Highly Permeable Sulfonated Polydopamine Integrated MXene Membranes for Efficient Surfactant-Stabilized Oil-in-Water Separation

Enhancement of Mechanical, Thermal, and Barrier Behavior of Sustainable PECF Copolyester Nanocomposite Films Using Polydopamine-Functionalized MXene Fillers

The development of high-strength titanium carbide (Ti3C2Tx) MXene-PDA nanosheet-based sustainable poly(ethylene-co-1,4-cyclohexane dimethylene 2,5-furan dicarboxylic acid) (PECF) copolyester nanocomposites with superior tensile, thermal, and barrier properties is a promising avenue for advanced materials. However, achieving Ti3C2Tx MXene-based polyester nanocomposites that exhibit exceptional thermal conductivity, and enhanced mechanical and barrier properties remains a significant challenge. In this study, we employed self-assembly technology through layer-by-layer (LBL) coating to create highly saturated Ti3C2Tx MXene-PDA fillers that are uniformly dispersed and strongly bonded within the PECF matrix. This approach enabled the formation of dense nanocomposites with diverse functional properties. Specifically, MPP2 nanocomposites (0.3 wt %) demonstrated excellent mechanical performance, with a compressive tensile strength of 84 MPa and a modulus of 4.4 GPa, alongside remarkable O2, CO2, and H2O vapor barrier properties and superior thermal stability. Compared to pure PECF, the addition of Ti3C2Tx MXene-PDA at a loading of 0.3 wt % resulted in substantial improvements: a 30% increase in tensile strength, a 109% increase in modulus, and significantly enhanced barrier properties for O2 (27.3-times), CO2 (24.7-times), and H2O vapor (5.0-times). These findings highlight the potential of Ti3C2Tx MXene-PDA-reinforced PECF nanocomposites for high-performance applications, offering valuable insights for future materials development.

High-Flux Steady-State Demulsification of Oil-In-Water Emulsions by Superhydrophilic-Oleophobic Copper Foams with Ultra-Small Pores Under Pressure

3D superwetting materials struggle to maintain high-flux steady-state demulsification for oil-in-water emulsions because the accumulated oil within the material is difficult to discharge rapidly. The water flow shear force can swiftly remove the oil from the anti-fouling surface. In this study, by introducing nanofibers and carbon nanotubes and chemical modification, a superhydrophilic-oleophobic copper foam with pores of several micrometers is prepared, which can achieve a continuous demulsification process with steady-state flux over 57000 L m-2 h-1 for oil-in-water emulsions and rapid hydraulic-driven oil release under an additional pressure of 5 kPa. Thanks to the ultra-small pores of the copper foam, the steady-state demulsification efficiency can be still maintained at over 97.5%. During the demulsification process, the accumulation of oil and surfactants within the copper foam can be maintained at low levels, achieving dynamic equilibrium. With the aid of second-stage superhydrophilic copper mesh, the demulsified oil-water mixtures can be rapidly separated. This high-flux, steady-state, and efficient demulsification process shows great potential for industrial applications.

Improved Efficiency and Stability of MXene Membranes via Interlayer Space Tuning for Oily Water Separation

Surfactant-stabilized oil-in-water emulsions are a major environmental concern due to their severe consequences for aquatic organisms and humans. Two-dimensional materials, particularly MXenes, are widely used in various applications and could be used in designing advanced membranes. The narrow interlayer spacing and intrinsic oxidation severely limit mass diffusion and induce poor stability, respectively, of MXene-based separating layers on the membrane support, rendering it challenging to use for oil-water separation. Herein, a high-performing, minimally defective MXene membrane with large d-spacing was fabricated. The d-spacing of the MXene sheets was controlled using Si-based species as the intercalating agents. The modified MXene-based membrane (ultrasonication-assisted exfoliated MXene with Si pillars) (U-MX-Si) exhibited an enlarged interlayer spacing of 11 Å, increased surface energy of 41 mJ·m-2, and less defective separating layer compared to that of pristine MXene, which was due to enhanced interlayer spacing. This phenomenon induced a higher degree of exfoliated sheets that facilitated better MXene sheet self-assembly on the membrane support, thereby resulting in high separation efficiency (99%). An increase in the surface energy of the U-MX-Si membrane caused a constant permeate flux during operation, which demonstrated their practical implications. This study presents an important pathway for designing MXene-based membranes for separation applications.

Superhydrophilic Photothermal-Responsive CuO@MXene Nanofibrous Membrane with Inherent Biofouling Resistance for Treating Complex Oily Wastewater

MXene, a recently emerged 2D material, has garnered substantial attention for a myriad of applications. Despite the growing interest, there remains a noticeable gap in exploring MXene-based membranes for the simultaneous achievement of photomodulated oil/water separation, bacterial resistance, and the removal of pollutants in the treatment of oily wastewater. In this work, we have successfully synthesized a novel multifunctional CuO@MXene-PAN nanofibrous membrane (NFM) featuring unique nanograin-like structures. Benefitting from these unique structures, the resultant membrane shows excellent superwetting properties, significantly enhancing its performance in oil/water separation. In addition, the membrane's photothermal property boosts its permeance by 40% under visible light illumination within 30 min. Furthermore, the resultant membrane shows decent dye removal efficiency in an aqueous solution, e.g., Rhodamine B (RhB), promoting efficient degradation with high reusability under visible light. Most remarkably, the resultant membrane exhibits superior anti-biofouling capability and consistently resists the adhesion of microorganisms such as cyanobacteria over a 14 day period. Thus, the combined effect of superior superwetting properties, photothermal responsivity, photocatalytic activity, and the antibacterial effect in CuO@MXene-PAN NFM contributes to the efficient treatment of intricate oily wastewater. This synergistic combination of superior properties in the membrane could be an appealing strategy for the broad development of multifunctional materials to prevent fouling during actual separation performance.

Sulfonic Functionalized Polydopamine Coatings with pH-Independent Surface Charge for Optimizing Capillary Electrophoretic Separations

Enhancing the pH-independence and controlling the magnitude of electroosmotic flow (EOF) are critical for highly efficient and reproducible capillary electrophoresis (CE) separations. Herein, we present a novel capillary modification method utilizing sulfonated periodate-induced polydopamine (SPD) coating to achieve pH-independent and highly reproducible cathodic EOF in CE. The SPD-coated capillaries were obtained through post-sulfonation treatment of periodate-induced PDA (PDA-SP) coatings adhered on the capillary inner surface. The successful immobilization of the SPD coating and the substantial grafting of sulfonic acid groups were confirmed by a series of characterization techniques. The excellent capability of PDA-SP@capillary in masking silanol groups and maintaining a highly robust EOF mobility was verified. Additionally, the parameters of sulfonation affecting the EOF mobilities were thoroughly examined. The obtained optimum SPD-coated column offered the anticipated highly pH-independent and high-strength cathodic EOF, which is essential for enhancing the CE separation performance and improving analysis efficiency. Consequently, the developed SPD-coated capillaries enabled successful high-efficiency separation of aromatic acids and nucleosides and rapid cyclodextrin-based chiral analysis of racemic drugs. Moreover, the SPD-coated columns exhibited a long lifetime and demonstrated good intra-day, inter-day, and column-to-column repeatability.

Under-Oil Superhydrophilic/Superhydrophobic Janus Nanofibrous Membrane for Highly Efficient Separation of Surfactant-Stabilized Water-in-Oil Emulsions

Highly efficient separation of surfactant-stabilized water-in-oil emulsions with both a high separation efficiency and high permeation flux is still challenging. In this work, an under-oil superhydrophilic/superhydrophobic Janus membrane was fabricated by combining an electrospun poly(vinylidene fluoride-co-hexafluoropropylene) (PVDF-HFP) membrane and its modified membrane composited with poly(ethylene glycol) diacrylate (PEGDA). The incorporation of PEGDA is realized by in situ ultraviolet (UV)-initiated polymerization during the electrospinning process, and it endows the upper layer with unique under-oil superhydrophilicity that is very important for the demulsification of water-in-oil emulsions. The under-oil superhydrophobic lower layer serves to block the water and also can promote the permeation flux, because of its oil-absorbing ability. For surfactant-stabilized water-in-n-hexane emulsion (water content of 1 wt %), such a Janus membrane exhibits outstanding separation performance with a separation efficiency of >99.95% and permeation flux of >25 000 L m-2 h-1. Moreover, the Janus membrane shows excellent reusability and high applicability for water-in-diesel, water-in-hexadecane, and water-in-petroleum ether emulsions with separation efficiencies of 99.63%, 99.80% and 99.82%, respectively. These features make the Janus membrane a promising candidate as a separation membrane for surfactant-stabilized water-in-oil emulsions.