Zeolite MFI is a widely used catalyst and adsorbent that also holds promise as a thin-film membrane. The discovery of nanometre-thick two-dimensional (2D) MFI nanosheets has facilitated methods for thin-film zeolite fabrication that open new horizons for membrane science and engineering. However, the crystal structure of 2D-MFI nanosheets and their relationship to separation performance remain elusive. Using transmission electron microscopy, we find that one- to few-unit-cell-wide intergrowths of zeolite MEL exist within 2D-MFI. We identify the planar distribution of these 1D or near-1D-MEL domains, and show that a fraction of nanosheets have high (~25% by volume) MEL content while the majority of nanosheets are MEL-free. Atomistic simulations show that commensurate knitting of 1D-MEL within 2D-MFI creates more rigid and highly selective pores compared to pristine MFI nanosheets, and permeation experiments show a separation factor of 60 using an industrially relevant (undiluted 1 bar xylene mixture) feed. Confined growth in graphite is shown to increase the MEL content in MFI nanosheets. Our observation of these intergrowths suggests strategies for the development of ultra-selective zeolite membranes.

沸石 MFI 是一种广泛使用的催化剂和吸附剂，也有望用作薄膜膜。纳米厚的二维 (2D) MFI 纳米片的发现促进了薄膜沸石制造的方法，为膜科学和工程开辟了新的视野。然而，2D-MFI 纳米片的晶体结构及其与分离性能的关系仍然难以捉摸。使用透射电子显微镜，我们发现在 2D-MFI 内存在一个到几个单元细胞范围内的沸石 MEL 共生。我们确定了这些 1D 或近 1D-MEL 域的平面分布，并表明一小部分纳米片具有高 MEL 含量（按体积计约为 25%），而大多数纳米片不含 MEL。原子模拟表明，与原始 MFI 纳米片相比，在 2D-MFI 内相应编织 1D-MEL 会产生更刚性和高选择性的孔，渗透实验表明使用工业相关（未稀释的 1 bar 二甲苯混合物）进料的分离因子为 60。石墨中的受限生长被证明可以增加 MFI 纳米片中的 MEL 含量。我们对这些共生的观察表明了开发超选择性沸石膜的策略。