PhD Oral Exam - Mahsa Motamedi, Civil Engineering

When studying for a doctoral degree (PhD), candidates submit a thesis that provides a critical review of the current state of knowledge of the thesis subject as well as the student’s own contributions to the subject. The distinguishing criterion of doctoral graduate research is a significant and original contribution to knowledge.

Once accepted, the candidate presents the thesis orally. This oral exam is open to the public.

Abstract

This work introduces a novel photocatalytic methodology that leverages the synergistic action of visible light and H₂O₂ with a green catalyst for the efficient degradation of tris(1-chloro-2-propyl) phosphate (TCPP). A PPy-g-C₃N₄-MIL88B photocatalyst was synthesized with a narrowed bandgap, high structural stability, minimized iron leaching, and enhanced charge transfer properties. Comprehensive characterization using HAADF-FE-SEM, TEM, FTIR, XRD, XPS, BET, PL, and UV-DRS confirmed the successful fabrication of the photo-Fenton catalyst. UV-DRS analysis revealed a 28% bandgap reduction, from 3.2 eV (MIL-88B) to 2.3 eV (PPy-g-C₃N₄-MIL88B). The PPy-g-C₃N₄-MIL88B/H₂O₂/LED system was subsequently employed for TCPP degradation, where five by-products (BPs) were detected and quantified, each showing significant reduction within 20 minutes. Toxicity assays demonstrated improved ecological safety, as the LC₅₀ (96 h) for fathead minnows increased from 7.24 mg/L (TCPP) to 19.12 mg/L (BP175) and 58.23 mg/L (BP323) after treatment. Kinetic modeling through response surface methodology and central composite design identified a reduced quartic model with strong significance (p < 0.0001). ANOVA-based optimization indicated near-complete TCPP degradation (99.29%) under optimal conditions of 59 min irradiation, 100 mg/L catalyst dosage, pH 5, and 15 L/min airflow. Finally, the applicability of PPy-g-C₃N₄-MIL88B was validated in real water matrices from four Canadian lakes and rivers, achieving over 65% contaminant removal. These findings highlight the potential of PPy-g-C₃N₄-MIL88B as a sustainable photocatalyst for addressing emerging water pollutants.