Abstract: A respiratory protection filter includes filtration media. The filtration media includes an iron-doped manganese oxide material having an average pore size (BJH method) in a range from 1 to 4 nm and a surface area (BET) of at least 300 m2/g, or at least 350 m2/g, or at least 400 m2/g.

Abstract: The air filter device includes a main member, a conduit member, a sealing piece, a pressurizing piece, a filter element, and a cap. The conduit member, sealing piece, pressurizing piece, and filter element are sequentially stacked in the main member. The conduit member provides a spiral duct with a second inlet and a second outlet. The second inlet is conducted to an outlet opening of the pressurizing piece. The second outlet is conducted to a plug extended from a bottom side of the main member. The cap is fastened to the main member with airflow paths between the cap and main member. The main member may be joined to the inlet terminal of any air compressor. External air is drawn into the air compressor through the filter element, pressuring element, conduit member, and the plug so as to achieve smooth, steady, and quiet air intake.