NOVELTY - Preparing magnetic activated carbons comprises (a) treating an aqueous solution comprising a biomass hydrothermally at autogenic pressure at 180-250 degrees C under acidic conditions in the presence of iron ions to obtain a precursor product, and (b) activating the precursor product obtained in step (a) by mixing an activating agent at elevated temperature of 550-850 degrees C for up to 9 hours.    USE - The method is useful for preparing magnetic activated carbon, which is useful for the separation and storage of gases, purification of liquids such as water and gases, removing pharmaceutical residues from sewage residue water and drinking water, heterogen catalyses support, aquariums and industrial fish farms, industrial water treatment, decaffeination processes, chemical spill clean-up, electromagnetic heated composite in oils, liquids, paint, pipes and building materials, decolorization, odor removal, purification of nitrogen, oxygen and methane, biogas upgrading, natural gas upgrading and cleaning electrodes in fuel cells, supercapitors and batteries (claimed).    ADVANTAGE - The method is capable of economically preparing the magnetic activated carbon in an efficient manner.    DETAILED DESCRIPTION - INDEPENDENT CLAIMS are included for:    (1) magnetic activated carbon prepared by the method;    (2) a method for separation of particles from liquid and/or gas comprising (1) providing the magnetic activated carbon in a container adapted to hold liquid and/or gas, (2) contacting the liquid and/or gas with the magnetic activated carbon in the container to purify the liquid and/or gas from particles, (3) applying an electromagnetic field to the container to separate the magnetic activated carbon from the liquid and/or gas, (4) removing the liquid and/or gas from the container, (5) ceasing the electromagnetic field, and (6) filling the container with the liquid and/or gas to purify and then repeating the steps (3)-(5), and (7) upgrading or destroying the magnetic activated carbon;    (3) a method for regenerating magnetic activated carbon comprising applying an oscillating electromagnetic field for heating the iron particles embedded in the magnetic activated carbon; and    (4) a method for heating a liquid or a solid comprising applying an oscillating electromagnetic field for heating the iron particles embedded in the magnetic activated carbon.