Butanol is considered a promising, infrastructure-compatible biofuel. Butanol has a higher energy content than ethanol and can be used in conventional gas engines without modifications. Unfortunately, the fermentation pathway for butanol production is restricted by its toxicity to the microbial strains used in the process. Butanol is toxic to the microbes, and this can slow fermentation rates and reduce butanol yields. Gas stripping technology can efficiently remove butanol from the fermentation broth as it is produced, thereby decreasing its inhibitory effects. Traditional butanol separation heavily depends on the energy intensive distillation method. One of the main issues in acetone-butanol-ethanol fermentation is that butanol concentrations in the fermentation broth are low, ranging from 1 to 1.2 percent in weight, because of its toxicity to the microorganisms. Therefore distillation of butanol is even worse than distillation of corn ethanol. Even new separation methods, such as solid- extraction methods involve adding substances, such as polymer resin and zeolite or activated carbon, to biobutanol fermentatioon broth did not achieve energy efficient separation of butanol due to low adsorption selectivity and fouling in broth. Gas-stripping - condensation is another new butanol recovery method, however, the butanol in gas-stripping stream is too low to be condensed without using expensive and energy intensive liquid nitrogen. Adsorption can then be used to recover butanol from the vapor phase. Activated carbon (AC) samples and zeolite were investigated for their butanol vapor adsorption capacities. Commercial activated carbon was modified via hydrothermal H2O2 treatment, and the specific surface area and oxygen-containing functional groups of activated carbon were tested before and after treatment. Hydrothermal H2O 2 modification increased the surface oxygen content, Brunauer-Emmett-Teller surface area, micropore volume, and total pore volume of active carbon. The adsorption capacities of these active carbon samples were almost three times that of zeolite. However, the un-modified active carbon had the highest adsorption capacity for butanol vapor (259.6 mg g-1), compared to 222.4 mg g-1 after 10% H2O2 hydrothermal treatment. Both modified and un-modified active carbon can be easily regenerated for repeatable adsorption by heating to 150 °C. Therefore, surface oxygen groups significantly reduced the adsorption capacity of active carbons for butanol vapor. In addition, original active carbon and AC samples modified by nitric acid hydrothermal modification were assessed for their ability to adsorb butanol vapor. The specific surface area and oxygen-containing functional groups of AC were tested before and after modification. The adsorption capacity of unmodified AC samples were the highest. Hydrothermal oxidation of AC with HNO3 increased the surface oxygen content, Brunauer-Emmett-Teller (BET) surface area, micropore, mesopore and total pore volume of AC. Although the pore structure and specific surface area were greatly improved after hydrothermal oxidization with 4 M HNO3, the increased oxygen on the surface of AC decreased the dynamic adsorption capacity. In order to get high adsorption capacity adsorbents, we used corn stalk as precursor to fabricate porous carbon. ACs were prepared through chemical activation of biochar from whole corn stalk (WCS) and corn stalk pith (CSP) at varying temperatures using potassium hydroxide as the activating agent. ACs were characterized via pore structural analysis and scanning electron microscopy (SEM). These adsorbents were then assessed for their adsorption capacity for butanol vapor. It was found that WCS activated at 900 °C for 1 h (WCS-900) had optimal butanol adsorption characteristics. The BET surface area and total pore volume of the WCS-900 were 2330 m2 g-1 and 1.29 cm3 g-1, respectively. The dynamic adsorption capacity of butanol vapor was 410.0 mg g-1, a 185.1 % increase compared to charcoal-based commercial AC (143.8 mg g -1). Based on the adsorption experiments of butanol vapor, we found the chemical properties of the AC surface play an important role in adsorbing molecules. The adsorption of creatinine on active carbons was also studied, which is a toxic compound generated by human. High levels of creatinine in the blood stream is normally caused by malfunction or failure of the kidneys. Activated carbons is taken by the patients orally to reduce creatinine level. In order to figure out whether chemical modification could increase the adsorption capacity of creatinine, AC samples modified by nitric acid hydrothermal modification were assessed for their ability to adsorb creatinine. The pore structure and surface properties of the AC samples were characterized by N 2 adsorption, temperature programmed desorption (TPD), Fourier Transform Infrared spectroscopy (FTIR), and X-ray photoelectron spectrometer (XPS). It indicated that 4M HNO3 hydrothermal modification with 180 °C was an efficient method in improvement of the creatinine adsorption. The improved adsorption capacity can be attributed mainly to an increase in the acidic oxygen-containing functional groups. The adsorption of creatinine over AC may involve an interaction with the acidic oxygen-containing groups on AC. Langmuir and Freundlich adsorption models were applied to describe the experimental isotherm and isotherm constants. Equilibrium data fitted very well to the Freundlich model in the entire saturation range (3.58-59.08 mg L-1 ). The maximum adsorption capacities of AC modified with 180 °C is 62.5 mg g-1 according to the Langmuir model. Pseudo first-order and second-order kinetic models were used to describe the kinetic data and the rate constants were evaluated. The experimental data fitted well to the second-order kinetic model, which indicates that the chemical adsorption was the rate-limiting step, instead of mass transfer. (Abstract shortened by ProQuest.). ProQuest Subject Headings: Chemical engineering, Materials science.
Sensitive detection for DNA has drawn great attention in plenty of different areas such as genetics therapy and basic discovery research. Recently, nucleic acid lateral flow biosensor (NALFB) has gained considerable attention for DNA analysis. Compared with the traditional immunoassays, NALFB has these advantages: short assay time and a low cost. In this thesis, we report a carbon nanotubes (CNTs)-based NALFB for rapid and sensitive detection of DNA. Amine-modified DNA detection probe was covalently immobilized on the CNTs via diimide-activated amidation between the carboxyl groups on the CNTs surface and amine groups on the detection DNA probes. Sandwich-type DNA hybridization reactions were performed and the captured MWCNTs on test zone and control zone produced the characteristic black bands. Based on the catalytic property of CNTs to enhance the Chemiluminescence intensity of the reaction between hydrogen peroxide and Lumigen APS-5, a rapid detection of DNA sequence with high sensitivity is achieved.
This dissertation examines cohort changes in young women's and men's intentions to pursue science majors and achievements of a science degree between the 1970s and 1990s. The National Longitudinal Study of High School Seniors of 1972 (1972--1979) and the National Education Longitudinal Study 1988 (1992--2000) are used to test Jacobs' argument that young women's success in science majors is hampered by a life-long process of social control. Gender socialization teaches boys and girls to expect different rewards and responsibilities from work and family. Consequently, as young women and men make decisions about their educational and career pursuits, they do so in gender-specific ways (Jacobs 1989; 1995; 2003). I test Jacobs' social control hypothesis by examining changes in how adolescents' early valuation of family affects young women's and men's intentions to pursue science and achievement of a science degree in the 1970s and 1990s. In the 1970s, family commitment operated in a gender-specific way, hampering only young women's science intentions and achievements, but not significantly affecting men's. By the 1990s, both young men's and women's science intentions are dampened by their commitment to family. However, young women's science achievements continue to be hindered by their valuation of family, while men's science success is not similarly affected. My findings indicate some convergence in the effect of family commitment on young women's and men's plans to major in science, but also suggest the resilience of gender in shaping young adults' science achievements. The second part of this dissertation uses the NELS to examine social-psychological mechanisms that reproduce contemporary gender segregation of college majors. Competing explanations of gender segregation in academic majors are examined: the perceived competency (Correll) and social control (Jacobs) hypotheses. Specifically, I assess the influence of math efficacy and valuation of family on adolescents' intended college majors and their earned degrees. Majors are categorized as: traditionally female majors, non-physical sciences, social sciences, business, and physical science/engineering. My results suggest that math-efficacy promotes adolescents' science intentions and achievements, but does not explain the gender segregation of majors. Instead, early orientations toward family are essential to understanding contemporary gender segregation of academic majors.