Aus dem Max-Planck-Institut für Kolloid- und Grenzflächenforschung A neglected World: Transition Metal Nitride and Metal Carbide Based Nanostructures Novel Synthesis and Future Perspectives Habilitationsschrift Zur Erlangung des akademischen Grades Doktor rerum naturalium habilitatus (Dr. rer. nat. habil.) in der Wissenschaftsdisziplin Physikalische Chemie eingereicht an der Mathematisch-Naturwissenschaftlichen Fakultät der Universität Potsdam von Dr. Cristina Giordano geboren am 07.05.1974 in Palermo Potsdam, im März 2014 Published online at the Institutional Repository of the University of Potsdam: URN urn:nbn:de:kobv:517-opus4-75375 http://nbn-resolving.de/urn:nbn:de:kobv:517-opus4-75375 Alla mia famiglia, per l´infinito amore… TABLE OF CONTENTS 1. Introduction ............................................................................................................. 1 2. Nanosized Materials: into the World of Discontinuity ........................................ 4 2.1 The Importance of Materials ...................................................................... 4 2.2 What is a Nanomaterial? ............................................................................. 5 3. Transition Metal Nitrides and Carbides ............................................................... 8 3.1 Properties ................................................................................................. 11 3.2. Applications ............................................................................................. 20 3.3. Synthesis ................................................................................................. 22 4. Novel Synthetic Strategies .................................................................................... 25 4.1 The “Urea-Glass Route” (UGR) ............................................................... 27 4.1.1 Advantages of the “Urea-Glass Route” ............................................ 41 Effect of the heating rate .................................................................. 41 Effect of the urea/metal ratio (R) ..................................................... 42 Effect of a second metal component ................................................ 47 4.1.2 Magnetic Nitrides and Carbides: the case of iron .............................. 55 Iron carbide nanoparticles (np-Fe3C) ................................................ 56 From Fe3N to Fe7C3 and Fe3C nanoparticles ..................................... 59 Iron carbide based nanosheets (ns-Fe3C) .......................................... 63 Mesoporous iron carbide nanocomposite (mp-Fe3C)........................ 66 Fe3C and Fe3N from FeOx: a transcription route .............................. 68 4.2 The “Biopolymer Route” (BpR) ............................................................... 72 4.2.1 Ternary Systems via the “Biopolymer Route” ................................... 79 4.3 La Via dello Zucchero (the “Sugar Route”) .............................................. 82 5. MN/MC based Nanocomposites .......................................................................... 90 5.1 Manganese and Nickel Nitride Nanocomposites ...................................... 90 5.2 MN/MC in Liquid Media: post-synthesis preparation .............................. 95 6. Processing: beyond spherical shape .................................................................. 104 6.1 Spin-Coating ........................................................................................... 105 6.2 Printing ................................................................................................... 108 6.3 Electrospinning ....................................................................................... 110 6.3.1 Chromium based Fibres ........................................................... 112 6.3.2 Iron based Fibres ...................................................................... 114 6.4 Bio-templating and the Cyber-Leaf ........................................................ 116 6.5 Aerosol Spray ......................................................................................... 120 7. Testing ................................................................................................................. 127 7.1 Environmental Applications ................................................................... 128 7.2. Catalysis ................................................................................................. 131 7.3. Batteries ................................................................................................. 146 8. Conclusions and Outlook ................................................................................... 150 9. Appendix ............................................................................................................. 153 List of Abbreviations .................................................................................... 153 Additional Figures and Tables ...................................................................... 154 10. Chemical Details and Techniques ................................................................... 162 11. Acknowledgments ............................................................................................. 168 12. References.......................................................................................................... 170 13. List of Publications ........................................................................................... 187 M´illumino d´Immenso Mattina, Giuseppe Ungaretti 1917 Introduction Chapter 1 1. Introduction/Motivation The most fascinating aspect of nature is surely its multiplicity and, through evolution, its capacity to adapt to current necessities. Similarly, humankind has adapted and, with a bit of ingenuity, has revolutionized its everyday life in the name of progress. In this (re)evolution, materials have surely fulfilled a key role, so much that key steps of human development have been denoted with material names (age of stone, bronze, iron, etc.). However, while earliest craftsmen based their processes on the “trial and error” approach, nowadays new materials are prepared with awareness and, thanks to technology, enhanced control over the whole process. This way, the attention can be more and more focused toward complex materials (ternary and quaternary systems, smart materials, composites, etc.), in some cases taking again inspiration from nature (biomimetic approach). One important contribution in the search for new materials is surely the discovery of the nano-world. In this realm, properties are sensible to size and morphology, so that each nano-system can be considered as a potential new material. Potentiality of nano-sized materials has been largely proved, and a massive part of both fundamental and applied research is today devoted to the study and field of applications of these materials. It will be sufficient to go to Web of KnowledgeSM and type “nano*” to find more than 1 Million1 entries concerning related publications, about 130.000 only in 2012. However, a closer look will show that a significant percentage of this research is related to oxides and metals (over 40.000 entries), while the number drastically drops when searching for other systems, such as metallic ceramics (namely transition metal nitrides and metal carbides), which display less than 100 entries (2012). These numbers have to be considered just as a rough estimation of course, but can still give an idea about the worldwide predilection for some classes of materials over others. Specifically for metallic ceramics, the lack of publications does not reflect their potential but rather the difficulties related to their synthesis as dense (compact) and defect-free structures, fundamental prerequisites for advanced mechanical applications. However, potentialities of these materials go far beyond engineering purposes. As suggested by their name, metallic ceramics possess an intriguing combination of properties that place them between high performance ceramics and pure metals. The number of 1 This number does not contain medical, biomedical, geological and environmental entries. 1/191 Introduction Chapter 1 envisaged applications can then be very broad and can even be broadened going to the nanoscale (e.g. higher surface area, tailored properties via size-control, easier shaping and processing, quantum effects, etc.). In simpler words, there is more than just tougher cutting tools to be discovered. One steady step, however, must be overcome: the necessity to simplify their production to make these systems readily available, in reasonable amounts, both for better investigation and easier testing/processing. The present habilitation work aims to close the gap between preparation and processing, indicating novel synthetic pathways for an easier, unexpansive, and sustainable synthesis of transition metal nitride and carbide based nanostructures and easier processing thereafter. In particular, aiming at expanding the coverage of ceramic materials in applied science, several key-points are encompassed in the present work, for instance the influence of the starting materials was carefully studied, also using complex precursors (e.g. biopolymers), to gain control over composition, size and morphology. In this way, hierarchical structures (such as fibres, mesoporous materials, replica of bio-objects etc.) could also be obtained. The presented routes are, concept-wise, similar, and they all start by building up a