In situ carbonization of a soft-template to directly synthesize crystalline mesoporous metal oxides with high surface areas
In situ carbonization of a soft-template to directly synthesize crystalline mesoporous metal oxides with high surface areas
复制标题
DOI：
10.1039/c4nj01034e
复制
发表时间：
2014-11
影响因子：
3.3
通讯作者：
Limin Guo;S. Ida;T. Daio;Hidehisa Hagiwara;T. Ishihara
中科院分区：
文献类型：
--
作者：
Limin Guo;S. Ida;T. Daio;Hidehisa Hagiwara;T. Ishihara
以Pluronic三嵌段共聚物P-123为结构导向剂，通过一锅法合成了高比表面积的晶态介孔d 0金属氧化物如Ta 2 O 5、Nb 2 O 5和TiO 2。在这种合成中，通过高温煅烧在金属氧化物结晶过程中难以保持介观结构稳定性。在这项研究中，两种热处理被证明在实现这一目标方面发挥了关键作用。第一个是中间热处理，预固结的介观结构和部分分解的P-123成富碳物种。第二热处理依赖于在惰性气氛下的高温煅烧，以同时在金属氧化物上原位形成碳包裹并实现金属氧化物的结晶。这两种处理方法成功地抑制了高温晶化过程中多孔结构的坍塌和晶粒尺寸的长大。所合成的结晶介孔金属氧化物显示由多晶组成的无序介孔结构。值得注意的是，通常使用的P-123表面活性剂没有sp2杂化碳原位形成许多无定形碳，这有效地限制了结晶过程中的传质，从而成功地防止了晶体尺寸的增长。所合成的结晶介孔Ta 2 O 5、Nb 2 O 5和TiO 2分别显示出117.0、125和76.2 m2 g-1的表面积，以及5.4、8.1和13.9 nm的孔径。介孔Ta 2 O 5、Nb 2 O 5和TiO 2的晶体尺寸分别为19、28和34 nm。多孔和晶体结构的合成样品的特征在于使用X-射线衍射，热重-差热分析，扫描电子显微镜，透射电子显微镜，X-射线光电子能谱，和N2吸附技术。并对合成的介孔Ta 2 O 5的光催化性能进行了评价。使用NiOx作为助催化剂，所制备的结晶介孔Ta 2 O 5显示出稳定的整体水裂解下氙灯照射（全弧）。当光强固定在0.17-0.18 W cm−2时，最高放氢速率为709.1 μmol g−1 h−1。
High-surface-area crystalline mesoporous d0 metal oxides such as Ta2O5, Nb2O5, and TiO2 were synthesized via a one-pot method using pluronic triblock copolymer P-123 as a structure directing agent. Mesostructure stability during metal oxide crystallization via high temperature calcination is difficult to maintain in such synthesis. In this study, two heat treatments were proven to play a key role in achieving this goal. The first one is the intermediate heat treatment that preconsolidates the mesostructure and partially decomposes P-123 into carbon-rich species. The second heat treatment relies on high temperature calcination under an inert atmosphere to simultaneously form carbon wrapping on the metal oxides in situ and achieve crystallization of metal oxides. These two treatments successfully restricted the porous structure collapse and crystal size growth during high temperature crystallization. The as-synthesized crystalline mesoporous metal oxides show disordered mesoporous structures consisting of polycrystals. Notably, the commonly used P-123 surfactant without the sp2-hybridized carbon forms much amorphous carbon in situ, which effectively restricts mass transfer during crystallization and thus successfully prevents crystal size growth. The as-synthesized crystalline mesoporous Ta2O5, Nb2O5, and TiO2 displayed surface areas of 117.0, 125, and 76.2 m2 g−1, respectively, and pore sizes of 5.4, 8.1, and 13.9 nm, respectively. Crystal sizes amounted to 19, 28, and 34 nm for mesoporous Ta2O5, Nb2O5, and TiO2, respectively. Porous and crystal structures of the as-synthesized samples are characterized using X-ray diffraction, thermogravimetric-differential thermal analysis, scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, and N2 sorption techniques. The photocatalytic performance of the as-synthesized crystalline mesoporous Ta2O5 is also evaluated. Using NiOx as a cocatalyst, the as-prepared crystalline mesoporous Ta2O5 showed stable overall water splitting under Xe lamp irradiation (full arc). When the light intensity is fixed at 0.17–0.18 W cm−2, the highest H2 evolution rate is 709.1 μmol g−1 h−1.