Polyvinylidene fluoride composite nanofibrous filter for high-efficiency PM_2.5 capture

Highlights

• PVDF composite nanofibrous filters were fabricated via electrospinning technology with rotary bead-wire spinnerets.

• PVDF composite nanofibrous filters show high filtration efficiency and ventilation rate.

• The high-performance composite nanofibrous filters achieve high productivity (1000 m²/day).

• The PVDF composite filter has a stable and efficient PM_2.5 removal rate and a long lifetime.

Abstract

Filter materials are widely used in the capture of fine particulate matter (PM), however, there are some problems such as low filtration efficiency, difficult cleaning and low air flow still need to be solved eagerly. In this work, a high-performance PM_2.5 capture as well as high productivity (1000 m²/day) was fabricated by introducing an ultra-thin polyvinylidene fluoride (PVDF) nanofibrous layer on the filter materials via electrospinning technology with rotary bead-wire spinnerets. The electrospun PVDF nanofibers exhibit a strong ability to intercept and attract PM, thus, the filtering efficiency of the filter material for PM_2.5 improved significantly (69.958%–98.161%). The composite filter has a higher air flow (278.4 mm/s) and lower pressure drop (30 Pa). Furthermore, long-term filtration and ventilation rate experiments show that the composite filter has stable high filtration efficiency (98.137%–96.36%) and ventilation rate. Electrospun PVDF fibers also have a certain degree of hydrophobicity, which could increase the long lifetime of composite filter effectively. This high-performance composite nanofibrous membrane would be a promising filter for large-scale PM_2.5 capture production and personal health protection.

Introduction

Rapid heavy consumption and combustion of fossil fuels, biomass and garbage would directly emit a large number of various pollutants into the atmosphere environment around human beings. Fine particulate matter (PM) is the most polluted and influential pollutant, which consists of various solid particles and droplets, and contains hundreds of chemical components [1,2]. According to the size of the particle size, PM can be divided into PM_2.5 and PM₁₀, which means that the aerodynamic diameter of the particles is less than 2.5 μm and 10 μm. The PM_2.5 can enter the human body through the process of breathing and accumulate in the trachea or lungs, inducing a serious threaten to human health. A large number of epidemiological studies have shown that long-term exposure to PM_2.5 can cause a variety of respiratory, cardiovascular diseases and even lung cancer, thus increasing morbidity and mortality. It also brought serious damage to the climate and ecological environment [3,4]. In the past 10 years, PM_2.5 air pollution has become more and more severe, which have seriously threaten to the human beings and the environment, especially in some developing countries with large manufacturing industries. During the last decade, due to the extremely high PM_2.5 content, the visibility was greatly reduced, and the air quality has become very poor. Therefore, it is urgent to develop filtration technology to prevent the harm of fine particles [[5], [6], [7]].

One of the most effective way to remove particles from the air stream is through a filter. Currently, many traditional filter media (cotton, nylon, polyester, traditional cellulose, etc.) are used. However, due to the large gap between the fibers (12–60 μm), many sub-micron fine particles can easily penetrate into the fiber, causing clogging and difficult to discharge, and the filtration efficiency will be reduced, as the dust particles entering the filter material block the filtration element [8,9]. With the accumulation of fine particles on the filter, the pressure loss of the air flow would also increase. Using electrospinning technology to deposit a layer of ultra-thin nanofibers on traditional filter materials would be a very good choice to get high performance PM_2.5 filter [10,11]. Electrospinning is a promising and rapid developing technology that can easily fabricate nanofiber materials with controllable membrane parameters such as pore size, fiber diameter, and thickness. Nanofibrous membrane prepared by electrospinning technology has the advantages of high porosity, micro-nano channel interconnection, and high specific surface area [[12], [13], [14], [15], [16], [17], [18]]. Composite nanofibrous filter has many advantages than traditional filter as the followings: Firstly, electrospun nanofibers have good mechanical properties, can directly intercept PM and have a strong adsorption effect on PM [[19], [20], [21], [22], [23], [24]]. The electrospun nanofibrous membrane would not only improve the filtration efficiency but also service life of the filter material. Secondly, the electrospun nanofibers have a strong interaction with the substrate, which ensure the nanofiber layer would not fall off when removing dust away from the surface of the filter material [25,26]. Finally, electrospun hydrophobic materials (such as polyvinylidene fluoride (PVDF) and thermoplastic polyurethanes (TPU)) could be facilely integrated to improve the hydrophobicity of the composite filter paper and increase the long lifetime of the filter material. Li et al. reported that the composite filter paper fabricated by electrospinning polyvinyl alcohol (PVA) nanofibers on a non-woven polypropylene (PP) substrate using needle-free electrospinning technology, and the PM_2.5 capture efficiency was 99.95% [27]. Patanaik et al. electrospun polyethylene oxide (PEO) nanofibers on nonwovens and evaluated long-term stability [28]. However, these composite filters (PVA and PEO) are hydrophilic and easily damaged by water [[29], [30], [31], [32]]. More importantly, although these composite media have good performance, the research is only carried out in the laboratory, little research focused on the industrialization of composite filter media.

As a new type of membrane material, PVDF has attracted wide attention due to its excellent mechanical strength, thermal stability, chemical resistance and high hydrophobicity. In this work, an ultra-thin PVDF nanofiber layer was introduced on the traditional filter media via spinner with rotary bead-wire spinnerets to large-scale fabricate high performance composite filter membrane. The results show that this composite filter can effectively improve the filtration efficiency and achieve high industrialization productivity. In addition, as the diameter of nanofibers and the thickness of fiber membrane have a great influence on the filtration efficiency, and the electrospinning technology can precisely control the thickness of the nanofibrous membrane, the prepared composite filter membrane exhibits high filtration efficiency. The stability of this composite filter membrane was also systematically further studied, including wettability, long-term PM_2.5 filtration efficiency and ventilation rate.