Understanding the Nanotube Growth Mechanism: A Strategy to Control Nanotube Chirality during Chemical Vapor Deposition Synthesis

For two decades, single-wall carbon nanotubes (SWCNTs) have captured the attention of the research community, and become one of the flagships of nanotechnology. Due to their remarkable electronic and optical properties, SWCNTs are prime candidates for the creation of novel and revolutionary electronic, medical, and energy technologies. However, a major stumbling block in the exploitation of nanotube-based technologies is the lack of control of nanotube structure (chirality) during synthesis, which is intimately related to the metallic or semiconductor character of the nanotube. Incomplete understanding of the nanotube growth mechanism hinders a rationale and cost-efficient search of experimental conditions that give way to structural (chiral) control. Thus, computational techniques such as density functional theory (DFT), and reactive molecular dynamics (RMD) are valuable tools that provide the necessary theoretical framework to guide the design of experiments. The nanotube chirality is determined by the helicity of the nanotube and its diameter. DFT calculations show that once a small nanotube 'seed' is nucleated, growth proceeds faster if the seed corresponds to a high chiral angle nanotube. Thus, a strategy to gain control of the nanotube structure during chemical vapor deposition synthesis must focus on controlling the structure of the nucleated nanotube seeds. DFT and RMD simulations demonstrate the viability of using the structures of catalyst particles over which nanotube growth proceeds as templates guiding nanotube growth toward desired chiralities. This effect occurs through epitaxial effects between the nanocatalyst and the nanotube growing on it. The effectiveness of such effects has a non-monotonic relationship with the size of the nanocatalyst, and its interaction with the support, and requires fine-tuning reaction conditions for its exploitation. RMD simulations also demonstrate that carbon bulk-diffusion and nanoparticle supersaturation are not needed to promote nanotube growth, hence reaction conditions that increase nanoparticle stability, but reduce carbon solubility, may be explored to achieve nanotube templated growth of desired chiralities. The effect of carbon dissolution was further demonstrated through analyses of calculated diffusion coefficients. The metallic nanocatalyst was determined to be in viscous solid state throughout growth, but with a less solid character during the induction/nucleation stage

Arc-discharge In Solution: A Novel Synthesis Method For Carbon Nanotubes And In Situ Decoration Of Carbon Nanotubes With Nanoparticles

Nanotechnology has reached the status of the 21st century\u27s leading science and technology based on fundamental and applied research during the last two decades. An important feature of nanotechnology is to bridge the crucial dimensional gap between the atomic and molecular fundamental sciences and microstructural scale of engineering. Accordingly, it is very important to have an in-depth understanding of the synthesis of nanomaterials for the use of state-of-the-art high technological devices with enhanced properties. Recently, the \u27bottom-up\u27 approach for the fabrication of nanomaterials has received a great deal of attention for its simplicity and cost effectiveness. Tailoring the various parameters during synthesis of selected nanoparticles can be used to fabricate technologically important components. During the last decade, carbon nanotubes (CNTs) have been envisioned for a host of different new applications. Although carbon nanotubes can be synthesized using a variety of techniques, large-scale synthesis is still a great challenge to the researchers. Three methods are commonly used for commercial and bulk productions of carbon nanotubes: arc-discharge, chemical vapor deposition and laser ablation. However, low-cost, large-scale production of high-quality carbon nanotubes is yet to be reported. One of the objectives of the present research is to develop a simplified synthesis method for the production of large-scale, low-cost carbon nanotubes with functionality. Herein, a unique, simple, inexpensive and one-step synthesis route of CNTs and CNTs decorated with nanoparticles is reported. The method is simple arc-discharge in solution (ADS). For this new method, a full-fledged optoelectronically controlled instrumen is reported here to achieve high efficiency and continuous bulk production of CNTs. In this system, a constant gap between the two electrodes is maintained using a photosensor which allows a continuous synthesis of the carbon nanostructures. The system operates in a feedback loop consisting of an electrode-gap detector and an analogue electronic unit, as controller. This computerized feed system was also used in single process step to produce in situ-decorated CNTs with a variety of industrially important nanoparticles. To name a few, we have successfully synthesized CNTs decorated with 3-4 nm ceria, silica and palladium nanoparticles for many industrially relevant applications. This process can be extended to synthesize decorated CNTs with other oxide and metallic nanoparticles. Sixty experimental runs were carried out for parametric analysis varying process parameters including voltage, current and precursors. The amount of yield with time, rate of erosion of the anode, and rate of deposition of carbonaceous materials on the cathode electrode were investigated. Normalized kinetic parameters were evaluated for different amperes from the sets of runs. The production rate of pristine CNT at 75 A is as high as 5.89 ± 0.28 g.min-1. In this study, major emphasis was given on the characterizations of CNTs with and without nanoparticles using various techniques for surface and bulk analysis of the nanostructures. The nanostructures were characterized using transmission electron microscopy, high resolution transmission electron microscopy, scanning transmission electron microscopy, energy dispersive spectroscopy and scanning electron microscopy, x-ray photo electron spectroscopy, x-ray diffraction studies, and surface area analysis. Electron microscopy investigations show that the CNTs, collected from the water and solutions, are highly pure except the presence of some amorphous carbon. Thermogravimetric analysis and chemical oxidation data of CNTs show the good agreement with electron microscopy analysis. The surface area analysis depicts very high surface area. For pristine multi-walled carbon nanotubes, the BET surface area is approximately 80 m2.g-1. X-ray diffraction studies on carbon nanotubes shows that the products are clean. Nano-sized palladium decorated carbon nanotubes are supposed to be very efficient for hydrogen storage. The synthesis for in-situ decoration of palladium nanoparticles on carbon nanotubes using the arc discharge in solution process has been extensively carried out for possible hydrogen storage applications and electronic device fabrication. Palladium nanoparticles were found to form during the reduction of palladium tetra-chloro-square planar complex. The formation of such a complex was investigated using ultraviolet-visible spectroscopic method. Pd-nanoparticles were simultaneously decorated on carbon nanotubes during the rolling of graphene sheets in the arc-discharge process. Zero-loss energy filtered transmission electron microscopy and scanning transmission electron microscopy confirm the presence of 3 nm palladium nanoparticles. The deconvoluted X-ray photoelectron spectroscopy envelope shows the presence of palladium. Surface area measurements using BET method show a surface area of 28 m2.g-1. The discrepancy with pristine CNTs can be explained considering the density of palladium (12023 kg.m-3). Energy dispersive spectroscopy suggests no functionalization of chlorine to the sidewall of carbon nanotubes. The presence of dislodged graphene sheets with wavy morphology as observed with high-resolution transmission electron microscopy supports the formation of CNTs through the \u27scroll mechanism\u27

Synthesis of Carbon Nanotubes and their Application in TiO2 Photocatalysis

Doctor of PhilosophyDepartment of Chemical EngineeringPlacidus B AmamaIn the 21st century, scientists and engineers are tasked with furthering technological innovation while simultaneously achieving environmental sustainability. This necessitates the scalable development and implementation of advanced materials. The following work includes insight into the growth of single wall carbon nanotubes (SWCNTs) which are desired for a wide array of applications due to their exceptional, tunable properties. It also explores the use of composite materials comprised of CNTs and titanium dioxide (TiO2) for environmental remediation applications. The research presented in this document establishes the ability of FTS-GP (Fischer Tropsch Synthesis Gas Precursor, a waste product of industrial processes) to generate water in situ via gas phase reaction of CO with H2. The work demonstrates that this generated water is responsible for prolonged catalyst lifetime compared to a conventional precursor such as ethylene (C2H4). Experiments from both a conventional chemical vapor deposition (CVD) system and an autonomous research system (ARES) are supported by thermodynamic analysis, which together provide insight into the role of FTS-GP in generating on-site water during growth of SWNCT carpets. SWCNT growth is further investigated using Ru as a promoter to increase the selectivity of small-diameter SWCNTs (diameters below 1 nm). By performing over 200 growth experiments in ARES with different feedstocks and extensive multi-excitation Raman spectroscopic characterization, we demonstrate that the Ru-promoted Co catalyst doubles the selectivity of small-diameter SWCNTs (diameters below 1 nm) at 750 °C in comparison to Co, increasing to a factor of three at higher temperatures. Density functional theory (DFT) calculations with 13 and 55 atom CoxRuy clusters (ranging from 0 to 22% Ru content) reveal increases in cluster cohesive energies (EC) with Ru content. As these findings are indicative of increases in melting temperature and reduction in atom mobility with Ru content, they are consistent with the presence of ∼10% Ru in our Co catalyst which increases sintering resistance and stability of small nanoparticles, resulting in high selectivity toward small-diameter SWCNTs. After the discussion on SWCNT growth, the work in this document examines the fabrication of CNT-TiO2 composite materials and their ability to efficiently eliminate airborne pollutants. It begins with the synthesis of CNT-TiO2 composites and the role of CNTs in degradation of acetaldehyde, a representative volatile organic compound (VOC) in a batch reactor. The study indicates that a small amount of multi-walled carbon nanotubes (MWCNTs) increases catalyst performance compared to TiO2, whereas the addition of CNTs beyond the optimum loading ratio of 1:100 (MWCNT:TiO2) diminishes the effectiveness of the photocatalyst and the synergistic effect between MWCNTs and TiO2. CNT-TiO2 photocatalyst composites are subsequently implemented for degradation of NOx in a continuous flow reactor. This study demonstrates the use of CNT-TiO2 photocatalyst films for effective transformation of NOx into nitrates. Using the objective figure of merit for NOx abatement, DeNOx index, the catalyst performance in a laminar-flow reactor was evaluated under different conditions, including relative humidity (RH), initial NOx concentration, reactor geometry (headspace distance), and state of the catalyst (fresh vs. recycled). Our results reveal CNT-TiO2 significantly outperforms P25 in a humid environment despite exhibiting comparable NO conversion at low RH. In addition, mass transfer from the bulk airflow limits NO conversion when the reactor headspace is too large (>3 mm), due to limited diffusion of NOx to the photocatalyst surface. The remarkable DeNOx activity of CNT-TiO2 over a wide range of RH levels is rationalized based on the ratio of physisorbed-to-chemisorbed water on the photocatalyst surface and the effect of this physisorbed water in increasing the amount of superoxide (O2•-) radicals generated

Synthesis and Applications of One- and Two-Dimensional Polymer-Carbon Nanomaterial Composites

This dissertation describes the synthesis of polymer and carbon nanomaterial composites and their applications in drug delivery, chemical sensing, and catalytic oxidative patterning. The first part studies polyethylene glycol functionalized oxidized single-walled carbon nanotubes (PLPEG/ox-SWCNT) as a drug nanocarrier to prolong the circulation of two mitochondria targeting radiomitigators TPP-IOA and XJB-5-131. In in vivo tests with mice exposed to a single total body irradiation of 9.25 Gy, the PL-PEG/ox-SWCNT nanocarrier prolongs the circulation of TPP-IOA without developing apparent toxicity and exhibits radiation mitigating effects, slightly better than that of free TPP-IOA. The in vivo drug effect of the XJB-5-131 conjugate is inconclusive. The stability of Doxorubicin-loaded PL-PEG/ox-SWCNT is investigated under oxidative bursts that occur in neutrophils and macrophages. Myeloperoxidase-catalyzed and peroxynitrite-mediated oxidations of the drug conjugate are studied ex vivo, and the in vitro tests in B16 melanoma cells and tumor-activated myeloid cells are conducted. Both ex vivo and in vitro results indicate that the nanocarrier protects Doxorubicin from the oxidative degradation. The second part of the dissertation discusses the synthesis and applications of twodimensional polymers. A novel crystalline polybenzobisimidazole-based two-dimensional supramolecular polymer (2DSP-PBBI) is synthesized by condensation/precipitation polymerization under solvothermal conditions. The surface morphology of 2DSP-PBBI is analyzed with electron and atomic force microscopy, revealing planar surfaces formed by hydrogen bonding. An iron(III)-coordinated porphyrin-based covalent organic framework (Fe-DhaTph-COF) is synthesized for the fabrication of oxidatively patterned graphite in the presence of H2O2 and/or NaOCl. The vertical channel created by patterning is ~3 nm in depth, and liquidexfoliation of the patterned graphite provides few-layer porous graphene. Although the shape and size of the pores are not uniform, this study demonstrates that metallated COFs can be utilized as surface catalysts and master templates for patterning

Infrastructure of Synchrotronic Biosensor Based on Semiconductor Device Fabrication for Tracking, Monitoring, Imaging, Measuring, Diagnosing and Detecting Cancer Cells

Copper Zinc Antimony Sulfide (CZAS) is derived from Copper AntimonySulfide (CAS), a famatinite class of compound. In the current paper, thefirst step for using Copper, Zinc, Antimony and Sulfide as materials inmanufacturing synchrotronic biosensor-namely increasing the sensitivity of biosensor through creating Copper Zinc Antimony Sulfide, CZAS(Cu1.18Zn0.40Sb1.90S7.2) semiconductor and using it instead of CopperTin Sulfide, CTS (Cu2SnS3) for tracking, monitoring, imaging, measuring,diagnosing and detecting cancer cells, is evaluated. Further, optimization oftris(2,2'-bipyridyl)ruthenium(II)(Ru(bpy)32+) concentrations and CopperZinc Antimony Sulfide, CZAS (Cu1.18Zn0.40Sb1.90S7.2) semiconductor as two main and effective materials in the intensity of synchrotron fortracking, monitoring, imaging, measuring, diagnosing and detecting cancercells are considered so that the highest sensitivity obtains. In this regard,various concentrations of two materials were prepared and photon emissionwas investigated in the absence of cancer cells. On the other hand, ccancerdiagnosis requires the analysis of images and attributes as well as collectingmany clinical and mammography variables. In diagnosis of cancer, it isimportant to determine whether a tumor is benign or malignant. The information about cancer risk prediction along with the type of tumor are crucialfor patients and effective medical decision making. An ideal diagnosticsystem could effectively distinguish between benign and malignant cells;however, such a system has not been created yet. In this study, a model isdeveloped to improve the prediction probability of cancer. It is necessary tohave such a prediction model as the survival probability of cancer is highwhen patients are diagnosed at early stages

Classical and reactive molecular dynamics: Principles and applications in combustion and energy systems

Molecular dynamics (MD) has evolved into a ubiquitous, versatile and powerful computational method for fundamental research in science branches such as biology, chemistry, biomedicine and physics over the past 60 years. Powered by rapidly advanced supercomputing technologies in recent decades, MD has entered the engineering domain as a first-principle predictive method for material properties, physicochemical processes, and even as a design tool. Such developments have far-reaching consequences, and are covered for the first time in the present paper, with a focus on MD for combustion and energy systems encompassing topics like gas/liquid/solid fuel oxidation, pyrolysis, catalytic combustion, heterogeneous combustion, electrochemistry, nanoparticle synthesis, heat transfer, phase change, and fluid mechanics. First, the theoretical framework of the MD methodology is described systemically, covering both classical and reactive MD. The emphasis is on the development of the reactive force field (ReaxFF) MD, which enables chemical reactions to be simulated within the MD framework, utilizing quantum chemistry calculations and/or experimental data for the force field training. Second, details of the numerical methods, boundary conditions, post-processing and computational costs of MD simulations are provided. This is followed by a critical review of selected applications of classical and reactive MD methods in combustion and energy systems. It is demonstrated that the ReaxFF MD has been successfully deployed to gain fundamental insights into pyrolysis and/or oxidation of gas/liquid/solid fuels, revealing detailed energy changes and chemical pathways. Moreover, the complex physico-chemical dynamic processes in catalytic reactions, soot formation, and flame synthesis of nanoparticles are made plainly visible from an atomistic perspective. Flow, heat transfer and phase change phenomena are also scrutinized by MD simulations. Unprecedented details of nanoscale processes such as droplet collision, fuel droplet evaporation, and CO2 capture and storage under subcritical and supercritical conditions are examined at the atomic level. Finally, the outlook for atomistic simulations of combustion and energy systems is discussed in the context of emerging computing platforms, machine learning and multiscale modelling

Photoluminescence Properties of Carbon Nanomaterials during Coronation and Biodegradation

Carbon nanomaterials (CNMs) have been widely used in biomedical applications such as drug delivery, biosensing, and bioimaging. Due to their interactions with the biological systems in these applications, it is important to understand what happens to CNMs in vivo. Upon introduction into a biological environment, CNMs are rapidly coated with biomolecules (90% lipids) resulting in so-called ‘biocorona’. CNMs can also undergo additional bio-transformations including partial or complete biodegradation. This dissertation focuses on using fluorescence spectroscopy to study the chemical reactions between CNMs and different biomolecules upon coronation and biodegradation. We first use fluorescence spectroscopy to study the reactions between the single-walled carbon nanotubes (SWCNTs) and the biologically important oxygenated lipid metabolites. A photoinduced cycloaddition reaction between metabolites bearing enone functional groups and SWCNTs is reported here. By creating covalent and tunable sp3 defects in the sp2 carbon lattice of SWCNTs through [2π + 2π] photocycloaddition, a bright red-shifted photoluminescence (PL) was gradually generated. The mechanism of the photocycloaddition reaction was further investigated by comparing the reactivity with various organic molecules and computational calculations. The results of this study can enable engineering of the optical and electronic properties of semiconducting SWCNTs and provide understanding into their interactions with the lipid biocorona. In addition to coronation, CNMs could induce a robust inflammatory response. Our research group has found that these effects can be mitigated by enzymatic biodegradation of CNMs through a peroxidase enzyme released by neutrophils during inflammation, myeloperoxidase (MPO). We performed PL studies on the MPO-catalyzed oxidation of graphene oxide (GO) and surfactant-coated SWCNTs. We further constructed two ratiometric sensors using SWCNT/GO nanoscrolls by incorporating surfactant-wrapped SWCNTs as the internal either turn-off or reference sensor. Our sensors show linear response to MPO oxidative machinery and hold the promise to be used as self-calibrating CNMs-based MPO activity indicators. Finally, the composition and structures of the fluorescent GO degradation products, in the form of polyaromatic hydrocarbons (PAHs), were analyzed using liquid chromatography–mass spectrometry and computational calculations. Our results indicated that structures with several conjugated benzene rings are likely to generate the observed PL

Study on the Mechanical Properties of Carbon Nanotube Coated‒Fiber Multi-Scale (CCFM) Hybrid Composites

L'abstract è presente nell'allegato / the abstract is in the attachmen

Carbon Nanotube/Polymer Hybrid Material Design via Modular Ligation Techniques

Cyclopentadienyl end-capped poly(methyl)methacrylate, poly(N-isopropyl)acrylamide and poly(3-hexyl)thiophene are employed in a one-step Diels-Alder reaction to generate hybrid materials based on single-walled carbon nanotubes (SWCNTs). Variable analytical methods reveal the presence of the polymer strands after the ligation. The grafting density of the hybrid materials was compared to a conventional ligation technique involving an acidic pre-functionalization of the SWCNTs