Synthesis Of Magnetic Nanomaterials And Application Of Organic Estrogens In Environment

Water is the source and support of life on Earth. However, ever-increasing amounts of pollutants are entering the global waters as a result of intensive industrialization. It was found that most of environment estrogens were aromatic compounds including Polycyclic aromatic hydrocarbons （PAHs） and phthalate esters （PAEs）. These environment estrogens can enrich in animal body, and then passed into human body through food chain. Due to their trace concentration and wide distribution in water environments, it is required and vital to develop efficient analytical techniques. However, the direct determination of extremely low concentrations of analytes can be difficult, owing to matrix interferences or insufficient sensitivity of analytical techniques. Therefore, preliminary separation and preconcentration of trace analytes from matrices is usually required.Of these techniques for sample preconcentration methods, SPE has become a powerful tool in trace analysis, because of its high recoveries, enrichment factors, low consumption of organic solvents, and the possibility of combining with chromatography and spectroscopic techniques. SPE based on the partition coefficient of the analytes between the mobile phase and the solid sorbent. A high recovery and enrichment factor can be obtained only if a suitable sorbent is used. A suitable sorbent with large surface area, strong interactions with analytes and easily dispersed in water etc.Graphene carbon nitride （g-C₃N₄） has a stacked two-dimensional structure （2D sheets of tri-s-triazine connected via tertiary amines） and is made from simple precursors under ambient conditions at a low cost. Moreover, it is the most stable all otrope of carbon nitride. The structure of g-C₃N₄ is similar to graphene （G）, but the dispersity of g-C₃N₄ in water is much better and easier to exfoliation than G. The in-built N-rich functional groups and electronic delocalization properties endow the g-C₃N₄ with strong affinity （π-Ï€ conjugation, hydrogen bond interaction, electrostatic interaction and hydrophobic effect） for nonpolar carbon-based ring compounds. These properties suggest the possibility of g-C₃N₄ as a novels orbent for SPE and as a new material for the adsorption and preconcentration of organic analytes. However, sufficient dispersity of g-C₃N₄ usually creates difficulties in separating and recycling. On the other hand, g-C₃N₄ aggregate easily and cannot adsorb analytes effectively because of the simplicity of its surface.As one of the most widely used magnetic materials, Fe₃O₄ nanoparticles, has good stability, easy synthesis, high surface area and good solubility in water. Therefore, immobilizing Fe₃O₄ particles on the surface of nanomaterials is an effective solution, as it can easily be separated from solution with an external magnet. This approach can efficiently increase the recovery of nanoparticles and recycle time, and it is therefore our goal to design and prepare g-C₃N₄/Fe₃O₄ composite materials. Moreover, the application of this kind of magnetic material for SPE was defined as magnetic solid phase extraction （MSPE）. MSPE technology exhibits significant advantages in separation science. The sorbent is dispersed in a sample solution instead of being packed into an SPE cartridge providing a sufficiently large contact area between sorbents and analytes, and can be rapidly separated from the matrix by an external magnetic field. To examine the feasibility of this g-C₃N₄/Fe₃O₄ nanocomposite for MSPE, PAHs and PAEs were selected as model compounds. Key factors, including concentration of analytes, ionic strength, pH, eluent, amount of sorbent, time, etc., were systematically optimized to achieve excellent MSPE efficiency. Moreover, a quick, selective and sensitive method was established by combining MSPE with high performance liquid chromatography（HPLC） to analyze seven PAHs in real water samples. Under the optimized conditions, the proposed method showed good limits of detection （LOD, S/N=3） in the range of 0.05-0.1ng/mL and precision in the range of 1.8%-5.3%（RSDs, n=3）. Good spiked recoveries over the range of 80.0%-99.8% were obtained. This method was also successfully applied to the analysis of PAEs. It showed excellent sensitivity with limits of detection （S/N= 3） in the range of 0.05-0.1μg/L and precision in the range of 1.1%-2.6%（n= 5）. And good spiked recoveries over the range of 79.4%-99.4% were obtained. This research provides an environment-friendly strategy to prepare suitable sorbents for extraction or adsorption of various compounds within different matrices.In order to further the efficiency of enrichment and preconcentration, porous C-g-C₃N₄ was successfully synthesized. Immobilizing Fe₃O₄ particles on the surface of C-g-C₃N₄ was successfully synthesized by co-precipitation method. The surface area of C-g-C₃N₄/Fe₃O₄ nanocomposite is larger than g-C₃N₄/Fe₃O₄ nanocomposite. Some brominated flame retardants （BFRs） were selected as model compounds to evaluate the possible application of this nanocomposite. Response surface methodology （RSM） was used to investigate some key factors including ionic strength, pH, and temperature. Moreover, a quick, selective and sensitive method was established by combining MSPE with high performance liquid chromatography （HPLC） to analyze the five BFRs in real water samples. The combined use of this new nanocomposite and experimental strategy showed excellent precision （2.7%-5.2%） and sensitivity （limits of detection （S/N=3）: 0.1 -0.2μg/L）. This method was successfully applied to the analysis of real water samples giving good spiked recoveries over the range of 92.4%-99.8%. This research provides a possibility to apply this nanocomposite for adsorption, preconcentration, or even removal of various carbon-based ring or hydrophobic pollutants.