Structurally Engineered Polyimide Microsphere/Nanofibrous Gradient Aerogels with Enhanced Dust-Holding Capacity for High-Temperature Air Filtration

With the increasing emission of particulate matter (PM) from industrial and transportation activities, the demand for filtration materials exhibiting high thermal and chemical stability is growing. Nanofiber materials have attracted significant attention owing to their small fiber diameter, high porosity, and large specific surface area, which enhance their initial filtration efficiency. However, their densely packed architectures and uniform pore distributions lead to rapid surface cake formation, increasing airflow resistance and limiting dust-holding capacity. In contrast, three-dimensional gradient aerogel structures incorporate multiscale pore channels that facilitate depth filtration. Such architectures provide greater dust storage capacity and delay pore blockage, thereby significantly improving overall filtration performance. Here, gradient nanofiber aerogels (MGPAs) with a microsphere structure were successfully fabricated based on a single-component polyimide system. Utilizing single-component materials enhances recyclability and ensures uniform thermal expansion under temperature fluctuations, which is crucial for high-temperature filtration applications. The prepared material exhibits a dual-layer gradient nanofiber aerogel structure, comprising coarse fibers (≈730 nm) and medium fibers (≈300 nm). Furthermore, a composite functional layer composed of microspheres (≈3.34 μm) and ultrafine fibers (≈60 nm) was deposited onto the medium-fiber layer surface. Benefiting from this hierarchical structure, the MGPAs exhibit a PM0.3 filtration efficiency of 99.996%, with an initial pressure drop as low as 45.08 Pa, and a dust-holding capacity of 127 g/m2. Even at 300 °C, it maintains a filtration efficiency of 99.91%. This demonstrates their excellent thermal stability. The developed MGPAs offer significant potential for high-temperature exhaust gas filtration applications.