Controllable and repeatable synthesis of thermally stable anatase nanocrystal-silica composites with highly ordered hexagonal mesostructures
Controllable and repeatable synthesis of thermally stable anatase nanocrystal-silica composites with highly ordered hexagonal mesostructures
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具有高度有序六方介观结构的热稳定锐钛矿纳米晶-二氧化硅复合材料的可控和可重复合成
DOI：
10.1021/ja073804o
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发表时间：
2007-11-14
影响因子：
15
通讯作者：
Zhao, Dongyuan
中科院分区：
文献类型：
--
作者：
Dong, Weiyang;Sun, Yaojun;Zhao, Dongyuan
在本文中，我们报道了一种可控制和可重复性的方法来制备高度有序的具有不同钛硅比(0到无穷大)的二维六方介孔晶态的二氧化钛-二氧化硅纳米复合材料。用X射线衍射仪、透射电子显微镜和氮气吸附技术系统地研究了其孔壁结构和热稳定性与合成条件的关系。合成的材料具有超高的稳定性(超过900℃)，具有大的均匀孔径(类似于6.8 nm)，以及高的Brunauer-Emmett-Teller比表面积(类似于290M-2/g)。以异丙醇钛(TIPO)和正硅酸乙酯(TEOS)为前驱体，以三嵌段共聚物P123为模板剂，采用溶剂挥发自组装法制备了纳米二氧化钛-二氧化硅介孔复合材料。我们的策略是通过微调周围气氛的相对湿度和蒸发温度，根据钛/硅比来同步组装钛酸酯和硅酸盐齐聚物与三嵌段共聚物P123。我们加入了大量的酸性，以降低TIPO的缩合和聚合速度，并加快了TEOS分子的速度。透射电子显微镜和X射线衍射仪的测量清楚地表明，二氧化钛是由高度结晶的锐钛矿型纳米颗粒组成的，这些纳米颗粒均匀地嵌入到孔壁中，形成了“砖状砂浆”骨架。无定形二氧化硅起到了连接二氧化钛纳米晶的胶粘剂的作用，提高了热稳定性。随着二氧化硅含量的增加，所制备的介孔二氧化钛-二氧化硅纳米复合材料的热稳定性增加，锐钛矿型纳米晶的尺寸减小。结果表明，独特的复合骨架使介孔结构具有压倒性的稳定性；即使在高的钛硅比(>；=80/20)下，复合材料的稳定性也高于900℃。介孔二氧化钛-二氧化硅纳米复合材料对水相悬浮液中罗丹明B的降解表现出优异的光催化活性(高于商用催化剂P25)。这种优异的光催化活性归功于高结晶度的锐钛矿型纳米粒子和高孔隙率的双功能效应。
In this article, we report a controllable and reproducible approach to prepare highly ordered 2-D hexagonal mesoporous crystalline TiO2-SiO2 nanocomposites with variable Ti/Si ratios (0 to infinity). XRD, TEM, and N-2 sorption techniques have been used to systematically investigate the pore wall structure, and thermal stability functioned with the synthetic conditions. The resultant materials are ultra highly stable (over 900 degrees C), have large uniform pore diameters (similar to 6.8 nm), and have high Brunauer-Emmett-Teller specific surface areas (similar to 290 M-2/g). These mesostructured TiO2-SiO2 Composites were obtained using titanium isopropoxide (TIPO) and tetraethyl orthosilicate (TEOS) as precursors and triblock copolymer P123 as a template based on the solvent evaporation-induced co-self-assembly process under a large amount of HCl. Our strategy was the synchronous assembly of titanate and silicate oligomers with triblock copolymer P123 by finely tuning the relative humidity of the surrounding atmosphere and evaporation temperature according to the Ti/Si ratio. We added a large amount of acidity to lower condensation and polymerization rates of TIPO and accelerate the rates for TEOS molecules. TEM and XRD measurements clearly show that the titania is made of highly crystalline anatase nanoparticles, which are uniformly embedded in the pore walls to form the "bricked-mortar" frameworks. The amorphous silica acts as a glue linking the TiO2 nanocrystals and improves the thermal stability. As the silica contents increase, the thermal stability of the resulting mesoporous TiO2-SiO2 nanocomposites increases and the size of anatase nanocrystals decreases. Our results show that the unique composite frameworks make the mesostructures overwhelmingly stable; even with high Ti/Si ratios (>= 80/20) the stability of the composites is higher than 900 degrees C. The mesoporous TiO2-SiO2 nanocomposites exhibit excellent photocatalytic activities (which are higher than that for commercial catalyst P25) for the degradation of rhodamine B in aqueous suspension. The excellent photocatalytic activities are ascribed to the bifunctional effect of highly crystallized anatase nanoparticles and high porosity.