Date of Award

12-2024

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

School

Mathematics and Natural Sciences

Committee Chair

Song Guo

Committee Chair School

Mathematics and Natural Sciences

Committee Member 2

Xiaodan Gu

Committee Member 2 School

Polymer Science and Engineering

Committee Member 3

Wujian Miao

Committee Member 3 School

Mathematics and Natural Sciences

Committee Member 4

Vijay Rangachari

Committee Member 4 School

Mathematics and Natural Sciences

Committee Member 5

Karl Wallace

Committee Member 5 School

Mathematics and Natural Sciences

Abstract

Doping is an effective technique used to modulate the band gap of semiconductor materials, allowing for the tuning of their optical and electrical properties. It can also be employed to enhance the conductivity and chemical properties of conductive organic polymers. This dissertation focuses on the development of novel composites based on doped semiconducting materials, including coordination polymers (such as MOFs) and metal oxides derived from them, as visible light photocatalysts for the photodegradation of organic dyes in wastewater. Additionally, doped organic polymer thin films are utilized in the fabrication of novel OECT biosensors for the selective and sensitive detection of neurotransmitters.

In the first project, ZIF-8, a wide band gap semiconductor, was doped with cobalt to improve its photocatalytic activity under visible light. Cobalt-doped ZIF-8 was synthesized using a rapid, one-pot, cost-effective, and environmentally friendly method. The introduction of cobalt reduced the band gap of ZIF-8, activating it under visible light. The Co-ZIF-8 showed significant photocatalytic activity under visible light, achieving 97% removal of MB. The Co-ZIF-8 was then used to create a magnetic composite with Fe3O4 nanoparticles modified with MCC to facilitate recycling and reuse of the photocatalyst after the photocatalytic process. The Fe3O4/MCC/Co-ZIF-8 composite exhibited comparable photocatalytic activity to Co-ZIF-8 and showed negligible reduction in photocatalytic efficiency after several cycles. However, Co-ZIF-8 and its magnetic composite were not effective photocatalysts for RhB.

In the second project, a Co3O4/ZnO p-n heterojunction composite was derived from Co-ZIF-8 through a pyrolysis process. This Co3O4/ZnO composite proved to be a promising photocatalyst for the photodegradation of RhB under UV light. The photocatalyst was further functionalized with Chla extracted from spirulina as a natural visible light photosensitizer to iv enhance its activity. The Chla functionalization improved the photocatalytic efficiency of the Co3O4/ZnO composite by 50%. The Chla-functionalized photocatalyst degraded RhB by promoting N-deethylation and the breakdown of the conjugated system of the chromophore. Additionally, the internal electric field at the junction between p-type Co3O4 and n-type ZnO enhanced the photocatalytic activity of Co3O4/ZnO/Chla by 10% compared to ZnO/Chla.

In the final project, doped polymer thin films were used to modify the gate electrode of an OECT sensor, creating a selective and sensitive sensor for SE detection. The gate electrode was modified with MIPs that featured cavities complementary to the shape of SE, blocking interferences from substances such as DA, AA, and UA. To further improve the selectivity and sensitivity of the biosensor through electrostatic interactions, the MIP layer was doped with PSSn, enhancing the interaction between the MIP cavities and SE, which is positively charged at physiological pH . This modification also repelled negatively charged interferents such as UA and AA, further enhancing the sensor’s selectivity. The DOMIP modified gate OECT exhibited a low LOD of 0.31 μM for SE and demonstrated high selectivity for SE over interferents such as AA, UA, and DA.

Overall, this research successfully employed doping to enhance the visible light photocatalytic activity of inorganic semiconducting materials. Modifying the gate electrode of the OECT with doped organic polymer thin films also improved the selectivity and sensitivity of the OECT biosensor for SE detection. The findings of this research contribute to the development of cost-effective and rapid methods for creating effective visible light photocatalyst materials and biosensor devices, paving the way for their scalable production.

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