A filter for removing contaminants from air. The filter includes (a) a substrate that does not have any volatile ammonia on the surface thereof; (b) copper that has been impregnated onto the substrate; and (c) molybdenum and/or tungsten that has been impregnated onto the substrate. The filter can be made using an aqueous solution(s) that contains one or more of a first copper salt and a second salt that include a polynuclear anion that contains molybdenum, tungsten, or both. Because the metals can be impregnated onto the substrate surface without using an ammonium-based solution, the need to manage ammonia off-gassing is avoided. Further, no volatile ammonia would be present on the resulting substrate surface.