Development of nanofiltration membranes using mussel-inspired sulfonated dopamine for interfacial polymerization

Nonpreferential Solvent Transport through an Intrinsic Cyclodextrin Pore in a Polyester Film

We performed equilibrium molecular dynamics simulations to study the transport of water and hexane solvents through cyclodextrin(CD)-based membranes (α-/β-/γ-CD/TMC). Although it is known that water and hexane can permeate through the macrocyclic cavity, surprisingly, when it is present in the CD-based membrane (α-/β-/γ-CD/TMC), these solvents are not permeating through the CD cavity. Interactions between membrane functional group atoms with the water and hexane suggest that these solvents primarily permeate through the polar aggregate pores formed via ester-linkage rather than the CD cavity. Our observation reveals that both solvents can permeate through the membrane; however, the hexane flux was one order of magnitude lower than water flux. Our study suggests that further work is needed to confirm the functional significance of the macrocyclic cavity in solvent permeation and the existence of Janus pathways.

Polyester Nanofiltration Membranes for Efficient Cations Separation

Polyester nanofiltration membranes highlight beneficial chlorine resistance, but their loose structures and negative charge result in poor cations retention precluding advanced use in cations separation. This work designs a new monomer (TET) containing "hydroxyl-ammonium" entities that confer dense structures and positive charge to polyester nanofiltration membranes. The TET monomer undergoes efficient interfacial polymerization with the trimesoyl chloride (TMC) monomer, and the resultant TET-TMC membranes feature one of the lowest molecular weight cut-offs (389 Da) and the highest zeta potential (4 mv, pH: 7) among all polyester nanofiltration membranes. The MgCl2 rejection of the TET-TMC membrane is 95.5%, significantly higher than state-of-the-art polyester nanofiltration membranes (<50%). The Li+ /Mg2+ separation performance of TET-TMC membrane is on par with cutting-edge polyamide membranes, while additionally, the membrane is stable against NaClO though polyamide membranes readily degrade. Thus the TET-TMC is the first polyester nanofiltration membrane for efficient cations separation.

A mucus-inspired solvent-free carbon dot-based nanofluid triggers significant tribological synergy for sulfonated h-BN reinforced epoxy composites

Nano-filler reinforced polymer-based composites have attracted extensive attention in tribology; however, to date, it is still challenging to construct a favorable lubricating system with excellent compatibility, lubricity and durability using nano-filler reinforced polymer-based composites. Herein, sulfonated boron nitride nano-sheets (h-BN@PSDA) are prepared and used as nano-fillers for epoxy resins (EPs), to improve friction and wear along with thermal conductivity. Furthermore, inspired by the lubricating principle and structure of snail mucus, a solvent-free carbon dot-based nanofluid (F-CDs) is fabricated and used for the first time as the lubricant for h-BN@PSDA/EPs. Both poly (4-styrene sulfonate) and polyether amine grafted on the surface of F-CDs contribute to branched structures and multiple interfacial absorption effects. Extraordinarily low friction and wear are detected after long-term sliding. The average coefficient of friction and wear rate of h-BN@PSDA/EPs composites are reduced by 95.25% and 99.42% respectively, in the presence of the F-CD nanofluid, compared to that of EPs. Besides, the added h-BN nano-sheets increase the thermal conductivity (TC) of EPs from 0.178 to 0.194 W (m-1 K-1). The distinguished lubrication performances are likely due to the formation of a hybrid nanostructure of 0D F-CDs and 2D h-BN@PSDA together with the "rolling-sliding" and "self-mending" effects of added F-CDs.

Enhancing Stability of Tannic Acid-FeIII Nanofiltration Membrane for Water Treatment: Intercoordination by Metal-Organic Framework

Tannic acid (TA)-Fe^III nanofiltration (NF) membrane has been demonstrated to possess more favorable removal of trace organic contaminants (TrOCs) over the conventional polyamide NF membrane. However, the drawback of acid instability severely hinders the practical application of TA-Fe^III NF membrane in the treatment of (weak) acidic wastewater containing TrOCs (e.g., pharmaceutical wastewater, surface water, and drinking water). Herein, we introduced the MIL-101(Cr) nanoparticle, a kind of metal-organic framework (MOF), into the TA-Fe^III selective layer to enhance the membrane acid stability. The acid-tolerance parameter of MIL-101(Cr)-stabilized TA-Fe^III membrane (TA-Fe^III-MOF membrane, 12,000 ppm/s^-1) was two orders of magnitude larger than that of the TA-Fe^III membrane (50 ppm/s^-1), and the TA-Fe^III-MOF membrane can withstand acid treatment at pH = 4 for more than 30 days. Meanwhile, the TA-Fe^III-MOF membrane displayed increased water permeance from 9.5 to 12.7 L/(m²·h·bar) after the MOF addition, without compromising the selectivity. The enhanced acid stability for the TA-Fe^III-MOF membrane was ascribed to an intercoordination mechanism, where Fe^III centers (from TA-Fe^III complex) coordinated with -COOH groups (from terephthalic acid of MOF) and Cr^III centers (from MOF) coordinated with -OH groups (from TA of TA-Fe^III complex), which was verified by the density functional theory calculation. This study highlights a new approach for the development of a TA-Fe^III-based NF membrane with markedly enhanced acid stability, which is important for its real application in wastewater treatment and water reuse.

Nafion Composite Membranes Impregnated with Polydopamine and Poly(Sulfonated Dopamine) for High-Performance Proton Exchange Membranes

We prepared Nafion composite membranes by impregnating Nafion-212 with polydopamine, poly(sulfonated dopamine), and poly(dopamine-co-sulfonated dopamine) using the swelling-filling method to generate nanopores in the Nafion framework that were filled with these polymers. Compared to the pristine Nafion-212 membrane, these composite membranes showed improved thermal and mechanical stabilities due to the strong interactions between the catecholamine of the polydopamine derivatives and the Nafion matrix. For the composite membrane filled with poly(sulfonated dopamine) (N-PSDA), further interactions were induced between the Nafion and the sulfonic acid side chain, resulting in enhanced water uptake and ion conductivity. In addition, filling the nanopores in the Nafion matrix with polymer fillers containing aromatic hydrocarbon-based dopamine units led to an increase in the degree of crystallinity and resulted in a significant decrease in the hydrogen permeability of the composite membranes compared to Nafion-212. Hydrogen crossovers 26.8% lower than Nafion-212 at 95% relative humidity (RH) (fuel cell operating conditions) and 27.3% lower at 100% RH (water electrolysis operating conditions) were obtained. When applied to proton exchange membrane-based fuel cells, N-PSDA exhibited a peak power density of 966 mW cm^-2, whereas N-PSDA showed a current density of 4785 mA cm^-2, which is 12.4% higher than Nafion-212 at 2.0 V and 80 °C.

Hybrid hydrogels derived from renewable resources as a smart stimuli responsive soft material for drug delivery applications

The design and synthesis of amphiphilic molecules play a crucial role in fabricating smart functional materials via self-assembly. Especially, biologically significant natural molecules and their structural analogues have inspired chemists and made a major contribution to the development of advanced smart materials. In this report, a series of amphiphilic N-acyl amides were synthesized from natural precursors using a simple synthetic protocol. Interestingly, the self-assembly of amphiphiles 6a and 7a furnished a hydrogel and oleogel in vegetable oils. Morphological analysis of gels revealed the existence of a 3-dimensional fibrous network. Thermoresponsive and thixotropic behavior of these gels were evaluated using rheological analysis. A composite gel prepared by the encapsulation of curcumin in the hydrogel formed from 7a displayed a gel-sol transition in response to pH and could act as a dual channel responsive drug carrier.

Multirole Regulations of Interfacial Polymerization Using Poly(acrylic acid) for Nanofiltration Membrane Development

Effective control of monomer diffusion and reaction rate is the key to achieving a controlled interfacial polymerization (IP) and a high-performance nanofiltration (NF) membrane. Herein, an integration of multirole regulations was synchronously realized using poly(acrylic acid) (PAA) as an active additive in a piperazine (PIP) aqueous phase. Thanks to synergistic interactions, including hydrogen bonding, electrostatic interaction, and covalent bonding between PAA and PIP molecules, together with the increased viscosity of the solution, PIP diffusion was rationally controlled. Moreover, interfacial polycondensation was also restrained via the modestly reduced pH of the aqueous solution. These contribute to the formation of a thinner, looser, more hydrophilic, and higher negatively charged PAA-decorated polyamide selective layer with a unique nanostrand-nodule morphology. The harvested NF-PAA/PIP membrane showed an ∼70% rise in water permeability (up to 23.5 L·m-2·h-1·bar-1) while retaining high Na2SO4 and dye rejections. Furthermore, the optimized NF-PAA/PIP membrane presented a superior fouling resistance capability for typical pollutants, as well as long-term stability during successive filtration. Thus, this work offers a straightforward and impactful approach to regulating IP and promoting NF membrane properties.

Naturally Extracted Hydrophobic Solvent and Self-Assembly in Interfacial Polymerization

Pharmaceutical, chemical, and food industries are actively implementing membrane nanofiltration modules in their processes to separate valuable products and recover solvents. Interfacial polymerization (IP) is the most widely used method to produce thin-film composite membranes for nanofiltration and reverse osmosis processes. Although membrane processes are considered green and environmentally friendly, membrane fabrication has still to be further developed in such direction. For instance, the emission of volatile solvents during membrane production in the industry has to be carefully controlled for health reasons. Greener solvents are being proposed for phase-separation membrane manufacture. For the IP organic phase, the proposition of greener alternatives is in an early stage. In this work, we demonstrate the preparation of a high-performing composite membrane employing zero vapor pressure and naturally extracted oleic acid as the IP organic phase. Its long hydrophobic chain ensures intrinsic low volatility and acid monomer dissolution, while the polar head induces a unique self-assembly structure during the film formation. Membranes prepared by this technique were selective for small molecules with a molecular weight cutoff of 650 g mol^-1 and a high permeance of ∼57 L m^-2 h^-1 bar^-1.

Surface Coatings via the Assembly of Metal-Monophenolic Networks

Mussel-inspired surface modification has received significant interest in recent years because of its simplicity and versatility. The deposition systems are still mainly limited to molecules with catechol chemical structures. In this paper, we report a novel deposition system based on a monophenol, vanillic acid (4-hydroxy-3-methoxybenzoic acid), to fabricate metal-phenolic network coatings on various substrates. The results of the water contact angle and zeta potential reveal that the modified polypropylene microfiltration membrane is underwater superhydrophobic and positively charged, showing applications in oil/water separation and dye removal. Furthermore, the single-face modified Janus membrane is promising in switchable oil/water separation. The results demonstrate a novel example of the metal-monophenolic deposition system, which expands the toolbox of surface coatings and facilitates the understanding of the deposition of phenols.