PVDF Nanofiber Modified with ZnO Nanowires/Polydopamine for the Treatment of Sewage Containing Heavy Metals, Organic Dyes, and Bacteria.

In various countries worldwide, the issue of wastewater contamination poses a significant threat due to its intricate composition of heavy metals, organic dyes, and microorganisms, thereby complicating the purification process. Consequently, researchers have expressed considerable interest in materials capable of eliminating organic, heavy metal, and microbial pollutants. This study focuses on the fabrication of a water purification membrane (PDA/ZnO-NWs/PVDF) with a hierarchical structure and the ability to remove multiple pollutants. The membrane was created by modifying poly(vinylidene fluoride) (PVDF) nanofiber with zinc oxide nanowires (ZnO-NWs) and reinforcing it with polydopamine (PDA). The experimental results demonstrate that the PDA/ZnO-NWs/PVDF membrane exhibits a range of functionalities, including long-lasting superhydrophilicity, Cu(II) adsorption, photocatalytic degradation, and antibacterial ability. The manipulation of the DA synthesis procedure allows for the adjustment of the wettability, adsorption, and photocatalytic and antibacterial activities of the PDA/ZnO-NWs/PVDF composite. According to the Langmuir isotherm, the maximum Cu(II) adsorption capacity of the PDA/ZnO-NWs/PVDF membrane is determined to be 65.75 mg/g, which is significantly higher (27.26 mg/g) than that of the ZnO-NWs/PVDF membrane (38.49 mg/g). The PDA/ZnO-NWs/PVDF composite exhibited a notable degradation capacity toward rhodamine B under natural sunlight, reaching a maximum of 5.97 mg/g. Additionally, the degradation rate achieved during daylight hours was as high as 90.42%. Furthermore, the antibacterial efficacy of the PDA/ZnO-NWs/PVDF composite against both Gram-positive and Gram-negative bacteria approached 100%. This work presents a promising approach for the treatment of wastewater containing various coexisting contaminants.

Washable and Flexible Screen-Printed Ag/AgCl Electrode on Textiles for ECG Monitoring.

Electrocardiogram (ECG) electrodes are important sensors for detecting heart disease whose performance determines the validity and accuracy of the collected original ECG signals. Due to the large drawbacks (e.g., allergy, shelf life) of traditional commercial gel electrodes, textile electrodes receive widespread attention for their excellent comfortability and breathability. This work demonstrated a dry electrode for ECG monitoring fabricated by screen printing silver/silver chloride (Ag/AgCl) conductive ink on ordinary polyester fabric. The results show that the screen-printed textile electrodes have good and stable electrical and electrochemical properties and excellent ECG signal acquisition performance. Furthermore, the resistance of the screen-printed textile electrode is maintained within 0.5 Ω/cm after 5000 bending cycles or 20 washing and drying cycles, exhibiting excellent flexibility and durability. This research provides favorable support for the design and preparation of flexible and wearable electrophysiological sensing platforms.

Broadband Acoustoelectric Conversion Based on Oriented Polyacrylonitrile Nanofibers and Slit Electrodes for Generating Power from Airborne Noise.

Electrospun nanofiber acoustoelectric devices typically have a bandwidth in the range of 100-400 Hz, which limits their applications. This study demonstrates a novel device structure with tunable acoustoelectric bandwidth based on oriented electrospun polyacrylonitrile (PAN) nanofibers and slit electrodes. When the PAN nanofibers were arranged perpendicular to the slits, the devices had a much wider bandwidth than their parallel counterparts, while the latter had a bandwidth similar to that of randomly oriented nanofibers. In all devices, the electrical outputs follow a similar trend with the slit aspect ratio. However, the slit number only affected the electrical output without changing the bandwidth characteristic. We further showed that both the slit electrode and the oriented nanofiber membranes played a role in tuning the frequency response. Under sound, the vibration of the electrode caused the slit to be misaligned on both sides. The anisotropic tensile properties of the oriented nanofiber membranes allowed the fibers to stretch differently depending on their angle of alignment with the slits. Those perpendicular to the slits received more intense stretching, contributing to a wider bandwidth. The wider bandwidth increases the electrical output, especially when harvesting multifrequency sound. A 4 × 3 cm2 device made of five-slit electrodes (slit width × length, 2 mm × 30 mm) with PAN nanofibers perpendicular to the slits showed a bandwidth of 100-900 Hz and electrical outputs of 39.85 ± 1.34 V (current output 6.25 ± 0.18 µA) under 115 dB sound conditions, which is sufficient to power electromagnetic wireless transmitters. When one such slit device was used as a power supply and another as a sound sensor, they formed a completely self-powered wireless system that could detect sounds from various scenarios, such as high-speed trains, airports, highway traffic, and manufacturing industries. The energy can also be stored in lithium-ion batteries and capacitors. We hope that such novel devices will contribute to the development of highly efficient acoustoelectric technology for generating electrical energy from airborne noise.

High-sensitivity acoustic sensors from nanofibre webs.

Considerable interest has been devoted to converting mechanical energy into electricity using polymer nanofibres. In particular, piezoelectric nanofibres produced by electrospinning have shown remarkable mechanical energy-to-electricity conversion ability. However, there is little data for the acoustic-to-electric conversion of electrospun nanofibres. Here we show that electrospun piezoelectric nanofibre webs have a strong acoustic-to-electric conversion ability. Using poly(vinylidene fluoride) as a model polymer and a sensor device that transfers sound directly to the nanofibre layer, we show that the sensor devices can detect low-frequency sound with a sensitivity as high as 266 mV Pa(-1). They can precisely distinguish sound waves in low to middle frequency region. These features make them especially suitable for noise detection. Our nanofibre device has more than five times higher sensitivity than a commercial piezoelectric poly(vinylidene fluoride) film device. Electrospun piezoelectric nanofibres may be useful for developing high-performance acoustic sensors.

Robust Mechanical-to-Electrical Energy Conversion from Short-Distance Electrospun Poly(vinylidene fluoride) Fiber Webs.

Electrospun polyvinylidene fluoride (PVDF) nanofiber webs have shown great potential in making mechanical-to-electrical energy conversion devices. Previously, polyvinylidene fluoride (PVDF) nanofibers were produced either using near-field electrospinning (spinning distance<1 cm) or conventional electrospinning (spinning distance>8 cm). PVDF fibers produced by an electrospinning at a spinning distance between 1 and 8 cm (referred to as "short-distance" electrospinning in this paper) has received little attention. In this study, we have found that PVDF electrospun in such a distance range can still be fibers, although interfiber connection is formed throughout the web. The interconnected PVDF fibers can have a comparable ß crystal phase content and mechanical-to-electrical energy conversion property to those produced by conventional electrospinning. However, the interfiber connection was found to considerably stabilize the fibrous structure during repeated compression and decompression for electrical conversion. More interestingly, the short-distance electrospun PVDF fiber webs have higher delamination resistance and tensile strength than those of PVDF nanofiber webs produced by conventional electrospinning. Short-distance electrospun PVDF nanofibers could be more suitable for the development of robust energy harvesters than conventionally electrospun PVDF nanofibers.