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大四写论文金虫 (正式写手)
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| Designed synthesis of zeolites with tailored microporosity and functionality has been impossible, partly due to a lack of understanding of their crystallization mechanisms. In addition,although they are formed as thermodynamically metastable phases, their phase selection occurs under kinetic control. Thus, the products that crystallize under particular conditions are hardly predictable. On the contrary, the surfactant-directed self-assembly process has been well studied as a route to control mesostructures of sol–gel-derived mesoporous silica, which can be achieved under both thermodynamic and kinetic control. Sol–gel-derived silica can be functionalized by introduction of organosilanes containing organic moieties with desired functionality. However,there are still difficulties in controlling local or atomic structures of sol–gel-derived silica networks, because such amorphous networks are formed randomly on the hydrolysis and polycondensation of the precursors.Progress toward locally ordered structures has been made in recent years, mainly by self-assembly of well-defined oligomers as molecular building units. |
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2楼2015-03-07 13:24:00
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大四写论文: 金币+20, ★★★很有帮助 2015-03-07 19:50:34
大四写论文: 金币+20, ★★★很有帮助 2015-03-07 19:50:34
| 对沸石进行设计合成使其具有特定的微孔结构和功能是不可能的，部分原因是对其结晶机制缺乏理解。另外，虽然最终获得的沸石由热力学亚稳相组成，但其在制备过程中到底会生成哪些相则是动力学控制的，因此其在特定条件下的结晶产物很难预料。与此相反，研究表明，溶胶-凝胶法制备的介孔二氧化硅的亚结构却可以通过由表面活性剂带动的自组装过程调整，且这种调整在热力学和动力学控制下均可实现。溶胶-凝胶法制备的二氧化硅也可以通过引入含有有机基团的有机硅烷以获得期望的功能。然而，对溶胶-凝胶法制备的二氧化硅网络进行局部或原子结构的控制仍有困难，因为这种无序的网络结构是在前驱体水解、缩聚后随机形成的。近年来在局部有序结构研究方面已经取得了一些进展，主要是通过以特定的低聚物作为分子结构单元的自组装来实现局部结构有序化。 |
3楼2015-03-07 19:16:35
