Porphyrin-functionalized Fe3O4@SiO2 core/shell magnetic colorimetric material for detection, adsorption and removal of Hg2+ in aqueous solution

A fluorimetric/colorimetric mercury(II) sensor based on porphyrin-functionalized Fe3O4@SiO2 core/shell magnetic microspheres has been developed and demonstrated by sol-gel grafting reaction. These multifunctional microspheres show excellent fluorescence sensitivity and selectivity towards Hg2+ over other metal ions (K+, Na+, Ba2+, Mn2+, Ca2+, Co2+, Cu2+, Ag+, Mn2+, Ni2+ and Pb2+). Upon addition of Hg2+, the color of porphyrin-functionalized Fe3O4@SiO2 microspheres changes from red to green within 1 min and the fluorescence of microspheres becomes obviously weak. Conversely, no significant changes in fluorescence emission or color are observed in the parallel experiment with other metal ions. Regarding the reversibility of the microspheres, the color and fluorescence of the porphyrin-functionalized Fe3O4@SiO2 microspheres in the presence of Hg2+ ion are found to be almost reversible when the microspheres are treated with EDTA solution. Furthermore, the used microspheres can efficiently remove Hg2+ ions in aqueous solution and easily separated from the mixture by adding an external magnetic field. Theses results suggest that functionalized Fe3O4@SiO2 core/shell magnetic microspheres are potentially useful materials for simultaneously detecting and removing environmental pollutants.