Application Of Thiol-functionalized Nano-Fe₃O₄ To The Mearement Of Trace Metal Ions In Seawater

Based on the modification and superparamagnetism characteristics of Fe₃O₄ nanoparticles,thiol-functionalised Fe₃O₄ nanoparticles was prepared in thesis through the modification of Fe₃O₄ nanoparticle by 3-Mercaptopropyltriethoxysilane.Trace levels of heavy metal ions in coastal and esturine seawater samples were first separated and enriched by the thiol-functionalised Fe₃O₄ nanoparticles,and then determined by atomic fluorescence spectrometry?AFS?and inductively coupled plasma mass spectrometry?ICP-MS?.This thesis contains four chapters as below.Chapter 1 is a review of the literature.The measuring method of heavy metals in seawater,the synthetic technhiques and modified methods of Fe₃O₄ nanoparticles were summarized.Then,the research aims and contents were figured out accordingly.The synthetic technique and modified method of Fe₃O₄ nanoparticles was set up in Chapter2.Fe₃O₄ nanoparticles were prepared through chemical coprecipitation method and the modification was applied by using the 3-Mercaptopropyltriethoxysilane?MPTES?.The characteristics of Fe₃O₄ nanoparticles and thiol-functionalised Fe₃O₄ nanoparticles were investigated by the scanning electron microscope?SEM?,the superconducting quantum interference device,the fourier transform infrared spectrometer,the Ellman's method and the simultaneous thermal analysis.Experiment results indicated that the partical size of Fe₃O₄nanoparticles ranged from 20 to 30 nm,but Fe₃O₄ nanoparticles showed agglomeration.The saturation magnetization intensity of Fe₃O₄ nanoparticles was 67.99 emu/g.The result suggested that Fe₃O₄ nanoparticles had favorable magnetizability which could be strongly responsive to an external magnetic field.After modification,the partical size of thiol-functionalised Fe₃O₄nanoparticles increased to 50⁶0 nm.The results showed that thiol-functionalised Fe₃O₄nanoparticles have strong superparamagnetism,but the saturation magnetization intensity slightly declined.The infrared spectrum confirmed that the surface of Fe₃O₄ was modified with–SH by the MPTES.The amount of thiol groups grafting on Fe₃O₄ measured by the Ellman method was 17.8?mol/g.In Chapter 3,a new AFS method was eveloped to measure Hg²⁺in seawater after separation and enrichment by thiol-functionalised Fe₃O₄ nanoparticles.The adsorption and elution condition of trace Hg²⁺by thiol-functionalised Fe₃O₄ nanoparticles were invetigated and optimized.Results suggested that the trace Hg²⁺in seawater cound be enriched using 0.5mg/mL of thiol-functionalised Fe₃O₄ nanoparticles at pH 6.0⁸.0 with adsorption time of20³0 min.Hg²⁺absorbed on the thiol-functionalised Fe₃O₄ nanoparticles was eluted with1.5%HCl.The proposed method was successfully used to detect Hg in seawater samples.The relatively stanard derivation?RSD?,detection limit and standard added recovery were 8.9%¹0.5%,5.3 ng/L and 86.1%¹25.9%,respectively.Results showed that the method of enrichment and separation of trace Hg²⁺in seawater by Fe₃O₄ nanoparticles was prominent.In Chapter 4,a new method to simotaneously enrich trace Cr²⁺,Cu²⁺,Zn²⁺,Cd²⁺and Pb²⁺in seawater samples by thiol-functionalised Fe₃O₄ nanoparticles,and detect by ICP-MS was proposed.The adsorption and elution conditions were also optimized.Results showed that the trace metal ions in seawater were enriched using thiol-functionalised Fe₃O₄ nanoparticles at pH 7.0⁸.0 with adsorption time of 20³0 min.and the adsorption metals could be eluted using 2%HNO₃.The developed method was used to determine tracemetals in seawater.The standard added recoveries of Cu²⁺,Cr²⁺,Cd²⁺,Zn²⁺and Pb²⁺were 87.8%¹14.7%,85.6%¹04.6%,95.4%¹41.8%,92.9%¹45.7%and 56.5%⁷8.1%,respectively.The detection limit of Cu²⁺,Cr²⁺,Cd²⁺,Zn²⁺and Pb²⁺were 0.15,0.10,0.38,0.07 and 0.13 ng/L,respectively.The RSD of the measurement was lower than 14.2%.The last of the thesis is the conclusion.The method for the preparation of Fe₃O₄nanoparticles and the modification of thiol-functionalised Fe₃O₄ nanoparticles was proposed.The trace Hg²⁺,Cr²⁺,Cu²⁺,Zn²⁺,Cd²⁺and Pb²⁺in seawater samples were enriched and separated using thiol-functionalised Fe₃O₄ nanoparticles and further detected by AFS and ICP-MS.