Surface-gel-conversion synthesis of submicron-thick MFI zeolite membranes to expedite shape-selective separation of hexane isomers

Ultrathin zeolite membranes are of paramount importance in accelerating gas transport during membrane separation,and lowering down their membrane thicknesses to submicron scale is deemed to be very challenging.Herein,we develop an advanced approach of surface gel conversion for synthesis of submicron-thick pure silica MFI(silicalite-1)zeolite membranes.Viscous gel is prepared by finely adjusting the precursor composition,enabling its reduced wettability.The unfavorable wetting of the support surface can effectively prevent gel penetration into alumina support voids.Aided by the seeds,the surface gel is directly and fully crystallized into an MFI zeolite membrane with minimal water steam.A membrane with a thickness of 500 nm is successfully acquired and it is free of visible cracks.Additionally,the as-synthesized membranes exhibit rapid and selective separation of hexane isomers by virtue of unprecedentedly high n-hexane permeance of 24.5×10^−7 mol m^−2 s^−1 Pa^−1 and impressive separation factors of 13.3-22.6 for n-hexane over its isomers.This developed approach is of practical interest for sustainable synthesis of high-quality zeolite membranes.

Design of Metal-Organic Assemblies via Shape Complementarity and Conformational Constraints in Dual Curvature Ligands

While common in biological systems,building blocks with low symmetry and flexibility pose numerous problems for synthetic self-assembly,such as the formation of isomers of assemblies that are difficult to distinguish and purify.In this work,three aromatic amide-based ligands(L1–L3)with a central 1,8-diazatriptycene core were designed and used for selfassembly with Pd^(2+).While hundreds of stereoisomers based on the conformational flexibility around the amides and the unsymmetrical nonplanar structure of the core are possible upon coordination with the metal,the constraints designed into the ligands direct the self-assembly toward only a single Pd_(2)L_(4)cage(L1)or Pd_(4)L_(8)double-walled metallomacrocycle(L2)structure,even in mixtures of the ligands.This structural approach and the modularity of the ligand synthesis affords ready access to deep cavitands with endohedral functionalization(L3).These results highlight the potential of this new design strategy and open the door to selectively functionalized cavity-based architectures for numerous applications.