Molecularly-Regulated Interfacial Polymerization to Engineer Selective Polyamide Reverse Osmosis Membranes

University Of Alabama Tuscaloosa, Tuscaloosa AL

Investigators

Abstract

Seawater desalination is the process of removing salts and dissolved solids from seawater. Energy-efficient seawater desalination offers many societal benefits such as accessible fresh water for drinking and agricultural irrigation and mitigating the environmental and human health impacts associated with regional water scarcity. Polyamide reverse osmosis (PARO) membranes are the workhorse technology of the seawater desalination industry. PARO membranes are fabricated using a chemical reaction called interfacial polymerization (IP) that occurs at the interface between a two-phase liquid system (e.g., oil and water). However, the IP technique lacks the control and precision needed to produce highly selective PARO membranes that can remove small organic contaminants from water. Surfactant molecules can be used within the IP process to improve PARO membrane selectivity. However, it is unclear how the surfactants change the molecular-level mechanisms of the IP process and which surfactants work best. A combined computational-experimental approach will be used to understand the effect of the surfactant molecular structure on the IP reaction and resultant membrane performance properties. This knowledge can be applied to produce PARO membranes with enhanced performance abilities. Graduate and undergraduate students will collaboratively execute research plans and participate in new courses related to water treatment and membranes. This project aims to enhance PARO membrane selectivity by investigating the structure-property relationships of monomeric and gemini surfactants and their effects on the IP reaction to create fully aromatic PARO membranes. Gemini surfactants are composed of at least two hydrophilic/functional head groups and two hydrophobic tails linked by a spacer at or near the head group. The investigators hypothesize that by understanding surfactant behavior during the surfactant-assisted IP reaction, it is possible to achieve a homogenous polyamide layer with sharp selectivity without sacrificing water permeance, particularly for challenging separations. This hypothesis will be tested through experiments informed by molecular dynamics simulations and machine learning methods. This project seeks to advance knowledge on the effects of monomer and gemini surfactant properties on m-phenylenediamine diffusion, the minimum area per surfactant, PARO membrane selectivity, and polyamide layer free volume hole and pore size distribution, all of which are needed for the fabrication of selective membranes. 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.