【作者】 戴兢陶；

【导师】 江龙；

【作者基本信息】 苏州大学 ， 物理化学， 2007， 博士

【摘要】 因为磁性纳米粒子具有独特的化学和物理性质以及在高密度磁记录介质、生物技术、磁流体和构建纳米复合永磁材料等领域有着广泛的应用,所以科研工作者对其制备和性能展开了大量的研究。纳米粒子的控制合成是纳米科学和纳米技术的重要部分之一。与物理制备方法相比,近年来化学方法制备磁性纳米粒子备受重视,因为用化学方法制备的单金属、合金等纳米粒子具有非常高的单分散性。此外,纯金属磁性纳米粒子的磁性质单一,不能满足当今多功能磁性材料的飞速发展。钴及其与其它金属复合纳米颗粒被认为是未来最有希望应用于高密度磁记录材料、吸波材料、磁制冷材料等领域,所以对于钴基纳米材料的研究显得尤为重要。本论文主要探索简单易操作的、绿色的化学液相钴基纳米复合材料的合成路线,制备耐氧化、抗聚结磁性钴基纳米粒子,并研究了它们的磁性质。详细内容归纳如下:1.利用化学还原法制备了不同类型水溶性铂和钴双金属复合纳米粒子。用NaBH₄作还原剂还原H₂PtCl₆和CoCl₂的混合溶液制备Pt₃Co纳米合金,然后通过吸氢还原法合成了平均粒径为3.6 nm,标准偏差为0.9 nm核壳型纳米粒子Pt₃Co/Pt。在空气气氛中经高温热处理后,Pt₃Co纳米粒子中的钴被氧化,而具有核壳结构的Pt₃Co/Pt纳米粒子则表现出较强的抗氧化性;热处理后,Pt₃Co/Pt由fcc转变成fct结构,室温下其矫顽力达276 Oe。利用一步共还原法在导电高分子聚二氧乙基噻吩/聚对苯乙烯磺酸（PEDOT/PSS）水溶液中合成了平均粒径为9.6 nm磁性复合纳米粒子Pt₃Co-PEDOT/PSS,Pt₃Co纳米粒子为面心立方结构（fcc）:用旋转涂膜法制备的Pt₃Co-PEDOT/PSS薄膜导电率（σ）在1.6～4 S/cm之间;超导量子干涉仪（SQUID）测量了磁性质,200 Oe下的ZFC-FC曲线显示了复合纳米粒子Pt₃Co-PEDOT/PSS的阻塞温度T_b为110.5 K,当温度高于T_b时,纳米粒子显示出超顺磁,低于T_b时,呈铁磁性,在5 K时其剩磁（M_r）和矫顽力（H_c）分别为4.1 emu/g和701 Oe。2.分别在水相和反胶束溶液中合成了三金属PtCo/Au纳米粒子。水溶性的PtCo/Au纳米粒子以NaBH₄作还原剂两步反应合成,平均粒径约为2.5 nm的PtCo/Au纳米粒子为fcc结构,PtCo/Au纳米粒子具有较高的抗聚集和抗氧化作用。振动样品磁强计（VSM）研究的PtCo/Au纳米粒子磁性质表明,合成的纳米粒子呈超顺磁状态,经高温处理后呈铁磁状态,矫顽力H_c为510 Oe。反胶束制备的硫醇包裹的PtCo/Au纳米粒子粒径分布很窄,TEM表明了该纳米粒子能铺展在覆有炭膜的铜网上,并自组装成二维单层排列;纳米粒子在200 Oe外磁场下的阻塞温度T_b为69 K,高于T_b粒子呈超顺磁行为,而低于T_b粒子则呈铁磁行为;5 KPtCo/Au粒子的矫顽力和剩磁分别为628 Oe和5.2 emu/g。3.水热再还原四步制备了SmCo₅纳米粒子。调节SmCl₃和CoCl₂混合溶液的pH至合适值后,加热回流,使得Sm³⁺和Co²⁺水解共沉淀。150℃下水热反应9 h,制得粒径约为20 nm的立方钐钴氧化物纳米粒子。最后,将纳米氧化物粒子在氢气流中,以金属钠为还原剂,制得粒径为约为20 nm的SmCo₅纳米粒子。300 K纳米粒子呈超顺磁状态,而5 K时粒子呈铁磁状态,矫顽力为268 Oe。4.运用不同的合成路线在水体系中制备了Pt₃Co/Fe₃O₄和CoFe₂O₄纳米粒子。Pt₃Co纳米粒子由于Fe₃O₄的掺入导致Pt₃Co/Fe₃O₄复合纳米粒子的晶相从fcc向fct转变,两超顺磁的Pt₃Co和Fe₃O₄纳米粒子构成的Pt₃Co/Fe₃O₄复合纳米粒子在室温下由于它们相互间的交换耦合而呈铁磁性,纳米粒子中铁、铂的比例对其磁性质起着调节作用。立方尖晶石型CoFe₂O₄磁性纳米粒子以水热共沉淀法制备,扫描电子显微镜（SEM）研究表明,水热时间是控制纳米粒子的形貌和大小的关键。当150℃水热8 h,CoFe₂O₄粒子呈立方体,SQUID研究表明,水热后30 nm的CoFe₂O₄纳米粒子在5 K矫顽力高达10.7×10³ Oe。更多还原

【Abstract】 A considerable amount of research has been devoted to the study of magnetic nanoparticles due to its unique chemical and physical properties,and potential for a variety of important applications,such as high density recording media,biotechnology,ferrofluids, and fabrication of exchange-coupled nanocomposite permanent magnets.Manipulated synthesis of nanoparticles is one of the most important sections of nanoscience and nanotechnology,also the base of investigating distinctive properties and applications of nanoparticles.Recently,chemically synthesized magnetic nanoparticles have drawn much more attention than physical because it can yield highly monodisperse magnetic nanoparticles of pure metals,metal alloys,and so on.Moreover,it is well known that the properties of pure metals nanoparticles lack diversification which is an obstacle to rapid development of the multifunctional material.Today,cobalt-based nanoparticles are emerging as the "hot spot" of many investigations owning to their important technological applications in microwave absorption and magnetic refrigeration,especially,in high-density magnetic recording media.The objective of this dissertation is to explore facile and green chemical solution-based synthesis routes to prepare the cobalt-based magnetic nanoparticles which can prevent from oxidation and conglomeration,and study their magnetic property.More details are summarized below:1.Bimetal Pt and Co nanoparticles were prepared using reduction method in aqueous phase.The core-shell Pt₃Co/Pt nanoparticles were synthesized via reduction method of hydrogen absorption on the surface of Pt₃Co alloy nanoparticles which were prepared by the reduction of the mixture of H₂PtCl₆ and CoCl₂ solutions using NaBH₄ as a reducing agent.Average size and standard deviation of Pt₃Co/Pt nanoparticles were 3.6nm and 0.9 nm,respectively.Heating Pt₃Co/Pt nanoparticles in air at high temperature,Co in Pt₃Co nanoparticles was oxidized,while no oxidation tendency was detected for Pt₃Co/Pt nanoparticles.The crystallize structure changed from fcc to fct after the heating treatment. The coercivity of the heated Pt₃Co/Pt is 276 Oe at room temperature.Magnetic composite PEDOT/PSS—Pt₃Co nanoparticles with were synthesized using a step coreduction in an aqueous solution of conducting polymers PEDOT/PSS.The average size and standard deviation of PEDOT/PSS—Pt₃Co nanoparticles were 9.6 nm and 1.4 nm.The films prepared from magnetic composite Pt₃Co-PEDOT/PSS nanoparticles were conductive with conductivity between 1.6 and 4 S/m.The composite nanoparticles are superparamagnetic above the blocking temperature（T_b=110.5 K） while they are ferromagnetic with H_c（701 Oe） and M_r（4.1emu/g） at 10K（below T_b）.Compared with the PVP-Pt₃Co,magnetic composite PEDOT/PSS-Pt₃Co nanoparticles are highly promising application in the magnetic films for recording media.2.Trimetal PtCo/Au nanoparticles were synthesized in aqueous phase and reverse micelle,respectively.PtCo/Au nanoparticles with anaverage size of 2.5 nm in aqueous are stable to congregation and oxidation due to the protected of Au.PtCo/Au nanoparticles display fcc structure,while the annealed PtCo/Au nanoparticles exhibit a ordered fct structure.SQUID studies reveal that the coercivity of PtCo/Au nanoparticles with an irreversible magnetization increases to 510 Oe after heat treatment at high temperature. Magnetic thiol-coated PtCo/Au nanoparticles prepared in a reverse micelle are narrow size distribution.TEM confirmed that the self-assembly of PtCo/Au nanoparticles was realized on the surface of carbon coated copper grids.SQUID studies reveal that the particles are superparamagnetic above the blocking temperature（T_b=69 K） while the particles are ferromagnetic with H_c（628 Oe） and M_r（5.2 emu/g） at 5K（below T_b）.3.SmCo₅ nanoparticles are the one of the most important binary transition metal-rare earth systems for magnetic materials.SmCo₅ nanoparticles were fabricated by a four-stage route.At first,the mixed aqueous soluble of SmCl₃ and CoCl₂ was adjusted to pH=9～10 using NaOH at 0℃.Secondly,two soluble metal-salts were forced hydrolysis to oxides under atmospheric refluxing at 80℃.Then,oxide nanoparticles with a ca average size of 20 nm were prepared at 150℃for 9 h through a convenient hydrothermal process.Finally, The SmCo₅ nanoparticles were attained via nanoparticles hydrothermally prepared deoxidized using Na under the hydrogen stream at 400℃.The SmCo₅ nanoparticles are superparamagnetic at 300 K while the particles are ferromagnetic with H_c（268 Oe） at 5K.4.The cobalt-based magnetic nanoparticle of iron-doped shows excellent magnetic properties due to its high anisotropy constant.We prepared dispersed Pt₃Co/Fe₃O₄ and CoFe₂O₄ nanoparticles in aqueous by different synthesis routes.The bimagnetic Pt₃Co/Fe₃O₄ nanocomposite can be successfully synthesized by the coprecipitation of Fe³⁺and Fe²⁺on the Pt₃Co nanoparticles in aqueous solution.Fe₃O₄ leads partial Pt₃Co phase transformation from fcc to fct.The as-synthesized composite nanoparticles exhibit ferromagnetic properties at room temperature due to the exchange coupling between superparamagnetic Pt₃Co and Fe₃O₄.Magnetic properties of Pt₃Co/Fe₃O₄ nanoparticle can be tuned by varying of the molar ratio of iron to platinum.Pt₃Co/Fe₃O₄ nanoparticles exhibit higher saturation magnetization when the molar ratio of iron to platinum is 1 because Pt₃Co and Fe₃O₄ is more intimate direct contact to ensure their stronger exchange coupling.Cubic spinel CoFe₂O₄ magnetic nanocrystal was hydrothermally prepared by coprecipitation technique using ferrous chloride（FeCl₂·4H₂O）,cobalt chloride （CoCl₂·6H₂O） and sodium hydroxide（NaOH） as starting materials.SEM shows the shap and size of CoFe₂O₄ nanoparticles were controlled by the hydrothermal time.After 8 h under 150℃,the particle with ca 30 nm is cubic nanocrystal.SQUID studies reveal that the coercivity of CoFe₂O₄ nanocrystal is 10.7×10³ Oe at 5K。更多还原