Froth flotation is a widely used, cost effective particle separation process. However, its high performance is limited to a narrow particle size range, e.g., between 50 µm and 600 µm for coal and between 10 µm and 100 µm for minerals. Outside this range, the efficiency of froth flotation decreases significantly, especially for difficult-to-float particles of weak hydrophobicity (e.g., oxidized coal). Nanobubbles integrated into a specially designed column flotation expanded the particle size range for efficient froth flotation as a result of increased probabilities of particle- bubble collision and attachment and reduced probability of detachment. The major advantages of nanobubble enhanced flotation include lower collector and frother dosages since nanobubbles that are mostly smaller than 1 µm can be formed selectively on hydrophobic coal particles from dissolved air in coal slurry. Nanobubbles act as a secondary collector on particle surfaces, thereby resulting in considerably lower operating costs. A systematic parametric investigation of the proposed technology was performed to understand the effects of process variables on separation performance with a typical coal sample using a specially designed flotation column and three 10-liters conventional flotation cells. Results indicate that the combustible recovery of a -150 µm coal increased by 5-50% in the presence of nanobubbles, depending on process operating conditions. Nanobubbles also significantly improved process separation efficiency and increased the flotation rate constant by more than 40%. Theoretical evaluation of the innovative flotation technology was employed using specially designed apparatus to study the nanobubbles stability and the roles of nanobubbles on particle-bubble interactions, froth stability, and surface area flux. In addition, a detailed technical performance and economic evaluation was performed.

Ultrafine bubbles, often referred to as nanobubbles, have been used in various applications from environmental remediation to medicine. Even though the technology to generate ultrafine bubbles has been around for many years, the full potential of its applications has not been completely studied. This project seeks to study the use of ultrafine bubble technology for water treatment in combination with ozone gas. A factorial design experiment was chosen to test the effects of ultrafine bubbles on the concentration of an indicator organism, E. coli, in water as well as their effects on ozone gas being injected into water. Ozone gas or nitrogen gas was injected into water contaminated with E. coli as either ultrafine bubbles or fine bubbles as treatments for up to 60 minutes. Ultrafine bubbles were found to not have any significant effect on the concentration of E. coli in water. However, ultrafine bubbles did provide benefits when used in conjunction with ozone gas that regular, fine bubbles did not provide. The benefits included allowing the concentration of dissolved ozone in the water to decrease at a slower rate as well as allowing more ozone to dissolve into water at a higher rate than conventional methods of bubbling in ozone. While in this particular set of experiments the concentration of dissolved ozone in water didn't surpass 2 mg/L, which didn't allow for rapid disinfection and treatment of water, it is believed that with a more powerful ozone generator better results can be achieved. This project demonstrates the benefits and potential of injecting ozone gas as ultrafine bubbles into water as a way to effectively and efficiently disinfect and treat water.

The overall goal of this project was to develop, optimize, and test an ultrasound-responsive targeted nanobubble for delivering osteoporosis-related silencing genes such as Cathepsin K small interfering RNA (CTSK siRNA) for osteoporosis treatment. The nanobubbles were synthesized using an in situ sonochemical method. The nanobubble (NB) is composed of a gas core made from perfluorocarbon, stabilized with albumin, encapsulated with CTSK siRNA, and embedded with alendronate (AL) for bone targeting (CTSK siRNA-NB-AL). Following its development, the responsiveness of CTSK siRNA-NB-AL to a therapeutic ultrasound probe was examined. The results of biocompatibility tests with human bone marrow-derived mesenchymal stem cells proved no significant cell death (p > 0.05). When the CTSK siRNA-NB-AL was supplemented with human osteoclast precursors, they suppressed osteoclastogenesis. Thus, this project establishes the potential of nanotechnology and ultrasound to deliver genes into the osteoclasts. This research also presents a novel ultrasound responsive and targeted nanobubble platform that can be used as a gene, drug, and/or oxygen delivery system for various diseases including cancer, neurodegenerative diseases, or bone disorders.

Interactions between hydrophobic surfaces at short separation distances (at the nanometer scale) are very important in a number of industrial applications. For example, in the froth flotation mineral separation process it is the interaction between the hydrophobic particle and the bubble which is paramount in separating the valuable minerals from the gangue. A number of studies, most notably using the atomic force microscope (AFM) and the surface force apparatus (SFA) have found the existence of a long range hydrophobic attractive force between hydrophobic surfaces that cannot be explained by classical colloidal science theories. In many cases, this force is an artefact due to the accumulation of sub-microscopic bubbles, the so called nanobubbles, at the liquid-hydrophobic solid interface. Thus, what was thought to be a hydrophobic force was actually a capillary force resulting from the gaseous bridge formed from the coalescence of nanobubbles, that is, the nanobubble bridging capillary force (NBCF). It is the purpose of this thesis to provide further insight into the accumulation of soluble gases at the liquid-hydrophobic solid interface and the resulting NBCF. Specifically, this thesis studies these phenomena from a fundamental standpoint and additionally relates the findings to froth flotation mineral separation. A systematic method to measure the NBCF by controlling the size of the gaseous capillary bridge was devised in this thesis. Control of the capillary bridge was achieved by utilising the solvent-exchange method to accumulate nanobubbles at the surface, followed by surface scanning of the colloidal probe over the flat surface to harvest nanobubbles. Thus, the NBCF has been controlled to allow for greater success in modelling the interaction, understanding the geometric parameters of the bridge, observing changes in friction force due to nanobubbles and understanding the influence of ethanol on the force. An outcome of this thesis was the development of a capillary force model which describes the NBCF. The model considers a constant volume and constant contact angle assumption for a gaseous capillary bridge of toroidal geometry. The model was very successful in describing the NBCF at long separation distances (>20nm) for both the approach and retract interactions. The close fitting between the experimental data and the model allowed accurate determinations of the advancing and receding contact angles, bridge geometry and volume. The successful implementation of the capillary force model allowed a link between the bridge volume, and the resulting adhesion to the friction force between hydrophobic solid surfaces in water. Additionally, the model allowed the change from an attractive to a repulsive NBCF to be described by a change from a concave to convex bridge geometry. Thus, this thesis has added considerable knowledge to the fundamental aspects of nanobubbles and the NBCF. The final chapters of this thesis utilised the knowledge gained from the fundamental studies to understand the influence of nanobubbles on flotation. In the first study, the influence of NaCl concentration on the morphology of gaseous domains on a graphite surface is discussed in relation to the increased recovery of coal in saline water. In the second study, methanol treatment of a ZnS ore was found to increase the floatability due to slime removal and the artificial formation of nanobubbles.

The electromagnetic absorption properties of plasmonic nanostructures were utilized to develop mesoscopic sites for highly efficient photothermal generation steam, SERS biosensing, and light-triggered cellular delivery uptake. Plasmonic nanostructures embedded in common thermal solutions produces vapor without the requirement of heating the fluid volume. When particles are dispersed in water at ambient temperature, energy is directed primarily to vaporization of water into steam, with a much smaller fraction resulting in heating of the fluid. Solar illuminated aqueous nanoparticle solution can drive water-ethanol distillation, yielding fractions significantly richer in ethanol content than simple thermal distillation and also produced saturated steam destroying Geobacillus stearothermophilus bacteria in a compact solar powered autoclave. Subwavelength biosensing sites were developed using the plasmonic properties of gold nanoshells to investigate the properties of aptamer (DNA) target complexes. Nanoshells are tunable core-shell nanoparticles whose resonant absorption and scattering properties are dependent on core/shell thickness ratio. Nanoshells were used to develop a label free detection method using SERS to monitor conformational change induced by aptamer target binding. The conformational changes to the aptamers induced by target binding were probed by monitoring the aptamer SERS spectra reproducibility. Furthermore, nanoshells can serve as a nonviral light-controlled delivery vector for the precise temporal and spatial control of molecular delivery in vitro. The drug delivery concept using plasmonic vectors was shown using a monolayer of ds-DNA attached to the nanoshell surface and the small molecular “parcel” intercalated inside ds-DNA loops. DAPI, a fluorescent dye, was used as the molecular parcel to visualize the release process in living cells. Upon laser illumination at the absorption resonance the nanoshell converts photon energy into heat producing a local temperature gradient that induces DNA dehybridization, releasing the intercalated molecules.

Plasmonic properties and the related novel applications are studied on various types of metallic nano-structures in one, two, or three dimensions. For 1D nanostructure, the motion of free electrons in a metal-film with nanoscale thickness is confined in its normal dimension and free in the other two. Describing the free-electron motion at metal-dielectric surfaces, surface plasmon polariton (SPP) is an elementary excitation of such motions and is well known. When further perforated with periodic array of holes, periodicity will introduce degeneracy, incur energy-level splitting, and facilitate the coupling between free-space photon and SPP. We applied this concept to achieve a plasmonic perfect absorber. The experimentally observed reflection dip splitting is qualitatively explained by a perturbation theory based on the above concept. If confined in 2D, the nanostructures become nanowires that intrigue a broad range of research interests. We performed various studies on the resonance and propagation of metal nanowires with different materials, cross-sectional shapes and form factors, in passive or active medium, in support of corresponding experimental works. Finite- Difference Time-Domain (FDTD) simulations show that simulated results agrees well with experiments and makes fundamental mode analysis possible. Confined in 3D, the electron motions in a single metal nanoparticle (NP) leads to localized surface plasmon resonance (LSPR) that enables another novel and important application: plasmon-heating. By exciting the LSPR of a gold particle embedded in liquid, the excited plasmon will decay into heat in the particle and will heat up the surrounding liquid eventually. With sufficient exciting optical intensity, the heat transfer from NP to liquid will undergo an explosive process and make a vapor envelop: nanobubble. We characterized the size, pressure and temperature of the nanobubble by a simple model relying on Mie calculations and continuous medium assumption. A novel effective medium method is also developed to replace the role of Mie calculations. The characterized temperature is in excellent agreement with that by Raman scattering. If fabricated in an ordered cluster, NPs exhibit double-resonance features and the double Fano-resonant structure is demonstrated to most enhance the four-wave mixing efficiency.