Chemistry Masters Candidate Thesis Defense Presentation
Sam Thompson, Candidate
Dr. Elsayed Zahran (Advisor)
"Bismuth Oxide Nanocomposites for Photocatalytic Degradation of Halogenated Pollutants"
Monday, June 16th, 11am, Foundational Science Building - FB-253
Abstract: Halogenated organic compounds, notably polychlorinated biphenyls (PCBs), trichloroethylene (TCE), and per- and poly-fluoroalkyl substances (PFAS), present a substantial challenge for environmental remediation due to the extraordinary stability of their carbon-halogen (C-X) bonds. Photocatalysis utilizing metal oxide semiconductors has emerged as a promising approach for the sustainable degradation of a diverse array of organic pollutants. Most of the photocatalysts applied in the degradation of persistent organic pollutants (POPs) are metal oxide semiconductors with wide band gaps (>3.2 eV), which require UV irradiation to generate sufficient energy to overcome the high redox potential of C-X bonds. The development of heterostructured photocatalysts that exhibit broad visible light absorbance and possess critical redox potentials to effectively degrade these persistent contaminants remains a formidable challenge. This thesis presents the design and synthesis of a novel bismuth-based Z-scheme heterojunction specifically engineered for the efficient visible light-driven degradation of halogenated organic compounds. The heterostructured nanocomposite comprised of BiVO4 and BiOX was synthesized using a surfactant-assisted one-pot coprecipitation method and decorated with hydrothermally synthesized carbon dots (CD). Relevant optoelectronic properties were explored using diffuse reflectance spectroscopy (DRS), linear sweep voltammetry (LSV), electrochemical impedance spectroscopy (EIS), and transient photocurrent spectroscopy (TPC). Transmission and scanning electron microscopies (TEM/SEM) were used to visually confirm the overlapping crystal lattices of the component materials. X-ray photoelectron and diffraction spectroscopies (XPS/XRD) were used to explore the elemental composition and phase state of the materials. The BiVO4/BiOX Z-scheme heterojunction photocatalyst demonstrated significant activity in the degradation of both rhodamine B (RhB), a model organic dye, and a pervasive banned chlorinated VOC, trichloroethylene. Complete degradation of RhB by BiVO4/BiOX and CD@BiVO4/BiOX photocatalysts was achieved in 35 and 20 minutes of simulated sunlight irradiation with first-order rate constants of k = 0.0639 min-1 and 0.2401 min-1, respectively. TCE degradation was achieved in 20 and 10 minutes with rate constants of 0.1563 and 0.4950 min-1, respectively. These results demonstrate the potential application of CD@BiVO4/BiOX Z-scheme heterojunction nanocomposite in the visible light-activated degradation of persistent and emerging halogenated environmental contaminants.