新型磁性纳米材料和介孔氧化硅材料的设计合成及应用研究

【作者】 汤慧利；

【导师】 贺鹤勇；

【作者基本信息】 复旦大学 ， 物理化学， 2008， 博士

【摘要】 纳米材料因其具有特殊的结构和性能,在化工、生物、医药、电子等领域有着广泛的应用。但在实际应用中纳米材料常遇到难以分离的问题,限制了其在催化、吸附分离等领域的应用。磁性纳米粒子具有不同于常规磁性材料的超顺磁性,可利用外磁场将其分离和回收,外磁场消失后,又可恢复粒子的高度分散性。所以功能化的超顺磁性的纳米粒子在生物和催化方面有着广阔的应用前景。近年来,人们在磁性纳米粒子的合成和应用方面的研究取得了不少进展,但是仍然存在一些问题,如（1）核壳结构的磁性纳米粒子的尺寸均匀性难以控制,不易达到适用于高分散性的纳米粒子的要求,特别是经过表面功能化后,粒子的形貌、尺寸均匀度、分散度难以控制;（2）致密的纳米粒子的比表面仍有限,不易引入高含量的功能化基团和物质。介孔材料因其具有规则的孔道结构、纳米范围可调变的孔径以及高的比表面,成为良好的催化剂载体。但是传统的介孔材料的合成中常使用价高的表面活性剂或对环境有害的有机含氮模板剂,因此利用低价且对环境影响较小的模板剂来合成介孔材料,探索其在催化中的应用十分重要。另外介孔氧化硅材料的骨架由无定形氧化硅组成,反应活性低,直接应用受到限制,而有机—无机杂化介孔材料的出现拓展了介孔材料的应用领域,因而受到了人们的极大关注。针对上述磁性纳米材料和介孔材料研究的现状和面临的问题,本论文重点研究了核壳结构的磁性纳米材料的可控合成、组装和功能化,以及功能化介孔氧化硅材料的合成与应用,所开展的具体研究工作分为以下五个部分:一、利用层层沉积的方法,在超顺磁性FePt纳米粒子表面进行SiO₂保护层和金属氧化物层的可控沉积,合成了系列三重核壳结构的磁性纳米粒子FePt@SiO₂@TiO₂、FePt@SiO₂@ZrO₂和FePt@SiO₂@Al₂O₃。TEM表征说明这种核壳结构的纳米粒子尺寸均匀,在乙醇溶液中具有高度分散性,磁性表征说明其具有超顺磁性,等电点（IEP）测试发现粒子表层为混合金属氧化物。通过对不同Ti含量的FePt@SiO₂@TiO₂样品进行详细的TEM、EDX、UV-Vis、IEP表征后发现,在合成过程中,钛酸丁脂的水解产物扩散进入SiO₂层中,从而形成具有烯烃环氧化反应活性的Ti-O-Si物种,即分散在SiO₂骨架中的四配位Ti（OSi）₄物种。通过此方法合成的磁性可分离的FePt@SiO₂/TO₂纳米催化剂在反式二苯乙烯环氧化反应中表现的较高的活性和选择性,在TiO₂含量为9.2 wt%样品上的转化率达到15%,选择性为91.5%。二、通过调控“反相微乳法”的反应条件,控制合成了粒径可调、尺寸均匀、高度分散的核壳结构的磁性纳米粒子FePt@SiO₂,并利用表面活性剂CO-520的作用将FePt@SiO₂自组装成的三维磁性纳米阵列。SAXS、TEM、N₂吸附表征结果说明,这种三维纳米阵列具有高度有序的介孔结构,并可通过改变FePt@SiO₂的粒经,获得具有不同介孔尺寸的三维纳米阵列。磁性表征说明这种三维纳米阵列具有超顺磁性。这种超顺磁性介孔材料被成功地应用于蛋白分子的选择性吸附分离:在外磁场诱导下,三维磁性纳米阵列提供了一种强诱导和区域化的磁场力,可将具有顺磁性的、与孔隙大小类似的细胞色素B5吸附到其由纳米粒子堆积而成的介孔空隙中,且在撤去外磁场后可再次释放细胞色素B5到溶液中;此材料对没有磁性的牛血清蛋白吸附作用很小。三、利用表面活性剂CTAB的作用,在核壳结构的超顺磁性纳米粒子FePt@SiO₂表面沉积一层介孔SiO₂,得到一种磁性介孔复合纳米粒子。通过控制合成条件,可得到具有不同中间SiO₂保护层厚和介孔SiO₂层厚的核壳结构的磁性介孔复合纳米粒子。XRD、N₂吸附以及TEM表征说明,这种磁性介孔复合纳米粒子具有较高的比表面、狭窄的孔径分布和有序的介孔孔道结构,并且孔道方向沿着球形纳米颗粒的径向生长。进一步通过普通嫁接法和“一步萃取表面改性法”将有机官能团-SH,-SO₃H,-NH₂引入到具有高比表面介孔层中,得到表面功能化的磁性介孔复合纳米粒子。TEM、XRD和NMR表征结果表明:相对于普通嫁接法,“一步萃取表面改性法”可以引入较高含量的有机官能团,并且在改性过程中,有序的介孔结构得到保持。由“一步萃取表面改性法”制备的表面-SH功能化的磁性介孔纳米粒子可用作重金属离子吸附剂,-NH₂功能化的磁性介孔纳米粒子可用作DNA分子吸附剂,并均可通过外磁场分离回收。四、以廉价、短链的戊二酸为有机模板剂,合成了一系列不同Cu/Si比的含铜介孔材料CMM-x。XRD、N₂吸附、TEM和漫反射UV-Vis光谱表征结果说明,CMM-x具有类似HMS和MSU的三维连续蠕虫状的介孔孔道,比表面积在600-800m²g^-1,孔容在0.66-0.88 cm³g^-1,平均孔径在3.3-5.7 nm,且孔径分布狭窄。CMM-x中的铜物种主要以高分散的氧化铜形式存在于介孔二氧化硅的骨架中。通过研究含有不同Cu/Si比的CMM-x在液相双氧水氧化苯酚反应中的性能发现,其具有与TS-1相当的催化性能,其中CMM-1/50的活性最好,苯酚转化率达到25.1%,二酚选择性达到98.8%,H₂O₂的效率达到75.4%。此外,还以CMM-1/50为催化剂,详细考察了反应溶剂、反应温度、苯酚/H₂O、催化剂用量和苯酚/H₂O₂对苯酚羟基化反应的活性和选择性的影响,获得了优化的实验条件。同时还研究了该反应的动力学,并在以上研究基础上,提出了此催化剂上可能的反应机理。另外还发现此催化剂在循环使用三次以后仍保持较高的活性和选择性。五、通过一步共合成法,合成了含-SH的有机—无机杂化介孔SiO₂材料。利用-SH和Ag⁺的作用,将Ag⁺定量引入到在介孔表面,经过处理得到了Ag纳米粒子/介孔SiO₂复合材料,并详细研究了-SH改性比例对Ag纳米粒子的形貌和分散性的影响。其中在5%和10%-SH改性的介孔SiO₂上得到的Ag纳米粒子尺度均匀,在孔道中高度分散。在室温下,Ag/meso-SiO₂-S10在苯乙酮加氢反应中表现出稳定的催化活性。更多还原

【Abstract】 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（Ⅲ） 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（Ⅱ） 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.更多还原