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

Abstract 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.