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

Abstract

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.

Fabrication of desalination membranes by interfacial polymerization: history, current efforts, and future directions

“…For example, a recent study has observed the presence of non-selective defect channels with a size of B2 nm between embedded silver nanoparticles and polyamide matrix (Fig. 6A), 32 which are detrimental to membrane water-salt selectivity. Although modifying fillers with hydrophobic materials may enhance their miscibility in the polyamide matrix and thus inhibit the formation of the defect channels, 33 the high liquid entry pressure (LEP) in these hydrophobic nanopores would provide additional resistance to water transport.…”

Nanofiltration for separation and purification of saccharides from biomass

“…Incorperation of nanoparticles (NPs) (i.e., CuNPs, AgNPs, GONPs etc.) into coating layer results in formation of nanochannels for improving the membrane permeability without compro- mising the membrane selectivity [122]. The future direction of membrane modification technique will be focused on development of new methods that can be implemented in large-scale membrane fabrication through considering the stability and operating costs.…”

Nanoclays‐Incorporated Thin‐Film Nanocomposite Membranes for Reverse Osmosis Desalination

“…Thin‐film nanocomposite (TFN) membranes, a new type of nanotechnology‐enhanced membranes, are studied as a promising candidate for desalination purposes. [ 5,6,20–22 ] Many nanoparticles, such as zeolites, [ 6,23–25 ] silica, [ 26,27 ] metal‐organic frameworks−covalent‐organic frameworks (MOFs−COFs), [ 28–30 ] carbon nanotubes, [ 31,32 ] and carbon−graphene oxide quantum dots, [ 33–35 ] have been incorporated into the polyamide matrix of TFN membranes to increase membrane hydrophilicity and provide additional water pathways. [ 36 ] Nevertheless, most of the nanoparticles used are produced in laboratory scale and the yield is relatively low, which is difficult to scale up for commercialization when taking economic viability into account.…”