Controllable Interfacial Polymerization for Nanofiltration Membrane Performance Improvement by the Polyphenol Interlayer

Abstract

It is a huge challenge to have a controllable interfacial polymerization in the fabrication process of nanofiltration (NF) membranes. In this work, a polyphenol interlayer consisting of polyethyleneimine (PEI)/tannic acid (TA) was simply assembled on the polysulfone (PSf) substrate to fine-tune the interfacial polymerization process, without additional changes to the typical NF membrane fabrication procedures. In addition, three decisive factors in the interfacial polymerization process were examined, including the diffusion kinetics of fluorescence-labeled piperazine (FITC-PIP), the spreading behavior of the hexane solution containing acyl chloride, and the polyamide layer formation on the porous substrate by in situ Fourier transform infrared (FT-IR) spectroscopy. The experimental results demonstrate that the diffusion kinetics of FITC-PIP is greatly reduced, and the spreading behavior of the hexane solution is also impeded to some extent. Furthermore, in situ FT-IR spectroscopy demonstrates that by the mitigation of this PEI/TA interlayer, the interfacial polymerization process is greatly controlled. Moreover, the as-prepared NF membrane exhibits an increased water permeation flux of 65 L m –2 h –1 (at the operation pressure of 0.6 MPa), high Na 2 SO 4 rejection of >99%, and excellent long-term structural stability.

Probing the charged nature and ion-exclusion mechanism of fluorine-enriched non-ionogenic polyamide derived thin film composite nanofiltration membranes

“…The bands with lower intensities located at 1375 and 1373 cm À1 correspond to the C-N stretching vibration (n C-N ) of tertiary amide segments of the polyamide structures. 31,36,37 The peaks with higher intensities appearing around 1243 cm À1 and the shoulder peak appearing at 1166 cm À1 for both the membranes are assigned to the symmetric (n Sym. ) and asymmetric (n Asym. )…”

Monitoring the Interfacial Polymerization of Piperazine and Trimesoyl Chloride with Hydrophilic Interlayer or Macromolecular Additive by In Situ FT-IR Spectroscopy

“…The TA/PEI interlayer was fabricated on the porous substrate via Michael addition or Schiff base reaction between the amino groups and quinone groups [31]. TA (2.0 mg/mL) was dissolved in a Bicine buffer solution (pH = 7.8), then PEI (2.0 mg/mL) was added in the solution.…”

“…Additionally, Ren et al used FT-IR microscopy for IP reaction of microporous polymer film formed in the aqueous/organic interface for polyesterification by choosing the adequate phenol monomer [29]. Yang et al reduced the IP reaction rate of piperazine (PIP) and trimesoyl chloride (TMC) reaction system to a certain extent by introducing interlayers between the porous substrate and the polyamide layer [30][31][32]. Tan et al added the macromolecular additive of polyvinyl alcohol (PVA) in the aqueous solution of PIP and obtained the Turing structure [33].…”

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.…”