http://hdl.handle.net/1957/18466 2013-06-19T00:23:11Z http://hdl.handle.net/1957/39559 Finite volume method modeling of corona discharge microreactor oxidization of dibenzothiophene Fan, Xiangru The growing need for cleaner fuels requires the development of better deep fuel desulfurization methods. The current study presents a reaction model for the mechanism of dibenzothiophene oxidization by dissolved oxygen occurring in a corona discharge microreactor. In the present work, a Finite Volume Method model of the reactor is created and several possible reaction pathways investigated. The finite volume method model is first implemented in MATLAB and optimized to compute data efficiently. Without significant loss of precision, the FVM model implemented is between 50 and 400 times faster than COMSOL. Following model implementation, transport and reaction mechanism studies of 5 alternatives based on Reactions 1 through 6 below were investigated and results compared with existing experimental data for the reactor.; Reaction 1 O₂ + e- ------k1------> 2O. + e-; Reaction 2 2O. + e- ------k2------> O₂ + e-; Reaction 3 DBT + O. ------K4------> DBTO; Reaction 4 DBTO ------K4------> DBT + O.; Reaction 5 DBTO + O. ------K5------> DBTO₂; Reaction 6 DBTO₂ + DBTO₂ ------K6------> 2DBTO + 2O; The results indicate that: 1 - Transport in the microreactor is not the limiting factor, and 2 - The corona discharge reaction most likely involves a second order reverse reaction that converts DBTO₂ to DBTO and a first order reverse reaction that converts DBTO to DBT. The performance of the reactor is therefore restricted by a high rate of reverse reaction(s) when high concentrations of DBTO and DBTO2 are present. Graduation date: 2013 2013-05-20T00:00:00Z http://hdl.handle.net/1957/39070 Inhibition of the ammonia oxidizing bacteria Nitrosomonas europaea by the emerging contaminant triclosan Hughes, Jamie L. Identifying the inhibition of ammonia oxidizing bacteria (AOB) by emerging organic contaminants is crucial due to the importance of AOB in wastewater treatment, the widespread use of antibacterial agents such as triclosan (TCS) in consumer products, and the sensitivity of N. europaea to inhibitors. Triclosan inhibition of nitrification by AOB N. europaea cells was determined via suspended cell batch reactor experiments using cells grown in batch and in a chemostat. Specific oxygen uptake rate tests (SOURs) were performed on both the ammonia monooxygenase (AMO) and hydroxylamine oxidoreductase (HAO) enzymes to determine the enzyme inhibition mechanism of TCS. Inhibition of long term growth of N. europaea cells and development of antibacterial resistance when exposed to low concentrations of TCS were also studied via suspended cell batch growth experiments. A colorimetric nitrite assay was used to quantify nitrite production and UHPLC-MS analysis was used to analyze for the cometabolic transformation of TCS. Three hour inhibition tests showed that N. europaea cells are inhibited by TCS at concentrations ranging from 0.1 to 8 ppm TCS, but activity partially recovered when washed and re-suspended in fresh media. Triclosan inhibition results show a non-linear increase in nitrification inhibition with increasing TCS concentration with 40% inhibition occurring at 1 ppm TCS and 90% inhibition at 8 ppm TCS. The recovery of previously inhibited cells, relative to control cells, fit a semi-log plot, with cell inactivation being dependent on TCS concentration and the time of exposure, similar to models used for disinfection. Results of the exposure of chemostat-grown N. europaea cells to 1 ppm TCS showed less inhibition than observed with batch-grown cells. SOURs results indicate that the AMO enzyme is directly inhibited by TCS, either through competition for its active site or interactions of TCS with AMO, and that the HAO enzyme is not inhibited by TCS. Results of suspended cell growth experiments indicate that growth of N. europaea is inhibited by approximately 30% at 0.01 ppm TCS; where concentrations at or exceeding 0.05 ppm TCS significantly inhibit cell growth. Resistance tests showed no development in resistance to 0.01 ppm TCS over three growth cycles or approximately 67 generations of growth. UHPLC-MS analyses indicate that TCS is not transformed in the presence of N. europaea over a three hour direct exposure period or during long term growth of several days. Graduation date: 2013 2013-05-21T00:00:00Z http://hdl.handle.net/1957/38765 Growth, characterizations and applications of copper sulfide thin films by solution-based processes Vas-Umnuay, Paravee Copper sulfides (Cu[subscript x]S) are compound semiconductor materials that exhibit considerable optical and electrical properties varying significantly as a function of the composition. Copper sulfide thin films can be used in many applications, such as solar control coatings, solar cells, photothermal conversion of solar energy, electroconductive coatings, and microwave shielding coatings. A variety of solution-based and vapor-based techniques are suitable for their deposition. Solution-based processes have the advantages of simplicity, low capital cost, and low processing temperature. In this work, copper sulfide thin film deposition by a number of solution-based processes was investigated. These processes include chemical bath deposition (CBD), Microreactor Assisted Solution Deposition (MASD), and PhotoChemical Deposition (PCD). The growth kinetics of copper sulfide thin films by CBD was monitored using an in-situ quartz crystal microbalance for the first time. CBD growth was studied as a function of time, temperature, concentrations of reactants, and pH. The reaction activation energy was determined based on initial growth rates. The result indicates the rate limiting step of the deposition is the chemical reaction rather than mass transport. The structure, morphology, composition and optical absorption of the films were found to depend strongly on the deposition conditions. Results from the study of CBD reactions indicated the need to de-reduce the undesirable homogeneous particle formation. The MASD process was developed to achieve this objective. The continuous flow process together with the microreactor design not only improve the mixing of reactants and provide a better temporal control over the reaction which result in higher quality films and a higher deposition rate. A particle-free flux was obtained after adjusting the key process parameters (concentration of mixed reactants, solution temperature, substrate temperature, and residence time). Significantly improved copper sulfide thin film deposition with a good selectivity of heterogeneous surface reactions was achieved. PCD basically employs the UV illumination to excite the irradiated region of the substrate in a deposition solution. It has the potential to reduce the homogeneous particle formation. We investigated the growth kinetics of copper sulfide thin films by PCD under various deposition conditions (e.g. pH, substrate position, reactant concentration, deposition time, and temperature) that influence on the film properties and characteristics. Moreover a detailed mathematical model that describes the multiple chemical reactions in the deposition mechanism was also developed in this work to have a better understanding of the reaction mechanism. Reaction rate constants were successfully estimated from the experimental data based on this model. The calculated results agree well with the experimental data. This model could serve as a useful tool for the control and optimization of photochemical deposition of copper sulfide thin films. Both CBD and PCD processes suffer from severe homogeneous particle formation which has resulted in lower deposition rate. In contrast, MASD provides good selectivity towards heterogeneous surface deposition using molecular precursors at a much higher deposition rate. Thus MASD process was used to deposit copper sulfide layers on textured substrates with nice conformal coverage. Dense, crack-free CuInSe₂ thin films were fabricated successfully after adding an indium precursor layer, and followed by a selenization process. This approach offers a potential low-cost route to fabricate thin absorber solar cells. Graduation date: 2013 2013-04-30T00:00:00Z http://hdl.handle.net/1957/38760 CO₂ reduction in aqueous-ionic liquid solution in microscale-based corona reactor; CO2 reduction in aqueous-ionic liquid solution in microscale-based corona reactor Miao, Yu Global warming problem is becoming an increasingly important environmental concern and CO₂ is considered as the major cause of global warming. Among various methods of CO₂ utilization, conversion of CO₂ to value added chemical products is the most attractive. In this study, a microscale-based corona reactor is introduced for reduction of CO₂. Two kinds of solvent were used in this study for absorbing CO₂: DI-water and ionic liquid 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM][BF4]). The latter one has a much higher solubility of CO₂. After saturated with CO₂, solution was introduced into the microreactor built around the concept of corona discharge. The corona was created through a significant potential difference between two graphite electrodes. The current that passed through two electrodes acted as a catalytic agent for the reduction of CO₂. The experiments were conducted at room temperature and at steady state. The ranges of the operating conditions were: mean residence time 5 to 100 (sec), thickness of spacer 200 and 500 (μm), and voltage applied across the reactor 20 and 22.5 (V). Reactions happened in the bulk of the reactor and five main products were detected at the outlet stream: i) formic acid (HCOOH), ii) formaldehyde (HCHO), iii) methanol (CH₃OH), iv) methane (CH₄) and v) hydrogen (H₂). Among these compounds, formic acid, formaldehyde and methanol are intermediate products. The conversion of CO₂ in aqueous solution can reach as high as 94.8% at mean residence time of 100 sec. Although in ionic liquid solution the conversion of CO₂ is much lower (19.3% at mean residence time of 100 sec), consumption of CO₂ in ionic liquid is 6-7 times larger than that in water when generating same volume of products. A mathematical model reflecting geometry and flow conditions inside the microreactor was developed to simulate the process of CO₂ reduction. The model was solved numerically using COMSOL Multiphysics software package. The simulated results were optimized to fit the experimental data using COMSOL-Matlab LiveLink software package. Primary reaction rate constants for CO₂ reduction were predicted. The mathematical model was found to explain the experimental data pretty well. Graduation date: 2013 2013-05-21T00:00:00Z