Carbide and Carbide-Derived Carbon Materials with Hierarchical Pore Architecture D I S S E R T A T I O N zur Erlangung des akademischen Grades Doctor rerum naturalium vorgelegt der Fakultät Mathematik und Naturwissenschaften der Technischen Universität Dresden von Dipl.-Chem. Lars Borchardt geboren am 08.03.1985 in Görlitz Eingereicht am ……………… Die Dissertation wurde in der Zeit von 10 / 2009 bis 01 / 2013 im Institut für Anorganische Chemie I angefertigt. L'inquiétude naît du cœur des vivants. Mais le calme recouvrira ce cœur vivant: Voici toute ma clairvoyance. Albert Camus dedicated to R. and M. Table of Contents TABLE OF CONTENTS 1. Motivation ................................................................................................................................. 5 2. Theoretical Part ...................................................................................................................... 8 2.1 Hierarchical Materials ............................................................................................................................. 8 2.2 Hard-Templating........................................................................................................................................ 9 2.3 Soft-Templating ....................................................................................................................................... 11 2.3.1 Evaporation-Induced Self-Assembly ........................................................................................12 2.3.2 Microemulsion ...................................................................................................................................13 2.3.3 Miniemulsion ......................................................................................................................................15 2.4 Porous Carbides ...................................................................................................................................... 16 2.4.1 Precursor-Derived Ceramics ........................................................................................................18 2.4.2 Structure of Carbides ......................................................................................................................20 2.5 Porous Carbons........................................................................................................................................ 22 2.6 Carbide-Derived Carbons ................................................................................................................... 25 2.7 Catalysis ...................................................................................................................................................... 27 3. Characterization Techniques ............................................................................................31 3.1 Theory of N2 Physisorption ............................................................................................................... 31 3.1.1 Adsorption Mechanism ..................................................................................................................31 3.1.2 Pore Size Estimation Using the BJH Method .........................................................................33 3.1.3 Pore Size Estimation Using the Density Functional Theory ...........................................33 3.1.5 Determination of the Total Pore Volume ...............................................................................36 3.1.6 Determination of the Micropore Volume ...............................................................................37 3.1.7 Determination of the Specific Surface Area ..........................................................................38 3.1.8 Hysteresis, Pore Blocking and Cavitation ..............................................................................39 3.2 Low-Angle X-Ray Diffraction ............................................................................................................. 41 3 Table of Contents 4. Experimental Part ................................................................................................................43 4.1 Instrumental Setup ................................................................................................................................ 43 4.2 Synthetic Aspects .................................................................................................................................... 46 4.2.1 List of Used Chemicals ....................................................................................................................46 4.2.2 List of Used Gases..............................................................................................................................48 4.2.3 Synthesis of Ordered Mesoporous Carbides and CDCs by Nanocasting ....................48 4.2.4 High Temperature Chlorine Treatment..................................................................................51 4.2.5 Synthesis of Ordered Mesoporous Carbides and CDCs by Soft-Templating .............51 4.2.6 Synthesis of Transition Metal Loaded CDCs Using a Microemulsion Approach ....53 4.2.7 Synthesis of SiC Nanospheres and CDCs Using a Miniemulsion Approach ..............54 4.2.8 Synthesis of Titanium Carbide and CDC Macrospheres ...................................................55 5. Results and Discussion ........................................................................................................57 5.1 Ordered Mesoporous Carbides and CDCs by Hard-Templating (Nanocasting) ....... 57 5.1.1 Ordered Mesoporous Silicon Carbide and its Corresponding CDC ..............................58 5.1.2 Ordered Mesoporous Boron Carbide and its Corresponding CDC ...............................65 5.1.3 Ordered Mesoporous Tungsten Carbide and its Corresponding CDC.........................69 5.1.4 Ordered Mesoporous Titanium Carbide and its Corresponding CDC .........................74 5.1.5 Discussion of OMCs and OM-CDCs Synthesized from Nanocasting .............................78 5.2 Ordered Mesoporous Carbides and CDCs by Soft-Templating ......................................... 80 5.2.1 Ordered Mesoporous SiC, TiC and CDC Synthesized by EISA .........................................81 5.2.2 Transition Metal Loaded SiC-CDCs Synthesized by a Microemulsion Approach ...94 5.3 SiC and SiC-CDC Nanospheres Prepared by a Miniemulsion Approach .....................105 5.4 TiC/C and TiC-CDC Macrospheres ................................................................................................112 6. Conclusion and Outlook ................................................................................................... 121 7. References ........................................................................................................................... 126 8. Appendix .............................................................................................................................. 136 4 Motivation 1. MOTIVATION A whole subdiscipline within chemistry, by name the organic chemistry is dealing with compounds of the chemical element carbon. The majority of scientists come to the agreement that „Life“ can only be constructed from carbon. Carbon is an impressive and unique element of outstanding importance, not only in the processes in living nature, but also in inorganic chemistry and in materials science. In its diamond modification carbon is the hardest material on earth, as graphite one of the best electrically conducting materials and in CO2 it is part of the carbon cycle and impacts the climate. As carbonate carbon forms rocks, as coal it provides humans with energy since centuries and as fullerene and graphene it is one of the most fascinating materials in present science. This thesis is about carbon. On the one hand it deals with carbons in compound with metals, so called carbides and on the other hand with porous carbons that are derived from these carbides, and are therefore called carbide-derived carbons (CDCs). Both material classes stand out due to chemical inertness and high temperature stability. Carbides in particular show high hardness, wear resistance, high strength, and creep resistance at elevated temperatures. It is one aim of this thesis to combine these advantages with those of porous materials, namely high specific surface areas and high pore volumes and to develop new synthesis strategies towards porous carbide materials. The second key issue is the synthesis of new carbide-derived carbons comprising a large group of highly porous carbons resulting from the extraction of metal atoms from their carbides. Due to their outstanding properties CDCs are currently occupying leading positions in many applications such as electrode materials in supercapacitors and batteries, in protein adsorption or as filter media in numerous purification processes. Indeed, specific surface area and total pore volume are important parameters for many applications but often pore accessibility and pore size are of comparable significance. High specific surface areas are useless if the pores are too small for certain molecules or the diffusion paths within the material are far too long. Therefore, hierarchical materials are largely required for numerous applications. This means that they consist of small micropores (< 2nm), responsible for storage and adsorption and of larger mesopores (2- 50 nm) or macropores (>50 nm) that are responsible for rapid materials transport.