NSF-SNSF: Membranes from Interrupted Zeolite Frameworks

Separating chemical mixtures into their individual components is often the most energy-intensive step in chemical manufacturing. More efficient separation and purification methods could reduce energy demands and costs of chemical production. Highly selective membranes can separate complex gas mixtures at low cost and high energy efficiency. Zeolites are crystalline materials with arrays of pores that separate gas molecules based on their size, shape, and interactions with the pore walls. Zeolites are exceptionally well-suited for use as industrial gas separation membranes due to their excellent selectivity and chemical and thermal stability. Zeolite membranes have been commercialized for a few applications, but synthesizing thin zeolite films cost-effectively remains challenging, which limits their practical use. This project will develop a new type of zeolite membrane consisting of very thin sheets of a zeolite with pores small enough to perform difficult gas separations such as separating ammonia from hydrogen and nitrogen. The project is an international collaboration between Johns Hopkins University, USA, and Ecole Polytechnique Federal de Lausanne, Switzerland. It will generate new fundamental knowledge necessary for innovation in the multi-billion-dollar global molecular separations market, increasing U.S. and Swiss economic competitiveness in critical industries. This project will investigate a scalable approach for synthesizing selective zeolite membranes on porous supports. Specifically, zeolite nanosheets – high-aspect-ratio two-dimensional (2D) zeolite crystals possessing pores with eight-member-ring (8-MR) apertures – will be used as building blocks for preparing gas-selective membranes. Exfoliated zeolite nanosheets with the 8-MR pores orthogonal to the lateral dimension of the layer have not yet been synthesized. The project aims are to (i) synthesize highly crystalline, intergrowth-free, and high-aspect ratio 8-MR layers, (ii) exfoliate the 8-MR layers, (iii) deposit thin films on hollow fiber supports, and (iv) prepare graphene-supported nanometer-thick films. The study includes the development of novel zeolite nanosheet synthesis approaches combined with state-of-the-art thin film assembly, microstructural characterization, and membrane performance testing. This work will produce processing-structure-function relations for nanoporous thin film membranes. Fundamental knowledge will be gained about nanoporous materials synthesis, multiscale assembly at interfaces, and gas transport in complex microstructures. This collaborative U.S.-Swiss project is supported by the U.S. National Science Foundation (NSF) and the Swiss National Science Foundation (SNSF), where NSF funds the U.S. investigator and SNSF funds the partners in Switzerland. This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.