M. Tech. Department of Chemical, Metallurgical and Materials Engineering. / Discusses how to synthesize a titanium-manganese oxide composite electrode with improved supercapacitive properties. The research aim was achieved through the following objectives: 1. the mechanisms of the synergistic incorporation of manganese oxide for improving the supercapacitive properties of titanium oxide electrodes. 2. Investigate possible metallurgical interactions and phenomenon during the sintering of the composite. 3. Investigate the electrochemical characteristics of titanium-manganese composite electrodes.

This thesis reports the development of a novel drug delivery system consisting of hollow nanoparticles, formed from manganese dioxide (δ-MnO2) sheets, that are coated with polydopamine and folic acid to selectively target cancer cells. The biodegradability and colloidal stability of the uncoated hollow nanoparticles were investigated in comparison to solid MnO2 nanoparticles and graphene oxide sheets. The MnO2 hollow nanoparticles degraded at a faster rate and seem to have a higher surface area and better colloidal dispersion than solid MnO2 nanoparticles. Xanthan gum was proven to improve colloidal dispersion of these hollow nanoparticles and were used for further cell studies. In this study, cancer and healthy cells were treated with coated hollow nanoparticles, and results indicate that this novel hollow nanoparticle may preferentially target and kill cancer cells. Particle aggregation has shown to be toxic to cells. Further studies with this novel drug delivery system may lead to a groundbreaking solution to targeted cancer therapy. / Includes bibliography. / Thesis (M.S.)--Florida Atlantic University, 2020. / FAU Electronic Theses and Dissertations Collection

In situ chemical oxidation using permanganate is an approach to organic contaminant site remediation. Manganese dioxide particles are products of permanganate reactions. These particles have the potential to deposit in the subsurface and impact the flow-regime in/around permanganate injection, including the well screen, filter pack, and the surrounding subsurface formation. Control of these particles can allow for improved oxidant injection and transport and contact between the oxidant and contaminants of concern. The goals of this research were to determine if MnO2 can be stabilized/controlled in an aqueous phase, and to determine the dependence of particle stabilization on groundwater characteristics. Bench-scale experiments were conducted to study the ability of four stabilization aids (sodium hexametaphosphate (HMP), Dowfax 8390, xanthan gum, and gum arabic) in maintaining particles suspended in solution under varied reaction conditions and time. Variations included particle and stabilization aid concentrations, ionic content, and pH. HMP demonstrated the most promising results, as compared to xanthan gum, gum arabic, and Dowfax 8390 based on results of spectrophotometric studies of particle behavior, particle filtration, and optical measurements of particle size and zeta potential. HMP inhibited particle settling, provided for greater particle stability, and resulted in particles of a smaller average size over the range of experimental conditions evaluated compared to results for systems that did not include HMP. Additionally, HMP did not react unfavorably with permanganate. These results indicate that the inclusion of HMP in a permanganate oxidation system improves conditions that may facilitate particle transport.

Thesis (Ph.D.(Physics)) -- University of Limpopo, 2020 / We employ molecular dynamics simulations, using DL_POLY code, to study the structural behaviour of β-MnO2 cathode material during discharging through lithium-ion intercalation into the bulk, nanoparticle, nanorod, nanosheet, and nanoporous β-MnO2. It is shown that lithium-ions have an average coordination number of about 5.70 and prefer surface sites with high oxygen coordination. The average lattice parameter values at intercalation of 0.85 Li/Mn are found to be under 4% relative to the experimental values obtained at 0.92 Li/Mn. Moreover, all the lithiated β-MnO2 structures did not collapse at 0.85 Li/Mn as observed in the β-MnO2 mesoporous in experimental work. As lithium is limited, sodium is a good alternative charge carrier in lithium-ion batteries. As a result, we have also performed studies on sodium intercalation into bulk, nanoparticle, nanorod, nanosheet and nanoporous β-MnO2. The microstructures and radial distribution functions show that the β-MnO2 structures could be intercalated up to 0.24 Na/Mn without any obvious structural degradation. Beyond this sodium concentration, the microstructure collapses and become amorphous thus predicting a potentially lower capacity for Na-MnO2-β batteries. Also, as the voltage is an important factor in the energy density of lithium-ion batteries, we have studied the trends in the average intercalation potentials in relation to the various nano architectures. The trend, in increasing value of average intercalation potentials, were found to be bulk structure, nanorod, nanosheet, nanoporous and nanoparticle. This suggests that nanostructuring can enhance cell voltage. Mechanical properties studies on the pure and lithiated bulk and nanorod β-MnO2 were also performed through uniaxial compressive and tensile strain application. The results show that under compressive strain the bulk structure and nanorod mitigate stress through the contraction and collapse of the inherent tunnel structures, known to cause electrochemical inactivity, and also through the shifting of the MnO6 octahedral planes. The collapsing of tunnels was found to occur more on the bulk structure and less on the nanorod, while the MnO6 octahedral plane shifts were found to occur more on the nanorod and less on the bulk structure. Unoccupied 1x2 or conjoined 1x2 were found to result in structural collapse irrespective of the host nanoarchitecture. The X-ray diffraction pattern (v) plots suggest that lithium intercalation and compressive stress application have a similar impact on the underlying structure of the various nanostructures. The microstructure analysis for bulk β-MnO2 under tensile strain reveals that fracture occurred in the brookite region and along the dislocation/stacking fault. The nanorod β-MnO2 mitigated stress through a rutile-to-brookite phase transition which occurred in the unstrained Li0.73MnO2-β and under tensile strain in LixMnO2-β for x = 0.00, 0.03, 0.12, and 0.24. In both the bulk and nanorod β-MnO2 the brookite phase was succeeded by structural breakdown leading to fracture and served as an indicator for imminent structural failure upon more tensile strain application. / National Research Foundation (NRF)

Arsenic is a known carcinogen, causing cancers of the skin, lungs, bladder and kidney. Current research suggests that drinking water is the most common pathway for long-term low dose exposure. Arsenic contaminated drinking water has caused serious health problems in many countries including: India, Bangladesh, Argentina, Chile, Taiwan, the United States and Canada. Nanofiltration (NF) is a promising technology for arsenic removal since it requires less energy than traditional reverse osmosis membranes. Several studies have shown that nanofiltration is capable of removing the oxidized form of arsenic [As(V)] while the reduced form of arsenic [As(III)] is poorly removed. To exploit this difference it has been suggested that a pretreatment step which oxidizes the As(III) to As(V) would improve the performance of membrane filtration, but this has never been demonstrated. The research had three objectives: The first was to investigate the ability of NF membranes to treat arsenic contaminated groundwater and evaluate the influence of the membrane type and operating conditions. Secondly, the effectiveness of a solid phase oxidizing media (MnO2) to oxidize arsenite to arsenate was investigated. Lastly, the MnO2 was combined with NF membrane filtration to determine the benefit, if any, of oxidizing the arsenic prior to membrane filtration. A pilot membrane system was installed to treat a naturally contaminated groundwater in Virden, Manitoba, Canada. The groundwater in Virden contains between 38 and 44 µg/L of arsenic, primarily made up of As(III), with little particulate arsenic. In the first experiment three Filmtec® membranes were investigated: NF270, NF90 and XLE. Under all conditions tested the NF90 and NF270 membranes provided insufficient treatment of Virden's groundwater to meet Canada's recommended Interim Maximum Acceptable Concentration (IMAC) of 25 µg/L. The XLE membrane provided better arsenic removal and under the conditions of 25 Lmh flux and 70% recovery produced treated water with a total arsenic concentration of 21 µg/L. The XLE membrane is therefore able to sufficiently treat Virden's ground water. However treatment with the XLE membrane alone is insufficient to meet the USEPA's regulation of 10 µg/L or Canada's proposed Maximum Allowable Concentration (MAC) of 5 µg/L. The effects of recovery and flux on total arsenic passage are consistent with accepted membrane theory. Increasing the flux increases the flow of pure water through the membrane; decreasing the overall passage of arsenic. Increasing the recovery increases the bulk concentration of arsenic, which leads to higher arsenic passage. The second experiment investigated the arsenic oxidation capabilities of manganese dioxide (MnO2) and the rate at which the oxidation occurs. The feed water contained primarily As(III), however, when filtered by MnO2 at an Empty Bed Contact Time (EBCT) of only 1 minute, the dominant form of arsenic was the oxidized form [As(V)]. At an EBCT of 2 minutes the oxidation was nearly complete with the majority of the arsenic in the As(V) form. Little arsenic was removed by the MnO2 filter. The third and final experiment investigated the benefit, if any, to combining the membrane filtration and MnO2 treatment investigated in the first and second experiments. The effect of MnO2 pretreatment was dramatic. In Experiment I, the NF270 and NF90 membranes were unable to remove any arsenic while the XLE removed, at best, approximately 50% of the arsenic. Once pretreated with MnO2 the passage of arsenic through all of the membranes dropped to less than 4 µg/L, corresponding to approximately 91% to 98% removal. The dramatic improvement in arsenic removal can be attributed to charge. All three membranes are negatively charged. Through a charge exclusion effect the rejection of negatively charged ions is enhanced. During the first experiment, As(III) (which is neutrally charged) was the dominant form of arsenic, and was uninfluenced by the negative charge of the membrane. Once oxidized to As(V), the arsenic had a charge of -2, and was electrostatically repelled by the membrane. This greatly improved the arsenic rejection characteristics of the membrane. Nanofiltration alone is not a suitable technology to remove arsenic contaminated waters where As(III) is the dominant species. When combined with MnO2 pre-oxidation, the arsenic rejection performance of nanofiltration is dramatically improved.

Arsenic is a known carcinogen, causing cancers of the skin, lungs, bladder and kidney. Current research suggests that drinking water is the most common pathway for long-term low dose exposure. Arsenic contaminated drinking water has caused serious health problems in many countries including: India, Bangladesh, Argentina, Chile, Taiwan, the United States and Canada. Nanofiltration (NF) is a promising technology for arsenic removal since it requires less energy than traditional reverse osmosis membranes. Several studies have shown that nanofiltration is capable of removing the oxidized form of arsenic [As(V)] while the reduced form of arsenic [As(III)] is poorly removed. To exploit this difference it has been suggested that a pretreatment step which oxidizes the As(III) to As(V) would improve the performance of membrane filtration, but this has never been demonstrated. The research had three objectives: The first was to investigate the ability of NF membranes to treat arsenic contaminated groundwater and evaluate the influence of the membrane type and operating conditions. Secondly, the effectiveness of a solid phase oxidizing media (MnO2) to oxidize arsenite to arsenate was investigated. Lastly, the MnO2 was combined with NF membrane filtration to determine the benefit, if any, of oxidizing the arsenic prior to membrane filtration. A pilot membrane system was installed to treat a naturally contaminated groundwater in Virden, Manitoba, Canada. The groundwater in Virden contains between 38 and 44 µg/L of arsenic, primarily made up of As(III), with little particulate arsenic. In the first experiment three Filmtec® membranes were investigated: NF270, NF90 and XLE. Under all conditions tested the NF90 and NF270 membranes provided insufficient treatment of Virden's groundwater to meet Canada's recommended Interim Maximum Acceptable Concentration (IMAC) of 25 µg/L. The XLE membrane provided better arsenic removal and under the conditions of 25 Lmh flux and 70% recovery produced treated water with a total arsenic concentration of 21 µg/L. The XLE membrane is therefore able to sufficiently treat Virden's ground water. However treatment with the XLE membrane alone is insufficient to meet the USEPA's regulation of 10 µg/L or Canada's proposed Maximum Allowable Concentration (MAC) of 5 µg/L. The effects of recovery and flux on total arsenic passage are consistent with accepted membrane theory. Increasing the flux increases the flow of pure water through the membrane; decreasing the overall passage of arsenic. Increasing the recovery increases the bulk concentration of arsenic, which leads to higher arsenic passage. The second experiment investigated the arsenic oxidation capabilities of manganese dioxide (MnO2) and the rate at which the oxidation occurs. The feed water contained primarily As(III), however, when filtered by MnO2 at an Empty Bed Contact Time (EBCT) of only 1 minute, the dominant form of arsenic was the oxidized form [As(V)]. At an EBCT of 2 minutes the oxidation was nearly complete with the majority of the arsenic in the As(V) form. Little arsenic was removed by the MnO2 filter. The third and final experiment investigated the benefit, if any, to combining the membrane filtration and MnO2 treatment investigated in the first and second experiments. The effect of MnO2 pretreatment was dramatic. In Experiment I, the NF270 and NF90 membranes were unable to remove any arsenic while the XLE removed, at best, approximately 50% of the arsenic. Once pretreated with MnO2 the passage of arsenic through all of the membranes dropped to less than 4 µg/L, corresponding to approximately 91% to 98% removal. The dramatic improvement in arsenic removal can be attributed to charge. All three membranes are negatively charged. Through a charge exclusion effect the rejection of negatively charged ions is enhanced. During the first experiment, As(III) (which is neutrally charged) was the dominant form of arsenic, and was uninfluenced by the negative charge of the membrane. Once oxidized to As(V), the arsenic had a charge of -2, and was electrostatically repelled by the membrane. This greatly improved the arsenic rejection characteristics of the membrane. Nanofiltration alone is not a suitable technology to remove arsenic contaminated waters where As(III) is the dominant species. When combined with MnO2 pre-oxidation, the arsenic rejection performance of nanofiltration is dramatically improved.

Thesis (MSc. (Physics)) -- University of Limpopo, 2016 / Nanostructured materials are attractive candidates for efficient electrochemical energy storage devices because of their unique physicochemical properties. Introducing nanotube systems as electrode materials represents one of the most attractive strategies that could dramatically enhance the battery performance. Nanostructured manganese based oxides are considered as ideal electrode materials for energy storage devices such as high energy and high power lithium-ion batteries. In this study, computer simulation strategies were used to generate various structures of MnO2 and spinel LiMn2O4 nanotubes; where Miller index, diameter and symmetry are considered as variables. The effect of these variables on nanotube generation was investigated. MnO2 and spinel LiMn2O4 nanotubes were generated using MedeA® software. Lower Miller indices, namely; {001}, {100}, {110} and {111} with diameter ranging from 5Å30Å were investigated for both systems. There are two ways that a nanotube structures could be wrapped along different directions, i.e., a_around_b or b_around_a. It was observed that wrapping direction has an effect on the geometrical structure of the nanotube. MnO2 nanotube generated from {110} revealed that nanotube wrapped along b_around_a gave a close-packed structure compared to its counterpart nanotube wrapped a_around_b. Diameter represents an important structural parameter of nanotubes; however, precise control of nanotube diameter over a wide range of materials is yet to be demonstrated. In this study, it was found that as the diameter of the nanotube is changed, parameters such as cross-sectional area and bond length change as well. The average bond distance of the nanotubes is less than that of MnO2 and LiMn2O4 bulk structure. Molecular dynamics simulation is further used to investigate the structure of MnO2 and LiMn2O4 nanotubes and the effect of temperature on the generated systems. Molecular graphical images used for the atomic positions for the nanotubes were investigated. The nanotube structures are described using radial distribution functions and XRD patterns. The calculated XRD patterns are in good agreement with the experiments, thus validating the generated structural models for the nanotubes. The resulting models conform to pyrolusite polymorph of MnO2 and LiMn2O4, featuring octahedrally coordinated manganese atoms. It was established that the variables have a direct control on nanotube morphology and the stability of generated nanotube model depends on surface morphology and termination. / National Research Foundation (NRF) and Centre for High Performance Computing (CHPC) of CSIR

Advanced dispersants were discovered for the fabrication of homogeneous suspensions of multi-walled carbon nanotubes (MWCNT), graphene, and manganese dioxide (MnO2) in both ethanol and water. Thin films of MWCNT, graphene, MnO2, composite films of MWCNT-MnO2 and MWCNT-graphene were prepared using electrophoretic deposition (EPD) and electrolytic deposition (ELD) methods. The mechanisms of dispersion and deposition were investigated. Cathodic EPD was achieved for MWCNT and graphene using positively charged dispersants. Co-deposition of MWCNT and MnO¬2 was performed using a co-dispersant, which dispersed both MWCNT and MnO2 in ethanol. Composite films were tested for electrochemical supercapacitor (ES) purposes. Pulse ELD was used to deposit porous MnO2 coatings on Ni foam substrates from KMnO4 solutions. Cathodic deposition offered advantages, compared to anodic deposition, because the problems, related to anodic dissolution of metallic substrates, can be avoided. The pulse ON/OFF times had significant influence on the morphology and structure of MnO2 films, which further determined the capacitive performance. The influence of MnO2 film thickness on specific capacitance was investigated. Porous and conductive vanadium nitride (VN) was synthesized using melamine as a reducing agent. To further improve film conductivity and specific surface area, MWCNT were incorporated into VN matrix during synthesis. VN-MWCNT composite electrodes and VN-MWCNT/MnO2-MWCNT asymmetric supercapacitor cells were fabricated and tested. The electrodes and cells exhibited excellent electrochemical capacitive performance with good cyclic stability. The asymmetric supercapacitor device showed a voltage window up to 1.8 V, which was the combination of voltage window of VN-MWCNT (-0.9 V--0 V) and MnO2-MWCNT (0 V--0.9 V). Polypyrrole (PPy) coated MWCNT were synthesized in ethanol with ammonium peroxydisulfate solution as an oxidant. The effects of dopants to PPy morphology and conductivity was investigated. Dopants with electrochemical active groups were selected for the synthesis of PPy nanoparticles, where dopants also contributed to the capacitance of the polymer based materials. Both PPy-MWCNT/PPY-MWCNT symmetric supercapacitors and VN-MWCNT/PPY-MWCNT asymmetric supercapacitors were fabricated and tested, where the voltage windows were 0.9 V for the former and 1.3 V for the later. The increase of voltage window was ascribed to the asymmetric structure and negative voltage window of VN-MWCNT composite. / Thesis / Doctor of Philosophy (PhD)

Electrochemical supercapacitors (ECs) attract significant attentions for their unique characteristics of high power density, good cycling capability and low cost. This dissertation will focus on fabrication of composite materials for electrodes and devices of ECs. A conceptually new colloidal approach to the fabrication of metal oxide – multiwalled carbon nanotube (MWCNT) composites is proposed. The heterocoagulation of positively charged oxide nanoparticles and negatively charged MWCNT allows the fabrication of advanced nanocomposites with improved dispersion of individual components. The proof-of-principle was demonstrated by the fabrication of MnO2-MWCNT electrodes for ECs with excellent performance. We proposed another novel concept based on electrostatic heterocoagulation of MnO2-MWCNT composites in aqueous environment. In this case, Benzyldimethylhexadecylammonium chloride (BAC) surfactant and caffeic acid (CA) were selected for adsorption and dispersion of MWCNT and MnO2, respectively, and this allowed the formation of stable aqueous suspensions of positively charged MWCNT and negatively charged MnO2. The asymmetric device showed high capacitance, high powerenergy characteristics with enlarged voltage window of 1.8 V, good capacitance retention at high charge-discharge rates and cyclic stability. A novel capacitive material BiMn2O5 was firstly discovered and synthesized for ECs applications in our studies. The BiMn2O5 nanocrystals were prepared by a hydrothermal method. We demonstrated for the first time that BiMn2O5 – MWCNT composite can be used as a new active material for positive electrodes of ECs. The composite electrode with high mass loading showed a capacitance of 6.0 F cm-2 (540 F cm-3) at a scan rate of 2 mV s-1 and excellent capacitive behavior at high scan rates. As-fabricated device showed good cyclic stability in a voltage window of 1.8 V with energy density of 13.0 Wh L-1 (9.0 Wh kg-1) and power density of 3.6 kW L-1 (2.5 kW kg-1). We firstly discovered that Poly[1-[4-(3-carboxy-4 hydroxyphenylazo)benzenesulfonamido]- 1,2-ethanediyl, sodium salt] (PAZO) can be used as an universal dispersant for various materials and its thin film fabricated by electrophoretic deposition (EPD) exhibited photo-induced birefringence. Our new findings indicated that PAZO is good candidate for diverse materials dispersing because it contains diaromatic monomers with salicylate ligands, which can provide multiple adsorption sites for efficient adsorption on particles and impart electrical charges to the particles. Additionally, the use of PAZO polymer offers the advantages of improved steric stabilization. We discovered that Celestine blue (CB) can be developed as an efficient dispersing agent for the nanoparticles. We found that CB includes a catechol ligand, which can provide CB adsorption on inorganic nanoparticles. The relatively large size of the CB molecules is beneficial for the electrosteric dispersion. The benefits of cathodic EPD for nanotechnology were demonstrated by the formation of nanostructured MnO2 films on commercial high surface area current collectors for energy storage in ECs. / Thesis / Doctor of Philosophy (PhD)

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