Department of Chemical Engineering, Monash University, Clayton, Victoria 3800, Australia.
J Am Chem Soc. 2010 Sep 1;132(34):12042-50. doi: 10.1021/ja104379a.
In this paper, an efficient route is developed for controllable synthesis of ordered mesoporous alumina (OMA) materials with variable pore architectures and high mesoporosity, as well as crystalline framework. The route is based on the nanocasting pathway with bimodal mesoporous carbon as the hard template. In contrast to conventional reports, we first realize the possibility of creating two ordered mesopore architectures by using a single carbon hard template obtained from organic-organic self-assembly, which is also the first time such carbon materials are adopted to replicate ordered mesoporous materials. The mesopore architecture and surface property of the carbon template are rationally designed in order to obtain ordered alumina mesostructures. We found that the key factors rely on the unique bimodal mesopore architecture and surface functionalization of the carbon hard template. Namely, the bimodal mesopores (2.3 and 5.9 nm) and the surface functionalities make it possible to selectively load alumina into the small mesopores dominantly and/or with a layer of alumina coated on the inner surface of the large primary mesopores with different thicknesses until full loading is achieved. Thus, OMA materials with variable pore architectures (similar and reverse mesostructures relative to the carbon template) and controllable mesoporosity in a wide range are achieved. Meanwhile, in situ ammonia hydrolysis for conversion of the metal precursor to its hydroxide is helpful for easy crystallization (as low as approximately 500 degrees C). Well-crystallized alumina frameworks composed of gamma-Al(2)O(3) nanocrystals with sizes of 6-7 nm are obtained after burning out the carbon template at 600 degrees C, which is advantageous over soft-templated aluminas. The effects of synthesis factors are demonstrated and discussed relative to control experiments. Furthermore, our method is versatile enough to be used for general synthesis of other important but difficult-to-synthesize mesoporous metal oxides, such as magnesium oxide. We believe that the fundamentals in this research will provide new insights for rational synthesis of ordered mesoporous materials.
本文开发了一种高效的路线，用于可控合成具有可变孔结构和高介孔率以及结晶骨架的有序介孔氧化铝（OMA）材料。该路线基于双模态介孔碳作为硬模板的纳米铸造途径。与传统报道相比，我们首次通过使用源自有机-有机自组装的单一碳硬模板实现了创建两种有序介孔结构的可能性，这也是首次采用此类碳材料来复制有序介孔材料。为了获得有序的氧化铝介孔结构，对碳模板的介孔结构和表面性质进行了合理设计。我们发现，关键因素依赖于碳硬模板的独特双模态介孔结构和表面功能化。也就是说，双模态介孔（2.3 和 5.9nm）和表面功能化使得氧化铝主要选择性地负载到小孔中，或者在大初级介孔的内表面上以不同的厚度涂覆一层氧化铝，直到完全负载。因此，实现了具有可变孔结构（相对于碳模板具有相似和反向介孔结构）和可控制孔率的 OMA 材料，孔率范围很宽。同时，金属前体原位氨解转化为其氢氧化物有助于易于结晶（低至约 500°C）。在 600°C 下烧掉碳模板后，得到由 6-7nm 尺寸的γ-Al2O3纳米晶组成的结晶良好的氧化铝骨架，优于软模板氧化铝。相对于对照实验，证明并讨论了合成因素的影响。此外，我们的方法具有足够的通用性，可用于一般合成其他重要但难以合成的介孔金属氧化物，例如氧化镁。我们相信，这项研究的基础将为有序介孔材料的合理合成提供新的见解。
