Air filters formed from mats of protein-containing nanowires are provided. The nanowires are formed into a mat with pores that allow air to pass through while physically filtering particulate matter. The protein in the protein-containing nanowires also serves to chemically filter polluted air passed through the filter. Specifically, chemical functional groups from the many amino acids that comprise the protein of the protein-containing nanowire react with certain chemical pollutants (e.g., carbon monoxide and formaldehyde) in order to capture or otherwise neutralize the pollutant. Accordingly, the single nanofiber mat performs two filtering functions. Methods of filtering air using the provided air filters are also disclosed, as well as methods for making the air filters from protein-containing nanofibers.