Solubilisation, Purification and Processing of Single Walled Carbon Nanotubes Using Organic Molecules

The aims of this research are seven fold; • To enhance the solubility of SWNTs in organic solvents. • To purify an untreated sample of SWNTs that contains many side products. • To gain a greater understanding of the interaction between the polycyclic aromatic hydrocarbons and SWNTs. • To debundle and disperse SWNTs. • To select SWNTs of a specific structure based on the structures of the polycyclic aromatic hydrocarbons used. • To observe and compare the interaction of polycyclic aromatic hydrocarbons with SWNTs produced by different methods. • To elucidate factors which contribute to different degrees of interaction between different SWNT samples and the hydrocarbon molecules. In this research, the solubilisation, purification and debundling of single walled carbon nanotubes (SWNT) on interaction with the polycyclic aromatic hydrocarbons (PAHs), anthracene and p-terphenyl are explored. The investigations were performed in toluene due to its poor affinity for the retention of SWNTs. Thus this solvent can act as a good indicator for improvements in the solubility of the SWNTs due to the presence of the PAHs. The hydrocarbons anthracene and p-terphenyl were chosen because of their high degree of solubility in toluene and their simple structure that is proposed in this research to exhibit molecular recognition of SWNTs with a similar backbone structure to that of the hydrocarbon. The study begins with the exploration of the interaction between the SWNTs in an untreated sample and the PAHs, and results reveal an enhanced solubility of the SWNTs in toluene and subsequently the purification of the SWNT sample. Interaction between the PAHs and the SWNTs draws the SWNTs into solution allowing all side products to precipitate out. The composite solution is a stable suspension of finely dispersed SWNTs with no evidence of SWNT precipitation observed in over a five year period. This observation indicates an enhanced stability of the SWNTs in solutions due to an interaction with the PAH molecules and this observation is supported by Raman and fluorescence spectroscopic studies which are presented in this thesis. Both anthracene and p-terphenyl map via a π - π interaction to the SWNT backbone with strong indications of structural selectivity between the SWNT surfaces and PAHs. The literature is scarce with regard to the interaction between organic molecules and SWNTs. In this research an investigation into the interaction that occurs between PAHs and SWNTs is conducted. The interactions and debundling of SWNTs over a broad concentration range are probed through spectroscopic methods including fluorescence and Raman. Fluorescence concentration dependence studies define the concentration range where aggregated PAHs and isolated PAHs exist. A fluorescence model based on the fraction of free hydrocarbons is used to indicate the concentration range where debundled and bundled SWNTs and PAHs are interacting with atomic force microscopic (AFM) studies supporting the results. AFM is used to obtain a surface profile of the SWNTs at a range of concentrations to image the debundling of SWNTs with decreasing concentration. The fluorescence model also allows the calculation of a binding energy between the SWNTs and PAHs at low concentrations. The binding energy determined is further supported by alternative theoretical models and the results obtained correlate well. Raman studies support fluorescence and AFM studies with regard to the interaction and debundling of SWNTs and the Raman radial breathing modes (RBMs) are probed to investigate selective interaction of the RAH molecules at low concentrations and results reveal a degree of selective interaction. To conclude this work, a study of SWNTs produced by different methods is performed to investigate any changes which may occur to the SWNT/PAH/solvent system as a result of replacing one tube type for another. The study elucidates factors that are favourable for interaction with the hydrocarbon in the given solvent toluene. Spectroscopic methods such as fluorescence and microscopic studies such as AFM are used as the investigative tools. The studies reveal that large bundles with larger diameter SWNTs are most favourable for interaction with p-terphenyl and debundling in toluene. Such a study is of interest for the development of a standardised purification and processing protocol

A Comparative Study of the Interaction of Different Polycyclic Aromatic Hydrocarbons on Different Types of Single Walled Carbon Nanotubes

A comparative study of the solubilising effect of polycyclic aromatic hydrocarbon (PAHs) on single walled carbon nanotubes (SWCNTs) produced by high pressure decomposition of carbon monoxide (HiPco) and the arc discharge (AD) method has been carried out with the aid of fluorescence and Raman spectroscopy. For this study, polyphenyl and polyacene PAHs of different lengths are used. From the study it has been found that the binding energy of PAHs with AD SWCNTs is the same as that with HiPco SWCNTs. Shorter PAHs molecules better solubilise SWCNTs and in general smaller diameter SWCNTs. Thus, given their smaller diameter profile, significantly larger amounts of HiPco SWCNTs are solubilised than AD SWCNTs

Enhancing Feedback: key Issues and Solutions From the Literature to Help New Lecturers in Higher Education

The National Strategy for Higher Education to 2030 highlights that whilst modularisation has allowed for greater flexibility, it has also produced some problems including fragmentation of programmes with large numbers of modules leaving students feeling over assessed and staff burdened (Hunt, 2011). Nicol & Macfarlene-Dick (2006) have argued that formative assessment can promote better student learning and that assessment can be used more effectively by embedding ‘feedback’ and ‘feedforward’ in curriculum practices. Their studies identify how formative feedback does not have to solely come from the teacher, but can also be provided by peers and even generated by the students themselves. The Irish National Forum for the Enhancement of Teaching and Learning in Higher Education (NFETLHE) has put forward similar arguments to enhance learning if we move away from a purely ‘Assessment OF’ approach and shift towards a more ‘Assessment FOR’ and ‘Assessment AS Learning’ approach, giving the students a more central role (NFETLHE, 2017). Figure 1 below illustrates these concepts and highlights the dynamic relationship between formative assessment and learning (NFETLHE, 2017)

The Bundle Dispersion of SWNT on Interaction with P-Terphenyl

This paper investigates the interaction and bundle dispersion of single walled carbon nanotubes (SWNT) produced by arc discharge and by the high pressure decomposition of carbon monoxide, often referred to as the HiPco method, in the presence of the molecule p-terphenyl. The study will show that the extent of SWNT bundle dispersion and the degree of interaction with p-terphenyl is related to the level of purity of the SWNT sample. This study compares the bundle dispersion and interaction of SWNT with p-terphenyl in their as produced state and after purification. A number of spectroscopic and microscopic techniques are used to probe the SWNT and their interaction with p-terphenyl. A technique such as energy dispersive analysis by x-ray (EDAX) is used to give an elemental analysis of the SWNT samples before and after purification. Fluorescence and atomic force microscopy are used as techniques to assess the degree of interaction and bundle dispersion of the SWNT

A Raman Spectroscopy Study of the Solubilisation of SWCNTS by POlycyclic Aromatic Hydrocarbons

The effectiveness of polycyclic aromatic hydrocarbons (PAHs) for selective solubilisation of single walled carbon nanotubes (SWCNTs) has been studied by Raman spectroscopy. Polyphenyl and polyacene PAHs of different lengths are used. Selective interaction between the PAHs and SWCNT is investigated by analyzing the Raman radial breathing modes the frequency positioning of which yields information concerning the diameter distribution of the SWCNT sample. Samples were dispersed at concentrations below the debundling limit and deposited on quartz substrates. A combination of four laser excitation energies was utilized to establish the distribution of diameters present. The results show that the PAHs interact with a range of SWCNT diameters. In general a preference for smaller diameter SWCNTs is evident, although the longer PAHs have the capacity to solubilise larger diameter SWCNTs, due to their increased binding energy. Although a small degree of structural specificity is evident, all PAHs solubilise both chiral and nonchiral SWCNTs

Use of Raman Spectroscopy in the Investigation of Debundling of Single Walled Carbon Nanotubes

Samples of raw nanotubes are compared to those deposited from solutions to examine separation of nanotube bundles. Single wall nanotubes bundles produced by the arc-discharge and HiPco methods were solubilised in toluene, DMF and 1,2 dichloroethane. Resonant Raman spectroscopy was used to determine if debundling of the tubes sample occurred. The results showed some degree of debundling, best for the 1,2 dichloroethane solvent, which also shows long term solubility

A Systematic Study of the Dispersion of SWNTs in Organic Solvents

Dispersions of as-produced HiPco single-walled carbon nanotubes (SWNTs) in a series of organic solvents were prepared by dilution with the aid of tip sonication. Mild centrifugation (~ 945 g) was carried out to remove large bundles. Atomic force microscopy (AFM) studies revealed that the bundle size decreased as the dispersion was diluted. By measuring the UV-vis-NIR absorption before and after centrifugation as a function of the concentration, the dispersion limit of SWNTs in each solvent can be determined. Correlations between the dispersion limit and solvent solubility parameters, including the Hildebrand solubility parameter and three dimensional Hansen solubility parameters, are explored, demonstrating that SWNTs are easily dispersed in solvents with Hildebrand solubility parameter range from ~22-24 MPa1/2 and Hansen polarity component (δP) ~12-14 MPa1/2. No clear correlation between dispersion limits and the dispersion force (δD) or hydrogen bonding force (δH) are evident. It is found, however, that the degree of dispersion depends critically on sample preparation conditions and in particular sonication time. Increased sonication times increase the amount of SWCNTs debundled and solubilised but do not appear to affect the dispersion limit. However, increased sonication also induces discernible changes to the SWNTs themselves and in itself influences their solubility, under which conditions no clear solubility parameters can be determined

The Physical Interactions between HiPCo SWNTs and Semi-conjugated Polymers

Hybrid systems of the conjugated organic polymer poly (p-phenylene vinylene-co-2,5- dioctyloxy -m-phenylene vinylene) (PmPV) and HiPco SWNT are explored using spectroscopic and thermal techniques to determine specific interactions. Vibrational spectroscopy indicates a weak interaction and this is further elucidated using Differential-Scanning Calorimetry and Temperature Dependent Raman pectroscopy. Two distinct transitions in region of -60C and + 60C are investigated

Temperature Dependent Spectroscopic Studies of HiPco SWNT Composites

Hybrid systems of the conjugated organic polymer poly(p-phenylene vinylene-co-2,5-dioctyIoxy-m-phenylene vinylene)(PmPV) and HiPco SWNTs are explored using spectroscopic and thermal techniques to determine specific interactions. Vibrational spectroscopy indicates a weak interaction and this is further elucidated using Differential Scanning Calorimetry, Temperature Dependent Raman Spectroscopy and Temperature Dependent Infrared Spectroscopy of the raw materials and the composite. An endothermic transition is observed in the DSC of both the polymer and the 0.1% HiPco composite in the region of 60 °C. Also observed in the DSC of the composite is a doubly peaked endotherm at -39 °C and -49 °C, which does not appear in the polymer film. The Raman of the polymer backbone upon increasing the temperature to 60 °C shows diminished phenyl Ag modes at 1557 cm−1 and 1575 cm−1, with an increase in the relative intensity of the vinyl mode at 1630 cm−1. This change in the Raman of the polymer is translated to the Raman of the composite upon increase to 60 °C, where the spectrum becomes abruptly dominated by nanotubes. The Raman of the composite shows no change in the lower temperature regions, however infrared suggests that the transition at -39 °C derives from an interaction with the polymer side chains. The composite at -39 °C shows a change in the absorption of the polymer side chain aryl-oxide linkage at 1250 cm−1. while Raman suggests a change to the polymer backbone configuration at 60 °C. Implications are discussed