Novel Magnetic Nano-materials, And Mesoporous Silica Materials Were Designed And Synthesized And Applied Research

Nano-structured materials have wide potentials in chemical industry, biotechnology,medicals and electronics because of their special structures and properties.However,the difficulty of separation of nano-structured materials (especially for nanoparticles) limits their application in catalysis,adsorption, separation,etc.Magnetic nanoparticles display superparamagnetism,which means that the particles can be removed and recycled from solution using an external magnetic field and redispersed in solution after the removal of the external magnetic field.Hence,functionalized superparamagnetic nanoparticles show a great potential in many areas,such as catalysis,biomedical applications,etc.Significant progress has been made in the preparation and application of magnetic nanoparticles.However, some major problems still remain.It is difficult to control size distribution and morphology of magnetic nanoparticles,particularly those surface-functionalized ones. Also,it is difficult to introduce large amount of functional group to functionalize the surface of nanoparticles because of the low surface area of magnetic nanoparticles.Mesoporous materials have been used in many areas,such as catalyst supporters, owing to their highly ordered structures,tunable pore sizes in nanometer region,high surface areas and high pore volumes.Mesoporous materials are normally synthesized by using highly-cost surfactant or non environmental-friendly nitrogen-containing compound as the template.It is worthwhile to develop low-cost and environmental-benign templates for the preparation of mesoporous materials. Meanwhile,mesoporous silica materials usually consist of amorphous inorganic silica with little activity in catalysis.The discovery of organic-inorganic hybrid mesoporous materials broadened their application fields and attached much attention.According to the above problems encountered in magnetic nanomaterials and mesoporous materials,this thesis sheds light on the two main research topics,the controlled preparation,assembly and functionalization of magnetic core-shell nanoparticles and the preparation and application of functionalized mesoporous silica. The detailed research work is divided into following five parts.(1) FePt superparamagnetic nanoparticles were controllably coated with a silica protection shell and subsequent metal oxide shell to form a series of three-layer core-shell structured magnetic nanoparticles,FePt@SiO₂@TiO₂,FePt@SiO₂@ZrO₂ and FePt@SiO₂@Al₂O₃ by using a simple stepwise layer-by-layer deposition technique.TEM results show that the core-shell structured nanoparticles have very narrow particle size distribution and can be dispersed in ethanol with little aggregation. Magnetism characterization(VSM) demonstrates that the particles are superparamagnetic.IEP values of the nanoparticles reflect the external shell of the nanoparticles consist of mixed metal oxides.Through the detailed characterization of FePt@SiO₂@TiO₂ samples with different Ti content by TEM,EDX,UV-Vis,Zeta potential and catalytic test,it disclosed that the external shell of the nanoparticle is a Ti-O-Si mixture layer with tetrahedral Ti species dispersed in SiO₂(Ti(OSi)₄).The core-shell structured nanoparticles FePt@SiO₂@TiO₂ show high activity and selectivity for the trans-stilbene oxidation to the corresponding epoxide.The best activity was obtained over the sample with 9.2 wt%TiO₂ content,with conversion of 15%and selectivity of 91.5%.(2) The magnetic nanoparticles FePt@SiO₂ were synthesized by reverse emulsion method and self-assembled to three-dimensional(3D) superlattices under the contribution of the surfactant(CO-520).The SAXS,TEM and N₂ adsorption results show the 3D superlattices display highly ordered mesostructure and the pores size are tunable by changing the size of the FePt@SiO₂ nanoparticles.VSM characterization demonstrates the 3D superlattices are superparamagnetic.The superparamagnetic mesoporous materials can provide a strong induced localized magnetic force at well defined but controllable dimension of interstitial sites to attract and retain paramagnetic bio-or chemical entities.Our experiments demonstrate that Cytochrome B5 protein containing paramagnetic Fe(â…¢) with comparable size as the tailored interstices can be selectively retained by the 3D superlattices under an external magnetic filed whereas no such effect is observed over the larger size Bovine serum albumin protein with no paramagnetic centre.(3) A mesoporous SiO₂ layer was deposited on superparamagnetic FePt@SiO₂ nanoparticles using CTAB as template and the magnetic mesoporous composite nanoparticles were obtained.The thicknesses of inner SiO₂ protection layer and mesoporous silica layer may be controlled.The magnetic mesoporous nanoparticles show large surface area,narrow pore size distribution and highly ordered mesoporous channels radiated from the silica cores.The mesoporous layers were functionalized with the organic groups of -SH,-SO₃H and -NH₂ using common grafting method or one-step extraction-functionalization method.The results of TEM,XRD and NMR demonstrate that one-step extraction-functionalization method can introduce much more organic functional groups and retain the mesostructure better than the common grafting method.The -SH functionalized magnetic mesoporous composite nanoparticle may be used as heavy metal adsorbent and -NH₂ functionalized magnetic mesoporous composite nanoparticle as DNA adsorbent for magnetic separation.(4) A series of novel Cu-incorporated mesoporous materials(CMMs) with molar ratios of Cu/Si ranging from 1/200 to 1/20 were synthesized by the sol-gel method using glutaric acid as template.The characterization results indicate that the CMMs have a 3D worm-like mesoporous structure similar to HMS and MSU and narrow pore size distribution,with surface area of 600-800 m²g^-1,pore volume of 0.66-0.88 cm³g^-1,and average pore diameter of 3.3-5.7 nm.Copper species in the materials are highly dispersed Cu(â…¡) oxide within mesoporous siliceous matrices.The catalytic activity of these CMMs with different Cu/Si molar ratio in the phenol hydroxylation using H₂O₂ as oxidant was investigated and the catalysts showed the activity comparable to that of TS-1.Among all the catalysts,CMM-1/50 showed the highest activity:the conversion,diphenol selectivity and efficiency of H₂O₂ were 25.1,98.8 and 75.4%,respectively.The influence of various reaction parameters was investigated in detail,including solvent,reaction temperature,phenol/H₂O ratio, catalyst amount and phenol/H₂O₂ ratio,and the optimized reaction condition was acquired.The catalyst showed good catalytic performance after three cycles.(5) Thiol functionalized organic-inorganic hybrid mesoporous silicas were prepared by a one-step co-condensation method.After introduction of silver cation and following treatments under air and hydrogen atmosphere,Ag nanoparticles dispersed in mesoporous silica were obtained.The content of thiol in hybrid mesoporous SiO₂ shows great effect on the morphology and dispersibility of Ag nanoparticles.The Ag nanoparticles,which were prepared using the thiol functionalized mesoporous SiO₂ with the S/Si molar ratio of 5%and 10%,were high dispersed in the mesopores.The activity of Ag/meso-SiO₂-S10 sample for the acetophenone hydrogenation was investigated.