Hierarchically Structured All-biomass Air Filters with High Filtration Efficiency and Low Air Pressure Drop Based on Pickering Emulsion

Although a high-efficiency air filter can be achieved from electrospun nanofabrics, it has been challenging to reduce the pressure drop, increase the filtration capacity, and improve the production rate of the electrospinning process. Here, we report a hierarchically structured all-biomass air filter with high filtration efficiency and low air pressure drop based on applying Pickering emulsions to generate protein-functionalized nanostructures. Specifically, the air filter consists of cellulose nanofibers (CNF)/zein nanoparticles as active fillers prepared from Pickering emulsions and porous structures of microfibers as the frame from wood pulp (WP). The zein-protein-coated nanoparticles, CNF/zein, contribute in multiple ways to improve removal efficiency of the filters. First, the exposed functional groups of zein-protein help to trap air pollutants including toxic gaseous molecules via interaction mechanisms. Second, the nanoparticles with a high surface area promote the capture capability for small particulate pollutants. Meanwhile, the long-micron WP fibers forming a frame with large pores significantly reduce the pressure drop. Via adjusting the component ratios of in the Pickering emulsion, we report an optimized air filter with the high efficiency for capturing both types of pollutants: particulate matter (PM) and chemical gasses such as HCHO and CO, and the extremely low normalized pressure drop, that is, approximately 1/170 of the zein-based nano air filter by electrospinning. This study initiates a cost-effective strategy for forming a hierarchical nano- and microstructure, enabling high efficiency of capturing particulate pollutants of a wide size range and more species. More significantly, this is the first study in which Pickering emulsion is applied as a critical approach with integration of bio- and nano-technology to make high-performance, green air filters.