Krista Carlson

Self-Ordered Titanium Dioxide Nanotube Arrays: Anodic Synthesis and Their Photo/Electro-Catalytic Applications

Metal oxide nanotubes have become a widely investigated material, more specifically, self-organized titania nanotube arrays synthesized by electrochemical anodization. As a highly investigated material with a wide gamut of applications, the majority of published literature focuses on the solar-based applications of this material. The scope of this review summarizes some of the recent advances made using metal oxide nanotube arrays formed via anodization in solar-based applications. A general methodology for theoretical modeling of titania surfaces in solar applications is also presented.

DNA adsorption onto calcium aluminate and silicate glass surfaces.

A common technique for small-scale isolation of genomic DNA is via adsorption of the DNA molecules onto a silica scaffold. In this work, the isolation capacities of calcium aluminate based glasses were compared against a commercially available silica scaffold. Silica scaffolds exhibit a negative surface at the physiological pH values used during DNA isolation (pH 5-9), while the calcium aluminate glass microspheres exhibit a positive surface charge. Isolation data demonstrates that the positively charged surface enhanced DNA adsorption over the negatively charged surface. DNA was eluted from the calcium aluminate surface by shifting the pH of the solution to above its IEP at pH 8. Iron additions to the calcium aluminate glass improved the chemical durability without compromising the surface charge. Morphology of the glass substrate was also found to affect DNA isolation; 43-106 μm diameter soda lime silicate microspheres adsorbed a greater quantity of genomic DNA than silica fibers with an average diameter of ∼2 μm.

Development of a field enhanced photocatalytic device for biocide of coliform bacteria

A field enhanced flow reactor using bias assisted photocatalysis was developed for bacterial disinfection in lab-synthesized and natural waters. The reactor provided complete inactivation of contaminated waters with flow rates of 50mL/min. The device consisted of titanium dioxide nanotube arrays, with an externally applied bias of up to 6V. Light intensity, applied voltage, background electrolytes and bacteria concentration were all found to impact the device performance. Complete inactivation of Escherichia coli W3110 (~8×10(3)CFU/mL) occurred in 15sec in the reactor irradiated at 25mW/cm(2) with an applied voltage of 4V in a 100ppm NaCl solution. Real world testing was conducted using source water from Emigration Creek in Salt Lake City, Utah. Disinfection of natural creek water proved more challenging, providing complete bacterial inactivation after 25sec at 6V. A reduction in bactericidal efficacy was attributed to the presence of inorganic and organic species, as well as the increase in robustness of natural bacteria.

Development Of Titanium Dioxide Nanotube-based Arrays For The Electrocatalytic Degradation And Electrochemical Detection Of Emerging Pharmaceuticals In Water

The electrocatalytic degradation and electrochemical detection of ibuprofen (IBU) in water was performed using titanium dioxide nanotube (TiO2-NT) arrays. IBU solutions with starting concentrations of 30 ppm were degraded by 50% in 15 min using a TiO2-NT array annealed in a reducing atmosphere. Inactivation of E.Coli 25922 was used to determine the radical species generated during degradation in both flow and batch reactors. Semi-quantitative radical concentrations were obtained by using a UV-Vis spectrophotometer to monitor the color change of an oxidation sensitive DPD dye. Electrochemical detection limits of 4 ppb IBU in 50 ppm NaCl were obtained using a gold coated TiO2-NT array annealed in oxygen. These results demonstrated the feasibility of a combined system that could be deployed for inline effluent treatment as these types of systems are robust, chemical free and could be automated for remote control.

Electrochemical detection of E. Coli O157: H7 in water after electrocatalytic and ultraviolet treatments using a polyguanine-labeled secondary bead sensor

The availability of clean drinking water is a significant problem worldwide. Many technologies exist for purifying drinking water, however, many of these methods require chemicals or use simple methods, such as boiling and filtering, which may or may not be effective in removing waterborne pathogens. Present methods for detecting pathogens in point-of-use (POU) sterilized water are typically time prohibitive or have limited ability differentiating between active and inactive cells. This work describes a rapid electrochemical sensor to differentially detect the presence of active Escherichia coli (E. coli) O157:H7 in samples that have been partially or completely sterilized using a new POU electrocatalytic water purification technology based on superradicals generated by defect laden titania (TiO2) nanotubes. The sensor was also used to detect pathogens sterilized by UV-C radiation for a comparison of different modes of cell death. The sensor utilizes immunomagnetic bead separation to isolate active bacteria by forming a sandwich assay comprised of antibody functionalized secondary magnetic beads, E. coli O157:H7, and polyguanine (polyG) oligonucleotide functionalized secondary polystyrene beads as an electrochemical tag. The assay is formed by the attachment of antibodies to active receptors on the membrane of E. coli, allowing the sensor to differentially detect viable cells. Ultravioloet (UV)-C radiation and an electrocatalytic reactor (ER) with integrated defect-laden titania nanotubes were used to examine the sensors’ performance in detecting sterilized cells under different modes of cell death. Plate counts and flow cytometry were used to quantify disinfection efficacy and cell damage. It was found that the ER treatments shredded the bacteria into multiple fragments, while UV-C treatments inactivated the bacteria but left the cell membrane mostly intact.

Axisymmetric evaluation of analytic potentials around thin disks

ABSTRACT Axisymmetric potential fields among disk conductors are an important consideration for evaluation and testing of near field electric field gradients in electrical systems. As contrasted with numerical methods, analytical methods give exact solutions via the fundamental symmetry, and, in addition, we can compare the solutions to the accuracy of the test procedure. Analysis and superposition of the disk potentials is a valuable way to study the optimal characteristics of the fringing fields in dielectric systems. Cylindrical and ellipsoidal coordinate based analytical approaches are provided for the determination of the theoretical potentials in disk electrode systems.