【作者】 刘淑娟；

【导师】 俞书宏；

【作者基本信息】 中国科学技术大学 ， 无机化学， 2009， 博士

【摘要】 鉴于VSB-5和TiO₂两种材料在催化科学领域占有的重要地位,基于当前液相化学方法合成纳米催化材料的研究进展,本论文以VSB-5和TiO₂为研究对象,发挥液相化学合成技术在控制材料的微结构、形貌和尺寸等方面的优势,合成了新型过渡金属磷酸盐微孔材料VSB-5和具有优异光催化能力的TiO₂纳米结构,详细探索了金红石TiO₂独特的晶体生长转化过程,包括经典机理与非经典机理（即介观晶体的形成和取向搭接机理）的应用,补充完善了介观晶体演变为单晶需要通过取向搭接进行转化的机制。具体内容主要包括以下几个方面:1、通过简单调控反应溶液的pH值,采用六亚甲基四胺（HMT）作为结构导向剂,NaH₂PO₂作为还原剂和磷源,控制α-Ni（OH）₂的沉积速率和H₂PO₂^-到PO₄^3-的氧化速率,利用简便的水热方法获得了VSB-5微/纳米线以及由其组装成的VSB-5微球。此外,还详细研究了VSB-5选择性催化各种不饱和有机物加氢的性能,如苯乙烯、硝基苯（NB）、2-氯代硝基苯（2-CNB）、肉桂醛（CAL）和异戊烯醛（MCA）等。结果表明,VSB-5分子中的Ni（Ⅱ）具有较高的选择性催化加氢活性。2、采用温和水热方法,获得组成为（TiO₂）₂·C₄H₆O₅·6H₂O的具有裂隙的长方体实心结构,利用该长方体前驱物粒子上的裂隙作为模板,生成具有双层壁、插入层和分隔室的锐钛矿TiO₂空心盒子。此外,我们还详细研究了反应时间,温度和D,L-苹果酸与TiCl₄的摩尔比对于TiO₂形成的影响。结果表明,D,L-苹果酸与TICl₄的摩尔比越大,越有利于形成具有大的长径比的TiO₂空心盒子。而且,这些特殊结构具有优越的光催化性质,有望在光催化领域得到应用。3、最近,C（o|¨）lfen等人在前人工作的基础上,归纳了已知自然界存在的三种可能的晶体生长路径,即经典的晶体生长路径,纳米粒子的取向搭接,介观晶体的形成。但是,目前对于晶体生长机理的研究并不完全。关于介观晶体如何转化成单晶的过程还未见详细报道。在温和的反应条件下,以L-丝氨酸和N,N’-二环己基二酰亚胺（DCC）作为生物添加剂,合成了具有独特结晶过程和转化方式的新型TiO₂空心球。我们详细讨论了晶体的生长、转化以及结构重组和形貌转变过程。其中包括多晶出现,介观转化为具有扇形形貌的介观晶体,经过取向搭接过程由介观晶体转化为单晶棒束,同时经扇形组装为实心球,伴随Ostwald熟化机理空化实心球过程在整个体系内发生。此外,对于不同反应阶段生物添加剂的作用以及介观晶体在不同反应温度下的稳定性也做了深入研究。结果表明,介观晶体在低温下能够保持更长时间;高温溶液条件下,适当的选择有机添加剂也有利于增强介观晶体的稳定性。更多还原

【Abstract】 Based on the development of the solution methodology to synthesize nanomaterials with catalytic properties nowadays,we have synthesized the newly emerging microporous molecular sieve of VSB-5 and TiO₂ nanostructures with distinctive photocatalytic properties.The distinctive growth and transformation process of TiO₂ crystal includes the classical crystal growth mechanism and the nonclassical one of mesocrystal formation and oriented attachment.It is found that the transformation of TiO₂ mesocrystals to single crystal proceeds based on the mechanism of oriented attachment.Considering the significance of VSB-5 and TiO₂ in the area of catalytic materials,we chose them as the model system in this dissertation.The main results can be summarized as follows:1.By using hexamethylenetetramine（HMT） as a structure-directing agent, NaH₂PO₂ as a reducing agent and phosphor source,VSB-5 microspheres assembled by wires and rods with different ranges of diameters and aspect ratios can be obtained hydrothermally via adjusting the pH value of the reaction solution with control of the precipitation rate ofα-Ni（OH）₂ and redox rate of HPO₂^- to PO₄^3-.It is demonstrated that the pH value,reaction time as well as the ratio of HMT to NaHPO₂·H₂O have crucial influence on the morphology and quality of the final products.In addition,the catalytic property of VSB-5 in selective hydrogenation of several unsaturated organic compounds such as trans-cinnamaldehyde（CAL）, 3-methylcrotonaldehyde（MCA）,nitrobenzene（NB） and 2-chloronitrobenzene （2-CNB） has been tested.The results demonstrated that Ni（Ⅱ） in VSB-5 have the catalytic activity in the process of selective catalytic hydrogenation,showing that a new kind of catalyst has sprout out and the VSB-5 would have potential applications in developing dyes,agrochemicals,and pharmaceuticals perfume industries.2.Novel TiO₂ microboxes and tree-like structures assembled by hollow cubes via conversion from the rectangular particulates with cracks and a composition of （TiO₂）₂·C₄H₆O₅·6H₂O can be synthesized in large scales by a simple hydrothermal method.It is demonstrated that the boxes grow with double-layer walls and in the inner part there may exist inserted layers or several separate room.The influences of the reaction time,temperature and molar ratio between D,L-malic acid and TiCl₄ on the formation of this distinctive structure have been investigated in detail.The results demonstrate that a larger molar ratio of D,L-malic acid and TiCl₄ would benefit for the formation of TiO₂ hollow boxes with larger aspect ratios.Moreover, these distinctive structures show excellent photocatalytic properties,which would find potential applications in photocatalytic fields.3.Using N,N’-dicyclohexylcarbodiimide（DCC） and L-serine as biologic additives,rutile TiO₂ hollow spheres assembled by nanorods can be synthesized by a simple hydrothermal reaction route.A distinctive crystallization and transformation routte of the rutile TiO₂ hollow spheres has been proposed,which includes emergence of polycrystalline,mesoscale transformation to mesocrystals with morphologies of sectors,transformation of mesocrystals to bundles of rods based on oriented attachment,the simultaneous assembled process of sectors to solid spheres,and a cavitating process of solid spheres through the Ostwald ripening mechanism.Two ways of oriented attachment,side-by-side and end-to-end,were observed during the assembly process.It has been found that the presence of DCC and L-serine and their synergistic effects are essential for the formation of rutile TiO₂ hollow spheres.The stability of the rutile TiO₂ mesocrystals has been studied.The results revealed that the mesocrystals could be maintained longer at lower temperature,while proper choice of organic additives can also enhance the stability of mesocrystals at higher temperature under solution conditions.更多还原