In 2009, hydrophilic surface of silica particles was made partially hydrophobic by adsorbing cetyltrimethylammonium bromide. Ferric oxide has a high affinity for adsorbing dissolved metals such as arsenic. Natural gas may be stored by adsorbing it to the porous solids called sorbents. Bentonite has the property of adsorbing relatively large amounts of protein molecules from aqueous solutions. Some carbons are more adept at adsorbing large molecules. Therefore, sensitivity can be increased by adsorbing more sensitizing dye. Surface modification techniques have been extensively researched for the application of adsorbing biological molecules. Activated charcoal works by adsorbing the toxin. A famous example involves thiols (RS-H) adsorbing onto the surface of gold. Also, as an antidiarrheal, it was believed to work by adsorbing the diarrheal pathogen. The previous derivations assumes that there is only one species, "A", adsorbing onto the surface.