Enhanced Ti4O7 Reactive Electrochemical Membranes for Water Treatment Applications

This dissertation focused on developing and modifying reactive electrochemical membranes (REMs) for water treatment applications. The specific goals for this work were to: 1) Increase the adsorption capacity of the REMs for disinfection by products (DBPs) such as N-Nitrosodimethylamine (NDMA) and haloacetic acids (HAAs), 2) Overcome several limitations of current DBP removal techniques, such as high energy consumption, high capital cost, and low removal rate, 3) Employ a new method using simultaneous adsorption and electrochemical reduction of DPBs with carbon-Ti4O7 REMs, which would lead to a major electrochemical reduction of these contaminants, 4) Test the carbon-Ti4O7 REMs for use in removing various HAAs, not limited to one experiment, collect and analyze samples, perform data analysis, and develop transport models, which would show that carbon-Ti4O7 REMs were more suitable for removing HAAs by using low-cost carbon, which also would require less energy and time invested, and 5) Achieve electrocatalytic ClO-4 reduction for water purification using a heterogeneous catalyst containing Re single-sites deposited on Ti4O7 REMs to eliminate the need for the precious metal Pd catalyst, by utilizing REM substrate to reduce the Re center after the oxygen atom transfer (OAT) step under cathodic polarization. These goals were achieved by employing different experimental and theoretical techniques. Experimental techniques included chronoamperometry for performing reduction experiments, electrochemical impedance spectroscopy (EIS), cyclic voltammetry (CV), and many other electrochemical techniques. Theoretical methods such as density functional theory (DFT), reactive transport simulations, and Tafel plot analysis were used to interpret the experimental data, study the rate-determining step of the reactions, and understand the reaction mechanism thoroughly. The accomplishments of this work include: 1) carbon-Ti4O7 REMs were studied to increase adsorption capacities for NDMA, which increased NDMA removal from water up to a 4-log removal in a single pass flow-through reactor with residence time < 15 s. 2) carbon-Ti4O7 REMs were evaluated for their ability to simultaneously adsorb and reduce HAAs in both synthetic and tap water solutions. Results showed that this method was suitable for electrochemical reduction of HAAs, up to 96%. 3) a reactive transport model was developed for interpretation of the experimental data and density functional theory simulations were conducted to evaluate relevant reaction mechanisms. 4) stable ClO-4 reduction was accomplished in the groundwater sample using the Re/REM system for 467 h, where ClO-4 concentrations were below the 10 ppb detection limit for the first 93.5 h and lower than the EPA guideline ClO-4 (56 ppb) for 374 h with constant permeate flux of 200 LMH and constant cathodic polarization of -1 V/SHE, and 5) mechanistic study of the electrocatalytic reduction mechanism of ClO-4 was conducted in aqueous and nonaqueous solutions.