Polyamide Brush Active-Layer Membranes for Fundamental Understanding of Structure-Function Relationships in Thin-Film Composite Reverse Osmosis Membranes

Auburn University, Auburn AL

Investigators

Abstract

Nearly two-thirds of the world faces water scarcity due to growing populations and pollution. Membrane-based separations, such as reverse osmosis (RO), use up to 90% less energy than thermal methods like distillation and evaporation. This makes them an efficient way to increase freshwater supplies through desalination while minimizing environmental impact. Although current commercial RO polyamide membranes effectively remove salt from water, they are prone to biofouling, where bacteria form biofilms that reduce water production rates. Chlorine-based treatments can remove the biofilms, but the membrane will eventually disintegrate because the chlorinated chemicals break down the membrane's molecular structure. This research aims to better understand why RO polyamide membranes remove salt so effectively and use this knowledge to develop a new type of RO membrane that performs as well as current commercial membranes and resists chlorine damage. Additionally, this research's connection to real-world problems will be leveraged to inspire young students to pursue engineering careers and tackle challenges in their communities and worldwide. This research aims to investigate the hypothesis that weak intermolecular interactions play key roles in the performance of polyamide RO membranes. The effects of crosslinking, amide, benzyl, and carboxyl density will be explored by producing a highly tailorable, novel polyamide membrane comprised of a dense layer of brush polymers. This platform will incorporate proportions and densities of functional groups that mimic polyamide structures and properties through well-controlled, bottom-up synthesis using surface-initiated atom-transfer radical polymerization (SI-ATRP). Membrane performance will be assessed by measuring salt and water permeability and molecular weight cutoff while targeting selectivity comparable with commercial RO membranes. The control over membrane thickness and grafting density will also be exploited to hone membrane transport models. The findings will be used to develop an effective RO membrane that avoids the aromatic polyamide functional group, improving its resistance to chlorine. With the ability of SI-ATRP to sequentially produce block copolymers, other dense, uniformly distributed top layers will be considered for performance enhancement, including antifouling polyelectrolytes. The themes of this work will be incorporated into undergraduate chemical engineering courses and activities for science camps and workshops for high schoolers considering science, technology, and engineering fields. Further, the outcomes of this work have implications for designing defect-free biomimetic membranes for solute-solute separations, such as those used to recover valuable species like lithium for sustainable energy solutions. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.