Browsing by Author "Weisman, Bruce"

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    Covalent and Non-Covalent Functionalization of ssDNA-Wrapped Single-Wall Carbon Nanotubes: Computational and Experimental Studies
    (2023-04-13) Alizadehmojarad, Ali A.; Weisman, Bruce; Kolomeisky, Anatoly
    Single-wall nanotubes (SWCNTs) are nanomaterials with a wide range of optical and electronic properties that depend on their physical structure, which is indexed by a pair of integers (n,m). The discovery and interpretation of nanotube fluorescence has taken SWCNT research to a new level by enabling novel studies of structure-specific reactions and processes. These require the suspension of individualized SWCNTs in liquids through non-covalent functionalization by dispersants such as polymers, conventional surfactants, and single-stranded DNA (ssDNA). Understanding the specific interactions between nanotubes and coatings is important for advancing both basic and applied research. Both computational and experimental investigations have been conducted to understand the mechanism of separation and sorting of specific (n,m) species coated by DNA oligonucleotides. In addition to non-covalent SWCNT functionalization, covalent functionalization has also added a new research dimension and the ability to modify important properties of pristine nanotubes. In this thesis, novel computational and experimental methods were developed to further understand non-covalent and covalent functionalization of SWCNTs dispersed in DNA oligonucleotides and in a conventional surfactant. Computational studies were performed to understand how a DNA oligo distinguishes two enantiomers of an (n,m) species. Replica exchange molecular dynamics (REMD) simulations revealed that this recognition is directly correlated with the nanotube surface area exposed to the environment when wrapped by a DNA oligo. In the case of covalent functionalization of guanine nucleobases to SWCNTs, steered MD (SMD) simulations showed that the nucleotides in the middle of a DNA strand are found in closer proximity to nanotube surface than those at the strand end. These observations are aligned with experimental findings suggesting that a greater degree of guanine functionalization is achieved with 31-nucleotide DNA oligos containing only one guanine in the middle than DNA oligos with one guanine near the end of a DNA strand. A novel experimental method was developed to measure extinction coefficient of SWCNTs in the UV region. These results have enabled the simple determination of total SWCNT concentrations in aqueous dispersions. The DNA/SWCNT mass ratio was then quantitatively evaluated to provide an important parameter for understanding conformations of DNA oligos wrapped around SWCNTs. Through this method, the dependence of DNA/SWCNT mass ratio on DNA oligo base sequence was experimentally determined. Those conformations around different (n,m) species were then further explored using standard MD simulations. In this way, the strength of interactions between nanotubes and DNA oligos was investigated, revealing that thymine-rich DNA oligos interact with nanotube surfaces more strongly than cytosine-rich oligos. The guanine functionalization of SWCNTs was conducted using excitation of metalloporphyrin photosensitizers with violet light. Guanine functionalization of nanotubes was monitored by red-shifts in their absorption and fluorescence spectra. The great advantage of using metalloporphyrin dyes instead of rose bengal as a photosensitizer is that they are more photostable and cause less interference with SWCNT absorption and fluorescence spectra. Consequently, kinetic studies of guanine functionalization of SWCNTs were performed to find the correlation between kinetic parameters and either dye concentration or guanine contents of the DNA oligos. Quantum chemistry methods were used to predict find the most stable product of covalent attachment of guanine to SWCNT side walls and to correlate the formation enthalpy of each adduct with nanotube diameter. The semi-empirical quantum chemistry results show that 4,5-guanine peroxide (GPO) attached to either ortho L30 or ortho L-30 positions on the nanotubes’ surface give the most energetically stable products of guanine functionalization. Excited state calculations then predict that 4,5-GPO attached at the ortho L30 positions results in the most red-shifted (6,5) absorption peak compared to other adducts. In a separate experimental study, the first structure-selective guanine functionalization of SWCNTs was achieved using near-infrared or visible photochemistry. Specific (n,m) SWCNT species were excited by monochromatic excitation at their characteristic E11 or E22 transitions. Energy transfer to dissolved O2 then generated singlet oxygen, which led to formation of guanine peroxide (GPO) and its bonding to SWCNT side walls. The guanine functionalization was selective for the excited nanotubes. Finally, MD simulations were used to investigate the noncovalent adsorption of the surfactant sodium dodecyl sulfate (SDS) on SWCNT surfaces. This study uncovered four different SDS morphologies, characterized their structures, and found the combinations of SDS concentrations and nanotube diameters leading to the different morphologies.
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    Flash Joule heating for nanomaterials synthesis, waste upcycling, and hydrogen production
    (2023-08-11) Wyss, Kevin Michael; Tour, James M; Weisman, Bruce
    Many sustainable technologies, such as chemical recycling of waste plastics or the low-carbon intensity production of clean-burning hydrogen gas, have existed for decades. However, despite current political and societal initiatives to minimize plastic waste or transition to hydrogen energy sources, little global progress has been made in their widescale adoption. Over-complexity or critical shortcomings in the economic viability and scalability of these processes often limit their industrial implementation and overall impact. Similarly, although hailed a 21st century ‘wonder-material’, graphene has followed a related trajectory because of the same limiting factors. Flash Joule heating represents a new strategy that can be adapted to address many applications including plastic recycling or upcycling, low-carbon intensity hydrogen production, and graphene synthesis. Flash Joule heating is scalable, low in process complexity, and affords low-cost, efficient, and environmentally friendly production of high-value nanomaterials. This thesis begins by introducing current industrial graphene production methods and applications in chapter 1. Chapters 2-4 highlight the synthesis, characterization, and application of turbostratic graphene from amorphous carbonaceous feedstocks. In chapter 2, simple flash Joule heating synthesizes graphene from waste materials such as ash resulting from the chemical recycling of plastics. The graphene quality is optimized and characterized, and the value of the produced graphene is demonstrated as a reinforcing additive in various composite applications. In chapter 3, graphene with varying 13C/12C isotopic content is prepared, up to 99% 13C content, which results in unexpected spectroscopic findings. In chapter 4, graphene is formed from mixed waste plastics, with quantified efficiency and tabulated environmental burdens, and compared to current industrial methods, using a perspective life-cycle assessment. Taking inspiration from chemical vapor deposition and different bottom-up reaction strategies, other exciting classes of graphitic carbon nanomaterials can be synthesized using flash Joule heating. Holey and wrinkled graphene with significantly increased surface area is synthesized from mixed waste plastics in chapter 5, and applied in electrocatalytic and energy-storage applications. A similar material can be synthesized in a scalable manner using simple alkaline salt templating, and used for water purification applications, as demonstrated in chapter 6. Carbon nanotubes, nanofibers, and hybrid 1-dimensional and 2-dimensional materials can also synthesized through the in situ formation of catalytic growth nanoparticles, upcycling mixed waste plastic to outperform carbon nanotubes and graphene in composite applications, with significant improvements in environmental impact as compared to current carbon nanotube production methods. Lastly, in chapter 8, production of clean hydrogen gas from waste plastic at zero net-cost is demonstrated, due to the co-production of high-value graphene. Through process optimization, flash Joule heating of plastics, with no added catalyst, the highest yet-published yields of hydrogen gas from plastics is achieved and demonstrated for all common consumer waste plastics. Life-cycle assessment and techno-economic analysis demonstrate that the flash Joule heating hydrogen production strategy releases less CO2 than all current methods excluding electrolysis, while affording extreme cost-competitiveness for hydrogen production. Further, through study of the reaction intermediates and other volatiles coupled with thermodynamic and molecular dynamics simulations, the seed-growth, bottom-up hypothesis of graphene formation during flash Joule heating can be further substantiated.
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    Next-Generation 2D Optical Strain Mapping: Strain-Sensing Smart Skin vs. Digital Image Correlation
    (2022-08-10) Meng, Wei; Nagarajaiah, Satish; Weisman, Bruce
    Structures in various fields such as offshore oil platforms, air-crafts, and dams, play a vital role for the prosperity of our economy and technology. Many of them are critical to our lives and often subjected to severe environmental conditions, such as earthquakes, winds, and waves. In many accidents, destructive failure was initiated by small structural defects. Hence, an accurate local damage detection technique based on strain monitoring is important to ensure the safe functioning of these structures. Traditional techniques, such as resistance strain gauges and fiber Bragg grating (FBG) sensors, monitor only at discrete locations along a specific direction, and have limited ability to measure strains on small length scales. Moreover, practical issues such as deployment, connection and high-cost further limit its application. Over the past twenty years, new generation of 2D optical strain sensing techniques have been proposed and studied. Belonging to the category of image-based method, Digital Image Correlation (DIC) presents surface strain distribution by analysing optical features on photographs taken in different deforming states. As an indirect method, the strain map is generated from computation instead of measurement. Its accuracy heavily depends on camera quality and image-processing algorithms. For spectroscopy-based strain sensing method, the strain induced change of nanotube electronic structure can be directly measured as peak shifts in the single-walled carbon nanotubes (SWCNTs) near-infrared (NIR) fluorescence emission spectrum. Based on this property, strain-sensing smart skin (S4) technique was proposed. S4 uses SWCNTs embedded in thin polymer coatings as microscopic sensors. Strains in the specimen surface are transmitted to the nanotubes, causing systematic changes and spectral shifts in their NIR fluorescence signatures. Analysis of fluorescence spectra from S4 sensing films then gives local strain values based on non-contact optical measurements. This technique has been tested successfully on metal specimens. The agreement between S4 strain map and theoretical computation motivates us to explore more applications on other materials and compare it against the well established techniques such as DIC. In this thesis, we report refinements to the previously developed S4 method and comparisons against the established DIC method on noncontact strain sensing. The refined S4 design includes a dual-layer base coating consisting of an opaque primer that can block any interfering emission from the specimen plus another layer to provide a smooth surface for the sensing layer and protect the primer from solvent damage during sensing layer application. This coating design reduces spectral inhomogeneity in the nanotube sensors and avoids the need for annealing at elevated temperatures. Tests were performed on acrylic, concrete and aluminum specimens that had been shaped and stressed to generate particular strain patterns. The strain maps measured with the refined S4 films were compared with DIC and finite element method (FEM). The strain patterns presented by FEM simulations are more clearly revealed by S4 than DIC, particularly for sub-millistrain levels and on sub-millimeter length scales, which is critical in structural damage detection. These findings show the potential of S4 strain measurement technology as a promising alternative or complement to existing technologies for fracture mechanism studies, non-destructive evaluation and structural health maintenance.