Electrochemical double layer capacitors (EDLCs, also called supercapacitors or ultracapacitors) are high power density energy storage devices that operate through the separation of charge at the electrochemical interface between an electrode and a supporting electrolyte. Numerous types of carbon materials with high surface area and internal porosity, such as activated carbon, carbon fabrics, nanotubes, and reduced graphene oxide have been studied as electrode materials. Electrolytes such as aqueous alkaline and acid solutions usually give high capacitance, while organic and ionic liquids provide a wider operation voltage. Graphene, due to its high theoretical surface area of 2630 m2/g, good electrical conductivity, and relatively low density, is being studied as an electrode material in EDLCs. The objective of this dissertation is thus to study effective methods for synthesis of graphene-based materials, and to investigate their behavior in EDLCs. This work explored microwave assisted synthesis of graphite oxide (‘MEGO’, prepared in less than one minute by irradiation of graphite oxide by microwave). This material was further chemically activated to obtain a unique carbon material, activated microwave exfoliated graphite oxide (‘a-MEGO’) with specific surface areas up to 3100 m2/g. Gas adsorption measurements were used to study the specific surface area and porosity of a set of a-MEGO samples, which were also studied by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) for their structure, and by combustion analysis (i.e., elemental analysis) and X-ray photoelectron spectroscopy (XPS) to understand their elemental composition. Cyclic voltammetry (CV), galvanostatic charge/discharge, and frequency response, tests were done in order to study the performance of these new carbon materials as electrodes in both aqueous and organic electrolytes in a two electrode cell set up. / text

This research mainly includes two parts. First, monodispersed silica spheres with diameter about 58 and 73 nm were successfully synthesized. The tablet-like silica template could be made using a stainless steel mold by pressing the mold with a pressure ~ 10 MPa. The advantage of this molding process is it takes only a short time to accomplish the total fabrication. Second, infiltration of the carbon precursor was done using the monomers resorcinol (R) and furfural (F) in the interval of tablet-like silica template, and then polymerization and drying. It was subsequently carbonized in N2 atmosphere at 800 ¢J and then the silica template was removed by 20 wt % HF solution. The activated porous carbon material has larger specific surface area than the traditional powder carbon material. The chemical activation process by KOH plays a vital role in raising the specific surface area, since the KOH would etch the carbon pore surface to produce a large number of micropores (diameter < 2 nm), forming a macro-micro or meso-micro porous carbon materials. The F/R molar ratios for polymerization between 2.0 to 3.0 were applied and the carbon yields of these resins were higher than 51% in this range. An F/R ratio below 2.0 or 3.0 gave a lower carbon yield when carbonization at 800 ¢J. X-ray diffraction analyses on the macroporous carbon materials indicate a semi-crystalline structure which belong to the hexagonal crystal system with (002) d-spacing of = 0.373 nm, which is larger than the 0.339 nm of graphite. In Raman spectra analysis, the integral area of D-peak (ID) and G-peak (IG) is an index to define the degree of graphitization. The ratios ID/IG of lie between 1.7 - 1.8, which are larger than that of graphite (ID/IG = 0.1 - 0.3), so the FR series macroporous carbon is mostly amorphous and is far from highly crystallized structure. The un-activated macroporous carbon materials has open pore structure, the pore diameter is 56 nm which is classified to the macroporous scale. The nitrogen adsorption/desorption isotherm of the porous carbon materials belongs to the type IV, with H1 type hysteresis. The BET results show that the specific surface area increases with increasing KOH concentration; whereas the open pore structure remain the same. SEM observations reveal the pore structure doesn¡¦t collapse but the pore wall does become thinner. From this work, macroporous carbon materials with total pore volume as high as 2.23 cm3/g and the specific surface area as high as 658 m2/g have successfully been synthesized. Activation by KOH creates more micropores on its carbon walls, resulting in a macro-microporous carbon material having two scales of pores in the same time and with a high surface area of 1404 m2/g.

The Electrochemical Activation (ECA) of water is introduced as a novel refinement of conventional electrochemical processes and the unique features and attributes are evaluated against the universal principles that have described the electrolytic processes to date. While the novel and patented novel reactor design retains the capacity to generate products common to conventional electrolysis, it also manipulates the properties of the reagent solutions to achieve an anomalous Oxidation-Reduction potential (ORP or REDOX) that cannot be replicated by traditional chemical and physical interventions. As a contemporary development in the field, the technology continues to undergo rigorous assessment and while not all of its theoretical aspects have been exhaustively interrogated, its undisputed biocidal efficacy has been widely established. Microbial vitality has been shown to be directly dependent upon the confluence of a diverse variety of physical and chemical environmental conditions. Fundamentally important in this regard is the electronic balance or REDOX potential of the microbial environment. The intricate balance of metabolic pathways that maintain cellular integrity underwrites the measures of irritability required for sustained viability. Aside from the direct effects of the conventional electrolysis products, overt electronic disruption of the immediate microbial environment initiates a cascade of secondary and largely independent autocidal molecular events which compromise the fundamental integrity of the microbe and leads to cell death. The distinctive capacity to impart unique physicochemical attributes to the ECA derived solutions also facilitates the characterisation of the same outside of the conventional physicochemical and gravimetric measures. These adjunct measures display a substantial relationship with the predictability of antimicrobial effect, and the direct relationship between inactivation of a defined microbial bioload and the titratable measures of REDOX capacity have been shown to describe a repeatable benchmark. The use of ultra-microscopy to investigate the impact of the ECA products on bacterial cell structures has shown this tool to have distinctive merit in the imaging and thus refined description of the consequences of exposure to biocidal solutions. The distinctive differences of the ECA solutions relative to conventional antibacterial compounds would suggest a heightened suitability for application in conditions where the efficacy of conventional biocidal compounds had been limited. Aeroslisation of the ECA solutions for the decontamination of airspaces challenged with tuberculosis pathogens revealed that despite initial success, further refinements to the application model will be required to meet the unresolved challenges. The health care benefits associated with the application of the ECA solutions in a medical environment substantiate the merits for the adoption of the technology as a complementary remedy for the management of nosocomial infections. The relative novelty of the technology in the commercial domain will raise questions regarding the potential for resistance development, and it has been proposed that the distinctive mechanism of biocidal action will not contribute to diminished bacterial susceptibility, as it does not reveal any cross- or co-resistance when assessed against multiple antibiotic resistant strains. These benefits are further reinforced by the capacity to install the technology for both onsite and on-demand availability, and being derived from natural ingredients (salt and water) the ECA solutions are regarded as safe and compatible for general in-contact use. Notwithstanding the multiple benefits that the technology may provide, further assessments into materials compatibility as well as potential by-products formation following environmental exposure are imperative before the unfettered adoption of this technology as a cost-effective, safe and reliable alternative to conventional disinfection can be promoted. / Thesis (PhD)--University of Pretoria, 2011. / Microbiology and Plant Pathology / unrestricted

The steady growth of the rubber industry requires attention regarding the waste management and the methods applied in recycling and in the reclaiming processes. The ok in this thesis responds to the demand for an efficient recycle method for EPDM rubber waste. A solvent free chemical activation method to recycle EPDM rubber waste which provides high-quality recycled products, despite of the high amount of recycled particles used as a substitute of the raw material, was developed. The process needed to be both environmentally sustainable and applicable on an industrial scale without requiring special equipment. The final aim of this project was to use the activated particles in the production of seals and sealing systems on an industrial scale. In order to achieve this, the recycling of EPDM rubber waste particles by means of chemical activation using low molecular weight polymers (liquid polymers) was investigated. These liquid polymers are highly compatible with the waste rubber particles from the EPDM rubber and also suitable for sulphur vulcanisation. In comparison with other methods used for recycling of rubber and when considering environmental and economic aspects, chemical activation at the surface particle using low molecular weight polymers offers great recycling potential. In order to demonstrate the potential of the activated particles as a substitute for the raw material, aspects were investigated including: (1) characterization of the EPDM rubber waste particles; (2) optimization of the ratio between the waste rubber particles and the low molecular weight polymers; (3) investigation of the influence of various amounts of curing system; (4) study of the effect of the diene and ethylene percentage contained by the low molecular weight polymer used for activation of the particles; (5) investigation of the influence of the amount of activated particles used as substitute of the raw material; (6) study of the type of curing system used and (7) application of the process on an industrial scale.

The Carbon Capture and Storage method has been acknowledged for the capabilities of reducing up to 20% CO2 emissions. Development of porous carbon materials prepared from polyurethane foam adsorbent were investigated for capture of CO2. In this thesis work, the carbon material was chemically activated through the direct and indirect methods. Pre-carbonization, mass ratio KOH/char, activation temperature, and activation time, the effect of the preparation conditions on the porous adsorbent were evaluated for the purpose of managing pore sizes and developing high adsorption capacity of CO2. During the direct method, polyurethane foam was directly treated with KOH before activation. Whereas during the indirect method, the foam was pre-carbonized to form char, which was treated instead. The indirectly and directly activated adsorbent prepared at optimum conditions show adsorption capacities of 152,10 and 151,29 mg/g at 1 atm and 25°C respectively. The produced adsorbents were evaluated for their CO2 separation performance with a thermogravimetric analyser with 100% CO2. The CO2 uptake and pore sizes were directly affected by the different parameters. A moderate activation time and temperature presented a higher adsorption capacity, where it decreased after reaching a higher time and temperature. A higher KOH/char mass ratio leads to a higher CO2 uptake, where it steadily increases from the lowest mass ratio.

The technical feasibility of producing sulphur-impregnated activated carbons (SIACs) from high-sulphur fluid coke by chemical activation was investigated. Using KOH and SO2, the activation process was able to produce SIACs with controllable specific surface area (SBET), pore size distribution and sulphur content. The highest SBET was over 2500 m2/g and the highest sulphur content was 8.1 wt%. K-edge X-ray Absorption Near Edge Structure (XANES) spectroscopy was employed to characterize the sulphur in fluid cokes and SIACs. The results revealed that the sulphur on fluid coke surface was mainly in the form of organic sulphide and thiophene (total 91-95 %), in addition to some sulphate (5 - 9%). The study of KOH-treated fluid coke suggested that KOH was effective in converting organic sulphide and thiophene to water soluble inorganic species which were readily removed by acid and water washing. SO2 treatment of fluid coke added sulphur to fluid coke through SO2-carbon reaction. Elemental sulphur was the main product, while part of the thiophene, sulphide and sulphate in the raw coke remained in the product. In KOH-SO2 activation, disulphide, sulphide, sulphonate and sulphate were identified on SIAC surface; no thiophene was found, suggesting a complete removal of thiophene. Sulphur content in specific forms in SIACs was therefore controllable by varying the ratio of KOH, SO2 and fluid coke. SIACs produced from KOH-SO2 activation showed a comparable Hg2+ adsorption capacity (43 – 72 mg/g) with those reported in the literature (35-100 mg/g) and that of a commercial SIAC (41 mg/g). Although a larger SBET often resulted in a greater Hg2+ adsorption capacity, the benefit started to diminish when SBET was greater than about 1000 m2/g. A statistically significant and positive correlation was found between Hg2+ adsorption capacity and total sulphur content. Elemental sulphur and reduced sulphur were largely responsible for the enhanced Hg2+ adsorption.

Activated carbons as emerging classes of porous materials have gained tremendous attention because of their versatile applications such as gas storage/separations sorbents, oxygen reduction reaction (ORR) catalysts and supercapacitor electrodes. This diversity originates from fascinating features such as low-cost, lightweight, thermal, chemical and physical stability as well as adjustable textural properties. More interestingly, sole heteroatom or combinations of various elements can be doped into their framework to modify the surface chemistry. Among all dopants, nitrogen as the most frequently used element, induces basicity and charge delocalization into the carbon network and enhances selective adsorption of CO2. Transformation of a task-specific and single source precursor to heteroatom-doped carbon through a one-step activation process is considered a novel and efficient strategy. With these considerations in mind, we developed multiple series of heteroatom doped porous carbons by using nitrogen containing carbon precursors. Benzimidazole-linked polymers (BILP-5), benzimidazole monomer (BI) and azo-linked polymers (ALP-6) were successfully transformed into heteroatom-doped carbons through chemical activation by potassium hydroxide. Alternative activation by zinc chloride and direct heating was also applied to ALP-6. The controlled activation/carbonization process afforded diverse textural properties, adjustable heteroatom doping levels and remarkable gas sorption properties. Nitrogen isotherms at 77 K revealed that micropores dominate the porous structure of carbons. The highest Brunauer-Emett-Teller (BET) surface area (4171 m2 g-1) and pore volume (2.3 cm3 g-1) were obtained for carbon synthesized by KOH activation of BI at 700 °C. In light of the synergistic effect of basic heteroatoms and fine micropores, all carbons exhibit remarkable gas capture and selectivity. Particularly, BI and BIPL-5 derived carbons feature unprecedented CO2 uptakes of 6.2 mmol g-1 (1 bar) and 2.1 mmol g-1 (0.15 bar) at 298 K, respectively. The ALP-6 derived carbons retained considerable amount of nitrogen dopants (up to 14.4 wt%) after heat treatment owing to the presence of more stable nitrogen-nitrogen bonds compared to nitrogen-carbon bonds in BILP-5 and BI precursors. Subsequently, the highest selectivity of 62 for CO2/N2 and 11 for CO2/CH4 were obtained at 298 K for a carbon prepared by KOH activation of ALP-6 at 500 °C.

In this study, we developed the manufacturing pathways of carbon nanofibers (CNF) and activated carbon nanofibers (ACNF) via the ¡§melt-spinning¡¨ method. A novel route based on the solvent-free core/sheath melt-spinning of polypropylene/ (phenol formaldehyde-polyethylene) (PP/(PF-PE)) to prepare CNF. The approach consists of three main steps: co-extrusion of PP (core) and a polymer blend of PF and PE (sheath), followed by melt-spinning, to form the core/sheath fibers; stabilization of core/sheath fibers to form the carbon fiber precursors; and carbonization of carbon fiber precursors to form the final CNF. Both scanning electron microscopy and transmission electron microscopy images reveal long and winding CNF with diameter 100 - 600 nm and length greater than 80 £gm. With a yield of ~ 45 % based on its raw material PF, the CNF exhibits regularly oriented bundles which curl up to become rolls of wavy long fibers with clean and smooth surface. Results from X-ray diffractometry, energy dispersive X-ray, Raman spectroscopy, and selected area electron diffraction patterns further reveal that the CNF exhibits a mixed phase of carbon with graphitic particles embedded homogeneously in an amorphous carbon matrix. The carbon atoms in CNF are evenly distributed in a matrix having a composition of 90 % carbon element and 10 % in oxygen element. A series of ACNF have also been prepared based on the chemical activation on the thus-prepared CNF; their morphological and microstructure characteristics were analyzed by scanning electron microscopy, atomic force microscopy (AFM), Raman spectroscopy, and X-ray diffractometry, with particular emphasis on the qualitative and quantitative AFM analysis. The effect of activating agent, potassium hydroxide and phosphorous acid, is compared; factors affecting the surface morphology and microstructure of ACNF are analyzed. The ACNF also exhibits a mixed phase of carbon with graphitic particles embedded homogeneously in an amorphous carbon matrix. The resulting ACNF consists of 73 % C element and 27 % O element. The total pore volume of the all activated ACNF is larger than that of un-activated CNF. It can be inferred that chemical activation by KOH results in increased micropore volume in carbon nanofibers; while the micropores produced by the chemical activation of H3PO4 may further be activated and then enlarged to become the mesopores at the expense of micropore volume. For the concentration effect of KOH on ACNF, it can be inferred that high concentration KOH activation results in increased SBET and micropore volume in carbon nanofibers. The average pore diameter of ACNF gradually decreases as the KOH concentration increases.

The technical feasibility of producing sulphur-impregnated activated carbons (SIACs) from high-sulphur fluid coke by chemical activation was investigated. Using KOH and SO2, the activation process was able to produce SIACs with controllable specific surface area (SBET), pore size distribution and sulphur content. The highest SBET was over 2500 m2/g and the highest sulphur content was 8.1 wt%. K-edge X-ray Absorption Near Edge Structure (XANES) spectroscopy was employed to characterize the sulphur in fluid cokes and SIACs. The results revealed that the sulphur on fluid coke surface was mainly in the form of organic sulphide and thiophene (total 91-95 %), in addition to some sulphate (5 - 9%). The study of KOH-treated fluid coke suggested that KOH was effective in converting organic sulphide and thiophene to water soluble inorganic species which were readily removed by acid and water washing. SO2 treatment of fluid coke added sulphur to fluid coke through SO2-carbon reaction. Elemental sulphur was the main product, while part of the thiophene, sulphide and sulphate in the raw coke remained in the product. In KOH-SO2 activation, disulphide, sulphide, sulphonate and sulphate were identified on SIAC surface; no thiophene was found, suggesting a complete removal of thiophene. Sulphur content in specific forms in SIACs was therefore controllable by varying the ratio of KOH, SO2 and fluid coke. SIACs produced from KOH-SO2 activation showed a comparable Hg2+ adsorption capacity (43 – 72 mg/g) with those reported in the literature (35-100 mg/g) and that of a commercial SIAC (41 mg/g). Although a larger SBET often resulted in a greater Hg2+ adsorption capacity, the benefit started to diminish when SBET was greater than about 1000 m2/g. A statistically significant and positive correlation was found between Hg2+ adsorption capacity and total sulphur content. Elemental sulphur and reduced sulphur were largely responsible for the enhanced Hg2+ adsorption.

The objective of this thesis is to study the effect of process conditions on structure and electrochemical properties of polyacrylonitrile (PAN)/carbon nanotube (CNT) composite film based electrodes developed for electrochemical capacitors. The process parameters like activation temperature, CNT loading in the composite films are varied to determine optimum process conditions for physical (CO2) and chemical (KOH) activation methods. The PAN/CNT precursors are stabilized in air, carbonized in inert atmosphere (argon), and activated by physical (CO2) and chemical (KOH) methods. The physical activation process is carried out by heat treating the carbon precursors in CO2 atmosphere at activation temperatures. In the chemical activation process, stabilized carbon precursors are immersed in aqueous solutions of activating media (KOH), dried, and subsequently heat treated in an inert atmosphere at the activation temperature. The structure and morphology are probed using scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. The specific capacitance, power and energy density of the activated electrodes are evaluated with aqueous electrolytes (KOH) as well as organic electrolyte (ionic liquid in acetonitrile) in Cell Test. The surface area and pore size distribution of the activated composite electrodes are evaluated using nitrogen absorption. Specific capacitance dependence on factors such as surface area and pore size distribution are studied. A maximum specific capacitance of 300 F/g in KOH electrolyte and maximum energy density of 22 wh/kg in ionic liquid has been achieved. BET surface areas in excess of 2500 m2/g with controlled pore sizes in 1 - 5 nm range has been attained in this work.