Magnetic Fe3O4/TiO2/graphene sponge for the adsorption of methylene blue in aqueous solution

Abstract

Graphene adsorbents are widely applied in pollutant removal with high adsorption capacities. However, the contradiction between high capacity and poor regeneration hinders the practical applications of graphene adsorbents in aqueous systems. In this study, we designed a magnetic Fe3O4/TiO2/graphene sponge (MFTGS) for dye adsorption in aqueous solution. Small Fe3O4 and TiO2 nanoparticles were decorated on the graphene sheets. MFTGS could be magnetically separated in aqueous systems with a saturated magnetization of 17.0 emu/g. MFTGS showed a moderately large capacity of 224 mg/g for methylene blue (MB). The adsorption could reach the equilibrium within 10 min with a k2 constant of 4.48 × 10−4 g/mg∙min−1. The adsorption of MB on MFTGS was driven by entropy production, so the capacity increased at higher temperature. The decrease of pH value and increase of ionic strength slightly lowered the adsorption capacity of MFTGS. MFTGS could be easily regenerated by ethanol washing, where 80% of the capacity retained after 4 cycles. Our results provided high-performance magnetic graphene adsorbents for dye removal and would benefit the development of graphene nanotechnology.