One-dimensional intergrowths in two-dimensional zeolite nanosheets and their effect on ultra-selective transport
One-dimensional intergrowths in two-dimensional zeolite nanosheets and their effect on ultra-selective transport
复制标题
DOI：
10.1038/s41563-019-0581-3
复制
发表时间：
2020-02-24
期刊：
影响因子：
41.2
通讯作者：
Mkhoyan, K. Andre
中科院分区：
文献类型：
--
作者：
Kumar, Prashant;Kim, Dae Woo;Mkhoyan, K. Andre
MFI沸石是一种广泛使用的催化剂和吸附剂，也有望用作薄膜。纳米厚度的二维MFI纳米片的发现促进了薄膜沸石的制备方法，为膜科学和工程开辟了新的视野。然而，2D-MFI纳米薄片的晶体结构及其与分离性能的关系仍然难以捉摸。通过电子显微镜观察，我们发现在2D-MFI中存在一个到几个单元宽的MEL分子筛的共生结构。我们确定了这些一维或近一维MEL结构域的平面分布，并表明一小部分纳米片具有高的MEL含量(体积分数为25%)，而大多数纳米片不含MEL。原子模拟表明，与原始的MFI纳米片相比，2D-MFI内1D-MEL的公度编织产生了更多刚性和高度选择性的孔，渗透实验表明，使用与工业相关的(未稀释的1巴二甲苯混合物)进料，分离系数为60。在石墨中的限制生长可以增加MFI纳米片中的MEL含量。我们对这些相互生长的观察为开发超选择性分子筛膜提供了策略。
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.