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Integrating nanostructured active materials, antimicrobial components, and rational porous structures is one of the promising approaches for simultaneously boosting removal efficiency, antimicrobial capacity, mechanical property, hydrophobic performance, and air permeability of air filters. However, realizing these performances of an air filter still remains a big challenge. Herein, a multifunctional air filter zNFs-Ag@PT, which is composed of a unique substrate prepared from Ag nanoparticles (AgNPs)-paper towel (PT) microfibers and an upper layer formed from aligned zein nanofibers (zNFs) inspired by a "tug-of-war" repulsion force, is reported. The Ag@PT substrate is fabricated via in situ reduction; and zNFs are prepared by electrospinning a well-prepared zein Pickering emulsion onto a specially designed collector. The innovative collector is a partially conductive design composed of an insulative middle section and two conductive ends. It is demonstrated that the introduction of AgNPs not only endows the zNFs-Ag@PT filter with an effective antimicrobial activity but also provides the substrate with an anisotropic electric field to achieve stretched and aligned zein fibers forming thinner nanofibers than that without AgNPs. As a result, the filtration performances of a zNFs-Ag@PT filter are enhanced. This study initiates an effective way to fabricate bio-based multifunctional air filters with antimicrobial and filtration performances via combining nano- and biotechnology.

Nowadays, separators with superior properties have drawn widespread attention for the development of advanced and safe large-scale lithium-ion batteries (LIBs). Yet it is still a great challenge fo...

Three-dimensional (3D) conductive scaffolds have attracted intensive interest recently for Li metal anode due to the capability of suppressing Li-dendrite growth. However, there is a lack of comprehensive understanding of its multiple roles including any side effects, which is critical for lithium metal anode technology. Here, we fabricate a type of Au-coated polyimide nanofabric as the scaffold for Li-metal anode and study the lithium plating/stripping behavior with different current densities. Different from reported studies which usually only discussed the benefits of 3D scaffolds, this study reveals unstabilized solid-electrolyte-interphase (SEI) with 3D architectures. It is found that 3D scaffold tends to form unstable SEI layer at high current density, which finally results in a short cell life due to continuous SEI accumulation and fast consuming of liquid electrolyte. To better understand this new finding, we propose an electrochemomechanical failure model for lithium metal anode, which will be instructive for designing advanced structures to electrochemomechanically stabilize Li-metal composite anode.

Herein, a novel core@sheath nanofibrous membrane with ultrahigh strength, superior fire resistance and high wettability is prepared for lithium-ion batteries separator via self-bonding and self-compression technique, using the polyimide nanofiber as the core material and polybenzimidazole as the reinforced sheath material. The self-bonding and self-compression make the polyimide@polybenzimidazole-reinforced nanofibrous membrane possess ultrahigh strength up to 59 MPa and more compact porous structure, which is an exciting finding. The as-synthesized nanofibrous membrane exhibits super high thermal dimensional stability up to 300 °C and satisfying wettability. Furthermore the good thermal stability of as-synthesized membrane enables it to preserve the integrity of backbone at temperatures as high as 540 °C. More significantly, the unique fire resistance of polybenzimidazole also ensures the high security of batteries. Notably, the battery using the as-synthesized separator displays much higher capability (130.2 mAh g−1, 5 C) than that with Celgard separator (95.4 mAh g−1, 5 C), and it can work steadily at 120 °C. Therefore, we believe that this work is really a significant breakthrough for the polyimide nonwoven separators, especially the ultrahigh mechanical strength, indicating the promising applications for the next generation high-safety and high-performance lithium-ion batteries.

Development of nonflammable separators with excellent properties is in urgent need by next-generation advanced and safe energy storage devices. However, it has been extremely challenging to simultaneously achieve fire resistance, high mechanical strength, good thermomechanical stability, and low ion-transport resistance for polymeric separators. Herein, to address all these needs, we report an in situ formed silica@silica-imbedded polyimide (in situ SiO2@(PI/SiO2)) nanofabric as a new high-performance inorganic-organic hybrid separator. Different from conventional ceramics-modified separators, this in situ SiO2@(PI/SiO2) hybrid separator is realized for the first time via an inverse in situ hydrolysis process. Benefiting from the in situ formed silica nanoshell, the in situ SiO2@(PI/SiO2) hybrid separator shows the highest tensile strength of 42 MPa among all reported nanofiber-based separators, excellent wettability to the electrolyte, good thermomechanical stability at 300 °C, and fire resistance. The LiFePO4 half-cell assembled with this hybrid separator showed a high capacity of 139 mAh·g-1@5C, which is much higher than that of the battery with the pristine PI separator (126.2 mAh·g-1@5C) and Celgard-2400 separator (95.1 mAh·g-1@5C). More importantly, the battery showed excellent cycling stability with no capacity decay over 100 cycles at the high temperature of 120 °C. This study provides a novel method for the fabrication of high-performance and nonflammable polymeric-inorganic hybrid battery separators.

Building nanostructured active materials and rational porous structures in air filters will be significant in realizing high filtration efficiency and low normalized pressure drop. The construction of nanofabrics by electrospinning can lead to large active surface areas, but it has been challenging to control the porous structures to reduce the normalized pressure drop, in particular for thick fabrics. To address this issue, here, we report a protein-functionalized composite air filter with hierarchical structures. This composite is made of bacterial nanocellulose coated by protein nanoparticles and microcellulose fibers from wood pulp. The protein-functionalized nanocellulose can not only help expose the functional groups of protein for trapping pollutants but also act as a binder to reinforce the composite fabrics. At the same time, the long microcellulose fibers form large pores, reducing normalized pressure drop and improving mechanical properties. By adjusting the component ratios, we demonstrate a h...

With more and more applications of Lithium-ion batteries (LIBs) in electronics, Polyolefin (PO) separators, including Polyethylene (PE) and Polypropylene (PP) separators, cannot meet the increasing requirements of high performance LIBs. Separators with good thermal stability and high electrochemical performance are in great demand. In this paper, Polyetherimide (PEI) fibrous membrane separators with crosslinking network morphologies have been successfully fabricated via electrospinning and in-situ micro-melting technique. The in-situ micro-melting process converts the loose and weak PEI nonwoven membrane to the compact and robust crosslinked fibrous membrane, and then improves the tensile strength of the membrane from 4 MPa to 21 MPa. The crosslinking structure greatly reduces the risk of fibrous membrane disassembling into the loose nonwovens during long-term battery cycling, and consequently improves the stability of LIBs. The results of Differential Scanning Calorimetry (DSC) and Thermogravimetric Analysis (TGA) show that the crosslinked PEI fibrous membrane presents excellent thermal stability (5% weight loss at about 522.2 °C) and thermal dimensional stability (without shrinkage below 240 °C), better than Celgard-2400 separator. The LIB with this separator shows higher capacity (113.3 mAh g−1, 5 C) than that with Celgard-2400 separator (95.2 mAh g−1, 5 C). More importantly, this PEI separator exhibits thermal shutdown function at 260 °C, which provides LIB with a safe guarantee under high temperature. All above-mentioned properties make crosslinked PEI fibrous membrane a good candidate as a separator of LIB.

Endowing separators with the polysulfide-blocking function is urgently needed for high-performance lithium–sulfur (Li–S) batteries. Thus far, most of the reported research has focused on modifying conventional polyolefin separators but with poor thermal stability and low ionic conductivity. To address these issues, herein we report a Janus separator based on a thermally stable polymeric nanofabric designed with abilities to trap polysulfides and facilitate the transport of Li+ simultaneously. This Janus separator possesses a configuration of a carbon nanofiber (CNF) layer toward the sulfur cathode and the polyimide (PI) nanofabric toward the Li metal anode. It is demonstrated that the conductive CNF layer can effectively anchor and convert the polysulfides; meanwhile, the excellent wettability with liquid electrolytes and the highly porous structure of the PI nanofiber layer significantly promote the Li+-transport. In addition, the Janus separator presents notable advantages in thermal dimensional stability benefiting from the PI nanofabric. As a result, the Li–S battery armed with the Janus separator shows a high initial capacity (1393 mA h g−1 at 0.1 A g−1), stable cycling performance (822 mA h g−1 at 1 A g−1) and high coulombic efficiency of 99.6%.

Here, we report for the first time on the successful fabrication of size-controlled silver@polyimide (Ag@PI) hybrid nanotubes (NTs) based on a silver ion-induced crosslinking effect via coaxial electrospinning and direct ion exchange-reduction techniques. By simply altering the coaxial electrospinning parameters and concentration of electrospinning solution, the diameter and wall thickness of the Ag@PI hybrid NTs could be finely tuned in the range of 300–900 nm and 50–200 nm, respectively. This hybrid material possesses a special conductive/dielectric-layered nanotubular structure, integrating the advantages of nanoscale silver and PI materials. The photocatalysis of the Ag@PI hybrid NTs was characterized by the decolorization of the Methylene Blue (MB) solution. The decolorization efficiency of MB can be as high as 90% within 210 min in the presence of Ag@PI NTs.

Surface-enhanced Raman scattering (SERS) spectroscopy is considered as a highly powerful analytical tool for environmental contaminants monitoring, detection of bio/chemical warfare agents, explosive detection and biological sensing. In this study, silver nanoparticles (Ag NPs) decorated polyimide (PI) nanofabric was successfully prepared as an active flexible substrate for SERS. Without any surface modification and activation, this Ag@PI nanofabric SERS substrate was prepared via an integrated process of electrospinning and ion exchange-in situ reduction. ATR-FTIR, ICP, XRD, SEM, and TGA were used to investigate the influencing factors during preparation. p-Aminothiophenol (p-ATP) was used as the probe molecule to characterize the SERS performance of Ag@PI nanofabric substrate. As a result, this Ag@PI nanofabric exhibits remarkable enhancement effect (EF = 9.0 × 103), good reproducibility, ultra-low detection limit (10−14 mol/L), and a good linear relationship between the concentration of p-ATP and intensity of its characteristic peak, making it a desirable candidate as the SERS substrate.

Herein, we demonstrate a strategy to improve the tensile strength, thermal safety issues, and electrochemical performance of an as-synthesized polyimide separator. By spraying the solution of a specific chemical constituent on both sides of a poly(amic acid) non-woven membrane followed by thermal treatment, a novel polyimide nanofibrous membrane with porous-layer-coated morphology was successfully fabricated by in situ self-bonding and micro-crosslinking technique. The self-bonding and micro-crosslinking techniques improve the tensile strength of the nanofiber membranes from 5 MPa to 28 MPa by forming a crosslinked network structure, thereby reducing the risk of nanofiber disassembly during long-term operation. The rigid structure and aromatic groups in the polyimide chain enable the separator to have outstanding thermal dimensional stability at temperatures as high as 300 °C and thermal stability (5% weight loss at about 528 °C). Additionally, the unique flame retarding capability of polyimide ensures high security of the battery as well. Notably, the lithium-ion battery using porous-layer-coated polyimide separator exhibits a much higher capability (129.9 mA h g−1, 5C) than that using a Celgard-2400 separator (95.2 mA h g−1, 5C) and could work steadily at 120 °C, thus implying promising application in next generation high-safety and high-performance lithium-ion batteries.

A simple and practical method for coating palladium/silver nanoparticles on polyimide (PI) nanotubes is developed. The key steps involved in the process are silver ion exchange/reduction and displacement reactions between silver and palladium ions. With the addition of silver, the conductivity of the PI nanotubes is greatly enhanced. Further, the polyimide nanotubes with a dense, homogeneous coating of palladium nanoparticles remain flexible after heat treatment and show the possibility for use as highly efficient catalysts. The approach developed here is applicable for coating various noble metals on a wide range of polymer matrices, and can be used for obtaining polyimide nanotubes with metal loaded on both the inner and outer surface.