In the water treatment field, activated carbons (ACs) have wide applications in adsorptions. However, the
applications are limited by difficulties encountered in separation and regeneration processes. Here, activated
carbon/Fe3O4 nanoparticle composites, which combine the adsorption features of powdered activated
carbon (PAC) with the magnetic and excellent catalytic properties of Fe3O4 nanoparticles, were
fabricated by a modified impregnation method using HNO3 as the carbon modifying agent. The obtained
composites were characterized by X-ray diffraction, scanning and transmission electron microscopy,
nitrogen adsorption isotherms and vibrating sample magnetometer. Their performance for methyl orange
(MO) removal by adsorption was evaluated. The regeneration of the composite and PAC-HNO3 (powdered
activated carbon modified by HNO3) adsorbed MO by hydrogen peroxide was investigated. The composites
had a high specific surface area and porosity and a superparamagnetic property that shows they can
be manipulated by an external magnetic field. Adsorption experiments showed that the MO sorption process
on the composites followed pseudo-second order kinetic model and the adsorption isotherm date
could be simulated with both the Freundlich and Langmuir models. The regeneration indicated that
the presence of the Fe3O4 nanoparticles is important for a achieving high regeneration efficiency by
hydrogen peroxide.