BACKGROUND A process was developed to produce mesoporous composites with magnetic cores involving the following sequential reactions: glycerol polymerization/iron(III) reduction/polyglycerol pyrolysis/activated carbon production. RESULTS Glycerol containing 1, 3, 5, or 8 mol% iron(III) was heat treated to 380, 600, or 800 degrees C. The scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction, Mossbauer spectroscopy, thermogravimetry/differential thermal analysis, Raman spectroscopy, and nitrogen adsorption/desorption results showed that the iron(III) salt promoted polymerization of glycerol up to 380 degrees C. At higher temperatures, up to 800 degrees C, three different processes simultaneously occurred: pyrolysis of polyglycerol, reduction of iron(III) ion (Fe3+) to Fe-0 and Fe3C, and activation of the carbonaceous matrix, yielding a composite with a BET surface area of 136 m(2) g(-1). Moreover, to verify a possible environmental application of the prepared composites and their ability to remain suspended in aqueous solution, they were tested as adsorbents of organic contaminants such as methylene blue and indigo carmine. The test results were satisfactory: 10 mg of the prepared composite (GFe3-800) adsorbed up to 80% of the dye [10 mL of solution (50 ppm)] within 30 min of contact, and the composite could be removed from the system by simple magnetic attraction. CONCLUSIONS Magnetic composites exhibited good dye adsorption, in addition, good resistance to acid leaching. (c) 2019 Society of Chemical Industry