(351g) Synthesis and Characterization of Fully Aromatic and Semi-Aromatic Polyamide Reverse Osmosis Membranes

Reverse osmosis (RO) membranes are the gold standard for water desalination and have been in use for over 30 years. In last three decades, an ample amount of work has been done to enhance the performance of RO polyamide membranes by changing the membrane surface chemistry, adding nanomaterials in and to, and altering the morphology of the polyamide separation layers. The morphology and structure of the polyamide layer is governed by the interfacial polymerization reaction between the amine monomer and the acid chloride monomer. The solubility and diffusivity of the monomers during the interfacial polymerization reaction affects the morphology and network structure. Thus, gaining fundamental knowledge on how the monomers affect the structure and morphology of the separation layer on molecular scale is very important because we do not fully understand the separation mechanism on a molecular level of these RO membranes. Additionally, current RO membranes do not reject neutral, small uncharged organic molecules to a level to produce potable water, especially at near neutral pH, which requires the synthesis of RO membranes with novel chemistries. In this work, we synthesized aromatic and the semi-aromatic polyamide RO membrane separation layers via the interfacial polymerization reaction between an amine monomer (m-phenylenediamine and 1,3-diaminopropane were used for aromatic and semi-aromatic polyamide layers, respectively) and an acid chloride monomer (trimesoyl chloride). The synthesized membranes were characterized using SEM, ATR-FTIR, contact angle, and positron annihilation lifetime spectroscopy (or PALS). Membranes were performance tested for water permeance, salt rejection, and neutral, small uncharged organic molecule (urea and boric acid) rejection. Polymerization conditions such as monomer concentration and polymerization time were varied to determine how each affects the polyamide separation layer. By understanding the fundamental reason(s) why different amine monomers and polymerization conditions affect polyamide separation layer morphology and structure, and therefore the desalination performance on the molecular level, RO membranes can be engineered to make membrane-based separation processes more energy-efficient and cost-effective.