Adsorbent materials are disclosed, along with filter elements containing the adsorbent materials methods of using adsorbents to remove siloxane contaminants from a gas stream. The method includes providing an adsorbent material that has been washed with an acid and passing a gas through the adsorbent material so as to reduce siloxane levels in the gas. A filter element for reducing siloxane levels in a gas includes a first adsorbent material, the first adsorbent material comprising an acid-washed adsorbent; and a second adsorbent material, the second adsorbent material comprising an acid-impregnated adsorbent.