| Core-shell Fe3O4@SiO2nanoparticles [NPs] have been widely applied in the fields of environment sciences, life sciences and biomedical sciences due to their novel and unique physicochemical properties, such as large specific surface area and specific surface energy, high adsorption capacity for heavy metal ions, easy separation, and effective retrievability. It is believed that the Fe3O4@SiO2NPs as a support for surface modification have following advantages. The presence of magnetic nanoparticles in the Fe3O4@SiO2NPs can facilitate the magnetic separation by adding external magnetic field. Moreover, an inert silica nanoparticles coating on the surface of Fe3O4NPs significantly prevents the aggregation in solution, improves the chemical stability of Fe3O4NPs, and provides better protection against toxicity. In addition, the silica nano-shell around magnetic core has large specific surface area to provide sites for surface modification. So the Fe3O4@SiO2NPs can be utilized as an ideal candidate for detection and enrichment of heavy metal ions.In our work, the Fe3O4nanoparticles were prepared based on the chemical co-precipitation strategy of Fe2+and Fe3+in alkaline medium, and the Fe3O4NPs were coated with silica nanoparticles via the sol-gel process by the hydrolysis and condensation of tetraethyl orthosilicate (TEOS), which resulted in the core-shell Fe3O4@SiO2microspheres. The obtained Fe3O4@SiO2NPs had uniform spherical morphology with a uniform diameter of about22nm, and had a visible core-shell structure. The inner layer was Fe3O4nanoparticles, and the outer layer was SiO2nanoparticles. Through a sol-gel process by the hydrolysis and condensation of TEOS in ethanol/ammonia mixture, uniform silica layer can be formed on individual magnetite particle seed, resulting in core-shell Fe3O4@SiO2microspheres. Subsequently, the Fe3O4@SiO2NPs were successfully functionalized with designed fluorescent probes by a silanization reaction. The functionalized Fe3O4@SiO2NPs could be used to detect heavy metal ions selectively and remove it simultaneously. We successfully grafted diverse molecular probes on the surface of NPs for detection, removal and separation of heavy metal ions. The as-synthesized NPs with different fluorescent chemosensors are as following.1) The core-shell Fe3O4@SiO2microspheres were preparated and successfully functionalized with different fluorescent probes. The Fe3O4@SiO2NPs were superparamagnetic, and the saturated magnetizations of Fe3O4@SiO2NPs attained38.1emu/g. The functionalized nano-composites also appeared superparamagnetism. The Fe3O4@SiO2NPs and functionalized Fe3O4@SiO2NPs are magnetic, easily separated from the mix by applying an external magnetic field. Actually it is an important property for decontaminating agent.2) Rhodamine derivatives with spirolactam structure or other closed-loop helical structures could lead the fluorescence quenching due to the photoinduced electron transfer effect (PET). The PET effect could be prevented when a sensing of heavy metal ion induced ring-opening of spirolactam of rhodamine derivatives via coordination or irreversible chemical reaction, resulting in color and fluoresent changes in macroscopic. The property of rhodamine derivatives provides an ideal mode to construct OFF-ON fluorescent switch sensors. The Fe3O4@SiO2NPs were modified with hexamethylene diisocyanate (HDI) by a dehydration reaction (as Fe3O4@SiO2-NCO). Subsequently the rhodamine derivatives (Rho6G-EDA) were introduced on the Fe3O4@SiO2-NCO surface. The obtained functionalized nanocomposites were severed as Fe3O4@SiO2-Rho. The Fe3O4@SiO2-Rho NPs exhibited selective "turn-on" type fluorescent enhancements and distinct color changes from colorless to pink with Hg ions, no significant fluorescent changes were prompted by addition of other metal ions (Ag+, Cu2+, Zn2+, Ni2+, Co2+, Cd2+, Mn2+, Pb2+, Cr3+and Fe3+) in the same suspension. So Fe3O4@SiO2-Rho NPs served as a chemosensor were utilized to detect Hg2+selectivity. The Fe3O4@SiO2-Rho NPs also showed a high capacity to remove Hg2+at room temperature, the removal efficiency of Hg2+attained85.44%.3) Rhodamine hydrazide (RhoB-NH2) was prepared by the reaction of Rhodamine B and hydrazine hydrate. The synthesis of N-(rhodamine-B) lactam-eth-ylenehydrazine (RhoB-en) was performed via reacting Rhodamine hydrazide and2-Hydroxy-l-naphthaldehyde. The Fe3O4@SiO2NPs were grafted with RhoB-en, defined as Fe304@Si02-Rho NPs. The obtained Fe3O4@SiO2-Rho NPs served as a fluorescent OFF-ON nanosensor was utilized to detect Zn2+selectivity in acetonitrile medium. The Fe3O4@SiO2-Rho NPs also showed high binding ability to Zn2+with a removal efficiency of87.34%at room temperature.4) The quinolines have fluorescence quenching for copper ion and have fluorescence enhancement for zinc ion. The end amino group functionalized Fe3O4@SiO2nanoparticles (Fe3O4@SiO2-APTES) were functionalized with8-chloroacetylaminoquinoline (CAAQ) as an efficient nanosensor for Zn2+and Cu2+detection and removal. The Fe3O4@SiO2-CAAQ can detect Zn2+by fluorescence enhancement method and detect Cu2+by fluorescence quenching method. The hybrid fluorescent material had the high affinity and sensitivity for highly efficient removal of Zn2+and Cu2+, and the removal efficiency of Cu2+and Zn2+could reach92.37%and91.65%at room temperature, respectively.The structure and chemical composition of Fe3O4@SiO2nanoparticles have been confirmed by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectra (FT-IR), X-ray photoelectron spectroscopy (XPS) et al.. Atomic absorption spectrum (AAS) and UV-vis spectra were employed to analysize the interactions between the functionalized Fe3O4@SiO2NPs and heavy metal ions. |
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