Synthesis And Transport Properties Of 2d Transition Metal Carbides Mxenes

Since the isolation and characterization of graphene, there has been a growing interest in 2D materials owing to their unique properties compared to their 3D counterparts. Recently, a family of 2D materials of early transition metal carbides and nitrides, labelled MXenes, has been discovered (Ti2CTz, Ti3C2Tz, Mo2TiC2Tz, Ti3CNTz, Ta4C3Tz, Ti4N3Tz among many others), where T stands for surface-terminating groups (O, OH, and F). MXenes are mostly produced by selectively etching A layers (where A stands for group A elements, mostly groups 13 and 14) from the MAX phases. The latter are a family of layered ternary carbides and/or nitrides and have a general formula of Mn+1AXn (n = 1-3), where M is a transition metal and X is carbon and/or nitrogen. The produced MXenes have a conductive carbide core and a non-conductive O-, OH- and/or F-terminated surface, which allows them to work as electrodes for energy storage applications, such as Li-ion batteries and supercapacitors. Prior to this work, MXenes were produced in the form of flakes of lateral dimension of about 1 to 2 microns; such dimensions and form are not suitable for electronic characterization and applications. I have synthesized various MXenes (Ti3C2Tz, Ti2CTz and Nb2CTz) as epitaxial thin films, a more suitable form for electronic and photonic applications. These films were produced by HF, NH4HF2 or LiF + HCl etching of magnetron sputtered epitaxial Ti3AlC2, Ti2AlC, and Nb2AlC thin films. For transport properties of the Ti-based MXenes, Ti2CTz and Ti3C2Tz, changing n from 1 to 2 resulted in an increase in conductivity but had no effect on the transport mechanism (i.e. both Ti3C2Tx and Ti2CTx were metallic). In order to examine whether the electronic properties of MXenes differ when going from a few layers to a single flake, similar to graphene, the electrical characterization of a single Ti3C2Tz flake with a lateral size of about 10 ?m was performed. These measurements, the first for MXene, demonstrated its metallic nature, along with determining the nature of the charge carriers and their mobility. This indicates that Ti3C2Tz is inherently of 2D nature independent of the number of stacked layers, unlike graphene, where the electronic properties change based on the number of stacked layers. Changing the transition metal from Ti to Nb, viz. comparing Ti2CTz and Nb2CTz thin films, the electronic properties and electronic conduction mechanism differ. Ti2CTz showed metallic-like behavior (resistivity increases with increasing temperature) unlike Nb2CTz where the conduction occurs via variable range hopping mechanism (VRH) - where resistivity decreases with increasing temperature. Furthermore, these studies show the synthesis of pure Mo2CTz in the form of single flakes and freestanding films made by filtering Mo2CTz colloidal suspensions. Electronic characterization of free-standing films made from delaminated Mo2CTz flakes was investigated, showing that a VRH mechanism prevails at low temperatures (7 to ? 60 K). Upon vacuum annealing, the room temperature, RT, conductivity of Mo2CTx increased by two orders of magnitude. The conduction mechanism was concluded to be VRH most likely dominated by hopping within each flake. Other Mo-based MXenes, Mo2TiC2Tz and Mo2Ti2C3Tz, showed VRH mechanism at low temperature. However, at higher temperatures up to RT, the transport mechanism was not clearly understood. Therefore, a part of this thesis was dedicated to further investigating the transport properties of Mo-based MXenes. This includes Mo2CTz, out-of-plane ordered Mo2TiC2Tz and Mo2Ti2C3Tz, and vacancy ordered Mo1.33CTz. Magneto-transport of free-standing thin films of the Mo-based MXenes were studied, showing that all Mo-based MXenes have two transport regimes: a VRH mechanism at lower temperatures and a thermally activated process at higher temperatures. All Mo-based MXenes except Mo1.33CTz show that the electrical transport is dominated by inter-flake transfer. As for Mo1.33CTz, the primary electrical transport mechanism is more likely to be intra-flake. The synthesis of vacancy ordered MXenes (Mo1.33CTz and W1.33CTz) raised the question of possible introduction of vacancies in all MXenes. Vacancy ordered MXenes are produced by selective etching of Al and (Sc or Y) atoms from the parent 3D MAX phases, such as (Mo2/3Sc1/3)2AlC, with in-plane chemical ordering of Mo and Sc. However, not all quaternary parent MAX phases form the in-plane chemical ordering of the two M metals; thus the synthesis of the vacancy-ordered MXenes is restricted to a very limited number of MAX phases. I present a new method to obtain MXene flakes with disordered vacancies that may be generalized to all quaternary MAX phases. As proof of concept, I chose Nb-C MXene, as this 2D material has shown promise in several applications, including energy storage, photothermal cell ablation and photocatalysts for hydrogen evolution. Starting from synthetizing (Nb2/3Sc1/3)2AlC quaternary solid solution and etching both the Sc and Al atoms resulted in Nb1.33C material with a large number of vacancies and vacancy clusters. This method may be applicable to other quaternary or higher MAX phases wherein one of the transition metals is more reactive than the other, and it could be of vital importance in applications such as catalysis and energy storage.

This book describes the rapidly expanding field of two-dimensional (2D) transition metal carbides and nitrides (MXenes). It covers fundamental knowledge on synthesis, structure, and properties of these new materials, and a description of their processing, scale-up and emerging applications. The ways in which the quickly expanding family of MXenes can outperform other novel nanomaterials in a variety of applications, spanning from energy storage and conversion to electronics; from water science to transportation; and in defense and medical applications, are discussed in detail.

MXenes and their Composites: Synthesis, Properties and Potential Applications presents a state of the art overview of the recent developments on the synthesis, functionalization, properties and emerging applications of two-dimensional (2D) MXenes and their composites.The book systematically describes the state-of-the-art knowledge and fundamentals of MXene synthesis, structure, surface chemistry and functionalization. The book also discusses the unique electronic, optical, mechanical and topological properties of MXenes. Besides, this book covers the various emerging applications of MXenes and their composites across different fields such as energy storage and conversion, gas sensing and biosensing, rechargeable lithium and sodium-ion batteries, lithium-sulphur and multivalent batteries, electromagnetic interference shielding, hybrid capacitors and supercapacitors, hydrogen storage, catalysis and photoelectrocatalysis, gas separation and water desalination, environmental remediation and medical and biomedical applications. All these applications have been efficiently discussed in the specific chapters and in each case, the processing of MXene composites has also been discussed.This book will be an excellent reference for scientists and engineers across various disciplines and industries working in the field of highly promising 2D MXenes and their composites. The book will also act as a guide for academic researchers, material scientists, and advanced students in investigating the new applications of 2D MXenes based materials. Covers fundamentals of technologically important MAX phases, MXene derivatives, MXene synthesis methods, intercalation and delamination strategies, surface functionalization, fundamental characteristics and properties Demonstrates major application areas of MXenes, including catalytic, energy storage and energy generation, flexible electronics, EMI shielding, sensors and biosensors, medical and biomedical, gas separation and water desalination Presents a detailed discussion on the processing and performance of various MXenes towards different applications

This is the very first book on the highly promising topic of MXenes; focusing on their fundamental characteristics and properties, fabrication techniques and applications. MXenes are two-dimensional materials consisting of few atoms thick layers of transition metal carbides or nitrides. These are characterized by high electrical conductivity, good hydrophilicity, chemical stability, and ultrathin 2D sheet-like morphology. Applications in the energy, environmental, biomedical and electronic industries include catalysis, membrane separation, supercapacitors, hybrid-ion capacitors, batteries, flexible electronics, hydrogen storage, nanoelectronics, and sensors.

Titanium Carbide MXenes Discover the future of solar energy with this introduction to an essential new family of materials MXenes are a recently-discovered family of two-dimensional organic compounds formed from transition metal carbides. Their unique properties, such as high stability and electron conductivity, have made them a sought-after commodity with many industrial applications in cutting-edge industries. In particular, titanium carbide MXenes look poised to have significant applications in the solar energy industry, with potentially revolutionary consequences for the sustainable energy future. Titanium Carbide MXenes offers a thorough and accessible introduction to this family of compounds and their possible applications. It begins by surveying the fundamentals of the MXene groups, before characterizing titanium carbide MXenes and their processes of synthesis. It then moves on to discuss applications, current and future. The result is a must-read for researchers and professionals looking to synthesize and construct these materials and apply them in sustainable industry. Titanium Carbide MXenes readers will also find: Detailed treatment of MXenes including nitrides composites, perovskites composites, and more Discusses applications in photocatalytic CO2 reduction, hydrogen production, water splitting, and more Roughly 100 figures illustrating key concepts Titanium Carbide MXenes is a must-have for materials scientists, catalytic chemists, and scientists in industry.

Smart Multifunctional Nano-inks: Fundamentals and Emerging Applications covers nano-inks and how they can be used in inkjet printers for printing complex circuitry on flexible substrates or as a paste for 3D printers. Microstructures can be 3D-printed using nano-inks in a combination of high-resolution plasma printing and subsequent rotogravure printing. In addition, smart multifunctional nano-inks are not only required for the electronic, but also in other applications, such as for secure inks, for currency, and in immigration documents. This book focuses on fundamental design concepts, promising applications, and future challenges of nano-inks in various areas, such as optoelectronics, energy, security and biomedical fields. The current challenge for the successful industrial application of nano-inks is in the preparation of a stable dispersion of advanced materials for nano-inks. The functionalization, synthesizing, and theoretical modeling provide the solution for most of the current issues, but there are still remaining challenges which are covered in this comprehensive resource. Outlines the major nanomaterials used in the manufacture of smart nano-inks Provides information on the major industrial applications of nano-inks Assesses the major challenges of using nano-inks in a cost-effective way, and on an industrial scale

In this comprehensive yet compact monograph, Michel W. Barsoum, one of the pioneers in the field and the leading figure in MAX phase research, summarizes and explains, from both an experimental and a theoretical viewpoint, all the features that are necessary to understand and apply these new materials. The book covers elastic, electrical, thermal, chemical and mechanical properties in different temperature regimes. By bringing together, in a unifi ed, self-contained manner, all the information on MAX phases hitherto only found scattered in the journal literature, this one-stop resource offers researchers and developers alike an insight into these fascinating materials.

Since their discovery in 2011, MXenes (2D carbides, nitrides, and carbonitrides of early transition metals) have developed into one of the largest and most intensively studied families of 2D materials. They offer unique properties and are being explored in a large variety of applications. This book compiles the most important research from a pioneer of the field, Professor Yury Gogotsi, and his interdisciplinary research team, as well as numerous collaborators worldwide. It reports on the discovery and rise of MXenes and describes their synthesis and processing, properties, and incorporation into polymer, ceramic, and metal matrices to produce composites. It also discusses the potential of MXenes for use in energy storage, optics, electronics, and sensing, as well as biomedical, environmental, and electrocatalysis applications. The book will appeal to anyone interested in nanomaterials and their synthesis, properties, and applications.