Hydrophilic Silver Nanoparticles Induce Selective Nanochannels in Thin Film Nanocomposite Polyamide Membranes

Thin-film nanocomposite (TFN) membranes have been widely studied over the past decade for their desalination applications. For some cases, the incorporation of nonporous hydrophilic nanofillers has been reported to greatly enhance membrane separation performance, yet the underlying mechanism is poorly understood. The current study systematically investigates TFN membranes incorporated with silver nanoparticles (AgNPs). For the first time, we reveal the formation of nanochannels of approximately 2.5 nm in size around the AgNPs, which can be attributed to the hydrolysis of trimesoyl chloride monomers and thus the termination of interfacial polymerization by the water layer around each hydrophilic nanoparticle. These nanochannels nearly tripled the membrane water permeability for the optimal membrane. In addition, this membrane showed increased rejection against NaCl, boron, and a set of small-molecular organic compounds (e.g., propylparaben, norfloxacin, and ofloxacin), thanks to its combined effects of improved size exclusion, enhanced Donnan exclusion, and suppressed hydrophobic interaction. Our work provides fundamental insights into the formation and transport mechanisms involved in solid-filler incorporated TFN membranes. Future studies should take advantage of this spontaneous nanochannel formation in the design of TFN to overcome the classical membrane permeability-selectivity trade-off.