Large-Scale Nanofiber Manufacturing| Self-powered superhydrophobic/oleophobicFR-PVDF/PA6 nanofiber membrane for longterm efficient filtration and respiratorymonitoring

Qingdao University’s Niu Haitao & Prof. Zhou Hua: Self-Powered Superhydrophobic/Oleophobic FR-PVDF/PA6 Nanofiber Membrane for Long-Term Efficient Filtration and Respiratory Monitoring

The acceleration of industrialization and worsening atmospheric pollution severely endanger public safety, becoming a globally critical concern. Suspended particulate matter (PM) with small particle sizes in the atmosphere is a major culprit of air pollution, significantly impacting air quality and human health. Highly permeable airborne particles (PM ≤ 0.3 μm) can carry toxic substances and deadly viruses, entering human bronchi and alveoli through respiration, causing lung damage. Thus, developing effective PM filters is imperative, especially smart air filters with self-powering or sensing capabilities, which will be a future research focus.

Recently, Prof. Niu Haitao and Zhou Hua’s team at Qingdao University published their latest research, *"Self-powered superhydrophobic/oleophobic FR-PVDF/PA6 nanofiber membrane for long-term efficient filtration and respiratory monitoring"*, in the Journal of Membrane Science. By co-spinning fluorinated resin (FR)-functionalized PVDF (FR-PVDF) and PA6, they fabricated an interpenetrating fiber-structured superhydrophobic/oleophobic FR-PVDF/PA6 membrane with bimodal fiber diameter distribution and piezoelectric/triboelectric properties. The study proposed a self-powered strategy to enhance the air filtration performance of electrospun nanofibers while granting the membrane additional respiratory monitoring capabilities. Under the synergistic effect of piezoelectric and triboelectric responses, the membrane achieved 99.5% filtration efficiency and a low pressure drop of 75 Pa, with long-term stability. This research provides an effective approach for developing multifunctional nanofiber filter membranes.

Fig. 1: Fabrication and properties of FR-PVDF/PA6 nanofiber membrane.

Fig. 2: Morphology and properties. (a) SEM of PVDF nanofibers. (b) FR’s effect on water/oil contact angles. (c-f) SEM images of (c) FR-PVDF, (d) PA6, and (e,f) FR-PVDF/PA6 nanofibers. (g) Diameter distribution. (h,i) Pore size distribution and porosity.

The FR-PVDF/PA6 nanofiber membrane exhibits an interpenetrating fiber structure with bimodal diameter distribution, small pore size, and high porosity, balancing low pressure drop and high PM removal efficiency. It also demonstrates excellent waterproofing, breathability, and moisture permeability. Moreover, the membrane shows stable electrical signal output under varying stimuli.

Fig. 3: (a) Water resistance, (b) breathability, (c) moisture permeability. (d) Voltage output. (e-h) Output voltage/current under (e,f) different frequencies and (g,h) forces.

The FR-PVDF/PA6 nanofiber membrane exhibits excellent waterproofing, breathability, and moisture permeability. Additionally, the FR-PVDF/PA6 nanofiber membrane demonstrates outstanding electrical signal output performance, stably generating electrical signals under varying degrees of stimulation.

Fig. 4: Filtration performance. (a) Efficiency and pressure drop of different membranes. (b) Surface potential during filtration. (c) Efficiency changes (after removing residual charges). (d) Correlation between efficiency and surface potential. (e) Filtration mechanism. (f) Graded efficiency for different PM sizes. (g) Efficiency/pressure drop at varying weights. (h) Performance under different humidity levels. (i) Efficiency/pressure drop at varying flow rates. (j,k) SEM images of (j) FR-PVDF and (k) FR-PVDF/PA6 after filtration.

The developed FR-PVDF/PA6 membrane possesses superior filtration performance, with its interpenetrating fiber structure featuring a bimodal diameter distribution enhancing the capture efficiency of airborne particulate matter. Furthermore, the charges generated by the piezoelectric and triboelectric effects continuously accumulate on the fiber surface, leading to electrostatic adsorption of particles and further improving filtration efficiency.Moreover, the FR-PVDF/PA6 nanofiber membrane has self-powering capability, ensuring stable performance even under harsh conditions (e.g., high humidity). 

Fig. 5: Respiratory monitoring performance of FR-PVDF/PA6 membrane. (a) Schematic setup. Voltage output under (b) varying breathing intensities and (c) different respiratory states. (d) Stability of the self-powered membrane.

Additionally, the FR-PVDF/PA6 nanofiber membrane exhibits excellent respiratory monitoring performance, with high sensitivity, accurate differentiation, and long-term stability. It holds broad application prospects in respiratory protection and real-time vital sign monitoring.