Understanding the formation of Al13 and Al30 polycations to the development of microporous materials based on Al13-and Al30-PILC montmorillonites: a review

Hydrolysis of aluminum cations (Al3+), the third most abundant metal in the Earth’s crust, is considered relevant in many academic fields, including materials science and chemical engineering. AlIII -polycations and their different uses have also been widely studied, as reflected in the extensive literature in that field. This review summarizes some of those studies, from Al3+ hydrolysis to form Al13 ([Al13O4(OH)24(H2O)12]7+) and Al30 ([(Al30O8(OH)56(H2O)24)]18+) polycations and their specific use as pillaring agents for montmorillonite, which is the most commonly used clay mineral in Aluminum Pillared Interlayered Clays (Al-PILC) synthesis. The experimental conditions published over the years regarding the synthesis of both these AlIII-polycations, as well as the conditions employed to synthesize Al-PILC montmorillonite using Al13 and Al30 polycation solutions, are also summarized. This review highlights some of the findings that have made it possible to explain the formation of Al13- and Al30-PILC montmorillonites, and allow us to clearly understand their differences. Finally, the new tendencies in the development of these materials based on Al-PILC and the applications are also highlighted.The authors are grateful for financial support from the Spanish Ministry of Economy, Industry and Competitiveness (AEI/MINECO) and the European Regional Development Fund (ERDF) through project MAT2016-78863-C2-R. YC thanks the Universidad Pública de Navarra for a pre-doctoral grant (IberusTalent, European Union’s H2020 research and innovation programme under Marie Sklodowska-Curie grant agreement N◦ 801586). AG also thanks Santander Bank for funding via the Research Intensification Program