Browsing by Subject "Microwave"
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Item Developing a socially-embedded point-of-use water treatment strategy incorporating silver nanoparticles and microwave radiation(2018-06-25) Ayres, Craig; Saleh, Navid B.Providing safe drinking water is a multifaceted problem that goes beyond a treatment device and deserves a holistic approach with respect to sanitation, handling, education, and customs of the target community. Socially-embedded point-of-use treatment strategies based on familiar components are more likely to receive prolonged use from the residents. Microwave ovens are a globally diffused, socially accepted technology that are enticing options for foundations of irradiation-based treatment. Taking advantage of the exceptional qualities of certain materials at the nano-scale allows one to utilize the low-energy radiation of microwave rays. This study focused on silver nanoparticles under the hypothesis that increased temperature from microwave exposure would result in increased ion dissolution and heat shock, thus enhancing antimicrobial potency. Using Escherichia coli (K12) as a model microorganism, 1 mL samples containing up to 1 mg/L of suspended silver nanoparticles were irradiated in a microwave reactor (2,450 MHz; 70 W) for 60 and 90 s. A clear synergistic effect between microwave radiation and silver nanoparticles was observed as microbial inactivation increased with additional microwave exposure and higher concentrations of silver. A maximum of 4.7 log₁₀ reduction was achieved after 90 s of irradiation, indicating rapid inactivation as typical batch studies involving silver nanoparticles take on the order of hours to achieve such inactivation. These results are promising for the development of nanomaterials capable of utilizing microwave radiation; however, efficiency will need to be increased in order to treat larger volumes of water. Incorporating various nanomaterials with several stress-inducing mechanisms has the potential to enable irradiation-based disinfection with the globally-diffused microwave oven for treatment at the household level.Item Metal oxide support effects on the hydrogenation of cyclohexene and crotonaldehyde using microwave synthesized rhodium and iridium nanoparticles(2017-09-15) Polanco, Luis Ruben; Humphrey, Simon M.Nanoparticles (NPs) are an exciting new class of materials with unique physical and chemical properties, which have been studied for applications in semiconductors, drug delivery, heavy metal sequestration, and heterogeneous catalysis. The last decade has seen an exponential growth in noble metal NP catalysis research. The scarcity and price of these metals has created a need for more highly efficient catalysts and the surface-area-to-volume ratio of NPs can alleviate that demand. Highly selective catalysis is still dominated by homogeneous catalysts, but their lack of recyclability makes them unusable for industrial settings where durability is the top priority. The Humphrey group has pioneered the synthesis of monometallic, core-shell, and alloyed noble metal NPs of different sizes and morphologies, facilitated by microwave heating. However, support media effects have not been studied in the group, as strong metal-support interactions (SMSI) and hydrogen spillover have been shown to alter the observed catalytic activities. v Herein, mono metallic Rh NPs (~5nm) have been immobilized on amorphous metal oxides (SiO₂, Al₂O₃, TiO₂, Nb₂O₅, and Ta₂O₅) to study the effects these supports play in the hydrogenation of alkenes and the chemoselectivity hydrogenation of α,β-unsaturated aldehydes. Cyclohexene was utilized as a model alkene to assess the reactivities of said catalysts. In addition, controlled growth of Ir NPs in aqueous media is in development. Computational and experimental data has shown higher selectivity towards unsaturated alcohol products from the hydrogenation of α,β-unsaturated aldehydes and ketones. Unfortunately, not much research has been done Ir NPs due to their small particles sizes. Viscous solvents are typically used in NP synthesis to avoid particle agglomeration, but Ir since NPs don’t typically grow past 2 nm, other solvents can be used during synthesis. This allows the use of less viscous, greener solvents, such as water. Herein, the synthesis of Ir NPs in water is explored and the largest free-standing Ir NPs (2.98 nm) are presented. Also, 2.71 nm Ir NPs can be achieved after 1 minute, making them desirable for large sacel synthesis of these materials.Item Nano-enabled water disinfection technology development that harnesses the power of microwaves(2017-05) Plazas Tuttle, Jaime Guillermo; Saleh, Navid B.; Freeman, Benny D; Katz, Lynn E; Kirisits, Mary J; Lawler, Desmond FDue to the position of microwave (MW) radiation in the electromagnetic spectrum, it has not yet been successfully utilized to inactivate waterborne microorganisms at a reasonable (energy) cost. Exceptional properties at the nano-scale, namely MW absorption-abilities of carbon nanotubes and excellent spectral conversion-capabilities of lanthanide series metal oxides in concert, hold promise to overcome the energetic barrier of this widely used and affordable MW technology. This dissertation reports the synthesis of a nano-heterostructure that combines carbon nanotubes’ and erbium oxides’ properties to generate reactive oxygen species (ROS) and inactivate Pseudomonas aeruginosa. Detailed characterization of the synthesized nanohybrid (NH) material with electron microscopy, X-ray techniques, and thermal gravimetric analysis confirms effective hybridization. At least one log unit of microbial inactivation was achieved via ROS generation with only 20 s of microwave irradiation at 110 W (0.0006 kW∙h energy use), using a conventional MW oven. Inactivation studies with ROS scavenger molecules prove that generated oxygen species played the dominant role in bacterial inactivation. The roles of wavelength, input power, and irradiation time on inactivation are explored, in an effort to unlock the mechanism of inactivation. To achieve such results with a high degree of control, a setup including a MW power generator and waveguide, capable of delivering precise frequency, while controlling input power and irradiation exposure time, has been designed and constructed. Results demonstrate inactivation of P. aeruginosa in presence of MW irradiation and aided by the nanohybrids. Finally, the inactivation efficacy of MW spectral conversion for a wide range of waterborne microorganism is determined. Inactivation of Legionella pneumophila, Flavobacterium columnare, Bacillus subtilis spores, and MS2 bacteriophages was also attempted using this system. A low degree of inactivation varying between (0.38 to 4.13 log removal) was achieved. These initial results are promising, but they do demonstrate a need for redesign of the NH and and reconsideration of the key irradiation parameters to achieve higher log removal, which will enable development of a technology that will be elevated from an agent of inactivation to an enabler of disinfection.Item RF/microwave absorbing nanoparticles and hyperthermia(2009-12) Cook, Jason Ray; Emelianov, Stanislav Y.; Pearce, John A.The primary purpose of this work was to evaluate the capability of nanoparticles to transform electromagnetic energy at microwave frequencies into therapeutic heating. Targeted nanoparticles, in conjunction with microwave irradiation, can increase the temperatures of the targeted area over the peripheral region. Therefore, to become clinically viable, microwave absorbing nanoparticles must first be identified, and a system to monitor the treatment must be developed. In this study, ultrasound temperature imaging was used to monitor the temperature of deep lying structures. First, a material-dependent quantity to correlate the temperature induced changes in ultrasound images (i.e. apparent time shifts) to differential temperatures was gathered for a tissue-mimicking phantom, porcine longissimus dorsi muscle, and porcine fat. Then microwave nanoabsorbers were identified using an infrared radiometer. The determined nanoabsorbers were then injected into ex-vivo porcine longissimus dorsi muscle tissue. Ultrasound imaging frames were gathered during microwave treatment of the inoculated tissue. Finally, the ultrasound frames were analyzed using the correlation between temperature and apparent shifts in ultrasound for porcine muscle tissue. The outcome was depth-resolved temperature profiles of the ex-vivo porcine muscle during treatment. The results of this study show that magnetite is a microwave nanoabsorber that increases the targeted temperature of microwave hyperthermia treatments. Overall, there is clinical potential to use microwave nanoabsorbers to increase the efficiency of microwave hyperthermia treatments.Item Subwavelength and nonreciprocal optical and electromagnetic systems for sensing and communications(2017-06-07) Williamson, Ian Alexander Durant; Wang, Zheng, Ph. D.; Alù, Andrea; Bank, Seth R; Wang, Yaguo; Yu, Edward TThis dissertation is organized into three parts. First, the design for a radio frequency fiber transmission line built out of a grid of micrometer-scale conductors embedded in an insulating polymer cladding is presented to mitigate the skin and proximity effects. By adopting a checkerboard out-of-phase current phasing scheme, the internal inductance of the line is significantly lower than in two-conductor lines and results in an LC bandwidth of approximately 2 GHz, with flat attenuation and linear phase dispersion. The device performance is characterized in terms of its geometric degrees of freedom and a fabricated prototype is presented. Second, the kinetic inductive and plasmonic response of monolayer graphene in the terahertz spectrum is examined in the context of several important applications. The dispersive responses of two-dimensional graphene and three-dimensional copper transmission lines are compared to map the dispersive signaling performance in terms of transmission line cross-sectional size. This demonstrates a surprisingly broadband LC response with flat attenuation in nano-scale lines. This kinetic inductive response of graphene is demonstrated to miniaturize the photonic band structure of a photonic crystal slab where an in-plane periodicity of 300 nm has its photonic band gap in the terahertz spectrum. The sub-diffraction photonic band structure resembles that of the two-dimensional photonic crystal, supporting a wide photonic band gap in extremely thin slabs. The viability of graphene for cavity optomechanics is analyzed from near infrared to terahertz wavelengths, demonstrating a large optomechanical coupling, on the order of 3D optomechanical materials. Third, a class of nonreciprocal devices is proposed based on coupling to the sideband states, called Floquet resonances, that arise in temporally modulated optical resonators. The degrees of freedom in the modulating waveform tailor the energy exchange and phase of the Floquet resonances to realize unique nonreciprocal spectral responses in compact devices. We examine optical scattering from Floquet resonators coupled to narrowband waveguides using temporal coupled-mode theory. A three-port circulator is built out of a cascade of Floquet resonators to demonstrate broadband forward transmission and ideal isolation for dual-carrier waves. Full-wave numerical simulations in the coupled frequency domain demonstrate the circulator in an on-chip photonic crystal platform