Moisture Effect on Particulate Matter Filtration Performance using Electro-Spun Nanofibers including Density Functional Theory Analysis

Biodegradable Electroactive Nanofibrous Air Filters for Long-Term Respiratory Healthcare and Self-Powered Monitoring

The concept of triboelectric nanogenerator (TENG)-based fibrous air filters, in which the electroactive fibers are ready to enhance the electrostatic adsorption by sustainable energy harvesting, is appealing for long-term respiratory protection and in vivo real-time monitoring. This effort discloses a self-reinforcing electroactivity strategy to confer extreme alignment and refinement of the electrospun poly(lactic acid) (PLA) nanofibers, significantly facilitating formation of electroactive phases (i.e., β-phase and highly aligned chains and dipoles) and promotion of polarization and electret properties. It endowed the PLA nanofibrous membranes (NFMs) with largely increased surface potential and filtration performance, as exemplified by efficient removal of PM0.3 and PM2.5 (90.68 and 99.82%, respectively) even at the highest airflow capacity of 85 L/min. With high electroactivity and a well-controlled morphology, the PLA NFMs exhibited superior TENG properties triggered by regular respiratory vibrations, enabling 9.21-fold increase of surface potential (-1.43 kV) and nearly 68% increase of PM0.3 capturing (94.3%) compared to those of conventional PLA membranes. The remarkable TENG mechanisms were examined to elaborately monitor the personal respiration characteristics, particularly those triggered large and rapid variations of output voltages like coughing and tachypnea. Featuring desirable biocompatibility and degradability, the self-powered PLA NFMs permit promising applications in the fabrication of ecofriendly air filters toward high-performance purification and intelligent monitoring.

Through-hole composite membrane with an ultrathin oxide shell for highly robust and transparent air filters

Exploring pore structures that are optically transparent and have high filtration efficiency for ultrafine dust is very important for realizing passive window filters for indoor air purification. Herein, a polyester track-etched (PETE) membrane with vertically perforated micropores is investigated as a cost-effective candidate for transparent window filters. The pore size, which governs transparency and filtration efficiency, can be precisely tuned by conformally depositing an ultrathin oxide layer on the PETE membrane via atomic layer deposition. The maximum visible light transmittance (∼81.2 %) was achieved with an alumina layer of approximately 55 nm, and the resulting composite membrane exhibited competitive filtration efficiency compared to commercial products. The chemically inert alumina layer also increased resistance to various external stimuli and enabled simple cleaning of the contaminated membrane surface with a solvent. The membrane installed on an insect screen effectively maintained its filtration performance (∼85 % for PM_2.5) even after 10 reuse cycles under extremely harsh conditions (PM_2.5 concentration: ∼5000 μg cm^-3). The proposed through-hole composite membrane can expand the choice of aesthetic window filters to situations that require high outside visibility and daylighting.

High-performance multifunctional electrospun fibrous air filter for personal protection: A review

With the increasingly serious air pollution and the rampant coronavirus disease 2019 (COVID–19), preparing high–performance air filter to achieve the effective personal protection has become a research hotspot. Electrospun nanofibrous membrane has become the first choice of air filter because of its small diameter, high specific surface area and porosity. However, improving the filtration performance of the filter only cannot meet the personal needs: it should be given more functions based on high filtration performance to maximize the personal benefits, called, multifunctional, which can also be easily realized by electrospinning technology, and has attracted much attention. In this review, the filtration mechanism of high–performance electrospun air filter is innovatively summarized from the perspective of membrane. On this basis, the specific preparation process, advantages and disadvantages are analyzed in detail. Furthermore, other functions required for achieving maximum personal protection benefits are introduced specifically, and the existing high–performance electrospun air filter with multiple functions are summarized. Finally, the challenges, limitations, and development trends of manufacturing high–performance air filter with multiple functions for personal protection are presented.

Improvement of an In-Duct Two-Stage Electrostatic Precipitator via Diffusion Charging

An in-duct two-stage electrostatic precipitator (ESP) improved by ion diffusion effect was studied. We increased the collection efficiency of a two-stage electrostatic precipitator without additional energy input by adjusting the space arrangement of the charger and the collector, which increased the particle diffusion charging time. The collection efficiency and the particle charge were systematically investigated according to the occurrence of diffusion charging and electric field charging in the charger as generated by the negative ions. The collection efficiency of the separated two-stage ESP was 39% higher, on average, than the theoretical efficiency at the same power consumption. Through simulation, it was verified that the ions generated in the carbon fiber ionizer penetrated the charger. We proposed a modified charging mechanism assuming that the penetrated ions cause additional particle charge. The optimal separation distance between the charger and the collector, which showed the maximum collection efficiency, was derived through the modified charging model. Therefore, the in-duct two-stage ESP developed in this study is a promising energy-efficient and cost-saving design for indoor air management.

Application of 2D Materials for Adsorptive Removal of Air Pollutants

Air pollution is on the priority list of global safety issues, with the concern of fatal environmental and public health deterioration. 2D materials are potential adsorbent materials for environmental decontamination, owing to their high surface area, manageable interlayer binding, large surface-to-volume ratio, specific binding capability, and chemical, thermal, and mechanistic stability. Specifically, graphene oxide and reduced graphene oxide have been attracting attention, taking advantage of their low cost synthesis, excessive oxygen containing surface functionalities, and intrinsic aqueous dispersibility, making them desirable for the development of cost-effective, high performance air filters. Many different material designs have been proposed to expand their filtration capability, including the functionalization and integration with other metals and metal oxides, which act not only as binding agents to the target pollutants but also as antimicrobial agents. This review highlights the advantages and drawbacks of 2D materials for air filtration and summarizes the interrelationships among various strategies and the resultant filtration performance in terms of structural engineering, morphology control, and material compositions. Finally, potential future directions are suggested toward the idealized designs of 2D material based air filters.

Synthesis of Electrospun PAN/TiO2/Ag Nanofibers Membrane As Potential Air Filtration Media with Photocatalytic Activity

The PAN/TiO2/Ag nanofibers membrane for air filtration media was successfully synthesized with electrospinning method. The morphology, size, and element percentage of the nanofiber were characterized by a scanning electron microscopy-energy dispersive spectroscopy, while X-ray fluorescence and FTIR were used to observe the chemical composition. The water contact angle and UV-vis absorption were measured for physical properties. Performance for air filtration media was measured by pressure drop, efficiency, and quality factor test. TiO2 and Ag have been successfully deposited in nonuniform 570 nm PAN/TiO2/Ag nanofibers. The nanofiber membrane had hydrophilic surface after TiO2 and Ag addition with a water contact angle of 34.58°. UV-vis data showed the shifting of absorbance and band gap energy of nanofibers membrane to visible light from 3.8 to 1.8 eV. The 60 min spun PAN/TiO2/Ag nanofibers membrane had a 96.9% efficiency of PM2.5, comparable to results reported in previous studies. These properties were suitable to be applied on air filtration media with photocatalytic activity for self-cleaning performance.

Wearable Cortisol Aptasensor for Simple and Rapid Real-Time Monitoring

The necessity of managing stress levels is becoming increasingly apparent as the world suffers from different kinds of stresses including the extent of pandemic, the corona virus disease 2019 (COVID-19). Cortisol, a clinically confirmed stress hormone related to depression and anxiety, affects individuals mentally and physically. However, current cortisol monitoring methods require expert personnel, large and complex machines, and long time for data analysis. Here, we present a flexible and wearable cortisol aptasensor for simple and rapid cortisol real-time monitoring. The sensing channel was produced by electrospinning conducting polyacrylonitrile (PAN) nanofibers (NFs) and subsequent vapor deposition of carboxylated poly(3,4-ethylenedioxythiophene) (PEDOT). The conjugation of the cortisol aptamer on the PEDOT-PAN NFs provided the critical sensing mechanism for the target molecule. The sensing test was performed with a liquid-ion gated field-effect transistor (FET) on a polyester (polyethylene terepthalate). The sensor performance showed a detection limit of 10 pM (<5 s) and high selectivity in the presence of interference materials at 100 times higher concentrations. The practical usage and real-time monitoring of the cortisol aptasensor with a liquid-ion gated FET system was demonstrated by successful transfer to the swab and the skin. In addition, the real-time monitoring of actual sweat by applying the cortisol aptasensor was also successful since the aptasensor was able to detect cortisol approximately 1 nM from actual sweat in a few minutes. This wearable biosensor platform supports the possibility of further application and on-site monitoring for changes of other numerous biomarkers.

Cellulose for the Production of Air-Filtering Systems: A Critical Review

The control of airborne contaminants is of great interest in improving air quality, which has deteriorated more and more in recent years due to strong industrial growth. In the last decades, cellulose has been largely proposed as suitable feedstock to build up eco-friendly materials for a wide range of applications. Herein, the issue regarding the use of cellulose to develop air-filtering systems is addressed. The review covers different cellulose-based solutions, ranging from aerogels and foams to membranes and films, and to composites, considering either particulate filtration (PM₁₀, PM_2.5, and PM_0.3) or gas and water permeation. The proposed solutions were evaluated on the bases of their quality factor (QF), whose high value (at least of 0.01 Pa^-1 referred to commercial HEPA (high-efficiency particulate air) filters) guarantees the best compromise between high filtration efficiency (>99%) and low pressure drop (<1 kPa/g). To face this aspect, we first analyzed the different morphological aspects which can improve the final filtration performance, outlining the importance on using nanofibers not only to increase surface area and to modulate porosity in final solutions, but also as reinforcement of filters made of different materials. Besides the description of technological approaches to improve the mechanical filtration, selected examples show the importance of the chemical interaction, promoted by the introduction of active functional groups on cellulose (nano)fibers backbone, to improve filtration efficiency without reducing filter porosity.

Ti-40Al-10Nb-10Cr Porous Microfiltration Membrane with Hierarchical Pore Structure for Particulate Matter Capturing from High-Temperature Flue Gas

TiAl-based porous microfiltration membranes are expected to be the next-generation filtration materials for potential applications in high-temperature flue gas separation in corrosive environments. Unfortunately, the insufficient high-temperature oxidation resistance severely limits their industrial applications. To tackle this issue, a Ti-40Al-10Nb-10Cr porous alloy was fabricated for highly effective high-temperature flue gas purification. Benefited from microstructural changes and the formation of two new phases, the Ti-40Al-10Nb-10Cr porous alloy demonstrated favorable high-temperature anti-oxidation performance with the incorporation of Nb and Cr high-temperature alloying elements. By the separation of a simulated high-temperature flue gas, we achieved an ultra-high PM-removal efficiency (62.242% for PM<2.5 and 98.563% for PM>2.5). These features, combined with our experimental design strategy, provide a new insight into designing high-temperature TiAl-based porous materials with enhanced performance and durability.

Magnetoelectric Membrane Filters of Poly(vinylidene fluoride)/Cobalt Ferrite Oxide for Effective Capturing of Particulate Matter

In the last decade, particulate matter (PM) has gradually become a serious public health issue due to its harmful impact on the human body. In this study, we report a novel filtration system for high PM capturing, based on the magnetoelectric (ME) effect that induces an effective surface charge in membrane filters. To elucidate the ME effect on PM capturing, we prepared electrospun poly(vinylidene fluoride)(PVDF)/CoFe2O4(CFO) membranes and investigated their PM capturing efficiency. After electrical poling under a high electric field of 10 kV/mm, PM-capturing efficiencies of the poled-PVDF/CFO membrane filters were improved with carbon/fluorine(C/F) molar ratios of C/F = 4.81 under Hdc = 0 and C/F = 7.01 under Hdc = 700 Oe, respectively. The result illustrates that electrical poling and a dc magnetic field could, respectively, enhance the surface charge of the membrane filters through (i) a strong beta-phase alignment in PVDF (poling effect) and (ii) an efficient shape change of PVDF/CFO membranes (magnetostriction effect). The diffusion rate of a water droplet on the PVDF/CFO membrane surface is reduced from 0.23 to 0.05 cm2/s by covering the membrane surface with PM. Consequently, the PM capturing efficiency is dramatically improved up to 175% from ME membranes with the poling process and applying a magnetic field. Furthermore, the PM was successfully captured on the prototype real mask derived from the magnetoelectric effect induced by a permanent magnet with a diameter of 2 cm without any external power.