Fabrication of Fe3O4@graphene oxide core-shell nanospheres for ferrofluid-based dispersive solid phase extraction as exemplified for Cd(II) as a model analyte

The authors describe the synthesis of core-shell structured Fe3O4@graphene oxide nanospheres (denoted as Fe3O4@GO NSs) via a chemical (covalent) bonding method. A chemical method was applied to cutting graphene oxide flakes into GO nanosheets. These were then covalently immobilized onto the surface of magnetite (Fe3O4) nanoparticles. The material was characterized by TEM, SEM, EDX, FTIR, vibrating sample magnetometry and Raman spectroscopy. The data confirmed the coexistence of Fe3O4 and GO nanosheets with a core-shell structure. The Fe3O4@GO NSs were applied to ferrofluid-based dispersive solid phase extraction of cadmium(II) as a model analyte using an ionic liquid carrier. This sorbent possesses as large contact surface area and a high density of polar groups on its surface. The nanoparticles, when finely dispersed in the sample solution, result in almost complete extraction of Cd(II) within a few seconds. Cd(II) was then quantified by FAAS. Under optimized conditions, the assay has the following features: (a) A detection limit of 0.12 ng mL−1, (b) a preconcentration factor of 250, (c) a relative standard deviation of 1.4 % (at a level of 50 ng mL−1; for n = 10); (d) a linear analytical range extending from 0.4 to 150 ng mL−1, (e) a maximal adsorption capacity of 33.7 mg g−1, and (e) a well expressed Langmuir adsorption isotherm.