Nanofiber Production Equipment| Engineering multifunctional and robustsuperhydrophilic nanofiber contaminationresistance membranes for ultrafast oil-water separation

Associate Professor Cao Ning & Professor Chen Chunxia from Northeast Forestry University: Designing Multifunctional and Robust Superhydrophilic Nanofiber Antifouling Membranes for Ultrafast Oil-Water Separation

In recent years, accidental spills of petroleum and its downstream liquid products have frequently occurred in rivers, lakes, bays, and oceans. These dispersed oily pollutants pose immediate threats to the ecological environment and cause long-term harm to aquatic life and human health. The high demand for ultra-stable, environmentally friendly, and multifunctional filtration membranes in practical complex oily wastewater treatment systems remains an unresolved challenge.In this work, we propose a simple fabrication strategy for a novel superhydrophilic, degradable, and recyclable membrane that demonstrates exceptional performance in ultrafast separation of oil-in-water emulsions under various harsh environmental conditions.

Recently, Associate Professor Cao Ning and Professor Chen Chunxia from Northeast Forestry University published their latest research titled "Engineering multifunctional and robust superhydrophilic nanofiber contamination resistance membranes for ultrafast oil-water separation" in the journal Separation and Purification Technology.The researchers developed a superhydrophilic and antifouling PLA@PAN/NiCo-LDH membrane through a secondary electrospinning technique. A superhydrophilic functional layer was prepared by incorporating layered double hydroxide (NiCo-LDH) into the polyacrylonitrile (PAN) electrospinning solution. During electrospinning, polylactic acid (PLA) served as the support layer, while PAN/NiCo-LDH tailored the morphology and structure of the PLA nanofiber membrane. 

This dual electrospinning approach effectively improved the atomic economy of LDH compared to reported LDH-based oil-water separation membranes.Furthermore, the PAN/NiCo-LDH functional layer induced a transition from hydrophobicity to superhydrophilicity, enabling the breakdown of oil-in-water emulsions - intercepting oil while promoting rapid water permeation. Due to LDH's strong visible light absorption, PLA@PAN/NiCo-LDH could rapidly and efficiently catalyze the degradation of dye solutions. The fabricated membrane also exhibited excellent antifouling capability, along with biodegradability, recyclability, and strong chemical stability. These multifunctional properties, combined with ultra-high flux capacity, make PLA@PAN/NiCo-LDH an ideal replacement for traditional non-recyclable polymer membranes. This advancement not only addresses critical environmental issues but also promotes sustainable resource utilization in separation technologies.

Fig. 1. Schematic of PLA@PAN/NiCo-LDH preparation and properties

Fig. 2. ATR-FTIR, XRD, SEM and AFM characterizations

To evaluate the construction of PLA@PAN/NiCo-LDH, we conducted ATR-FTIR and XRD characterizations, which confirmed the successful preparation of PLA@PAN/NiCo-LDH. The separation performance of the membrane is fundamentally governed by its structural and morphological properties. To systematically investigate these characteristics, we performed comprehensive morphological analyses on the fabricated membranes (PLA, PLA@PAN, and PLA@PAN/NiCo-LDH) as well as NiCo-LDH using SEM. As shown in Fig. 2c-h, the originally smooth PLA nanofiber membrane surface was successfully coated with a rough flower-like structure. Fig. 2i-j clearly demonstrates that NiCo-LDH exhibits a nanoflower morphology, a structural design that enables the membrane material to more effectively remove contaminants from water. Furthermore, AFM characterization results were highly consistent with SEM observations, where the significant increase in surface roughness greatly enhanced surface hydrophilicity and underwater oleophobicity (Fig. 2k-m). These synergistic surface modifications ultimately contributed to the outstanding oil-water separation performance.

Fig. 3. WCA and UWOCA measurements

The surface wettability of nanofiber membranes is crucial for oil-water separation. PLA@PAN/NiCo-LDH exhibits excellent superhydrophilicity, achieving a water contact angle (WCA) of 0° in air within 2 seconds (Fig. 3a-c). Additionally, comparative analysis revealed significant differences in underwater oleophobic behavior among the membranes: PLA and PLA@PAN membranes showed almost negligible underwater oleophobicity (Fig. 3d and e), while PLA@PAN/NiCo-LDH demonstrated exceptional performance with a UWOCA of 153.2°, providing a significant advantage for separating oil-in-water emulsions.

Fig. 4. Separation performance and antifouling tests

To optimize PLA@PAN/NiCo-LDH, the membrane fabrication parameters (PVP content, NiCo-LDH content, and PAN content) were thoroughly investigated. The results indicated that the optimal parameters were 0.1 g PVP, 6 mg NiCo-LDH, and 0.2 g PAN (Fig. 4a-c). The membrane exhibited outstanding separation performance in various SDS-stabilized oil-in-water emulsions (Fig. 4d), with a flux as high as 12,316 L·m⁻²·h⁻¹·bar⁻¹ for hexane-in-water emulsions and separation efficiencies exceeding 99%, demonstrating highly efficient oil-in-water emulsion separation. For Tween 80-stabilized emulsions, the membrane also showed excellent separation performance for various oil-in-water emulsions (hexane, petroleum ether, octane, and xylene) (Fig. 4e). A detailed separation setup is illustrated in Fig. 4f. Moreover, we fabricated a large-scale and scalable composite membrane using an electrospinning device, producing a 1.8 m long and 0.3 m wide PLA@PAN/NiCo-LDH membrane (Fig. 4g). These remarkable results strongly suggest that the membrane has significant potential for practical industrial-scale oily wastewater treatment applications.Antifouling properties are a critical parameter determining membrane durability and lifespan, which were systematically evaluated through comprehensive performance tests. PLA@PAN/NiCo-LDH exhibited excellent antifouling performance (Fig. 4h-j).

Fig. 5. Separation mechanism

Comparative images before and after separation of hexane and soybean oil emulsions showed no visible oil droplets in the filtrate (Fig. 5a and c), and particle size comparisons further confirmed the efficient separation of oil-in-water emulsions (Fig. 5b and d).A strong hydration layer is essential for purifying oil-in-water emulsions. The separation mechanism of PLA@PAN/NiCo-LDH involves the synergistic effects of surface hydration and size exclusion. When the emulsion contacts the membrane surface, the robust hydration layer formed by the superhydrophilic NiCo-LDH promotes selective water permeation while effectively intercepting oil droplets, achieving efficient emulsion destabilization. The membrane's precise pore structure further enhances this process, maintaining the discrete nature of surfactant-stabilized oil droplets. Under applied pressure, the combined effects of surface interactions and size exclusion lead to gradual emulsion breakdown at the membrane interface, enabling effective oil-water separation (Fig. 5e-f).

Fig. 6. Stability, photocatalytic, biodegradability and recyclability studies

In practical oil-water separation applications, factors such as wastewater pH, high salinity, and prolonged outdoor sunlight exposure can affect membrane performance. We investigated the resistance of PLA@PAN/NiCo-LDH in acidic and alkaline environments, and experimental results confirmed that the membrane remained stable in acidic or alkaline solutions (pH = 2, 4, 6, 8, 10) and 1 M NaCl for up to 30 days, with nearly unchanged separation performance. Additionally, to meet industrial application demands, there is an urgent need to develop UV-resistant separation membranes.

 We tested the UV resistance of PLA@PAN/NiCo-LDH, and the results in Fig. 6a demonstrate its excellent environmental durability. Fig. 6b shows that PLA@PAN/NiCo-LDH possesses good cyclic stability and self-cleaning properties.Since LDH contains transition metal elements with outstanding photocatalytic properties, PLA@PAN/NiCo-LDH can be applied in photocatalytic degradation, enabling simultaneous dye degradation during oily wastewater treatment (Fig. 6c). Fig. 6d-e further confirms the membrane's excellent photocatalytic degradation performance.As PLA is a biodegradable material, we immersed it in a protease K Tris-HCl buffer solution (pH = 8.5) for degradation. The functional layer was then recovered and re-spun, with no significant difference in separation performance compared to the original membrane (Fig. 6f). Fig. 6g compares the oil/water separation performance of PLA@PAN/NiCo-LDH with other reported superhydrophilic membranes, highlighting its superior performance among superhydrophilic membranes.

Paper link: https://doi.org/10.1016/j.seppur.2025.132868