This thesis presents an alternative approach for pre-concentrating heavy metals in aqueous environments using electro spun polymer nanofiber sorbents. The conditions for electrospinning polyethersulfone, polystyrene, polysulfone and polyamide-6 were optimized. The morphologies and porosities of the electrospun nanofibers were studied using SEM and BET nitrogen gas adsorptions. The nanofibers had mesoporous morphologies with specific surface areas up to 58 m2/g. The electro spun nanofiber sorbents were characterized in terms of their tunability for both uptake and release of heavy metals. The usability of the sorbent was also assessed. The sorbents showed fast adsorption kinetics for heavy metals « 20 min for As, Cu, Ni and Pb) in different aqueous environments. The adsorption characteristics of the sorbents best fitted the Freundlich isotherm and followed the first order kinetics. The efficiencies of adsorption and desorption of heavy metals on both imidazolyl-functionalized polystyrene and amino-functionalized polysulfone sorbents were more than 95% up to the fifth cycle of usage. Reusability improved dramatically (up to 10 runs of usage) when mechanically stable amino-functionalized nylon-6 electro spun nanofibers were used. The capacity of the amino-functionalized nylon-6 sorbent to pre-concentrate heavy metals compared very favourably with those of aqua regia and HN03+H202 digestions especially in less complex matrices. Due to their highly porous nature, the electro spun nanofibers exhibited high adsorption capacities (up to 50 mg/g) for heavy metal ions. The loading capacities achieved with the imidazolyl-functionalized sorbent were higher than those for amino-functionalized mesoporous silica and biomass-based sorbents. The electro spun nanofiber sorbents presents an efficient and cost effective alternative for preconcentrating heavy metals in aqueous environments.

Indiana University-Purdue University Indianapolis (IUPUI) / The purpose of this thesis is to use experimental methods to seek deeper understanding and better performance in the self-circulating self-regulating microfluidic gas generator initially developed in Dr. Zhu’s group, by changing the major features and dimensions in the reaction channel of the device. In order to effectively conduct experiments described above, a microfabrication method that is capable of making new microfluidic devices with low cost, short time period, as well as relatively high accuracy was needed first. Developing such a fabrication method is the major part of this thesis. We initially used patterned polymer films and glass slide, and bonded them together by sequentially aligning and stacking them into a microfluidic device with patterned double-sided tapes. Later we developed a more advanced microfabrication method that used only patterned polystyrene (PS) films. The patterned PS films were obtained from a digital cutter and they were bonded into a microfluidic device by thermopress bonding method that required no heterogeneous bonding agents. This new method did not need manual assembly which greatly improved its precision (~ 100 µm), and it used only PS as device material that has favorable surface wetting property for microfluidics applications. In order to find the optimized microfluidic channel design to improve gas generating performance, we've designed and fabricated microfluidic devices with different channel dimensions using the PS fabrication method. Based on the gas generation testing results of those devices, we were able to come up with the optimal dimensions for the reaction channel that had the best gas generation performance. To obtain a more fundamental understanding about the working mechanism of our device and its bubble dynamics, we have conducted ultrafast X-ray imaging test at Advanced Photon Source (APS), Argonne National Laboratory. High speed (100 KHz) phase contrast images were captured that allowed us to observe directly inside the reaction channel on the cross section view during the self-circulating catalytic reaction. The images provided us with lots of insightful information that in turn helped the dimensional improvement for the microchannel design. The 100 KHz high speed images also gave us useful information about the dynamics of bubble development on a catalyst bed, such as growth and merging of the bubbles.