Programs. 

School of Civil and Environmental Engineering

Ph.D. Thesis Defense Announcement

Development of Electrochemical Methods for the Oxidation and Reduction of Halogenated Organic Compounds  

By Zefang Chen

Advisor:

Dr. Xing Xie (CEE)

Committee Members:  Dr. Yongsheng Chen (CEE), Dr. Ching-Hua Huang (CEE), Dr. Sotira Yiacoumi (CEE), Dr. Nian Liu (ChBE)

Date and Time:  Friday, November 17th, 2023, 3:00 PM - 5:00 PM EST

Location:  DEEL 303; Zoom: https://gatech.zoom.us/j/96137326845

Halogenated organic compounds (HOCs) pose a great threat to human health and the aquatic environment because of their persistent toxicity from carbon-halogen bonds. Electrochemical methods, including electrochemical oxidation (EO) and electrochemical reduction (ER) processes, are promising technologies for the destruction of HOCs because of their advantages of strong oxidation/reduction ability, high efficiency, mild reaction conditions, and high automation. Our study aimed to (I) provide effective catalyst design strategies, and (II) bring both mechanistic and kinetic insights for employing both EO and ER processes for the treatment of typical HOCs.
EO has shown effectiveness on the destruction of many HOCs including perfluorooctanoic acid (C7F15COOH, PFOA), an emerging HOC that ubiquitously presents in the aquatic environment. However, the mechanisms and preferred pathway for PFOA mineralization in EO remain unknown. In addition, the substantial generation of chlorinated byproducts during EO is also hindering its practical applicability. To overcome these challenges, we made several improvements for EO PFOA treatment including mechanism exploration, kinetic model development, and anode hydrophobicity modulation. Specifically, we proposed a plausible optimum PFOA mineralization pathway to determine reaction limiting factors by combining density functional theory (DFT) simulations and experiments. In our proposed preferred pathway, PFOA loses COF2 group cyclically without generating short chain perfluoroalkyl carboxylic acids (PFCAs) until complete mineralization. Additionally, we developed a simplified kinetic model for PFOA degradation in EO and created an energy estimator to predict the energy use for various operational parameters (i.e., applied current densities, initial PFOA concentrations, and flow velocities) on EO PFOA treatment. Furthermore, the generation of chlorinated byproducts was successfully suppressed through anode hydrophobicity increase. At the meantime, the efficiencies for PFOA degradation and defluorination were also improved. 
In addition to EO, ER is also an effective method for the dehalogenation and destruction of HOCs. However, ER is limited by the insufficient efficiency in breaking C-F bonds (i.e., one of the strongest carbon bonds) even for the benchmark Pd electrocatalyst. To overcome this challenge, we incorporated boron into Pd electrocatalysts, which exhibited remarkably enhanced defluorination and detoxification efficiency. The boron inclusion boosted H* generation and induced a distinct C-F cleavage mechanism that achieves significantly improved defluorination efficiency for the model HOC, florfenicol (FLO).