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- All Subjects: nanotechnology
- Creators: Holman, Zachary C
Description
As engineered nanomaterials (NMs) become used in industry and commerce their loading to sewage will increase. However, the fate of widely used NMs in wastewater treatment plants (WWTPs) remains poorly understood. In this research, sequencing batch reactors (SBRs) were operated with hydraulic (HRT) and sludge (SRT) retention times representative of full-scale biological WWTPs for several weeks. NM loadings at the higher range of expected environmental concentrations were selected. To achieve the pseudo-equilibrium state concentration of NMs in biomass, SBR experiments needed to operate for more than three times the SRT value, approximately 18 days. Under the conditions tested, NMs had negligible effects on ability of the wastewater bacteria to biodegrade organic material, as measured by chemical oxygen demand (COD). NM mass balance closure was achieved by measuring NMs in liquid effluent and waste biosolids. All NMs were well removed at the typical biomass concentration (1~2 gSS/L). However, carboxy-terminated polymer coated silver nanoparticles (fn-Ag) were removed less effectively (88% removal) than hydroxylated fullerenes (fullerols; >90% removal), nano TiO2 (>95% removal) or aqueous fullerenes (nC60; >95% removal). Although most NMs did not settle out of the feed solution without bacteria present, approximately 65% of the titanium dioxide was removed even in the absence of biomass simply due to self-aggregation and settling. Experiments conducted over 4 months with daily loadings of nC60 showed that nC60 removal from solution depends on the biomass concentration. Under conditions representative of most suspended growth biological WWTPs (e.g., activated sludge), most of the NMs will accumulate in biosolids rather than in liquid effluent discharged to surface waters. Significant fractions of fn-Ag were associated with colloidal material which suggests that efficient particle separation processes (sedimentation or filtration) could further improve removal of NM from effluent. As most NMs appear to accumulate in biosolids, future research should examine the fate of NMs during disposal of WWTP biosolids, which may occur through composting or anaerobic digestion and/or land application, incineration, or landfill disposal.
ContributorsWang, Yifei (Author) / Westerhoff, Paul (Thesis advisor) / Krajmalnik-Brown, Rosa (Committee member) / Rittmann, Bruce (Committee member) / Hristovski, Kiril (Committee member) / Arizona State University (Publisher)
Created2012
Description
In the nano-regime many materials exhibit properties that are quite different from their bulk counterparts. These nano-properties have been shown to be useful in a wide range of applications with nanomaterials being used for catalysts, in energy production, as protective coatings, and in medical treatment. While there is no shortage of exciting and novel applications, the world of nanomaterials suffers from a lack of large scale manufacturing techniques. The current methods and equipment used for manufacturing nanomaterials are generally slow, expensive, potentially dangerous, and material specific. The research and widespread use of nanomaterials has undoubtedly been hindered by this lack of appropriate tooling. This work details the effort to create a novel nanomaterial synthesis and deposition platform capable of operating at industrial level rates and reliability.
The tool, referred to as Deppy, deposits material via hypersonic impaction, a two chamber process that takes advantage of compressible fluids operating in the choked flow regime to accelerate particles to up several thousand meters per second before they impact and stick to the substrate. This allows for the energetic separation of the synthesis and deposition processes while still behaving as a continuous flow reactor giving Deppy the unique ability to independently control the particle properties and the deposited film properties. While the ultimate goal is to design a tool capable of producing a broad range of nanomaterial films, this work will showcase Deppy's ability to produce silicon nano-particle films as a proof of concept.
By adjusting parameters in the upstream chamber the particle composition was varied from completely amorphous to highly crystalline as confirmed by Raman spectroscopy. By adjusting parameters in the downstream chamber significant variation of the film's density was achieved. Further it was shown that the system is capable of making these adjustments in each chamber without affecting the operation of the other.
The tool, referred to as Deppy, deposits material via hypersonic impaction, a two chamber process that takes advantage of compressible fluids operating in the choked flow regime to accelerate particles to up several thousand meters per second before they impact and stick to the substrate. This allows for the energetic separation of the synthesis and deposition processes while still behaving as a continuous flow reactor giving Deppy the unique ability to independently control the particle properties and the deposited film properties. While the ultimate goal is to design a tool capable of producing a broad range of nanomaterial films, this work will showcase Deppy's ability to produce silicon nano-particle films as a proof of concept.
By adjusting parameters in the upstream chamber the particle composition was varied from completely amorphous to highly crystalline as confirmed by Raman spectroscopy. By adjusting parameters in the downstream chamber significant variation of the film's density was achieved. Further it was shown that the system is capable of making these adjustments in each chamber without affecting the operation of the other.
ContributorsFirth, Peter (Author) / Holman, Zachary C (Thesis advisor) / Kozicki, Michael (Committee member) / Goryll, Michael (Committee member) / Arizona State University (Publisher)
Created2015
Description
Semiconductor nanostructures are promising building blocks for light management in thin silicon solar cells and silicon-based tandems due their tunable optical properties. The present dissertation is organized along three main research areas: (1) characterization and modeling of III-V nanowires as active elements of solar cell tandems, (2) modeling of silicon nanopillars for reduced optical losses in ultra-thin silicon solar cells, and (3) characterization and modeling of nanoparticle-based optical coatings for light management.
First, the recombination mechanisms in polytype GaAs nanowires are studied through photoluminescence measurements coupled with rate equation analysis. When photons are absorbed in polytype nanowires, electrons and holes quickly thermalize to the band-edges of the zinc-blende and wurtzite phases, recombining indirectly in space across the type-II offset. Using a rate equation model, different configurations of polytype defects along the nanowire are investigated, which compare well with experiment considering spatially indirect recombination between different polytypes, and defect-related recombination due to twin planes and other defects. The presented analysis is a path towards predicting the performance of nanowire-based solar cells.
Following this topic, the optical mechanisms in silicon nanopillar arrays are investigated using full-wave optical simulations in comparison to measured reflectance data. The simulated electric field energy density profiles are used to elucidate the mechanisms contributing to the reduced front surface reflectance. Strong forward scattering and resonant absorption are observed for shorter- and longer- aspect ratio nanopillars, respectively, with the sub-wavelength periodicity causing additional diffraction. Their potential for light-trapping is investigated using full-wave optical simulation of an ultra-thin nanostructured substrate, where the conventional light-trapping limit is exceeded for near-bandgap wavelengths.
Finally, the correlation between the optical properties of silicon nanoparticle layers to their respective pore size distributions is investigated using optical and structural characterization coupled with full-wave optical simulation. The presence of
scattering is experimentally correlated to wider pore size distributions obtained from nitrogen adsorption measurements. The correlation is validated with optical simulation of random and clustered structures, with the latter approximating experimental. Reduced structural inhomogeneity in low-refractive-index nanoparticle inter-layers at the metal/semiconductor interface improves their performance as back reflectors, while reducing parasitic absorption in the metal.
First, the recombination mechanisms in polytype GaAs nanowires are studied through photoluminescence measurements coupled with rate equation analysis. When photons are absorbed in polytype nanowires, electrons and holes quickly thermalize to the band-edges of the zinc-blende and wurtzite phases, recombining indirectly in space across the type-II offset. Using a rate equation model, different configurations of polytype defects along the nanowire are investigated, which compare well with experiment considering spatially indirect recombination between different polytypes, and defect-related recombination due to twin planes and other defects. The presented analysis is a path towards predicting the performance of nanowire-based solar cells.
Following this topic, the optical mechanisms in silicon nanopillar arrays are investigated using full-wave optical simulations in comparison to measured reflectance data. The simulated electric field energy density profiles are used to elucidate the mechanisms contributing to the reduced front surface reflectance. Strong forward scattering and resonant absorption are observed for shorter- and longer- aspect ratio nanopillars, respectively, with the sub-wavelength periodicity causing additional diffraction. Their potential for light-trapping is investigated using full-wave optical simulation of an ultra-thin nanostructured substrate, where the conventional light-trapping limit is exceeded for near-bandgap wavelengths.
Finally, the correlation between the optical properties of silicon nanoparticle layers to their respective pore size distributions is investigated using optical and structural characterization coupled with full-wave optical simulation. The presence of
scattering is experimentally correlated to wider pore size distributions obtained from nitrogen adsorption measurements. The correlation is validated with optical simulation of random and clustered structures, with the latter approximating experimental. Reduced structural inhomogeneity in low-refractive-index nanoparticle inter-layers at the metal/semiconductor interface improves their performance as back reflectors, while reducing parasitic absorption in the metal.
ContributorsVulic, Natasa (Author) / Goodnick, Stephen M (Thesis advisor) / Honsberg, C. (Christiana B.) (Committee member) / Holman, Zachary C (Committee member) / Smith, David J. (Committee member) / Arizona State University (Publisher)
Created2019
Description
High photoluminescence (PL) quantum yields reported from amorphous (a-Si) and crystalline (c-Si) nanoparticles have opened up lots of possibilities for use of silicon in optical applications such as light emitting diodes (LEDs), photonics and solar cells with added processing and cost benefits. However, the PL response and the mechanisms behind it are highly dependent on the matrix in which the nanoparticles are grown and on the growth method. While, the bottom-up approach for deposition of free standing nanoparticles seem to be perfectly suited for large area deposition for LED and solar cell applications, the dominant growth techniques (laser ablation and pyrolysis) have been shown to suffer from limitations in control over size distribution of nanoparticles and the requirement of equipment capable of withstanding high temperature. This led to the exploration of plasma based synthesis methods in this work.
Towards this effort, the development and automation of a novel tool “Anny” for synthesis of silicon nanoparticles using non-thermal plasma chamber is reported. These nanoparticles are then accelerated due to choked flow through a nozzle leading to substrate independent deposition. The nanoparticle properties are characterized against precursor gas flow rates and RF power to identify the optimum growth conditions for a stable, continuous deposition. It is found that amorphous nanoparticles offer a wide variety of chamber conditions for growth with a high throughput, stable plasma for continuous, long term operations.
The quantum confinement model for crystalline and spatial confinement models for amorphous nanoparticles in our size regime (6-8nm) are suggested for free standing nanoparticles and we report a high PL output from well passivated amorphous nanoparticles.
The PL output and its dependence on stability of surface hydrogen passivation is explored using Fourier Transform Infrared spectroscopy (FTIR). It is shown that the amorphous nanoparticles have a better and more stable passivation compared to crystalline nanoparticles grown under similar conditions. Hence, we show a-Si nanoparticles as exciting alternatives for optical applications to c-Si nanoparticles.
Towards this effort, the development and automation of a novel tool “Anny” for synthesis of silicon nanoparticles using non-thermal plasma chamber is reported. These nanoparticles are then accelerated due to choked flow through a nozzle leading to substrate independent deposition. The nanoparticle properties are characterized against precursor gas flow rates and RF power to identify the optimum growth conditions for a stable, continuous deposition. It is found that amorphous nanoparticles offer a wide variety of chamber conditions for growth with a high throughput, stable plasma for continuous, long term operations.
The quantum confinement model for crystalline and spatial confinement models for amorphous nanoparticles in our size regime (6-8nm) are suggested for free standing nanoparticles and we report a high PL output from well passivated amorphous nanoparticles.
The PL output and its dependence on stability of surface hydrogen passivation is explored using Fourier Transform Infrared spectroscopy (FTIR). It is shown that the amorphous nanoparticles have a better and more stable passivation compared to crystalline nanoparticles grown under similar conditions. Hence, we show a-Si nanoparticles as exciting alternatives for optical applications to c-Si nanoparticles.
ContributorsGarg, Prateek (Author) / Holman, Zachary C (Thesis advisor) / Zhang, Yong H (Committee member) / Bertoni, Mariana (Committee member) / Arizona State University (Publisher)
Created2015
Description
The advantages and challenges of combining zero-valent iron (ZVI) and microbial reduction of trichloroethene (TCE) and perchlorate (ClO4-) in contaminated soil and groundwater are not well understood. The objective of this work was to identify the benefits and limitations of simultaneous application of ZVI and bioaugmentation for detoxification of TCE and ClO4- using conditions relevant to a specific contaminated site. We studied conditions representing a ZVI-injection zone and a downstream zone influenced Fe (II) produced, for simultaneous ZVI and microbial reductive dechlorination applications using bench scale semi-batch microcosm experiments. 16.5 g L-1 ZVI effectively reduced TCE to ethene and ethane but ClO4- was barely reduced. Microbial reductive dechlorination was limited by both ZVI as well as Fe (II) derived from oxidation of ZVI. In the case of TCE, rapid abiotic TCE reduction made the TCE unavailable for the dechlorinating bacteria. In the case of perchlorate, ZVI inhibited the indigenous perchlorate-reducing bacteria present in the soil and groundwater. Further, H2 generated by ZVI reactions stimulated competing microbial processes like sulfate reduction and methanogenesis. In the microcosms representing the ZVI downstream zone (Fe (II) only), we detected accumulation of cis-dichloroethene (cis-DCE) and vinyl chloride (VC) after 56 days. Some ethene also formed under these conditions. In the absence of ZVI or Fe (II), we detected complete TCE dechlorination to ethene and faster rates of ClO4- reduction. The results illustrate potential limitations of combining ZVI with microbial reduction of chlorinated compounds and show the potential that each technology has when applied separately.
ContributorsMohana Rangan, Srivatsan (Author) / Krajmalnik-Brown, Rosa (Thesis advisor) / Delgado, Anca G (Committee member) / Lowry, Gregory V. (Committee member) / Arizona State University (Publisher)
Created2017
Description
Nanomaterials exhibit unique properties that are substantially different from their bulk counterparts. These unique properties have gained recognition and application for various fields and products including sensors, displays, photovoltaics, and energy storage devices. Aerosol Deposition (AD) is a relatively new method for depositing nanomaterials. AD utilizes a nozzle to accelerate the nanomaterial into a deposition chamber under near-vacuum conditions towards a substrate with which the nanomaterial collides and adheres. Traditional methods for designing nozzles at atmospheric conditions are not well suited for nozzle design for AD methods.
Computational Fluid Dynamics (CFD) software, ANSYS Fluent, is utilized to simulate two-phase flows consisting of a carrier gas (Helium) and silicon nanoparticles. The Cunningham Correction Factor is used to account for non-continuous effects at the relatively low pressures utilized in AD.
The nozzle, referred to herein as a boundary layer compensation (BLC) nozzle, comprises an area-ratio which is larger than traditionally designed nozzles to compensate for the thick boundary layer which forms within the viscosity-affected carrier gas flow. As a result, nanoparticles impact the substrate at velocities up to 300 times faster than the baseline nozzle.
Computational Fluid Dynamics (CFD) software, ANSYS Fluent, is utilized to simulate two-phase flows consisting of a carrier gas (Helium) and silicon nanoparticles. The Cunningham Correction Factor is used to account for non-continuous effects at the relatively low pressures utilized in AD.
The nozzle, referred to herein as a boundary layer compensation (BLC) nozzle, comprises an area-ratio which is larger than traditionally designed nozzles to compensate for the thick boundary layer which forms within the viscosity-affected carrier gas flow. As a result, nanoparticles impact the substrate at velocities up to 300 times faster than the baseline nozzle.
ContributorsHoffman, Trent (Author) / Holman, Zachary C (Thesis advisor) / Herrmann, Marcus (Committee member) / Kozicki, Michael (Committee member) / Arizona State University (Publisher)
Created2017
Description
Engineered nanomaterials (ENMs) are added to numerous consumer products to enhance their effectiveness, whether it be for environmental remediation, mechanical properties, or as dietary supplements. Uses of ENMs include adding to enhance products, carbon for strength or dielectric properties, silver for antimicrobial properties, zinc oxide for UV sun-blocking properties, titanium dioxide for photocatalysis, or silica for desiccant properties. However, concerns arise from ENM functional properties that can impact the environment and a lack of regulation regarding ENMs leads to potential public exposure to ENMs and results in ill-informed public or manufacturer perceptions of ENMs. My dissertation evaluates the environmental, human health, and societal impacts of using ENMs, with a focus on ionic silver and nanosilver, in consumer and industrial products. Reproducible experiments served as functional assays to assess ENM distributions among various environmental matrices. Functional assay results were visualized using radar plots and aid in a framework to estimate likely ENM disposition in the environment. To assess beneficial uses of ENMs, bromide ion removal from drinking waters to limit disinfection by-product formation was studied. Silver-enabled graphene oxide materials were capable of removing bromide from water, and exhibited less competition from background solutes (e.g. natural organic matter) when compared against solely ionic silver addition to water for bromide removal. To assess complex interactions of ENMs with the microbiome, batch experiments were performed using fecal samples spiked with ionic silver or commercial dietary silver nanoparticles. Dietary nanosilver and ionic silver exposures to the fecal microbiome for 24 hours reduce short chain fatty acid (SCFA) production and changes the relative abundance of the microbiota. To understand the social perceptions of ENMS, statistically rigorous surveys were conducted to assess related perceptions related to the use of ENMs in drinking water treatment devices the general public and, separately, industrial manufacturers. These stakeholders are influenced by costs and efficiency of the technologies, consumer concerns of the safety of technologies, and environmental health and safety of the technologies. This dissertation represents novel research that took an interdisciplinary approach, spanning from wet-lab engineering bench scale testing to social science survey assessments to better understand the environmental, human health, and societal impacts of using ENMs such as nanosilver and ionic silver in industrial processes and consumer products.
ContributorsKidd, Justin (Author) / Westerhoff, Paul (Thesis advisor) / Krajmalnik-Brown, Rosa (Committee member) / Perreault, Francois (Committee member) / Maynard, Andrew (Committee member) / Arizona State University (Publisher)
Created2020
Description
A new nanoparticle deposition technique, Aerosol Impaction-Driven Assembly (AIDA), was extensively characterized for material structures and properties. Aerogel films can be deposited directly onto a substrate with AIDA without the long aging and drying steps in the sol-gel method. Electron microscopy, pore size analysis, thermal conductivity, and optical measurements show the nanoparticle (NP) films to be similar to typical silica aerogel. Haze of nanoparticle films modeled as scattering sites correlates strongly with pore size distribution. Supporting evidence was obtained from particle sizes and aggregates using electron microscopy and small-angle X-ray scattering. NP films showed interlayers of higher porosity and large aggregates formed by tensile film stress.
To better understand film stress and NP adhesion, chemical bonding analyses were performed for samples annealed up to 900 °C. Analysis revealed that about 50% of the NP surfaces are functionalized by hydroxyl (-OH) groups, providing for hydrogen bonding. Ellipsometric porosimetry was used to further understand the mechanical properties by providing a measure of strain upon capillary pressure from filling pores. Upon annealing to 200 °C, the films lost water resulting in closer bonding of NPs and higher Young’s modulus. Upon further annealing up to 900 °C, the films lost hydroxyl bonds while gaining siloxane bonds, reducing Young’s modulus. The application of ellipsometric porosimetry to hydrophilic coatings brings into question the validity of pore size distribution calculations for materials that hold onto water molecules and result in generally smaller calculated pore sizes.
Doped hydrogenated microcrystalline silicon was grown on crystalline silicon NPs, as a test case of an application for NP films to reduce parasitic absorption in silicon heterojunction solar cells. Parasitic absorption of blue light could be reduced because microcrystalline silicon has a mix of direct and indirect bandgap, giving lower blue absorption than amorphous silicon. Using Ultraviolet Raman spectroscopy, the crystallinity of films as thin as 13 nm was determined rapidly (in 1 minute) and non-destructively. A mono-layer of nanocrystals was applied as seeds for p-doped microcrystalline silicon growth and resulted in higher crystallinity films. Applications of the method could be explored for other nanocrystalline materials.
To better understand film stress and NP adhesion, chemical bonding analyses were performed for samples annealed up to 900 °C. Analysis revealed that about 50% of the NP surfaces are functionalized by hydroxyl (-OH) groups, providing for hydrogen bonding. Ellipsometric porosimetry was used to further understand the mechanical properties by providing a measure of strain upon capillary pressure from filling pores. Upon annealing to 200 °C, the films lost water resulting in closer bonding of NPs and higher Young’s modulus. Upon further annealing up to 900 °C, the films lost hydroxyl bonds while gaining siloxane bonds, reducing Young’s modulus. The application of ellipsometric porosimetry to hydrophilic coatings brings into question the validity of pore size distribution calculations for materials that hold onto water molecules and result in generally smaller calculated pore sizes.
Doped hydrogenated microcrystalline silicon was grown on crystalline silicon NPs, as a test case of an application for NP films to reduce parasitic absorption in silicon heterojunction solar cells. Parasitic absorption of blue light could be reduced because microcrystalline silicon has a mix of direct and indirect bandgap, giving lower blue absorption than amorphous silicon. Using Ultraviolet Raman spectroscopy, the crystallinity of films as thin as 13 nm was determined rapidly (in 1 minute) and non-destructively. A mono-layer of nanocrystals was applied as seeds for p-doped microcrystalline silicon growth and resulted in higher crystallinity films. Applications of the method could be explored for other nanocrystalline materials.
ContributorsCarpenter, Joe Victor (Author) / Holman, Zachary C (Thesis advisor) / Bertoni, Mariana I (Committee member) / Chan, Candace K. (Committee member) / Smith, David J. (Committee member) / Arizona State University (Publisher)
Created2020