Methods and compositions for the adsorptive removal of methyl tertiary butyl ether (MTBE) from contaminated water sources and systems. The compositions contain acid-treated fly ash particles containing carbon, oxygen, and sulfur, and silver oxide nanoparticles having diameters in a range of 1-10 nm such that the silver oxide nanoparticles are present on the surface and in pore spaces of the acid-treated fly ash particles. The composition is in the form of particles having sizes in a range of 100 nm to 2.5 μm. Methods of preparing and characterizing the adsorbents are also provided.