Tailoring Polyamide Nanofiltration Membranes for the Removal of Environmental Micropollutants: Synergistic Diffusion-Reaction Modulation in Interfacial Polymerization
Zi Wang, Peng Liu, Zixin Wang, Hongzhi Liu, Gaoxin Dai, Shirong Li, Qian Zhao, Heng Liang, Langming Bai
Abstract
The presence of emerging micropollutants in surface waters necessitates the development of advanced separation technologies. However, conventional thin-film composite (TFC) nanofiltration membranes exhibit limited removal efficacy for organic micropollutants (OMPs) due to structural heterogeneities. This study pioneered quaternary ammonium carbon quantum dots (QACQDs) with dual functional roles of orchestration monomer diffusion and tuning the PA matrix introduced in the interfacial polymerization (IP) process, enabling molecular-level regulation of the polyamide (PA) layer microstructure, properties, and performance. Systematic characterization, including molecular dynamics (MD) simulations and positron annihilation spectroscopy (PAS), revealed that QACQDs synergistically slowed down the PIP diffusion rate while actively participating in IP cross-linking reactions, thereby crafting a PA layer with a denser matrix, uniform nanoporosity, lower carboxyl density, and ultrasmooth surface. The optimized membrane achieved a breakthrough performance with a 2-fold higher water permeance and 98% removal efficiency for structurally diverse OMPs. Molecular analyses further demonstrated that reduced mineral bridging via carboxyl minimization and hydrophilicity enhancement cooperatively strengthened interfacial repulsive forces by 2-5-fold, improving fouling resistance against organic substances and bacteria. Crucially, it maintains a stable performance in complex natural surface water. This work provides valuable guidance for fabricating high-performance nanofiltration membranes through ideal nanofiller construction and precision IP regulation, providing a sustainable pathway to address water security challenges.