Ferromagnetic Ni decorated ordered mesoporous carbons as magnetically separable adsorbents for methyl orange

► Magnetically separable Ni-decorated ordered mesoporous carbon (OMC) was successfully synthesized. ► The adsorption capacities for MO dyes on ordered mesoporous carbons, Ni-OMC and activated carbon powder were comparatively investigated. ► The effects of surface area, pore structure, and Ni deposition on the absorption capacities for MO were investigated. ► The ferromagnetic Ni decorated OMC can be easily dispersed in aqueous solution and removed by an external magnetic field.