Stretchable and Compressible Si₃N₄ Nanofiber Sponge with Aligned Microstructure for Highly Efficient Particulate Matter Filtration under High‐Velocity Airflow

Abstract

Particulate matter (PM), a complex mixture of small particles and liquid droplets floating in air, is a consequence of severe air pollution. [1][2][3] PM is usually classified as PM 2.5 and PM 10 , referring to particle sizes less than 2.5 µm and between 2.5 and 10 µm, respectively. The smaller the PM, the more hazardous it becomes because it can penetrate into human lungs and bronchi, causing many respiratory diseases, including cancer. [4][5][6][7][8] Nowadays, PM has become a cosmopolitan environmental crisis, especially in developing countries. Therefore, managing and reducing PM pollution is urgently needed. [9,10] Particulate matter (PM) is one of the most severe air pollutants and poses a threat to human health. Air filters with high filtration efficiency applied to the source of PM are an effective way to reduce pollution. However, many of the present filtration materials usually fail because of their high pressure drop under high-velocity airflow and poor thermal stability at high temperatures. Herein, a highly porous Si 3 N 4 nanofiber sponge (Si 3 N 4 NFS) assembled by aligned and well-interconnected Si 3 N 4 nanofibers is designed and fabricated via chemical vapor deposition (CVD). The resulting ultralight Si 3 N 4 NFS (2.69 mg cm −3 ) processes temperature-invariant reversible strechability (10% strain) and compressibility (50% strain), which enables its mechanical robustness under high-velocity airflow. The highly porous and aligned microstructure result in a Si 3 N 4 NFS with high filtration efficiency for PM 2.5 (99.97%) and simultaneous low pressure drop (340 Pa, only <0.33% of atmospheric pressure) even under a high gas flow velocity (8.72 m s −1 ) at a high temperature (1000 °C). Furthermore, the Si 3 N 4 NFS air filter exhibits good long-term service ability and recyclability. Such Si 3 N 4 NFS with aligned microstructures for highly efficient gas filters provides new perspectives for the design and preparation of high-performance filtration materials.Air filters applied at the source of PM are thought to be an effective way to reduce air pollution. [11,12] Usually, there are two types of air filters. One is a porous membrane air filter, which usually has small pores to capture PMs. However, once PMs deposit and block the pores, the pressure drop becomes large, and the filter fails. [13] The other is a fibrous air filter, which exhibits a highly porous microstructure that is assembled by micrometer-sized fibers or nanofibers and captures PMs via a series of mechanisms such as physical interception, adhesion, and electrostatic interaction. [14][15][16] Compared with micrometer-sized fibrous air filters, nanofiber-based filters have higher PM trapping efficiency owing to their smaller pores and higher porosity. Nanofibrous air filters also have a low pressure drop because of the similar size of the nanofiber diameter and the average path of air molecules. [11] Ceramic fibrous air filters have recently gained increased attention owing to their prominent chemical and physical stabilities and high-...

Resilient and Antipuncturing Si3N4 Nanofiber Sponge

“…The stress–strain curve (Figure d) during loading exhibits three typical deformation regions: an elastic region in the beginning (ε < 3%), next the yield region, in which tensile stress increases with strain nonlinearly until reaching the yield point, and last the extension region where stress decreases until break. The horizontal strain was 55% until yield, while the vertical strain was 45%, superior to other ultralight ceramic nanofibrous networks. ,, During the stretch, the sample showed obvious contraction perpendicular to the tensile direction, resulting in a Poisson’s ratio of about 0.28. Remarkably, wire drawing was observed obviously during the horizontal stretching, making the sponge extend after yielding instead of brittle failure (inset of Figure d).…”

“…Selected area electron diffraction (SAED) analysis is corresponds well with single-crystal α-Si 3 N 4 (inset of Figure f). The [100] growth direction of the nanofiber was also confirmed by the SAED, corresponding to one-dimensional α-Si 3 N 4 materials reported in other works. ,− Lattice stripes could be seen easily in the high-resolution TEM image (Figure g), and the interval of the lattice fringe is 0.67 nm corresponding to the (100) plane of α-Si 3 N 4 . Energy-dispersive spectroscopy (EDS, Figure h–k) analysis shows that the nanofiber bundle is composed of Si 3 N 4 crystal nanofibers with a very thin oxide shell.…”

“…The horizontal strain was 55% until yield, while the vertical strain was 45%, superior to other ultralight ceramic nanofibrous networks. 10,15,28 During the stretch, the sample showed obvious contraction perpendicular to the tensile direction, resulting in a Poisson's ratio of about 0.28. Remarkably, wire drawing was observed obviously during the horizontal stretching, making the sponge extend after yielding instead of brittle failure (inset of Figure 3d).…”

Recent Progress of the Preparation and Application of Electrospun Porous Nanofibers

“…Under the influence of external electrostatic fields, electrospinning technology, a sophisticated technique for fiber production, rapidly stretches polymers into continuous fibers with sizes varying from microns to nanometers [ 1 , 2 , 3 ]. Electrospinning technology has several advantages over other fiber film production techniques, including ease of operation, controllable process, high operability, low cost, and flexibility.…”

Review of the Principles, Devices, Parameters, and Applications for Centrifugal Electrospinning

“…Nanofibers have significant advantages over conventional thick fibers, such as a high specific surface area, high porosity, and easy functional design. [2][3] Based on these DOI: 10.1002/mame.202200057 advantages, nanofibers have attracted widespread attention and have been increasingly applied in scaffolds for tissue engineering, [4][5][6] drug delivery, [7][8][9] filtration, [10][11][12] adsorption, [13][14][15] energy, [16][17][18] electronic devices, [19][20][21] food packaging, [22][23][24] and other areas. [25][26][27] The commonly used methods for preparing nanofibers include centrifugal spinning, [28][29][30] electrospinning, [31][32][33] pressurized gyration, [34][35][36] self-assembly, [37][38][39] and chemical synthesis.…”