Schneider J J, Czap N, Hagen J, Engstler J, Ensling J, Gütlich P, Reinoehl U, Bertagnolli H, Luis F, de Jongh L J, Wark M, Grubert G, Hornyak G L, Zanoni R
Institut für Chemie, Anorganische Chemie, Karl-Franzens Universität Graz, Austria.
Chemistry. 2000 Dec 1;6(23):4305-21. doi: 10.1002/1521-3765(20001201)6:23<4305::aid-chem4305>3.0.co;2-n.
Iron and titanium oxide nanoparticles have been synthesized in parallel mesopores of alumina by a novel organometallic "chimie douce" approach that uses bis(toluene)iron(0) (1) and bis(toluene)titanium(0) (2) as precursors. These complexes are molecular sources of iron and titanium in a zerovalent atomic state. In the case of 1, core shell iron/iron oxide particles with a strong magnetic coupling between both components, as revealed by magnetic measurements, are formed. Mössbauer data reveal superparamagnetic particle behavior with a distinct particle size distribution that confirms the magnetic measurements. The dependence of the Mössbauer spectra on temperature and particle size is explained by the influence of superparamagnetic relaxation effects. The coexistence of a paramagnetic doublet and a magnetically split component in the spectra is further explained by a distribution in particle size. From Mössbauer parameters the oxide phase can be identified as low-crystallinity ferrihydrite oxide. In agreement with quantum size effects observed in UV-visible studies, TEM measurements determine the size of the particles in the range 5-8 nm. The particles are mainly arranged alongside the pore walls of the alumina template. TiO2 nanoparticles are formed by depositing 2 in mesoporous alumina template. This produces metallic Ti, which is subsequently oxidized to TiO2 (anatase) within the alumina pores. UV-visible studies show a strong quantum confinement effect for these particles. From UV-visible investigations the particle size is determined to be around 2 nm. XPS analysis of the iron- and titania- embedded nanoparticles reveal the presence of Fe2O3 and TiO2 according to experimental binding energies and the experimental line shapes. Ti4+ and Fe3+ are the only oxidation states of the particles which can be determined by this technique. Hydrogen reduction of the iron/iron-oxide nanoparticles at 500 degrees C under flowing H2/N2 produces a catalyst, which is active towards formation of carbon nanotubes by a CVD process. Depending on the reaction conditions, the formation of smaller carbon nanotubes inside the interior of larger carbon nanotubes within the alumina pores can be achieved. This behavior can be understood by means of selectively turning on and off the iron catalyst by adjusting the flow rate of the gaseous carbon precursor in the CVD process.
通过一种新颖的有机金属“温和化学”方法，在氧化铝的平行介孔中合成了铁和钛的氧化物纳米颗粒，该方法使用双（甲苯）铁（0）（1）和双（甲苯）钛（0）（2）作为前驱体。这些配合物是零价原子态铁和钛的分子源。对于1，形成了在两个组分之间具有强磁耦合的核壳铁/氧化铁颗粒，如磁性测量所揭示的那样。穆斯堡尔数据揭示了具有明显粒度分布的超顺磁性颗粒行为，这证实了磁性测量结果。穆斯堡尔谱对温度和粒度的依赖性通过超顺磁性弛豫效应的影响来解释。谱中顺磁双峰和磁分裂组分的共存进一步通过粒度分布来解释。从穆斯堡尔参数可以将氧化物相鉴定为低结晶度的水铁矿氧化物。与紫外可见研究中观察到的量子尺寸效应一致，透射电子显微镜测量确定颗粒尺寸在5-8纳米范围内。颗粒主要沿氧化铝模板的孔壁排列。通过在介孔氧化铝模板中沉积2形成TiO2纳米颗粒。这产生了金属Ti，随后在氧化铝孔内被氧化为TiO2（锐钛矿）。紫外可见研究表明这些颗粒具有很强的量子限制效应。从紫外可见研究中确定颗粒尺寸约为2纳米。对嵌入铁和二氧化钛的纳米颗粒进行X射线光电子能谱分析，根据实验结合能和实验线形揭示了Fe2O3和TiO2的存在。Ti4+和Fe3+是通过该技术可以确定的颗粒的唯一氧化态。在500℃下于流动的H2/N2中对铁/氧化铁纳米颗粒进行氢还原产生一种催化剂，该催化剂对通过化学气相沉积（CVD）过程形成碳纳米管具有活性。根据反应条件，可以在氧化铝孔内较大碳纳米管的内部实现较小碳纳米管的形成。通过在CVD过程中调节气态碳前驱体的流速来选择性地开启和关闭铁催化剂，可以理解这种行为。
