Ultrafast adsorption of organic dyes by activated-carbon@Fe₃O₄ nanoscale composites: An effective solution for water purification

Superparamagnetic (SPM) Fe₃O₄ nanoparticles (NPs) decorated activated charcoal (AC) skeletal (AC@Fe₃O₄) type nanoscale composites (NCs) have been prepared by a scalable and facile approach involving impregnation of AC with stable dispersion of SPM Fe₃O₄ NPs followed by controlled vacuum drying. These NCs exhibit coupled magnetic character and porosity which can be easily optimized by controlling weight ratio of two phases. The electron microscopy images show the presence of clustered Fe₃O₄ particles present all over the surface of porous AC particles and prevalence of meso-pores, which provides the channels for ingress and immobilization of sorbent moieties. The magnetometry and nitrogen adsorption measurements reveal that magnetic character increases whereas porosity decreases with the increase in Fe₃O₄ NP loading. These NCs have been demonstrated for purification of water containing methylene blue (MB) dye as an impurity. The porosity of these composites allow rapid adsorption (<1 min) of MB with good removal efficiency (> 99%) and their magnetic behaviour helps in instantaneous separation of MB adsorbed NC particles by the application of external magnetic field. The sorbent can be reused several times after proper regeneration with retention of more than 95% of the original adsorption capacity.