Synthesis of 2D type A molecular sieves by alkaline removal of natural kaolin

Abstract

Type A molecular sieves have been extensively employed in various fields. It is noteworthy that the direct synthesis of type A molecular sieves from natural kaolin is a common practice among researchers. Traditional type A molecular sieves are characterized by a three-dimensional cubic lattice structure. In this study, our objective is to facilitate the transformation of type A molecular sieves into a two-dimensional layered configuration by employing a two-dimensional layered material as a templating agent. In this research, natural kaolin serves as the primary source material. To eliminate impurities including quartz, illite, and dolomite, an alkali-based solvent extraction method is employed, yielding amorphous silicon and aluminum compounds. Subsequently, a graphene-based templating agent is introduced, and a hydrothermal synthesis process is employed to fabricate two-dimensional type A molecular sieves. The method described herein yields two-dimensional layered type A molecular sieves with a crystallinity exceeding 90%, thereby resulting in a specific surface area that is approximately 11-fold greater compared to their three-dimensional type A counterparts. The applicability of this methodology can be extended to the valorization of low-grade natural mineral resources, optimizing their utility. Furthermore, the approach presented herein for the synthesis of two-dimensional molecular sieves is of a universal nature, offering valuable insights that can serve as a reference for the synthesis of various other categories of two-dimensional molecular sieves.