Semiconductor and Graphene Oxide Nanomaterials for Sensing and Catalytic Degradation of Chemical Contaminants

With the everchanging landscape that is the world energy demand as it trends with increasing world population, an equally versatile approach capable of changing with this landscape is vital. Traditional energy conversion methods currently in use are unsustainable and compound global environmental issues as they rely on limited natural resources such as fossil fuels and natural gas; however, developing clean, renewable systems capable of generating this energy can begin to address these issues. Therefore, the discovery and development of materials and devices capable of not only promoting the clean energy agenda, but also serving as multifunctional systems to address additional issues has been the focus of my work thus far. Two major tasks focused on very distinct applications of reduced graphene oxide (RGO)-based multifunctional mats have been explored; the development of smart materials capable of sensing and degrading target compounds as well as designing graphene-supported catalysts towards the development of heterogeneous chemical fuel generation systems. The overall focus of this work is geared towards understanding the photophysical, electrochemical, and photoelectrochemical properties and performance of each catalyst for the proposed systems separately to later couple together with graphene.

First, the optical, photophysical and catalytic properties of CdSe/CdS heternanostructures were explored for application in chemical sensing and degradation. First, I will discuss the systematic evaluation of the light-matter interaction of CdSe/CdS QRs and the effects of CdS shell length on its photophysical properties as it was performed.¹ The qualification of electron transfer rates as well as application as a photocatalytic material was also explored. In direct continuation of this study, the CdSe/CdS QRs were then evaluated as biofunctionalized chemical sensors for the trace detection of chemical warfare agent simulants. The unparalleled high QYs and simple surface modification of the CdSe/CdS QR proved to provide as an excellent probe for organophsphonate detection via fluorescence quenching mechanism.

In the second portion of this dissertation, the electronic properties of RGO catalyst mats will be presented. Specifically, the fundamental analysis of the electron capture, storage, and discharge properties of RGO via two physiosorbed redox active species will be discussed. The quantification and extent of electronic communication between these two redox species was qualified and established. Upon demonstration of RGO as an electrocatalytic support, the same approach was used in collaboration with another group towards heterogenous CO₂ electrocatalytic reduction. We were able to demonstrate an unmatched transition from homogeneous to heterogenous catalysis without the loss of catalytic efficiency or rate, turnover frequency, or turnover rates.