Anti(-bio)fouling Nanostructured Membranes Based on the Cross-Linked Assembly of Stimuli-Responsive Zwitterionic Microgels

Abstract

This study embodies the development of a thermoresponsive nanostructured antifouling membrane based on cross-linkable zwitterionic microgels for tunable water filtration and molecular separation applications. The zwitterionic vinylimidazole propane sultone (VIPS) comonomer was synthesized by reacting vinylimidazole with 1,3-propane sultone. The microgels were synthesized utilizing a one-step precipitation polymerization approach by taking 10 and 20 wt % of the VIPS with N-isopropyl acrylamide (NIPAm), 2-aminoethyl methacrylate (AEMA), with the cross-linker N,N′-methylene bis­(acrylamide) (BIS) to produce MG-10 and 20, respectively. Various chemical and morphological characterizations were carried out to establish the synthesis and characteristics of microgels. Suction filtration of a dilute MG-20 dispersion was used to construct cross-linked microgel membranes of different thicknesses over a track-etched membrane support in the next step. Surface and morphological analyses validate the packed microgel layer formation. The constructed layer was temperature-switchable, resulting in a twofold increase in water flux from room temperature to 40 °C. The thin and closely packed microgel particles resulted in a sub-2 nm surface pore size, allowing for strong rejection (>99%) of small molecules. Because of the presence of VIPS, both of the microgels displayed excellent anti­(-bio)­fouling properties against bacterial and protein foulants. The surface demonstrated ultralow protein adsorption and a high flux-recovery ratio (>90%), resulting in antifouling performance. The stability of the cross-linked robust microgel layer without any leaching warrants dimensional stability and long-term permeability. This smart gating membrane with improved anti­(-bio)­fouling activity expands the scope of thermoresponsive microgel-based nanostructured membranes and has significant potential in water purification and molecular separation applications.

Advanced stimuli-responsive membranes for smart separation

“…190 This strategy could be further extended to the synthesis of stimuli-responsive membranes from other nanoparticles. [191][192][193] For instance, Jia et al demonstrated the fabrication of a thermo-responsive nanosheet membrane from Zn-tetrakis(4carboxyphenyl) porphyrin MOF nanosheet. 131 In this study, PVCL and polyvinylpyrrolidone (PVP) were used as intercalators between the nanosheets, which provided the MOF nanosheet membrane with exceptional thermo-responsive separation performance, driven by the reversible conformation change of PVCL chains, along with excellent structural stability, ascribed to the constant interlayer spacing enabled by PVP chains.…”

Responsive microgels and microgel assemblies in biocatalytic applications

“…Microgel immobilization on porous membranes provides an efficient strategy to develop membranes with integrated functions like smart-gating, stimuli-reversible and self-cleaning behaviors. 105,106 Additionally, to enhance the activity of immobilized enzymes on hydrophobic membrane, where wetting of the membrane pores is often prevented, hydrophilic microgel coating is formed on the membrane, followed by the immobilization of enzyme. The microgels are known to provide hydrated microenvironment to the enzymes conjugated to the hydrophobic membrane.…”

Nanostructured Zwitterionic Membranes: Harnessing Temperature-Responsive Microgels for Tunable Water Filtration and Molecular Separation

“…The use of soft polymeric nanostructured materials can address these challenges and provide additional benefits to the membranes due to their active functional nature and tunability. In this context, the adoption of soft microgels, which are micrometer-sized three-dimensional soft, porous, and cross-linked polymeric structures, has become a major focus in designing ultrathin nanostructured membranes with adjustable separation and filtration properties. ,− Microgels offer three key advantages critical for achieving these properties. First, their internal porous structure, which selectively allows specific solvents and solutes to pass through, can be adjusted by varying the type and quantity of comonomers and the environmental conditions.…”