Harnessing Structure-Dependent Separation Behavior of Thin Film Membranes

In obtaining highly permeable and selective membranes for separation processes, it is important to achieve well-defined structures in membranes through a detailed understanding of the processing-structure-property relationships. The layer-by-layer (LbL) framework allows us to synthesize membranes with controlled structure and chemistry. Using this framework, two different thin film membranes were synthesized: polyamide membranes embedded with graphene oxide nanoplatelets (GONPs) and carbon nanodots (CNDs) membranes. The GONPs-containing membranes were investigated for water desalination, and the incorporation of GONPs in polyamide membranes resulted in an increase in surface hydrophilicity and salt rejection properties but not a significant increase in flux compared to pristine membranes. Further, upon exposure to chlorine, GONPs embedded membranes retained salt rejection performance better than the pristine membranes, indicating increased chlorine resistivity of membranes. The CNDs containing membranes were obtained by reacting amine-functionalized CNDs with trimesoyl chloride and were also investigated for organic solvent nanofiltration applications. The synthesized membranes manifested high selectivity (up to 90%) when tested for dye molecules such as brilliant blue and disperse red in methanol. Taking advantage of the distinct fluorescence properties of CNDs and the films built with those, a crack in the film can be easily detected. This property can be harnessed for diagnostic purposes, such as tracking mechanical failure and fouling of the membrane.