CARBON NANOMATERIALS AND THEIR ELECTROCHEMICAL APPLICATIONS

Recent years have witnessed the continuously growing interest in the area of nanotechnology. Among the innumerable novel compounds and materials, carbon nanomaterials, especially carbon nanotubes (CNTs) and graphene, are undeniably two of the most glorious shining stars due to their unique structures and promising physical, chemical, and electrical properties. Numerous research projects have been focused on the synthesis, characterization, and functionalization of carbon nanomaterials, as well as their enormous possible applications in energy generation/storage, sensors, electronics, reinforcement of composite materials, and drug delivery. Of particular interest in this dissertation are the functionalization of carbon nanomaterials − either by decorating with Pt nanoparticles (NPs) or by doping with nitrogen atoms − and their electrochemical applications for both fuel cell catalysts (and supports) and electrochemical sensors/biosensors. I have successfully synthesized and characterized hybrid structures of Pt NP-CNTs or Pt NP-graphene, and also a novel carbon nanomaterial − nitrogen doped carbon nanotube cups (NCNCs). The electrochemical properties and applications of these nanomaterials were also investigated. Pt NP decorated CNTs or graphene were studied and compared for their electrochemical sensor performance in order to obtain further understanding on the structure-property relationship between 1-dimensional and 2-dimensional nanomaterials as the sensing platform. Both Pt-CNTs and NCNCs were investigated as fuel cell catalysts with the aim of improving the performance and stability, decreasing the amount of expensive Pt, and most importantly, understanding and optimizing NCNCs as non-precious-metal catalysts to ultimately replace expensive Pt-based catalysts. Pt-CNTs demonstrated extraordinary stability with less material used compared to commercial Pt/C catalysts in long term stability testing. NCNCs also exhibited good catalytic activity towards oxygen reduction reaction (ORR) which makes them promising alternatives to Pt-based catalysts. Further look into the ORR mechanism suggested that the presence of both nitrogen and iron from catalyst of NCNCs synthesis process is crucial for the improved ORR catalytic activity. From the materials point of view, a novel simple sonication method was studied to separate stacked NCNCs into individual nanocups structures, with the long-term objective of drug delivery or nano-reactor applications. Both the separation mechanism and the structure-property relationship of the stacked and separated NCNCs were investigated

Graphene for biomedical applications:a review

Since its discovery in 2004, graphene has enticed engineers and researchers from various fields to explore its possibilities to be incepted into various devices and applications. Graphene is deemed a ‘super’ material by researchers due to its extraordinary strength, extremely high surface-to-mass ratio and superconducting properties. Nonetheless, graphene has yet to find plausible footing as an electronics material. In biomedical field, graphene has proved useful in tissue engineering, drug delivery, cancer teraphy, as a component in power unit for biomedical implants and devices and as a vital component in biosensors. Graphene is used as scaffolding for tissue regeneration in stem cell tissue engineering, as active electrodes in supercapacitor for powering wearable and implantable biomedical devices and as detectors in biosensors. In tissue engineering, the extreme strength of monolayer graphene enables it to hold stem cell tissues as scaffold during in-vitro cell regeneration process. In MEMS supercapacitor, graphene’s extremely high surface-to-mass ratio enables it to be used as electrodes in order to increase the power unit’s energy and power densities. A small yet having high energy and power densities cell is needed to power often space constrainted biomedical devices. In FET biosensors, graphene acts as detector electrodes, owing to its superconductivity property. Graphene detector electrodes is capable of detecting target molecules at a concentration level as low as 1 pM, making it the most sensitive biosensor available today. Graphene continues to envisage unique and exciting applications for biomedical field, prompting continuous research which results and implementation could benefit the general public in decades to come

Single-step growth of graphene and graphene-based nanostructures by plasma-enhanced chemical vapour deposition

The realization of many promising technological applications of graphene and graphene-based nanostructures depends on the availability of reliable, scalable, high-yield and low-cost synthesis methods. Plasma enhanced chemical vapor deposition (PECVD) has been a versatile technique for synthesizing many carbon-based materials, because PECVD provides a rich chemical environment, including a mixture of radicals, molecules and ions from hydrocarbon precursors, which enables graphene growth on a variety of material surfaces at lower temperatures and faster growth than typical thermal chemical vapor deposition. Here we review recent advances in the PECVD techniques for synthesis of various graphene and graphene-based nanostructures, including horizontal growth of monolayer and multilayer graphene sheets, vertical growth of graphene nanostructures such as graphene nanostripes with large aspect ratios, direct and selective deposition of monolayer and multi-layer graphene on nanostructured substrates, and growth of multi-wall carbon nanotubes. By properly controlling the gas environment of the plasma, it is found that no active heating is necessary for the PECVD growth processes, and that high-yield growth can take place in a single step on a variety of surfaces, including metallic, semiconducting and insulating materials. Phenomenological understanding of the growth mechanisms are described. Finally, challenges and promising outlook for further development in the PECVD techniques for graphene-based applications are discussed

Challenges and recent advancements of functionalization of two-dimensional nanostructured molybdenum trioxide and dichalcogenides

Atomically-thin two-dimensional (2D) semiconductors are the thinnest functional semiconducting materials available today. Among them, both molybdenum trioxide and chalcogenides (MT&Ds) represent key components within the family of the different 2D semiconductors for various electronic, optoelectronic and electrochemical applications due to their unique electronic, optical, mechanical and electrochemical properties. However, despite great progress in research dedicated to the development and fabrication of 2D MT&Ds observed within the last decade, there are significant challenges affected their charge transport behavior, fabrication on a large scale as well as high dependence of the carrier mobility on thickness. In this article, we review the recent progress on the carrier mobility engineering of 2D MT&Ds and elaborate devised strategies dedicated to the optimization of MT&Ds properties. Specifically, the latest physical and chemical methods towards the surface functionalization and optimization of the major factors influencing the extrinsic transport at the electrode-2D semiconductor interface are discusse

Bactericidal vertically aligned graphene networks derived from renewable precursor

Graphene nanostructures exhibit a wide range of remarkable properties suitable for many applications, including those in the field of biomedical engineering. In this work, plasma-enhanced chemical vapor deposition was utilized at different applied RF power for the fabrication of vertical graphene nanowalls on silicon and quartz substrates from an inherently volatile carbon precursor without the use of any catalyst. AFM confirmed the presence of very sharp exposed graphene edges, with associated high surface roughness. The hydrophobicity of the material increased with the power of deposition, reaching the water contact angle of 123 ˚ for 500 W. Confocal scanning laser microscopy demonstrated that the viability of gram-negative Escherichia coli and gram-positive Staphylococcus aureus cells were 33% and 37% when incubated on graphene samples, respectively, compared to controls (quartz) that showed the viability of 82% and 84%, respectively. SEM verified significant morphological damage to bacterial cell walls by the sharp edges of graphene walls, with cells appearing abnormal and deformed. The presented data clearly contributed to the current understanding of the mechanical-bactericidal mechanism of vertically oriented graphene nanowalls upon direct contact with microorganisms

Noncovalent Functionalization of Graphene and Graphene Oxide for Energy Materials, Biosensing, Catalytic, and Biomedical Applications

This Review focuses on noncovalent functionalization of graphene and graphene oxide with various species involving biomolecules, polymers, drugs, metals and metal oxide-based nanoparticles, quantum dots, magnetic nanostructures, other carbon allotropes (fullerenes, nanodiamonds, and carbon nanotubes), and graphene analogues (MoS2, WS2). A brief description of pi-pi interactions, van der Waals forces, ionic interactions, and hydrogen bonding allowing noncovalent modification of graphene and graphene oxide is first given. The main part of this Review is devoted, to tailored functionalization for applications in drug delivery, energy materials, solar cells, water splitting, biosensing, bioimaging, environmental, catalytic, photocatalytic, and biomedical technologies. A significant part of this Review explores the possibilities of graphene/graphene oxide-based 3D superstructures and their use in lithium-ion batteries. This Review ends with a look at challenges and future prospects of noncovalently modified graphene and graphene oxideope

Plasma Nanoscience: from Nano-Solids in Plasmas to Nano-Plasmas in Solids

The unique plasma-specific features and physical phenomena in the organization of nanoscale solid-state systems in a broad range of elemental composition, structure, and dimensionality are critically reviewed. These effects lead to the possibility to localize and control energy and matter at nanoscales and to produce self-organized nano-solids with highly unusual and superior properties. A unifying conceptual framework based on the control of production, transport, and self-organization of precursor species is introduced and a variety of plasma-specific non-equilibrium and kinetics-driven phenomena across the many temporal and spatial scales is explained. When the plasma is localized to micrometer and nanometer dimensions, new emergent phenomena arise. The examples range from semiconducting quantum dots and nanowires, chirality control of single-walled carbon nanotubes, ultra-fine manipulation of graphenes, nano-diamond, and organic matter, to nano-plasma effects and nano-plasmas of different states of matter.Comment: This is an essential interdisciplinary reference which can be used by both advanced and early career researchers as well as in undergraduate teaching and postgraduate research trainin

The fabrication and application of carbon nanotube-based hybrid nanomaterials

The evolution of technology has reached a stage where the performances and dimension needed are outpacing what conventional materials can deliver. This has been made more acute with the further necessity of miniaturisation. Therefore, new materials which can overcome this bottleneck are required. Over the past few decades, it was found that when a material is reduced to the nanoscale, they can exhibit properties unparallel by their bulk counterparts. Therefore these nanomaterials poise as a promising candidate for future applications. Of the many nanomaterials, carbon nanotube (CNT) is among the most emblematic. CNT is a hollow one-dimensional structure comprising solely of carbon atoms. They are fascinating as they exhibit physical attributes which surpass many conventional materials and their nanoscale dimension allows greater flexibility in their deployments. However, the utilisation of CNTs is currently frustrated by a host of intrinsic and extrinsic factors. As a result, there are usually significant disparity between their predicted capability and real-world performance. Therefore, the practical application of CNTs remains unfeasible. The premise of this thesis is that by employing CNTs in conjunction with other materials, the hurdles which plague their utilisation may be overcome. Here, the concept of CNT-based hybrid nanomaterials is presented. This thesis demonstrates that by engineering complementary interaction between two materials, many challenges which hamper the utilisations of CNTs and other nanomaterials can indeed be negated. Furthermore, their synergistic interaction allows the performance of the CNT-based hybrid nanomaterials to be superior to their uncoupled precursors. Therefore, this could be a viable strategy to incorporating nanomaterials in a range of applications

The Art of Constructing Black Phosphorus Nanosheet Based Heterostructures: From 2D to 3D

Assembling different kinds of 2D nanosheets into heterostructures presents a promising way of designing novel artificial materials with new and improved functionalities by combining the unique properties of each component. In the past few years, black phosphorus nanosheets (BPNSs) have been recognized as a highly feasible 2D material with outstanding electronic properties, a tunable bandgap, and strong in-plane anisotropy, highlighting their suitability as a material for constructing heterostructures. In this study, recent progress in the construction of BPNS-based heterostructures ranging from 2D hybrid structures to 3D networks is discussed, emphasizing the different types of interactions (covalent or noncovalent) between individual layers. The preparation methods, optical and electronic properties, and various applications of these heterostructures—including electronic and optoelectronic devices, energy storage devices, photocatalysis and electrocatalysis, and biological applications—are discussed. Finally, critical challenges and prospective research aspects in BPNS-based heterostructures are also highlighted