Ultrastable Nanofiltration Membranes Engineered by Polydopamine-Assisted Polyelectrolyte Layer-by-Layer Assembly for Water Reclamation

Abstract

The layer-by-layer (LBL) electrostatic assembly is an effective method for fabricating high-performance nanofiltration (NF) membranes. However, the structural integrity of the separation layers can be compromised in strong acid and alkaline conditions, which limits their applications in water reclamation. Herein, we presented novel ultrastable LBL-based NF membranes engineered by mussel-inspired “bio-glue” polydopamine (PDA)-assisted polyelectrolyte LBL deposition (PDA-a-LBL) technique. Through alternative deposition of PDA/polyethylenimine (PEI) and poly­(sodium 4-styrenesulfonate) (PSS) layers onto polyethersulfone (PES) ultrafiltration substrates, tailorable pore size and tunable surface chemistry were achieved. The hydrophilicity and surface charge properties of the NF membranes were dependent on the functionality of the outermost layer. The novel PDA-a-LBL NF membranes presented molecular weight cut-off (MWCO) of 275–430 Da and more than 94% rejections against divalent anions along with pure water permeability of 7–13 L m–2 h–1 bar–1, which were competitive with the currently reported LBL-based NF membranes and commercial FilmTec NF-270 membrane. Significantly, the newly developed NF membrane (PES-50-3L) exhibited remarkable chemical stability in the pH range of 2–11, ascribing to the synergistic effects of covalent bonds, electrostatic interaction, and π–π stacking between PDA/PEI and PSS layers. In addition, the membrane exhibited robust performance in a continuous, 1 week long-term operation, demonstrating its great potential for sustainable water reclamation. Our findings may shed light on the future design of novel LBL-based NF membranes with enhanced chemical stability.

Engineering Antifouling Nanofiltration Membranes Using Amino-Quinone Networks–Phytic Acid Pseudo Zwitterionic Clusters for Water Treatment

“…The concentrations of salts and PEGs were measured by conductivity meter (DDSJ-308A, Leici, China) and total organic carbon analyzer (TOC-L, Shimadzu, Japan), respectively. Calculations of pure water permeability (PWP) and salt rejection can be referred to our previous studies …”

“…The details about the membrane fouling test have been reported elsewhere in the literature. , The filtration procedures included four steps: compaction, conditioning, fouling, and cleaning, as stated in our previous study . Briefly, the membrane was compacted using ultrapure water at 12 bar until the flux reached a steady sate.…”

“…Importantly, no stringent environment limits on LBL assembly compared with current zwitterionic modification methods. In addition, inspired by mussel and natural plants (e.g., walnuts and nepenthes), catechol-containing compounds have been introduced to surface modification owing to their strong adhesion and excellent hydrophilicity. − Our previous study reported a novel and chemical-stable NF membrane fabricated via polydopamine (PDA) assisted polyelectrolytes LBL assembly . However, the dopamine (DA) oxidation and polymerization largely depend on solution environments (e.g., dissolved oxygen, solution pH, and temperature), , and the PDA coatings are usually uneven due to forming large aggregates. , Although adding oxidants could improve the PDA deposition rate and uniformity, effective and precise-control surface coating strategies are urgent development …”

Upcycling agricultural waste into membranes: from date seed biomass to oil and solvent-resistant nanofiltration

“…The use of PDA catechol chemistry has been proved to enhance the long-term stability of NF membranes in strong alkaline and acidic conditions. 22 In addition, the layer-by-layer dip-coating method to prepare PDA-coated membranes is a simple way to increase membrane rejection, hydrophilicity, solvent stability, antifouling, and antibacterial performance. 20 Therefore, we postulated that coating biomass-based membranes with PDA could improve their separation performance.…”

Tuning the Biodegradability of Chitosan Membranes: Characterization and Conceptual Design

“…Membrane-based processes have been playing an important role in achieving sustainable development. − However, the current majority of commercially available membranes are fabricated using fossil-based polymers that are, to a great extent, nonrenewable resources. Most of these fossil-based polymers are difficult to naturally decay; the replacement of aging membranes would create an extra burden on the environment.…”