Proteins are well-known by their numerous active functional groups along the polypeptide chain. The variety of functional groups of proteins provides a great potential for proteins to interact with airborne pollutants with varying surface properties. However, to our knowledge, a successful demonstration of this potential has not been reported before. In this work, soy protein, a type of abundant plant protein, has been employed for the first time to fabricate multifunctional air-filtration materials. To take advantage of the functional groups of soy protein for air filtration, the soy protein was first well denatured to unfold the polypeptide chains and then fabricated into nanofibers with the help of poly(vinyl alcohol). It was found that the resultant nanofabrics showed high filtration efficiency not only for airborne particulates with a broad range of size but also for various toxic gaseous chemicals (e.g., formaldehyde and carbon monoxide), a capability that has not been realized by conventional air-filtering materials. This study indicates that protein-based nanofabrics are promising nanomaterials for multifunctional air-filtration applications.

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Highly polluted air is usually concentrated with particles of broad sizes and species of gaseous toxic chemicals. Filtration of these pollutants simply relying on size effects is not sufficient; instead, strong interactions between filtering materials and pollutants are in critical need. Moreover, to reduce or even avoid further pollution to the environment from disposing of the massive amount of used air filters demands the development of "green" air filtering materials. Here, we report a high-performance hybrid cellulose/protein air filter with nanofiber structures. Interestingly, it was discovered that textured cellulose paper towel can not only act as a flexible mechanical support but also as a type of air flow regulator that can improve pollutant−nanofilter interactions. Therefore, the high-performance natural protein-based nanofabrics are promoted both mechanically and functionally by textured cellulose paper towel. Study results indicate that this hybrid filtering material possesses excellent removal efficiency for particulate matter with a broad size range, in particular for small pollutants, the most challenging for air filtration, and multiple species of toxic chemicals. This study indicates that the protein/cellulose hybrid system can be used in high-performance air filters and are disposable due to the abundance and environmental friendliness of the original materials.

By combining the significant properties of nanofibers and the multi-functionality of pure proteins, “green” multifunctional air-filters with high removal efficiency of particulates and toxic gases is achieved.

Development of high-performance nanomaterials with not only strong ability to trap the pollutants but also good structure stability under varying environmental conditions is a critical need for air-filtration applications. However, it has been very challenging for a filtering material to simultaneously realize multifunctional air filtration and good environmental stability. Here, based on our previous studies on protein-based nanofilters, we report a cross-linked protein nanofabric to address this challenging issue. It is found that cross-linked protein nanofabrics can significantly improve the structure stability against different moisture levels and temperatures, while maintaining the multifunctional filtration performance. Moreover, it is demonstrated that the cross-linked protein nanomaterials also possess antibacterial properties, such as Shewanella oneidensis bacteria, further improving the environmental stability. The effects of cross-linking with different loadings of cross-linking agent on the structure stability and filtration performance are further investigated at different humidity levels and temperatures. This study provides a cost-effective solution for advanced "green" nanomaterials with excellent performance in both filtration functions and structure stability under varying environment.

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