Preparation And Application Of Novel Core-Shell Composite Microspheres Based On Phenol Aldehyde And Melamine Resins

Core-shell composite microspheres have been paid much attention to in field of new materials in recent years. Core-shell architecture can make full use of the advantagous properties of each component, make defects remedied, and even evoke some new functions. Thus, the design and develop of microspheres with core-shell structure are of great significance. In this thesis, uniform monodisperse novel core-shell composite microspheres have been prepared based on phenolic resin and melamine resin using facile methods. The as prepared composite microspheres were used as supercapacitor, surface enhanced Raman substrates, encoding microspheres for multiplex analysis of DNA dection. The obtained results are summarized as following:(1) An ultrafast, facile and efficient microwave hydrothermal approach was designed to fabricate magnetic Fe3O4/PF core-shell microspheres by the in-situ sol-gel polymerization of phenol and formaldehyde with magnetic Fe3O4clusters as the seeds. To make a controllable preparation, synthetic parameters including amounts of the reactant, reaction temperatures and reaction time were investigated in details. The PF shell was found to be coated on Fe3O4clusters within10minutes and uniformed spheres can be obtained in20min. The as-prepared microspheres were highly uniform in morphology and the method was found to allow the shell thickness to be finely controlled. The as-prepared Fe3O4/PF microspheres were monodisperse and highly dispersible in water, ethanol, N, N-Dimethyformamine and acetone, which is beneficial for the further functionalization and applications of the Fe3O4/PF microspheres.(2) The Fe3O4/PF composite microsphere was further modified to fabricate iron oxide/carbon/air/carbon composite nanospheres (RPCN) with uniform rattle-type architecture for high performance supercapacitor. The inner and outer carbon shells of RPCN were about50nm and70nm, respectively. The RPCN microspheres was found to owing double pore structure with narrow pore distribution at pore size of1.9nm and4nm.The RPCN had a highe surface area of616.7m2/g and corresponding total pore volume is0.68cm3/g. The unique pore structure of RPCN nanomaterial can be expected to be advantageous for application in supercapacitor. The cyclic-voltammogram and charge-discharge results show that, RPCN electrode specific capacitance was216F/g, which was much higher than that of each component. In addition, the composite nanospheres electrode exhibited excellent long cycling stability with capacitance retention of92.4%over1000cycles at current density of0.2A/g, which give a bright prospect for the application of supercapacitors. Electrochemical impedance spectroscopy test results show that, the resistance of the solution Rs was0.86Ω and the charge transfer resistance Rct was3.84Ω, indicating that the RPCN electrode has good conductivity and charge transfer ability.(3) Uniform MF/Ag-NPs core-shell composite microspheres were fabricated as isolated SERS-active substrates by a facile synthetic strategy through coating of Ag nanoparticles (Ag-NPs) onto MF (melamine-formaldehyde resin) microspheres. These microspheres can be imaged and individually manipulated under optical microscopes. Single Ag-NPs was saved as SERS-active substrates to detect etramethylthiuram disulfide. The typical SERS activities of these substrates were evaluated using ABT, CBT, and DTNB as the Raman reporting molecules. First, the MF microspheres were synthesized by polycondensation of melamine and formaldehyde. After the detailed investigation of the synthesis condition of MF microspehres, the optimized conditions have been obtained. The MF microspheres obtained under the maximum parameters were about4.8μm with a PDI of0.05. The effect of Ag-NPs amount on SERS activity of a single MF/Ag-NPs microsphere was examined. It was observed that higher amount of Ag-NPs lead to stronger SERS enhanced signal. With increasing silver coating, the SERS intensity increased. However, when the mass ratio of AgNO3and MF microspheres was over10:1, the extent of coverage of Ag-NPs and the SERS hot spots on MF microsphere reached the maximum limitation, so the SERS intensity did not increased further. Due to the significant electromagnetic coupling effect created by the Ag-NPs on the MF microspheres, the SERS detection limits for ABT, CBT, and DTNB were as low as10’9mol/L,10-10mol/L, and10-8mol/L, respectively. For tetramethylthiuram disulfide, the detection limit was as low as10-9mol/L with the as-fabricated single microsphere of MF/Ag-NPs as the SERS substrate.The SERS signal intensity is highly linear depending upon the concentrations of tetramethylthiuram disulfide, indicating that this SRES method can be used for quantitative analysis of tetramethylthiuram disulfide.(4) Based on the above work of MF/Ag-NPs core-shell microspheres, fluorescent molecules, FITC and PHB were encoded in to the MF/Ag-NPs microspheres to prepare a kind of novel Raman and fluorescent conjugated double sensitive encoding microspheres (SFBM). The as fabricated SFBM microsphers were applied to detect NDA. Fluorescence MF microspheres was prepared first, silver nanoparticles was then deposited to form a silver-nanoparticles shell following the modification progress of Raman label molecules. Finally, the composite microspheres were coated with a thin silica layer and the SFBM was obtained. According to the permutation and combination of two kinds of fluorescent molecules and four Raman label molecules, selective preparation of18kinds of coding microsphere were carried out. Fifteen kind of encoded microspheres were fabricated based on the combination of FITC, PHB, HBT and CBT, and they were encoded using the method of binary according to their Raman and fluorescence signal. The experimental results indicated that the coding capacity resulted from the combination of fluorescent and Raman molecules were far greater than the sum of separately approach. The SFBM microspheres fabricated by the combination approach was greatly increased the coding capacity. MF(FITC)/Ag (DTNB)/SiO2, MF(PHB)/Ag(HBT)/SiO2and MF (FITC-PHB1:15)/Ag (HBT-DTNB3:1) encoding-microspheres were prepared and modified by three kinds of probe-DNA to get FS-probe DNA with both fluorescent and Raman sensitive; Meanwhile, PAA coated Fe3O4clusters was modified by three kind of capture DNA to obtain three kinds of Mc-DNA. At last, the three kinds FS-probe DNA and Mc-DNA were binded to detect three kinds of target DNA. Out experimental results showed that only in the presence of the target DNA, which was complementary with FS-probe DNA and Mc-DNA, have positive reaction could occurr only in the presence of the target DNA, which was complementary with FS-probe DNA and Mc-DNA. It suggests the novel Raman and fluorescent double sensitive encoding microspheres (SFBM) can be used for specific multiplexed detection of DNA. The coding microspheres as perarared can be used for liquid phase chip for high-throughput detection system.