Catalytic Membranes for Drinking Water Treatment

The contamination of drinking water by oxyanions such as nitrate (NO3?), nitrite (NO2?), and bromate (BrO3?) presents a challenge for public health and water treatment systems due to their high solubility, persistence, and toxicity. Conventional treatment technologies often struggle with effective removal, frequently producing secondary waste that require additional treatment. This research addresses these limitations by exploring catalytic membrane systems, specifically the development and characterization of membranes embedded with palladium (Pd) nano catalysts for the hydrogenation and reduction of oxyanions in water.
The first objective of this work was to synthesize and characterize catalytic membranes that reduced contaminants in water while minimizing the use of precious metals. Poly(4-vinylpyridine) (P4VP) and its quaternized form (P4VP?) were used as polymeric supports to immobilize Pd species. Through controlled fabrication methods, nanoparticles were achieved and characterized using a range of advanced techniques including XPS, TEM, SEM, and ICP. Catalytic performance was evaluated via bromate removal experiments, demonstrating that membranes with well-dispersed Pd sites exhibited significant activity.
The second objective was to model the relationship between mass transfer and reaction kinetics within catalytic membranes, particularly accounting for variable pore size distributions. A mathematical model was developed to simulate the catalytic hydrogenation process across membranes with either uniform or variable pore structures. The modeling results revealed that membranes with broader pore size distributions experience more complex trade-offs between mass transfer resistance and reaction rates. High Damköhler (Da) and Stanton (St) numbers were correlated with optimal catalytic performance, and the analysis provided key design criteria to maximize contaminant conversion while minimizing residence time and material costs.
The third objective focused on evaluating the stability and availability of hydrogen, the critical electron donor in hydrogenation reactions. Various hydrogen delivery systems were tested, including commercial hydrogen-generating devices and a nanobubble generator. Hydrogen stability was assessed under different ionic strength conditions. The results showed that nanobubbles provided sustained hydrogen presence in water over extended periods, though their stability was highly sensitive to salinity.
Together, these studies demonstrate that catalytic membranes supported with Pd nano catalysts offer a promising pathway for the effective removal of oxyanions from drinking water sources. The research highlights the importance of membrane structure optimization, catalyst dispersion control, and hydrogen delivery management in advancing catalytic water treatment technologies.