Tannic Acid/Fe³⁺ Nanoscaffold for Interfacial Polymerization: Toward Enhanced Nanofiltration Performance

Abstract

Conventional thin-film composite (TFC) membranes suffer from the trade-off relationship between permeability and selectivity, known as the "upper bound". In this work, we report a high performance thin-film composite membrane prepared on a tannic acid (TA)-Fe nanoscaffold (TFC) to overcome such upper bound. Specifically, a TA-Fe nanoscaffold was first coated onto a polysulfone substrate, followed by performing an interfacial polymerization reaction between trimesoyl chloride (TMC) and piperazine (PIP). The TA-Fe nanoscaffold enhanced the uptake of amine monomers and provided a platform for their controlled release. The smaller surface pore size of the TA-Fe coated substrate further eliminated the intrusion of polyamide into the substrate pores. The resulting membrane TFC showed a water permeability of 19.6 ± 0.5 L m h bar, which was an order of magnitude higher than that of control TFC membrane (2.2 ± 0.3 L m h bar). The formation of a more order polyamide rejection layer also significantly enhanced salt rejection (e.g., NaCl, MgCl, NaSO, and MgSO) and divalent to monovalent ion selectivity (e.g., NaCl/MgSO). Compared to conventional TFC nanofiltration membranes, the novel TFC membrane successfully overcame the longstanding permeability and selectivity trade-off. The current work paves a new avenue for fabricating high performance TFC membranes.

Ultrathin Membranes: A New Opportunity for Ultrafast and Efficient Separation

“…Among recently reported ultrathin membranes, the most promising materials for OSN are the PA and DLC membranes 2,11. It is worth noting that ultrathin PA membranes are also widely used for water filtration 12–19. Other promising ultrathin membranes for water filtration include those constructed by proteins,7 single‐walled carbon nanotubes (SWCNT),21–24 metal oxide nanowires,25,26 metal hydroxide nanostrands,27–30 graphene nanosheets,31,32 graphene oxide (GO) nanosheets,33–38 WS 2 nanosheets,40 and MoS 2 nanosheets 41…”

“…Aside from OSN, TFC membranes are also widely used in water desalination and wastewater purification 12–19. Because the PA active layer determines the separation performance of the TFC membrane, the construction of an ultrathin and high‐quality PA active layer is critical for producing an advanced TFC membrane with high water permeance and solute rejection.…”

“…Compared with conventional ultrafiltration membrane support layers, the nanomaterial‐based networks have higher porosity, more uniform pores, and smoother surfaces, which enable a more homogeneous distribution and diffusion of monomers during the IP reaction, allowing more precise control over PA layer formation. The development of TFC NF membranes with ultrathin PA active layers break through the longstanding “tradeoff” relationship between permeance and salt rejection in TFC membranes and bring NF membrane performance to a new level 14,18,19. TFC forward osmosis (FO) membranes with ultrathin PA active layers can also be fabricated using a PD‐SWCNT network membrane as a support layer 16.…”

“…For instance, by using a porous nanostrand membrane as a sacrificial layer, polyamide (PA) membranes as thin as 8.4 nm and diamond‐like carbon (DLC) membranes with thickness down to 10 nm were fabricated via interfacial polymerization (IP) reaction and chemical vapor deposition (CVD), respectively 2,11. Moreover, a series of thin‐film composite (TFC) membranes with a PA active layer less than 15 nm were fabricated via IP reaction on porous nanostrands or nanotube support membranes 12–19. 1D (such as nanotubes,20–24 nanowires,25,26 and nanostrands27–30) and 2D nanomaterials (such as graphene nanosheet derivatives31–38 and metal sulfide nanosheets39,40) have also been widely adopted to fabricate ultrathin network or laminar membranes with thickness of tens of nanometers via vacuum filtration.…”

Effect of Porous and Nonporous Nanostructures on the Permeance of Positively Charged Nanofilm Composite Membranes

“…Indeed, through introducing voids and interlayer composite structures, high flux composite membranes are also developed recently. [11,33,[46][47][48][49][50][51][52] TFN nanofiltration membranes [53] with a high loading of TiO 2 nanoparticles (0-9 wt%) was developed in the earlier days; however, the nanoparticle loading remains inconclusive as an extremely poor rejection of MgSO 4 (≈95%) was achieved because of less crosslinked polyamide structure formed under 5 wt% loading. Incorporation of cellulose nanocrystals (CNCs) enhanced hydrophilicity and increased permeability.…”