Department of Chemistry and Biochemistry, Kent State University, Kent, OH 44240, United States.
Department of Chemistry and Biochemistry, Kent State University, Kent, OH 44240, United States.
J Colloid Interface Sci. 2019 Mar 1;537:725-735. doi: 10.1016/j.jcis.2018.11.044. Epub 2018 Nov 14.
The one-pot synthesis of nanostructured ternary mixed oxides is challenging due to the heterogeneous nature of the hydrolysis and condensation processes of all metal oxide precursors. In addition, the solvents and additives used can affect these processes too. Herein, we report the effect of different solvents (ethanol, 1- and 2-propanol, or butanol) and additives (citric acid or 1,3,5-triisopropylbenzene) used on the formation of binary and ternary alumina-based oxides, NiO-AlO, NiO-TiO-AlO, and NiO-ZrO-AlO in the presence of triblock copolymer Pluronic P123 used as a soft template. For comparison, this study includes also mesoporous AlO prepared at the same conditions. It is shown that the kinetics of hydrolysis and condensation processes of metal alkoxides, and consequently, the properties of the resulting alumina-based mixed metal oxides are controllable by varying the solvents used. The use of propanol instead of ethanol affords mixed metal oxides with improved degree of mesostructure uniformity as evidenced by narrower pore size distributions. This finding is attributed to the smaller exchange of propanol with propoxide groups in Al(OPr), Ti(OPr), and Zr(OPr) which results in an enhanced stability of the formed mesophase. Furthermore, the addition of citric acid leads to smaller pore sizes without significant changes in the textural properties of metal oxides, while addition of 1,3,5-triisopropylbenzene affords oxides with enlarged pores. The mixed metal oxides studied feature large specific surface areas (310-460 m·g), large pore volumes (0.5-0.75 cm·g), and uniform mesopores with widths ranging from 5 to 18 nm. Solid-state kinetic studies performed by thermal analysis using both isoconversional and model fitting methods reveal the complexity of the mesophase formation. The thermal decomposition of condensed oxoalkoxide species into metal oxides is mainly diffusion-controlled and affected by the type of solvent used too. This study shows that there are tremendous opportunities in tailoring porous structures of mixed metal oxides prepared via evaporation induced self-assembly (EISA) by selecting proper solvents and additives, and thermal treatment.
由于所有金属氧化物前体的水解和缩合过程的不均匀性质，因此，纳米结构三元混合氧化物的一锅合成具有挑战性。此外，所用的溶剂和添加剂也会影响这些过程。在此，我们报告了不同溶剂（乙醇、1-丙醇和 2-丙醇或丁醇）和添加剂（柠檬酸或 1,3,5-三异丙基苯）的使用对二元和三元氧化铝基氧化物的形成的影响，在三嵌段共聚物 Pluronic P123 存在下形成 NiO-AlO、NiO-TiO-AlO 和 NiO-ZrO-AlO，该三嵌段共聚物 Pluronic P123 用作软模板。为了进行比较，本研究还包括在相同条件下制备的介孔 AlO。结果表明，通过改变所用的溶剂，可以控制金属醇盐的水解和缩合过程的动力学，从而控制所得氧化铝基混合金属氧化物的性质。与乙醇相比，使用丙醇可以获得具有改进的介孔结构均匀度的混合金属氧化物，这表现在更窄的孔径分布上。这一发现归因于丙醇与 Al(OPr)、Ti(OPr)和 Zr(OPr)中的丙氧基交换较少，从而增强了形成的中间相的稳定性。此外，添加柠檬酸会导致孔径变小，而不会显著改变金属氧化物的结构特性，而添加 1,3,5-三异丙基苯会导致氧化物的孔径增大。所研究的混合金属氧化物具有大的比表面积（310-460 m·g）、大的孔体积（0.5-0.75 cm·g）和均匀的介孔，宽度范围为 5-18 nm。通过使用等转化率和模型拟合方法的热分析进行的固态动力学研究揭示了中间相形成的复杂性。缩合的氧代烷氧基物种分解为金属氧化物的热分解主要是扩散控制的，并且也受到所用溶剂的类型的影响。这项研究表明，通过选择适当的溶剂和添加剂以及热处理，可以在通过蒸发诱导自组装（EISA）制备的混合金属氧化物的多孔结构的定制方面具有巨大的机会。
