Facile method to synthesize fluorescent chitosan hydrogels for selective detection and adsorption of Hg/Hg.

Fluorescent chitosan-based hydrogel for the selective detection and adsorption of Hg/Hg in aqueous environment was prepared through three-step synthesis strategy. NO-Boron-dipyrrolemethene (BODIPY) was prepared firstly, and then the -NO group was reduced to -NH group. Finally, the NH-BODIPY was introduced to chitosan by Schiff base formation reaction through bi-aldehyde. Eventually, fluorescent chitosan hydrogel was obtained. The as-prepared fluorescent hydrogel probe could detect Hg/Hg through PET mechanism with the detection limit of 0.3 μM. The recognition site which combines Hg/Hg is CN, it is just formed in the reaction with chitosan and the amino group on BODIPY. Adsorption capacity of the fluorescent hydrogel is 121 mg·g, which is almost seven times of the original chitosan. The isotherm and kinetics of Hg/Hg removal follows Langmuir isotherm and pseudo-second order kinetics, respectively. Besides, a series of fluorescent hydrogels were prepared to compare the elasticity, hydropHilicity, fluorescence intensity and adsorption capacity.