Protein-Based Porous Materials for Sustainable, Multifunctional Filtration

shengnan Lin

doi:10.7273/000006399

Nowadays, air pollution has emerged as a serious problem for both the environment and society. It's important to use different types of air filters to protect human beings from various air pollutants (e.g. particulate matter (PM), toxic gaseous molecules, and microorganisms, etc.), especially since people spend most of their time indoors. However, in addition to limited functions, commercial air filters are made of petroleum-based polymers that are non-degradable and incompatible with the environment. Furthermore, synthesizing multifunctional filtering materials is costly, energy-consuming, and requires a complex process. Compared with other biomass, natural proteins, such as zein (corn protein) and gelatin, possess tremendous amounts of different chemical groups that can have interactions with various air pollutants. Thus, air filters derived from natural proteins that are biodegradable, multi-functional, and low-cost can potentially address the challenges of commercial air filters and avoid concerns associated with the synthesis of new filtration materials. This dissertation is on the studies of protein-derived air filters with rational structures leading to high filtration performances (high filtration efficiency and low pressure drop) and multifunctional filtration capabilities (more species of pollutants including toxic chemicals such as formaldehyde (HCHO)) for more effective, durable, and sustainable air filtration. For this purpose, three structures of protein air filters are designed and fabricated, which are two-dimension (2D) bimodal fabrics, quasi-3D fluffy fabrics, and 3D aerogels. Firstly, bimodal protein air filters are prepared to achieve high PM filtration efficiency and reduce pressure drop. It is found that the bimodal structure of the protein air filters can be tailored by co-spinning proteins in two solvent systems to enhance the filtration performance by controlling the denaturation of the proteins and the fiber diameter distribution. Secondly, a quasi-3D made of highly fluffy protein fibrous membranes to achieve high filtration performance is rationally generated by strong repulsion forces at the fiber-collector interface during electrospinning. It has been discovered that charged and hydrophilic forces, which are created and controlled by interactions at the protein-protein, collector-collector, and protein-collector interfaces, are critical in determining whether the final structure will be 2D compact or quasi-3D structures. Furthermore, to enhance the filtration capacities for multiple species of pollutants and maintain low pressure drop, 3D protein materials, zein nanofibrous aerogels and/or hybrid protein aerogels composed of zein nanofibers and gelatin foam are fabricated. The filtration performances of the resulting protein nanofibrous aerogels are remarkable in terms of both HCHO and PM2.5 removal efficiencies. Moreover, it is demonstrated that the hybrid aerogel air filters that are constructed from two types of natural proteins deliver versatile filtration capabilities, i.e., being able to capture oil/organic chemicals, toxic gaseous molecules, and PM, at a low pressure drop. This work indicates that protein-based porous materials are promising to incorporate environmental friendliness and multi-filtration capabilities for sustainable air-filtration systems.

Protein-Based Porous Materials for Sustainable, Multifunctional Filtration

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