A thesis submitted to the Faculty of Engineering and the Built Environment, University of the Witwatersrand, Johannesburg, in fulfilment of the requirements for the degree of Doctor of Philosophy Johannesburg, 2016 / Technologies for the separation of CO2 from flue gas require a feat of engineering for efficient achievement. Various CO2 capture technologies, including absorption, adsorption, cryogenics and membranes, have been investigated globally. The absorption technology uses mainly alkanolamine aqueous solutions, the most common being monoethanolamine (MEA); however, further investigation is required to circumvent its weakness due to degradation through oxidation, material corrosion and high energy costs required for regeneration. Attractive advantages in adsorption technology, including the ability to separate the more diluted component in the mixture with a low energy penalty, have been a motivation for many researchers to contribute to the advancement of adsorption technology in CO2 capture. The challenge in CO2 adsorption technology is to design a hydrophobic and biodegradable adsorbent with large CO2 uptake, high selectivity for CO2, adequate adsorption kinetics, water tolerance, and to require low levels of energy for regeneration processes. The existing adsorbent such as activated carbon, silica gel, zeolites, metal organic frameworks and others, have been ineffective where moisture occurs in flue gas. This work provides an advanced adsorption technology through a novel adsorbent, MWNT-PAA, designed from the noncovalent functionalization of multi-walled carbon nanotubes (MWNTs) by polyaspartamide (PAA) as product of amine grafted to polysuccinimide (PSI). Three types of PAA were prepared using ethylenediamine (EDA), 1, 3 propanediamine (PDA) and monoethanolamine (MEA) drafted to PSI to give PSI-EDA, PSI-PDA and PSI-MEA respectively. The CO2 adsorption capacity was 13.5 mg-CO2/g for PSI-PDA and 9.0 mg-CO2/g for PSI-MEA, which decreased significantly from PSI where the CO2 adsorption capacity was 25 mg-CO2/g. PSIEDA was selected as PAA, because the CO2 adsorption capacity was 52 mg-CO2/g which doubled from PSI. The polymer polyethylenimine (PEI), the most commonly polymer used in CO2 capture, was found to be non-biodegradable, while the polymer PAA showed the presence of CONH as a biodegradable bond functionality, occurring in the MWNT-PAA, as confirmed through Fourier Transform Infrared (FTIR) analysis. The adsorbent MWNT-PAA was demonstrated to have a water tolerance in the temperature range 25-55 ℃, where CO2 adsorption capacity increased with the increase of water in the adsorbent. The highest CO2 adsorption capacity recorded was 71 mg-CO2/g for the moist MWNT-PAA using 100% CO2 and 65 mg-CO2/g for the mixture of 14% CO2 with air. Under the same conditions, the dry MWNT-PAA adsorbed 70 and 46 mg-CO2/g respectively (100%, 14% CO2). The 2 regenerability efficiency of the MWNT-PAA absorbent was demonstrated at 100 ᵒC; after 10 cycles of adsorption-desorption 99% of adsorbed gas was recovered in the desorption process. The heat flow for the thermal swing adsorption system resulted in the net release of heat over the complete cycle; a cycle includes adsorption (heat release) and desorption (heat absorbance). Thus, this MWNT-PAA adsorbent demonstrates an advantage in terms of overall energy efficiency, and could be a competitive adsorbent in CO2 capture technology.

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Thesis (Ph.D.)--The Ohio State University, 2007. / Adviser: Douglas Southgate. Includes bibliographical references.

Thesis--Copenhagen. / Translated by Anna la Cour and Ibbetson James. Bibliography: p. [221]-229.

Thesis (licentiate)--Universität Bern, 1980. / Cover title. Includes bibliographical references (leaves i-ii).

Carbon electrodes have found widespread use in electrochemistry due to its broad versatility and low cost amongst other advantages. Recent innovations in carbon materials have added new dimensions to their utility in electrochemical applications. This thesis aims to investigate aspects of carbon materials, in particular boron-doped diamond (BDD) and nanocarbon composites, mainly for electrochemical analysis and energetics studies. The electrochemical behaviour of estradiol and other endocrine disrupting compounds was examined on the BDD electrode with different surface pretreatments, as well as on a nanocarbon-modified BDD electrode. It was shown that the precise control of surface chemical termination enabled the electrode to be tuned to exhibit diffusional or adsorptive voltammetry at oxidised and hydrogenated BDD interfaces respectively. Adsorption effects were also observed on the modified electrode leading to significant pre-concentration of the analyte onto the nanocarbon and a corresponding lowering of the limit of detection by ca three orders of magnitude to nanomolar levels. Surface modification of the BDD electrodes was then explored using a simple and convenient dropcast technique to deposit microcrystalline copper phthalocyanine onto the electrode. The influence of the surface chemical termination towards the interaction with the modifier compound was demonstrated in relation to the oxygen reduction reaction. Hydrogen terminated BDD modified in such a manner was able to significantly decrease the overpotential for the cathodic reaction by ca 500 mV when compared to the unmodified electrode while modified oxidised BDD showed no such electrocatalysis, signifying greater interaction of the phthalocyanine modifier with the hydrogenated surface. The lack of a further conversion of the peroxide product was attributed to its rapid diffusion away from the triple phase boundary (comprising the phthalocyanine microcrystallite, aqueous solution and BDD electrode) at which the reaction is expected to exclusively occur. Next carbon composites were studied in the form of carbon paste electrodes (CPEs). The practicality of a nanocarbon paste was established by cyclic voltammetry with several well-characterised redox systems commonly used to test electrode activity and was found to exhibit comparable behaviour to the more typical graphitic formulation. Reversible uptake of some analytes was observed at the CPEs, giving rise to complex double peak voltammetry. This uptake phenomenon was then further examined at the nanocarbon paste electrode to monitor the transfer of species between two dissimilar liquid phases. The interfacial behaviour gave rise to voltammetric peaks which were assigned to species originating from the aqueous, binder and carbon phases respectively and this enabled the measurement of Gibbs energies of transfer between oil and aqueous phases. Finally the effect of different ionic liquids as binder for carbon-ionic liquid composite electrodes was studied. Some ionic liquids were demonstrated to offer benefits in comparison to oil in the fabrication of carbon paste type electrode due to an increased adsorption of analytes. The ionic “liquid” (with a melting point above room temperature) <i>n</i>-octyl-pyridinium hexafluorophosphate [C₈py][PF₆] was shown to be useful in combination with carbon nanotubes as a composite electrode or as a modifier to a screen-printed electrode to significantly enhance the sensitivity of electrochemical detection via adsorptive stripping voltammetry. Overall the carbon-based electrodes studied have demonstrated excellent utility as electrode materials in the areas of electrochemical sensing and energetics investigations.

Carbon Capture and Storage is a nascent technology developed with the intention of collecting carbon dioxide emissions from the flue gasses of point source producers, such as power stations or cement works. The carbon dioxide is then stored in underground geological reservoirs so that it does not reach the atmosphere, reducing the rate at which greenhouse gasses accumulate and influence climate change. However, as with all nascent technologies, the benefits of these developments and concepts must be weighed against the risks of serious and long-term environmental impact should an accidental release occur. The aim of this thesis is to study the potential for environmental damage caused by a release of carbon dioxide into the marine environment from a sub-seabed carbon dioxide reservoir generated through carbon capture and storage development. The quantification of the rate of change caused by such an accidental release of carbon dioxide will be studied, as will the rate at which natural conditions are re-established upon cessation of the release.

Application of carbon nanomaterials like fullerene, carbon nanotubes, and graphene in solar cells using solution processable methods presents a great potential to reduce the cost of producing electricity from solar energy. However, carbon nanotubes and graphene materials are predominantly metallic and this limits their function in organic photovoltaic devices (OPVs) where semiconducting behavior is required. Doping of carbon nanomaterials is a well-known method for making them semiconducting. Doping of carbon nanomaterials with nitrogen and boron can tune their properties to suit the requirements for use in photovoltaic applications as n-type and p-type semiconducting materials, respectively. Indeed, the use of nitrogen doped and boron doped carbon nanotubes in organic solar cells together with fullerene acceptors can improve the current density of the OPV devices. Nitrogen doping of carbon nanotubes can be achieved by using nitrogen-containing precursor materials during chemical vapor deposition. However the doping of carbon nanotubes with nitrogen does not automatically make them n-type materials; they remain metallic unless a large amount of quaternary type nitrogen is incorporated in the carbon nanotubes. In this work we have developed a method to control the type of nitrogen that is incorporated in CNTs by using an appropriate synthesis temperature and use of oxygen-containing carbon precursors during the chemical deposition of carbon nanotubes. Quaternary N was incorporated in a CVD process when high temperatures and a high concentration of O in the precursor materials were used. We also showed that the type and amount of N can be changed from pyrrolic and pyridinic-N-oxide to pyridinic N and quaternary N by annealing N doped carbon nanotubes at temperatures above 400°C. At temperatures above 800°C most of the nitrogen is converted to quaternary nitrogen. N-CNT thin films were used in OPVs so as to modify the ITO electrode and transform it into a 3D electrode. The resulting effect was an improved short circuit current density in the devices containing an N-CNT thin film that was placed on top of the ITO electrode. A reduction in efficiency losses in OPVs at increasing light intensity was observed in the NCNT ITO modified electrode OPVs. This is a remarkable finding when considering that one of the main problems hindering commercialization of OPVs is the loss of efficiency at high light intensities. We related these effects to the efficient charge collection by the modified ITO electrode. Incorporation of N-CNTs in the bulk heterojunction layer of the OPV device resulted in poor performance when compared to an OPV device made without N-CNTs. This effect is caused by shorting of the OPVs. We used a method of incorporating N-CNTs whilst minimizing shorting and this showed potential for better performance. A study on the attempted doping of graphene with B to make it a p-type material showed that in the presence of a nitrogen carrier gas, BN instead of B was incorporated in graphene. This remarkable finding enabled us to grow a p-type graphene with a possible a band gap opening. This was corroborated by XPS and Raman spectroscopy studies of the material. This BN doped graphene material showed potential as a possible replacement of PEDOT:PSS as a hole transport material in OPVs. The BN doped graphene material can match the performance of PEDOT:PSS when the level of BN doping in graphene is increased.

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