Synthesis, alignment, growth mechanism and functional properties of carbon nanotubes and their hybrid materials with inorganic and biomaterials Dissertation von Ravi K. Joshi, M.S. aus Solapur, Indien September 2010 — Darmstadt — D 17 FachbereichAnorganischeChemie EduardZintlInstitutfürAnorganischeund PhysikalischeChemie Synthesis, alignment, growth mechanism and functional properties of carbon nanotubes and their hybrid materials with inorganic and biomaterials Vom Fachbereich Chemie der Technischen Universität Darmstadt zur Erlangung des akademischen Grades eines Doctor rerum naturalium (Dr. rer. nat.) genehmigte Dissertation eingereicht von M.S. Ravi K. Joshi aus Solapur, Indien Referent: Prof. Dr. Jörg J. Schneider Korreferenten: Prof. Dr. Christian Hess Prof. Dr. Ulrich Simon (RWTH Aachen) Tag der Einreichung 06. September 2010 Tag der mündlichen Prüfung 01. November 2010 Darmstadt - D17 2010 Dedicated to my parents, (who spent their life for career of their kids) to my beloved brother and soul love of my life (cid:115)(cid:92)(cid:103)(cid:81)(cid:67)(cid:64)(cid:118)(cid:109)(cid:94) (cid:115)(cid:92)(cid:118)(cid:100)(cid:64)(cid:118)(cid:109)(cid:94) (cid:115)(cid:77)(cid:118)(cid:111) (cid:109)(cid:110)(cid:65)(cid:92)(cid:115)(cid:70) (cid:106)(cid:65)(cid:110)(cid:116)(cid:65)(cid:109)(cid:94) । – (cid:27)(cid:96)(cid:118)(cid:3)(cid:100) । Sangacchadhwam, Samvadadhwam, Samvo Manamsi Jaanatham – a sukta from Rigveda (Let’swalktogether,let’sspeakthesamelanguage&letallthishappenafterknowingtheeachother’smindset) (Thissuktaexplainsthat,asobjectiveofourworkissame,letstalkoverit,trytounderstandeachother’spointofview;putheartandsoul intoeffortssothatasettlementcouldbereachedamicably.) Acknowledgment I express my sincere gratitude towards Prof. Dr. Jörg Schneider for allowing me to be a part of his research group, offering me a fair work bench, his valuable time and closely following my work during the course of my doctoral thesis. I appreciate his constant motivation throughout this period and his support in professional as well as personal life. I am indebted to Dr. Jörg Engstler and Dr. Jayprakash Khanderi for their invaluable time they gave in discussing various issues of my ongoing work. These discussions were of great importance to me from the aspect of experimental work, stimulating ideas and evaluation of the system. I am also thankful to both of them for their moral support in hard phase of this period, without which, it would have been difficult for me to arrive at this stage. Any amount I appreciate their help, it is not enough. Jörg shares extra gratitude for helping me to learn various characterization techniques. I reserve my special thanks for Dr. Oktay Yilmazoglu for a cooperative work, lengthy discussions, and constructive ideas. I really enjoyed working with him. I am also thankful to Christoph Nick for a collaborative work. The work we carried out together added a new dimension to my thesis. I take this chance to mention my cordial thanks to Deutsche Forschung Gemeinschaft (DFG, German Research Foundation) for financing my studies through the project. I have my heartfelt thanks to many people for constantly rendering help during this research activity. Few names those I remember are, Dr. Alexander Issanin for XPS measurements, Dr. Kathrin Hofmann and Jens Suffner for XRD measurements, Jens-Peter Biethan for electrical measurements, Dr. Stefan Lauterbach for helping to learn and operate TEM, Dr. Hergen Breitzke for MAS-NMR measurements Dr. Erwin Hildebrandt for SQUID measurements, Dr. Emanuel Ionescu for raman spectroscopy and Dr. Rudolf Hoffmann and Carina Vogel for oximato work. I specially mention the name of my friend Kamalpreet Kaur who gave me bunch of silicon wafers to initiate this thesis work. I am thankful to couple of my friends Dr. JitendraKumar,SapthagireeshSubbarayan,AnujChopraandRahulKulkarnifromdifferent parts of the world who patiently fulfilled my literature need. During this Ph.D. tenure, I have really enjoyed my work in this group. I had enormous fun withalmosteverypersonofmygroup. ItwasmyfirstcrossculturalexperienceandIreallyfound I my group mates warm and I never felt that I am anyway different from them. In particular Dr. Mathias Nowotny, Hermann Tempel and Ildiko Balogmademystayindisputablyenjoyable. I enjoyed learning German from these Germans and understanding blunders I did while showing my speaking talent. These are unarguably few best moments of my life. DuringthisstayinDarmstadt,IreallyhadjoytospendtimeandmaketripswithRajeev,Parag, Atul and his wife Meghana. It was undoubtly wonderful experience with different experiments in the kitchen. I am forever grateful to my parents and beloved brother for their understanding, moral support and continuous encouragement throughout my life. The secret of my success is hidden in the hard work they did to financially support my education. I feel myself fortunate to have such kind parents. Another strength of my life is Parisa, a soul love of my life. Over the last five years of my life, she is and will be the reason for my eternal happiness. There is an active and passive role of many people who helped me to arrive at this milestone. I may have forgotten to mention their names, but the help they offered has certainly made a home in my heart. Ravi K. Joshi II Abstract Carbon nanotubes with unique properties are interesting materials for various sensors (gas, light, or bio), electrical devices (transistors, cold cathodes), catalysis, and energy related applications. However, the real hindrance in visualizing state of the art applications of CNTs is lack of a technique for selective and qualitative growth of CNTs at a predefined position. Also, in order to visualize various sensors and device architectures, CNTs alone will not suffice. CNTs structures need to be modified using other materials to develop new hybrid materials. The present work addresses the need of growth of qualitative CNTs, pinpoint their growth mechanism and methodologies to develop its hybrid materials. Carbon nanotubes are synthesized using water-assisted chemical vapor deposition method (WCVD).Usingthismethod,synthesisofcrystalline,aligned,impurity-free,doublewalledCNTs of high aspect ratio (∼ 106) is achieved. Carbon nanotubes, as per need, are grown in vertical direction perpendicular to the substrate or even along the horizontal direction. A detailed study investigating different growth parameters in WCVD method is carried out to maximize the growth rate and quality of CNTs synthesized. Based on the experimental understanding, a conclusive growth mechanism elucidating the exact role of water as a catalyst activator is put forth. Also,astraightforwardmethodtopatternthecatalystandtherebyapossibilitytoachieve structured growth of CNTs is demonstrated. Pristine CNT structures are modified using various metal oxides (ZnO, TiO , Fe O ), platinum 2 3 4 nanoparticlesaswellasnervecellstoformvarioushybridmaterials. Depositionofmetaloxides is carried out using various methodologies to obtain their nano particulate layers or thin films on CNTs. Platinum nano particles (2 to 4 nm) are deposited on 2D-aligned CNT film using self reduction technique for fuel cell applications. Additionally, different block structures of CNTs are used as a substrate to grow nerve cells. The selective growth of nerve cells on CNTs structures and inter bridging of CNT blocks are additional key points of this work. Carbon nanotubes based devices such as field emission and field effect transistors are successfully realized. CNT based hybrid materials are tested for the potential applications such as modified field emission, super para magnetic applications, light sensors, fuel cells and gas sensors. Various other modules of CNT or its hybrid materials for are currently being tested for devices viz. photo catalysis, dye sensitized solar cells, magnetic actuators. III Contents 1 Introduction 1 1.1 From the element carbon to carbon nanotubes . . . . . . . . . . . . . . . . . . . . . 1 1.2 Properties and potential applications of carbon nanotubes . . . . . . . . . . . . . . 7 1.2.1 Mechanical properties of CNTs . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 1.2.2 Electrical properties of CNTs . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 1.2.3 Thermal conductivity of CNTs . . . . . . . . . . . . . . . . . . . . . . . . . . . 9 1.2.4 Optical properties of CNTs . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10 1.2.5 Other important properties of CNTs . . . . . . . . . . . . . . . . . . . . . . . . 10 1.3 Methods for synthesizing carbon nanotubes . . . . . . . . . . . . . . . . . . . . . . . 11 1.3.1 Arc discharge method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11 1.3.2 Laser ablation method . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12 1.3.3 Chemical vapor deposition method . . . . . . . . . . . . . . . . . . . . . . . . 13 1.4 Methods for characterizing carbon nanotubes . . . . . . . . . . . . . . . . . . . . . . 15 1.4.1 Raman spectroscopy . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16 1.4.2 Transmission electron microscopy (TEM) . . . . . . . . . . . . . . . . . . . . . 17 1.4.3 Atomic force microscopy (AFM) . . . . . . . . . . . . . . . . . . . . . . . . . . 20 1.4.4 Scanning electron microscopy (SEM) . . . . . . . . . . . . . . . . . . . . . . . . 20 1.4.5 X-ray diffraction (XRD) . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20 1.4.6 Thermo-gravimetric analysis (TGA) . . . . . . . . . . . . . . . . . . . . . . . . 21 1.5 Methods of purification and funtionlization of carbon nanotubes . . . . . . . . . . 21 1.6 Growth mechanism of carbon nanotubes . . . . . . . . . . . . . . . . . . . . . . . . . 22 1.6.1 General growth mechanism of CNTs . . . . . . . . . . . . . . . . . . . . . . . . 22 1.6.2 Growth mechanism of water assisted chemical vapor deposition (WCVD) . 25 1.7 Aim of the present work . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 27 2 Synthesis of carbon nanotubes 28 2.1 Synthesis of carbon nanotubes using water assisted chemical vapor deposition method. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 28 2.1.1 Characterization of CNTs grown using water assisted CVD method. . . . . 30 2.1.2 Engineering the catalyst to grow geometrically confined CNT structures. . 33 IV 2.2 Study of different growth parameters in WCVD method . . . . . . . . . . . . . . . 36 2.2.1 Effect of growth parameter : Aluminum . . . . . . . . . . . . . . . . . . . . . . 36 2.2.2 Effect of growth parameter : Iron . . . . . . . . . . . . . . . . . . . . . . . . . . 42 2.2.3 Effect of growth parameter : Hydrogen . . . . . . . . . . . . . . . . . . . . . . 43 2.2.4 Effect of growth parameter : Water. . . . . . . . . . . . . . . . . . . . . . . . . 46 2.3 Study of growth mechanism of water assisted CVD method (WCVD) . . . . . . . 48 2.3.1 Study of morphology and chemical state of the catalyst . . . . . . . . . . . . 48 2.3.2 Reaction mechanism of water assisted CVD method . . . . . . . . . . . . . . 60 2.3.3 Analytical understanding of the morphology of bimetallic catalyst nano particles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 63 2.4 Study of morphological aspects of carbon nanotubes . . . . . . . . . . . . . . . . . . 65 2.4.1 Nuclear magnetic resonance spectroscopy (NMR) of 13C doped CNTs . . . 65 2.4.2 Metal clusters mediated growth of CNTs . . . . . . . . . . . . . . . . . . . . . 68 2.5 Horizontal growth of individual carbon nanotubes . . . . . . . . . . . . . . . . . . . 71 3 Introduction to metal oxides 74 3.1 Potential applications of various metal oxides . . . . . . . . . . . . . . . . . . . . . . 76 3.2 Titanium dioxide (TiO ) as a photo-catalyst . . . . . . . . . . . . . . . . . . . . . . . 77 2 3.3 Zinc oxide (ZnO) as light sensor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 80 3.4 Iron oxide (Fe O ) as a magnetic material . . . . . . . . . . . . . . . . . . . . . . . . 82 3 4 4 Synthesis and characterization of carbon nanotube based hybrid materials 85 4.1 Deposition of zinc oxide on carbon nanotubes . . . . . . . . . . . . . . . . . . . . . . 85 4.1.1 Characterization of CNT - ZnO composite material . . . . . . . . . . . . . . . 85 4.1.2 Characterization of CNT - ZnO bilayer material . . . . . . . . . . . . . . . . . 88 4.2 Deposition of titanium dioxide on carbon nanotubes . . . . . . . . . . . . . . . . . . 95 4.2.1 Characterization of CNT - TiO composite material . . . . . . . . . . . . . . 96 2 4.2.2 Characterization of CNT - TiO bilayer material . . . . . . . . . . . . . . . . 101 2 4.2.3 Characterization of TiO thin film on CNT blocks . . . . . . . . . . . . . . . 104 2 4.3 Deposition of iron oxide on carbon nanotubes . . . . . . . . . . . . . . . . . . . . . . 107 4.3.1 Characterization of iron oxide obtained from oximato precursor . . . . . . . 107 4.3.2 Characterization of CNTs - Fe O composite material . . . . . . . . . . . . . 111 3 4 V 4.3.3 SQUID investigation of Fe O and CNT - Fe O composite . . . . . . . . . . 115 3 4 3 4 4.4 Platinum nano particle decorated carbon nanotubes film for PEM fuel cells . . . 118 4.4.1 Characterization of membrane electrode assembly (MEA) . . . . . . . . . . . 119 4.4.2 Characterization of CNT growth on carbon paper . . . . . . . . . . . . . . . . 123 4.5 Growth of neuron cells on structured carbon nanotubes blocks or films . . . . . . 125 4.5.1 Characterization of neuron cells growth on structured CNT blocks or films 126 4.5.2 Miniaturization of MEA for CNT - neuron cells structure . . . . . . . . . . . 131 5 Studies towards functional applications of carbon nanotubes and its hybrid materials133 5.1 Carbon nanotubes and their metal oxide composite for field emission applications.133 5.1.1 Field emission of CNT blocks. . . . . . . . . . . . . . . . . . . . . . . . . . . . . 134 5.1.2 Field emission of CNT - metal oxide composite blocks. . . . . . . . . . . . . . 138 5.2 Carbon nanotubes based field effect transistors . . . . . . . . . . . . . . . . . . . . . 140 5.3 Carbon nanotubes or their block structures for gas sensing . . . . . . . . . . . . . 143 5.3.1 Palladium deposited CNT blocks as a gas sensing module . . . . . . . . . . . 144 5.3.2 Growth of individual CNTs on silicon nano pillars . . . . . . . . . . . . . . . 147 5.4 Carbon nanotubes - ZnO bilayer film as a light sensor . . . . . . . . . . . . . . . . . 149 6 Summary and conclusion 152 7 Experimental procedure 156 7.1 Growth of CNTs using water assisted chemical vapor deposition method . . . . . 156 7.1.1 Growth of 13C enriched CNTs for NMR studies . . . . . . . . . . . . . . . . . 157 7.1.2 Growth of horizontally aligned CNTs . . . . . . . . . . . . . . . . . . . . . . . 158 7.2 Modification of as grown carbon nanotubes. . . . . . . . . . . . . . . . . . . . . . . . 159 7.2.1 Preparation of zinc oxide - CNTs hybrid material . . . . . . . . . . . . . . . . 159 7.2.2 Preparation of titania - CNTs composite material . . . . . . . . . . . . . . . . 160 7.2.3 Synthesis of magnetite - CNTs composite material . . . . . . . . . . . . . . . 162 7.2.4 Procedure for growing neuron cells on CNT blocks or films . . . . . . . . . . 163 7.2.5 Preparation of membrane electrode assembly for Fuel cell . . . . . . . . . . . 165 7.3 Characterization techniques . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 166 Bibliography 175 VI