Tug-of-War-Inspired Bio-Based Air Filters with Advanced Filtration Performance

Review of research advances in microbial sterilization technologies and applications in the built environment

As globalization accelerates, microbial contamination in the built environment poses a major public health challenge. Especially since Corona Virus Disease 2019 (COVID-19), microbial sterilization technology has become a crucial research area for indoor air pollution control in order to create a hygienic and safe built environment. Based on this, the study reviews sterilization technologies in the built environment, focusing on the principles, efficiency and applicability, revealing advantages and limitations, and summarizing current research advances. Despite the efficacy of single sterilization technologies in specific environments, the corresponding side effects still exist. Thus, this review highlights the efficiency of hybrid sterilization technologies, providing an in-depth understanding of the practical application in the built environment. Also, it presents an outlook on the future direction of sterilization technology, including the development of new methods that are more efficient, energy-saving, and targeted to better address microbial contamination in the complex and changing built environment. Overall, this study provides a clear guide for selecting technologies to handle microbial contamination in different building environments in the future, as well as a scientific basis for developing more effective air quality control strategies.

Sustainable nanofibrous membranes for air filtration, water purification and oil removal

The increasing demand for sustainable solutions to address environmental and energy challenges has driven the development of advanced materials. Among them, nanofibrous membranes have emerged due to their high surface area, tunable porosity and versatile mechanical properties. However, traditional nanofibrous membranes, made from petroleum-based synthetic polymers, pose significant environmental concerns due to their non-biodegradability and reliance on fossil resources. This paper reviews recent advancements in the development of sustainable nanofibrous membranes, focusing on the use of biobased and biodegradable materials, and circular design approaches aimed at reducing environmental impact throughout the membrane life cycle. Challenges associated with improving the mechanical strength and stability of biopolymer-based nanofibers and expanding application areas are discussed. By highlighting strategies to overcome these limitations, this review aims to provide insights into the future direction of sustainable nanofibrous membranes, paving the way for their broader adoption in eco-friendly technological solutions.

A holocellulose air filter with highly efficient formaldehyde adsorption prepared via low temperature pulping and partial dissolving from corn stalks

Emissions of particulate matter (PM) originating from industrial and agricultural incineration had emerged as a significant public health concern. Furthermore, the considerable annual production of straw remains underutilized, particularly in China. In this study, we proposed a novel approach for holocellulose air filter production from corn stalks via low-temperature anthraquinone pulping, partial dissolving, and high-speed shear-induced regeneration. About 61.40-78.23 % of hemicellulose in corn stalks was retained in holocellulose, furthermore, the delignification rate was up to 81.63-92.51 % after low temperature (<100 °C) alkaline exactment. Subsequently, holocellulose air filters (RHF) were prepared through regeneration with high-speed shear induced (25,000 rpm) and freeze-drying. The final air filters contained approximately 8.56-12.4 % hemicellulose, exhibiting a substantial adsorption capacity for low molecules such as formaldehyde. The results revealed remarkably low PM2.5 penetration ratio (0.12 %) and pressure drop (14.3 Pa) of the air filter, while exhibiting a remarkable formaldehyde adsorption capacity of 54.5 mg/g. Moreover, the characters of high crystallinity index and robust micro/nano-structure of regenerated cellulose were obtained. This study introduced an innovative and facile strategy for gaseous formaldehyde adsorption and introduced novel solutions for agricultural waste utilization.

Development of Environmentally Friendly Biocidal Coatings Based on Water-soluble Copolymers for Air-cleaning Filters

Air pollution by pathogens has posed serious concern on global health during the last decades, especially since the breakout of the last pandemic. Therefore, advanced high-efficiency techniques for air purification are highly on demand. However, in air-filtering devices, the prevention of secondary pollution that may occur on the filters remains a challenge. Toward this goal, in the present work, we demonstrate a facile and eco-friendly process for the biocidal treatment of commercial high-efficiency particulate air filters. The antibacterial filters were successfully prepared through spray coating of aqueous solutions based on biocidal water-soluble polymers, poly(sodium 4-styrene sulfonate-co-cetyl trimethylammonium 4-styrene sulfonate-co-glycidyl methacrylate) [P(SSNa24-co-SSAmC₁₆56-co-GMA20)] and poly(2-dimethylaminoethyl)methacrylate. Significantly, an optimized green route was developed for the synthesis of the used polymers in aqueous conditions and their stabilization through cross-linking reaction, leading to biocidal air filters with long-lasting activity. The developed coatings presented strong and rapid antibacterial activity against Staphylococcus aureus (in 5 min) and Escherichia coli (in 15 min). Moreover, the cytotoxicity test of the polymeric materials toward Α549 lung adenocarcinoma cells indicated very low toxicity as they did not affect either the cell growth or cell morphology. The above-mentioned results together with the scalable and easy-to-produce green methodology suggest that these materials can be promising candidates as filter coatings for use on air-purification devices.

Fabrication of air filters with advanced filtration performance for removal of viral aerosols and control the spread of COVID-19

COVID-19 is caused via the SARS-CoV-2 virus, a lipid-based enveloped virus with spike-like projections. At present, the global epidemic of COVID-19 continues and waves of SARS-CoV-2, the mutant Delta and Omicron variant which are associated with enhanced transmissibility and evasion to vaccine-induced immunity have increased hospitalization and mortality, the biggest challenge we face is whether we will be able to overcome this virus? On the other side, warm seasons and heat have increased the need for proper ventilation systems to trap contaminants containing the virus. Besides, heat and sweating accelerate the growth of microorganisms. For example, medical staff that is in the front line use masks for a long time, and their facial sweat causes microbes to grow on the mask. Nowadays, efficient air filters with anti-viral and antimicrobial properties have received a lot of attention, and are used to make ventilation systems or medical masks. A wide range of materials plays an important role in the production of efficient air filters. For example, metals, metal oxides, or antimicrobial metal species that have anti-viral and antimicrobial properties, including Ag, ZnO, TiO2, CuO, and Cu played a role in this regard. Carbon nanomaterials such as carbon nanotubes, graphene, or derivatives have also shown their role well. In addition, natural materials such as biopolymers such as alginate, and herbal extracts are employed to prepare effective air filters. In this review, we summarized the utilization of diverse materials in the preparation of efficient air filters to apply in the preparation of medical masks and ventilation systems. In the first part, the employing metal and metal oxides is examined, and the second part summarizes the application of carbon materials for the fabrication of air filters. After examination of the performance of natural materials, challenges and progress visions are discussed.

Advances in particulate matter filtration: Materials, performance, and application

Air-borne pollutants in particulate matter (PM) form, produced either physically during industrial processes or certain biological routes, have posed a great threat to human health. Particularly during the current COVID-19 pandemic, effective filtration of the virus is an urgent matter worldwide. In this review, we first introduce some fundamentals about PM, including its source and classification, filtration mechanisms, and evaluation parameters. Advanced filtration materials and their functions are then summarized, among which polymers and MOFs are discussed in detail together with their antibacterial performance. The discussion on the application is divided into end-of-pipe treatment and source control. Finally, we conclude this review with our prospective view on future research in this area.

Electrospun Nanofiber Membranes for Air Filtration: A Review

Nanomaterials for air filtration have been studied by researchers for decades. Owing to the advantages of high porosity, small pore size, and good connectivity, nanofiber membranes prepared by electrospinning technology have been considered as an outstanding air-filter candidate. To satisfy the requirements of material functionalization, electrospinning can provide a simple and efficient one-step process to fabricate the complex structures of functional nanofibers such as core-sheath structures, Janus structures, and other multilayered structures. Additionally, as a nanoparticle carrier, electrospun nanofibers can easily achieve antibacterial properties, flame-retardant properties, and the adsorption properties of volatile gases, etc. These simple and effective approaches have benefited from the significate development of electrospun nanofibers for air-filtration applications. In this review, the research progress on electrospun nanofibers as air filters in recent years is summarized. The fabrication methods, filtration performances, advantages, and disadvantages of single-polymer nanofibers, multipolymer composite nanofibers, and nanoparticle-doped hybrid nanofibers are investigated. Finally, the basic principles of air filtration are concluded upon and prospects for the application of complex-structured nanofibers in the field of air filtration are proposed.

A Hierarchical Structure of Flower-Like Zinc Oxide and Poly(Vinyl Alcohol-co-Ethylene) Nanofiber Hybrid Membranes for High-Performance Air Filters

In this article, we reported a hierarchical structure of flower-like zinc oxide (ZnO) and poly(vinyl alcohol-co-ethylene) (PVA-co-PE) nanofiber (ZnO@NF) hybrid membranes for high-performance air filters. Monodispersed flower-like ZnO superstructures were fabricated using a template-free and surfactant-free hydrothermal method, and PVA-co-PE nanofiber yarns were prepared using a melt extrusion phase separation approach. The PVA-co-PE nanofiber yarns were subjected to high-speed shearing in a mixed aqueous solution of isopropanol and water to obtain a stably dispersed nanofiber suspension. The ZnO@NF hybrid air filter was obtained by coating the mixture of flower-like ZnO superstructures and the PVA-co-PE nanofiber suspension on the surface of the polypropylene (PP) meltblown nonwoven with the electret charge eliminated. The filtration efficiency of the ZnO@NF hybrid air filter increases with increasing loading amount of the flower-like ZnO superstructures, while the pressure drop decreases. The flower-like ZnO superstructures were incorporated into the nanofiber-interconnected networks, which significantly reduces the pressure drop of the pure PVA-co-PE nanofiber air filter. The filtration efficiency of the ZnO@NF hybrid air filter is much higher than that of PP meltblown nonwoven with eliminated electret charge, solving the hidden problem of electret charge dissipation during the protection process. It is demonstrated that these nanofiber hybrid air filters have great application potential in some special areas such as high-temperature and high-humidity environments.

Multistructured Electrospun Nanofibers for Air Filtration: A Review

Air filtration materials (AFMs) have gradually become a research hotspot on account of the increasing attention paid to the global air quality problem. However, most AFMs cannot balance the contradiction between high filtration efficiency and low pressure drop. Electrospinning nanofibers have a large surface area to volume ratio, an adjustable porous structure, and a simple preparation process that make them an appropriate candidate for filtration materials. Therefore, electrospun nanofibers have attracted increased attention in air filtration applications. In this paper, first, the preparation methods of high-performance electrospun air filtration membranes (EAFMs) and the typical surface structures and filtration principles of electrospun fibers for air filtration are reviewed. Second, the research progress of EAFMs with multistructures, including nanoprotrusion, wrinkled, porous, branched, hollow, core-shell, ribbon, beaded, nets structure, and the application of these nanofibers in air filtration are summarized. Finally, challenges with the fabrication of EAFMs, limitations of their use, and trends for future developments are presented.

Preparation of aligned nanofibers using parallel inductive-plates assisted electrospinning

Electrospinning is a simple, cost-effective, and versatile technique for fabrication of nanofibers. However, nanofibers obtained from the conventional electrospinning are typically disordered, which seriously limits their application. In this work, we present a novel and facile technique to obtain aligned nanofibers with high efficiency by using parallel inductive-plates assisted electrospinning (PIES). In this new electrospinning setup, the electrostatic spinneret is contained in a pair of parallel inductive-plates, which can change the shape and direction of the electric field line during the electrospinning so as to control the flight trajectory and spatial alignment of the spinning nanofibers. This electrospinning setup can divide the electric field line into two parts which are respectively directed to the edge of the upper and lower inductive-plates. Then the nanofibers move along the electric field line, suspend and align between the parallel inductive-plates. Finally, the well aligned nanofibers could be easily transferred onto other substrates for further characterizations and applications. The aligned nanofibers with an average diameter of 469 ± 115 nm and a length as long as 140 mm were successfully achieved by using PIES technique. Moreover, nanofiber arrays with different cross angles and three-dimensional films formed by the aligned nanofibers were also facilely obtained. The novel PIES developed in this work has been proved to be a facile, cost-effective and promising approach to prepare aligned nanofibers for a wide range of applications.