Alumina Membranes as a Sacrificial Template.................................56
4.3.1 Chemicals..............................................................................................................56
4.3.2 Synthesis ...............................................................................................................56
4.3.3 Results and Discussions........................................................................................58
4.4. Conclusion71


5. Hydrothermal Carbonisation of Carbohydrates in the presence of Block Copolymer
Templates.......................................................................................................................... 73
5.1. Introduction.............................................................................................................73
5.2 Experimental............................................................................................................75
5.2.1 Chemicals..............................................................................................................75
5.2.2 Synthesis ...............................................................................................................75
5.3 Selection of Structural Directing Agents .................................................................76
5.4 Effect of F127-Fru Composition..............................................................................80
5.5 Carbon Framework and Carbon Surface Functionalities.........................................86
5.6 Pore Size Control .....................................................................................................90
5.7 Further Optimisation of Synthesis Conditions.........................................................97
5.7.1 Effect of Carbon Source........................................................................................97
5.7.2 Synthesis temperature ...........................................................................................99
5.7.3 Addition of acid catalyst .....................................................................................100
5.7.4 Avoiding pore shrinkage102
5.8 Proposed Mechanism.............................................................................................104
5.8.1 F127 block copolymer in an aqueous solution ...................................................104
5.8.2 Formation of micelles in an aqueous carbohydrate solution...............................106
5.8.3 Formation of ordered block copolymer – hydrothermal carbon composite........107
5.9 Conclusion .............................................................................................................111


6. Conclusion and Outlook 113

Appendix......................................................................................................................... 117
A-1) Synthesis of PO -b-AA block copolymer .......................................................117 40 40
A-2) Calculation of carbon yield .................................................................................118
A-3) List of pore properties of the synthesised carbonaceous materials via soft
templating ....................................................................................................................118
A-4) Instrumental.........................................................................................................120
A-5) List of main abbreviations and symbols..............................................................123
A-6) Acknowledgement...............................................................................................125
A-7) References ...........................................................................................................127





























「人間は 考え る葦であ る。 」

Man is but a reed, the weakest of nature, but he is a thinking reed.

L'homme n'est qu'un roseau, le plus faible de la nature; mais c'est un roseau pensant.

- Blaise Pascal -











1. Introduction

From ancient times, society has made use of porous carbon materials; charcoal was used
1for decolourisation of alcohol, water and sugar in ancient Egypt. In Asian history, it has
1also been used as an adsorbent in order to protect religious shrines from moisture attack.
Today, porous carbon materials are widely used in industry as adsorbents (e.g. activated
carbon) for drinking water, wastewater and gas purification or as catalysts or catalyst
2,3,4,5supports. The developed surface area and pore properties of such materials play an
important role enhancing the adsorption capacity or catalytic activity.
Carbon materials are essential in the applications associated with our daily life
and are becoming of increasing interest to the developing application fields of energy
6 7storage (e.g. electrodes for Li ion batteries or supercapacitors), fuel cells (e.g. novel
8,9,10catalysts for the oxygen reduction reaction) or chromatography technologies due to
the increasing need of sustainable energy supply and highly developed biological /
medical technologies (Figure 1.1). When compared to conventional electrolytic capacitors
-1or to batteries, carbon-based supercapacitors offer good specific energy (1-10 Wh kg ),
as recently demonstrated, for example, by carbon aerogels with high porosity and surface
2 -1 11,12area (> 50 %, 400 - 1000 m g ). Due to the extreme versatility of carbon materials
available (e.g. crystalline, amorphous, bulk, nanostructured, activated, functionalised), a
great deal of literature research has discussed the use of various electrodes configurations
1
for supercapacitors. This is a good example of how material porosity directly affects the
electrochemical performance. In order to improve even further the performance of carbon
materials, novel synthetic approaches as well as a developed fundamental understanding
of their properties are strongly desirable from materials chemistry point of view.
13,14,15Figure 1.1: Main application fields of porous carbon materials.

Carbon is one of the most versatile elements, which can be found as different
allotropes. The most common crystalline carbon allotropes are diamond and graphite. In
3 2diamond the carbon atoms have sp hybridisation and are tetrahedral, while sp
hybridisation occurs in graphite resulting in a layered, planer structure of hexagonal
16lattice. More recently discovered crystalline carbon nanostructures such as fullerenes,
17 18 19single or multiple walled carbon nanotubes or graphene exhibit unprecedented
physico-chemical properties. In addition to all these crystalline forms of carbon,
amorphous carbon is another allotrope. Amorphous carbons are polycrystalline materials
of graphite or diamond possessing no long - range crystalline order. Examples of
amorphous carbons are carbon black, activated carbons, glassy carbons, soot, chars etc.
(Figure 1.2).
2

Figure 1.2: The allotropes of carbon: (A) diamond, (B) graphite, (C) amorphous carbon, (D) fullerene, and
20(E) carbon nanotube.

The majority of carbon materials used in the aforementioned applications is
typically synthesised through the heat treatment of carbon-rich organic precursors. Such a
process is called “carbonisation”. These precursors undergo a thermal decomposition
(pyrolysis), which eliminates volatile compounds that include heteroatoms and become
carbon-rich. Upon increasing temperature, condensation / charring reactions occur and
localised aromatic units grow and become aligned into small microcrystallites (Figure
1.3). Depending on the temperature employed, such microcrystallites can arrange into a
hexagonal lattice, parallel to one another, an arrangement commonly known as
turbostratic carbon. This approach is normally applied to generate amorphous carbons,
whereas more crystalline materials (e.g. nanotubes) are often produced through more
21 22complicated / expensive techniques such as laser ablation, electro-arc discharge or
23 ochemical vapor deposition usually employing high temperatures (> 1000 C) and
therefore accessibility and sustainability of the procedure is somewhat limited.
3

24Figure 1.3: Structural changes in the carbon microstructure during carbonisation.

Contrary to all these high temperature procedures, the recently rediscovered
hydrothermal carbonisation (HTC) procedure offers new perspectives being performed
from renewable resources (e.g. biomass and its derivatives) at low-temperatures (e.g. 130
– 200 °C) in aqueous phase and under self-generated pressure. Although known since
1913, when Bergius demonstrated hydrothermal transformation of cellulose into coal-like
25materials, this technique has received much interest since 2000 and has been
extensively investigated for the production of various hydrothermal carbons with a wide
26,27,28range of applications. In this synthetic HTC procedure, the carbon precursor firstly
dehydrates to 5-hydroxymethyl-furfural, followed by subsequent condensation /
polymerisation reactions, to form a carbon-rich material consisting of interconnected
aromatised carbon cores composed of polyfuran-type units, with the surfaces essentially
terminated by a rim of functional polar groups, rendering their surfaces relatively
29 , 30 , 31hydrophilic. This synthesis route allows the facile and direct preparation of
monodisperse carbonaceous spherical particles in the micrometer size range in a one-pot
procedure. However, an open question remains concerning the porosity of these
carbonaceous materials, as conventional HTC material prepared in this straightforward
aqueous based synthesis presents very limited surface area and pore volumes, which in
4