How Does Alkali Etching Work on the Polyamide Membrane to Obtain an m-Phenylenediamine-Based NF Membrane?

Abstract

Fully aromatic polyamide (PA) membranes have been studied as nanofiltration (NF) membranes for decades because of their good chemical stability, but most of the membranes suffered from poor permeability and high rejection for monovalent ions. In this paper, an m-phenylenediamine (MPD)-based NF membrane was prepared by alkali activation on a reverse osmosis (RO) membrane. Characterization revealed the different etching paths on RO membranes fabricated by different concentrations of monomers of interfacial polymerization. The looser PA layer of RO membrane fabricated by lower-concentration monomers was easily invaded by NaOH molecules because of the higher molecular weight cutoff of 254 Da, which resulted in the transformation of separation grade from RO to NF. At the same time, the MPD-based NF membrane exhibited superior water permeability and pH resistance compared with a PIP-based membrane, which showed a potential to realize large-scale application in practical industry settings. It also provided a facile method for the preparation of a high-performance NF membrane with good chemical stability.

Effects of Porogen PEG and Pore Structure of PVDF Substrates on the Permeability–Selectivity Trade-off of TFC-NF Membranes

“…Combined with the TFC performance, the TFC membranes with rougher PA surfaces have higher ion rejection and selectivity, whereas those with smooth surfaces do not. These results are consistent with previous reports that the rougher morphologies with nano-foamed features can result in remarkable improvements in salt rejection. ,− …”

Polyamide-Based Ion Exchange Membranes: Cation-Selective Transport through Water Purification Membranes

“…The stability of PA-based membrane operating in alkaline conditions over the long term requires further research and improvement. Some research efforts have shown promise on developing alkali-resistant PA membranes, ,− which could address the stability challenge and promote the application of PA-based membranes in electrochemical flow systems.…”

Nitrate rejection of sulfonic acid group incorporated polyethersulfone‐type nanofiltration membrane and reutilization of the concentrated solution

“…39 In general, for the fabrication of NF surface ultrathin via an interfacial polymerization process, two systems, that is, piperazine-trimesoyl chloride (PIP-TMC) and m-phenylenediamine-trimesoyl chloride (MPD-TMC) can be adopted. 40,41 The PIP-TMC system will offer a large water permeation flux, but the rejection of monovalent ions is ineffective; for the MPD-TMC system, the case is just the reverse. Therefore, with respect to the desirable water permeation flux and monovalent ion rejection, the tradeoff of above-mentioned two systems had better be seriously considered.…”

“…In general, for the fabrication of NF surface ultrathin via an interfacial polymerization process, two systems, that is, piperazine‐trimesoyl chloride (PIP‐TMC) and m ‐phenylenediamine‐trimesoyl chloride (MPD‐TMC) can be adopted 40,41 . The PIP‐TMC system will offer a large water permeation flux, but the rejection of monovalent ions is ineffective; for the MPD‐TMC system, the case is just the reverse.…”