Herein are described compositions useful in the purification of hydrocarbon-contaminated liquids (e.g., oil-contaminated water), methods of their manufacture, and methods of their use. In one instance, the composition can include a porous agricultural substrate selected from the group consisting of walnut shell, pecan shell, apricot pit, peach pit, corn cob, and a mixture thereof; the porous agricultural substrate having an external surface and pores, wherein the external surface is hydrophilic; and an organo-amine carried within the pores of the porous agricultural substrate. These compositions are utilized as regenerable filter media in place of, for example, ground walnut media.
