Fluorescent dendritic fibrous nanosilica@chitosan porous composite microbeads: Selective and sensitive probes and removal adsorbents for Hg2+/Hg+ ions

Dendritic fibrous nano-silica (DFNS) possesses unique porous structure, making it an outstanding candidate for heavy metal adsorption and separation. It is interesting to introduce natural polymer (chitosan) into DFNS and produce natural materials-based porous DFNS. Initially, in this work, DFNS underwent modification to enlarge size and enrich with -C≡C bonds. And then, NH2-naphthalimide fluorophore was click-reacted with the modified DFNS, forming fluorescent DFNS (FL-DFNS). Eventually, chitosan was integrated into FL-DFNS using diacyl chloride, generating the organic–inorganic fluorescent composite micro-beads (FL-DFNS@CS-3). FL-DFNS acts as a “turn on” sensor for Hg 2+ /Hg + ions, showing up to 5 times fluorescence increase. Also, it exhibited effective mercury adsorption. Due to its porous structure, it demonstrated good performance in adsorbing and separating Hg 2+ /Hg + ions, achieving removal ratios of 98.8 % and 96.1 %, and adsorption capacities of 196.2 mg/g and 180.4 mg/g, respectively. It reached effective adsorption equilibrium within 15 min and was reusable up to seven times. Overall, this work confirms the practical applicability of FL-DFNS and FL-DFNS@CS micro-beads for identifying and removing Hg 2+ /Hg + ions. Further exploration is worthy to explore its potential in environmental science and engineering.