Preconcentration and fluorometric detection of mercury ions using magnetic core-shell chitosan microspheres modified with a rhodamine spirolactam

We describe core-shell structured magnetic chitosan microspheres (Rho-MCS) that were modified with a rhodamine spirolactam fluorescent probe. They are shown to be a viable fluorescent probe for the determination of mercury ion, and for its removal and preconcentration. The microspheres were characterized by FTIR, thermogravimetric analysis and high-resolution digital images, and these confirmed the successful loading with rhodamine probe. The microspheres represent excellent bare-eye colorimetric and fluorescent turn on probes for Hg(II) via a mechanism based on chelation-enhanced fluorescence. Hg(II) can be quantified with a limit of detection of 15 nM. The effects of pH, temperature, contact time and initial concentration on adsorption were also investigated. The results indicate that Rho-MCS possess high adsorption capacity (337 mg g−1) and superb removal capability (up to 97 %). A kinetic study shows that the adsorption mechanism can be described by a pseudo second-order equation, while the adsorption isotherm can be fit to a Langmuir model. Hg(II)-loaded Rho-MCS can be recycled by addition of ethylenediaminetetraacetic acid (EDTA). The capability for removal of Hg(II) was maintained above 86 % after five consecutive adsorption-desorption cycles.