Colorimetric fluorescent nanosensor based on hexamethylene diisocyanate for fluorescent responses and adsorption of heavy metal ions

An inorganic-organic hybrid material based on magnetic Fe₃O₄@SiO₂ nanoparticles was synthesized for fluorescent responses and removal of heavy metal ions, in which superparamagnetic Fe₃O₄@SiO₂ nanoparticles were firstly prepared and modified with hexamethylene diisocyanate (HDI) instead of 3-isocyanatopropyltriethoxysilane (IPTES) as the organic coupling agent, and then a rhodamine derivative with spirolactam structure (Rho-en) was conjugated on the HDI functionalized Fe₃O₄@SiO₂ nanoparticles through isocyanate groups. Both of functionalized Fe₃O₄@SiO₂ nanoparticles based on IPTES and HDI were characterized by FT-IR and XPS, and the results indicated that HDI was a good alternative as chemical bridge for surface modification on the surface of Fe₃O₄@SiO₂ nanoparticles. The inorganic-organic hybrid composites synthesized based HDI showed naked-eye color changes and fluorescent responses towards Zn²⁺, Cd²⁺, Mn²⁺, Pb²⁺, Hg²⁺ and Fe³⁺, which could serve as the available proofs for the qualitative analysis. Moreover, the as-obtained composites not only had excellent adsorption capability for Pb²⁺ and Hg²⁺, but also showed strong magnetic sensitivity, which could help to the removal and separation of functionalized magnetic nanocomposites after capturing the heavy metal ions. In addition, the plausible interaction mode of functionalized Fe₃O₄@SiO₂ nanoparticles with heavy metal ions was discussed.