Predictable Self-Assembly as an Unexplored Key Factor Influencing Membrane Separation: Insights from Monophenols

While nanofiltration (NF) holds promise for separating small molecules, effectively separating structurally similar compounds like monophenols remains challenging. This study unveils a novel NF separation strategy based on the often-overlooked phenomenon of solute self-assembly. Using a combination of experimental and computational approaches, a direct link between monophenol self-assembly and rejection behavior during NF is established. The self-assembly of monophenols, primarily driven by π-π stacking interactions, is shown to significantly influence their rejection rates, with larger, more numerous self-assemblies experiencing higher rejection. Furthermore, a clear relationship between monophenol structures and self-assembly strength is established, revealing that the number and Hydrogen (H)-bonding capacity of substituents on the aromatic ring dictate the propensity for self-assembly. This insight enables the development of a predictive model for monophenol self-assembly, which is validated through NF experiments using binary mixtures, confirming that predictable differences in self-assembly behavior can be leveraged for selective separation. This study establishes solute self-assembly as a tunable parameter for enhancing NF separation of similarly sized molecules.