Hybrid Materials for Sensing and Catalyst Applications
Abstract
Novel hybrid materials are fabricated with the goal of achieving properties that are superior to those of each component individually. The properties of hybrid materials can be tailored by changing the composition or configuration, making them attractive for use in a wide variety of applications ranging from photovoltaics to drug delivery systems. In this work, several hybrid material systems were fabricated and evaluated as photocatalysts or electrochemical sensors. Polyelectrolyte microspheres with different surface chemistry and charge were created through layer by layer deposition. Two model enzymes, acetylcholinesterase and horseradish peroxidase, were immobilized on the microsphere surfaces via electrostatic adsorption and hydrogen bonding. The polyelectrolyte-enzyme hybrids were incorporated into amperometric biosensors for the detection of organophosphate pesticides and hydrogen peroxide. The effect of surface charge of the terminal polyelectrolyte layer on enzyme activity was investigated. Biosensor performance for each system was evaluated by determination of detection limits, amperometric response, and long-term stability. Electrochemical sensors based on graphene were also fabricated in order to take advantage of graphene's superior electrical properties. In the first system, a graphene - chitosan hybrid film was investigated as an immobilization matrix for acetylcholinesterase. Dispersion of graphene throughout chitosan was dependent on pH of the polymer solution, since pH will greatly affect surface charge. An electrochemical hydrogen peroxide sensor was formed from the combination of graphene oxide with Ag2O nanocrystals synthesized with different morphologies (hexapods, octahedra, and cubes). Amperometric response and sensitivity were greatest for sensors fabricated with Ag 2O hexapods. The configuration of the system was optimized by layering graphene oxide and Ag2O and comparing electrochemical performance. Overall, the presence of graphene oxide resulted in decreased sensitivity and amperometric response compared to sensors made with Ag2O nanocrystals alone. In the final study, TiO2 nanoparticles were dispersed throughout a cellulose nanofiber matrix in order to form photocatalytically active films for the degradation of organic molecules in water. Concentration, volume, and pH of TiO2 and cellulose nanofiber dispersions were optimized in order to produce stable films through solvent evaporation casting. The surfaces of the films were subsequently modified by Au and Ag nanoclusters via in-situ reduction techniques. The three component hybrid systems displayed enhanced photocatalytic activity under simulated sunlight in addition to superior mechanical properties that allowed modified films to be reused for several irradiation cycles.
Degree
Ph.D.
Advisors
Stanciu, Purdue University.
Subject Area
Polymer chemistry|Materials science
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