Browsing by Subject "adsorption"

Now showing 1 - 4 of 4
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    Activated Carbon Fibers from Cellulosic Biomass with Surface Reductive Treatment for Air Cleanup and VOCs Sensing
    (2018-12) Wang, Yu-Hsiang
    Biological volatile organic compounds (Bio-VOCs) play crucial roles in living organisms such as plants, microbes, and the animals. Sub-ppm level of Bio-VOCs could work as indicators to provide information about metabolism or hormones to facilitate different stages of growth in an organism. For example, less than 25 ppb of ethylene can reduce flowering time, increase seed weight and promote ripening of plants. Thus, there is a need for sensitive detection to provide valuable information for in situ monitoring of biological ecology, as well as for environmental controlling and managing. In situ monitoring of Bio-VOCs requires highly sensitive detections (at mostly sub-ppm concentration level) using portable and accurate sensors, which is extremely challenging for most analytical methods currently available. This work examines the feasibility of an intensified capture and detection strategy for detection of trace amounts of Bio-VOCs, with the sensor unit suitable for miniaturized design for eventually remote and unmanned vehicle sensing applications. In the first part of the study, activated carbon fibers were developed using a reductive reduction procedure, and were examined for pre-concentrating of Bio-VOCs (from ppb-level raised to ppm-level). We expect the reductive carbonization can effectively remove the oxygenated groups from the cellulosic materials, producing fine-tuned electronic properties, which promote pi-pi interaction for intensified the adsorption of nonpolar VOCs (especially for multiple pi bonds compounds). The such produced carbon fibers were examined by XPS (X-ray Photoelectron Spectroscopy), which showed that 53% of the carboxylic and hydroxy groups have been successfully removed. The performance of reductive treated carbon fibers as an adsorbent was examined. Three nonpolar VOCs, methane, ethylene and benzene, were selected as typical biological and chemical VOCs. A sixteen-times increase of benzene (has multiple pi bonds) adsorption can be observed in comparison to carbon fibers without reductive treatment. The unique network structure of the reductive treated carbon fibers also provides a fine electrical conductivity (6.36 Ωcm), that makes it possible for electrothermal desorption for material regeneration. A full regeneration of VOCs was observed in repeated adsorption-desorption cycles, indicating excellent reusability and stability of reductive carbonized carbon fibers. When applied as a pre-concentration absorbent, the carbon fibers successfully increased the concentration of typical VOCs from 500 ppb to 3.5 ppm (700% increase) within 20 min. In order to develop a miniaturized sensor with ultra-high sensitivity and stability for in situ monitoring of Bio-VOCs, the electrochemical sensing system was employed because it is able to identify and quantify various VOCs with high accuracy and sensitivity. However, most of traditional electrochemical sensors have been developed for analysis of aqueous samples, they are easily impacted by the evaporation of water (changing the concentration of electrolyte) when applied to gaseous samples as concerned in the current work. To improve the stability of electrochemical sensing, we developed a unique thin film ionic liquid (IL)-gel coated sensor employing ionic liquids in poly(acrylamide) hydrogels as a solution-free electrolyte. We assumed the stability of the analysis can be improved since the solution of the electrochemical system can be locked in a gel phase, minimizing the evaporation. The ion liquids also have been selected as an electrolyte since the acidity of IL can facilitate the detection of ethylene (one critical Bio-VOCs), preventing the oxidization of the working electrode before ethylene oxidization. A series of experiments were conducted to confirm the performance of IL-gel coating sensor. The results showed the sensor has excellent sensitivity and linearity of our sensor with low detection limit to 650 ppb and 0.99 of R2 values within 0~15 ppm. Decent stability was obtained with a relative standard deviation below 1% for 1.5 months of storage. In addition, the strategy of using reductive fabricated carbon fibers as a pre-concentrating material and a thin film IL-gel coated sensor as a detection unit was also examined. Overall, our work successfully demonstrated the capture-detection strategy is suitable for stable detecting of an extremely low (sub-ppb level) concentration of VOCs. By integrating the preconcentration and senor units, we could eventually develop sensors that are capable of detecting VOC samples in the order of ppb. This approach is promising for building up miniatured Bio-VOCs sensors for in situ monitoring in future applications.
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    Characterizing mVenus adsorption to photodegraded polyethylene using circular dichroism and fluorescence spectroscopy
    (2022-08) Amaris, Althea
    Due to their versatility and relative cost-effectiveness, plastics as a material have gained increasing popularity and are heavily utilized by almost every major industry in the modern day. Their exponential rate of production coupled with a lack of proper disposal methods, however, have resulted in the global environmental issue of plastic pollution. Upon entering the ecosystem, plastic surfaces can act as a foundation for the formation of microbial communities known as biofilms. An initial key step to biofilm growth is the attachment of bacterial surface proteins onto the polymer. In this study, we examine structural changes of a “hard” model protein in the presence of environmentally relevant plastics. Using the intrinsic probes of the mVenus protein, a model yellow fluorescent protein (YFP), we study its structural response to variably photo-aged polyethylene (PE) through circular dichroism (CD) and tryptophan (W)/YFP-fluorescence spectroscopy. Upon binding to aged PE, mVenus undergoes mild secondary structure rearrangement. Interestingly, a forbidden transition in W-fluorescence is observed, evolving from the interaction between the sole tryptophan in mVenus and the increasingly hydrophilic surface of PE as the polymer is progressively photo-oxidized. The beta barrel and beta sheet structure of mVenus retains the overall stability of the protein, whereas the local structure and turn regions accommodate the protein-polymer interactions based on polymer surface chemistry. We can therefore start to predict that proteins bind variably during the initial docking of cells as the secondary structure behaves distinctly based on the age of the film to which it attaches. The dependence of protein docking on the extent of PE-irradiation reveals that film age, polymer type, and structural stability can either accelerate or inhibit biofilm growth.
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    Computationally Driven Characterization of Magnetism, Adsorption, and Reactivity in Metal-Organic Frameworks
    (2016-06) Borycz, Joshua
    Metal-organic frameworks (MOFs) are a class of nanoporous materials that are composed of metal-containing nodes connected by organic linkers. The study of MOFs has grown in importance due to the wide range of possible node and linker combinations, which allow tailoring towards specific applications. This work demonstrates that theory can complement experiment in a way that advances the chemical understanding of MOFs. This thesis contains the results of several investigations on three different areas of MOF research: 1) magnetism, 2) CO2 adsorption, and 3) catalysis. The calculation of magnetic properties within MOFs is quite problematic due to the weak nature of the interactions between the metal centers. The metal atoms in MOFs can be far apart due to the organic linkers and are often in unique chemical environments that are diffcult to characterize. These weak interactions mean that the computational methods must be carefully selected and tested to attain adequate precision. The objective of the work in this thesis was to determine the single-ion anisotropy and magnetic ordering of Fe-MOF-74 before and after oxidation. MOFs have desirable properties for CO2 adsorption such as large pores and high surface areas. Accurate force fields are required in order to make predictions for adsorption interactions with the internal surface of MOFs. Therefore it is important to have computational protocols that enable the derivation of reliable interaction parameters in order to study the trends of adsorption for different metal centers. In the research herein we used ab initio calculations to compute parameters for classical force fields for members of the IRMOF-10 and the MOF-74 series. MOFs have been considered for catalysis due to their thermal stability, reactive metal sites, and large diameter pores. In this thesis we report a series of studies that advance the understanding of the reactivity of MOFs containing Zr6 and Hf6 polyoxometalate nodes. In the first study the proton topology of the nodes within NU-1000 was determined. Several other studies that make use of these MOFs as supports for single-site metal catalysts are also reported. Finally, research where NU-1000 serves as a template for a thermally stable nanocasted material used for high temperature Lewis acid catalysis is also discussed.
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    Synthesis of Zeolite Nanosheets and Applications in Membranes and Adsorption Separation Processes
    (2016-05) Jeon, Mi Young
    In separation processes, desirable products with high purity are acquired at the expense of high energy cost procedures such as distillation. Alternative separation processes, such as zeolite membrane separation and adsorption processes, are promising to reduce the energy cost of production since zeolites can discriminate molecules on the basis of size/shape and functionality. Indeed, the high cost of zeolite membranes can be reduced by fabricating thin membranes with high throughput. High aspect ratio zeolite nanosheets can be used to fabricate zeolite membranes with high throughput on porous supports. To date, however, there is no published evidence that scientists have successfully achieved nanosheet synthesis under the direct hydrothermal treatment route. This dissertation documents a successful direct hydrothermal synthesis of zeolite nanosheets via seeded-growth—a process that leads to zeolite membranes that exhibit high performance on xylene isomer and butane isomer permeation. To the best knowledge, this is the first achievement to prepare zeolite nanosheets without complicated post treatment such as exfoliation and purification process (density gradient centrifugation). Extensive parametric studies are conducted in order to establish the optimal synthesis condition for high quality zeolite nanosheets. Additionally, in an effort to understand the mechanism of nanosheet formation, the sequential evolution of seed crystals into zeolite nanosheets is observed by time-resolved TEM imaging analysis. Keeping in mind that in the future polymers could be used to reduce the costs of membrane manufacture, the de-templation of MFI nanosheets without formation of aggregates is discussed in this dissertation. In addition to membrane applications, this dissertation probes the roles of hydrophobicity in ethanol adsorption when hydrophobic siliceous zeolites, and defective siliceous zeolite nanosheets with house-of-card architecture are provided as adsorbents. Vapor phase ethanol adsorption and aqueous phase ethanol adsorption are compared to investigate how water molecules affect ethanol adsorption onto siliceous zeolites in the aqueous phase.